# Design Discussion: High Performance CNC Spindle



## macardoso (Jan 14, 2020)

I have been doing research on building a high performance spindle for a medium to large size benchtop CNC mill for a few months. I recently found out that @shooter123456 was also working on similar goals and I wanted to create this post to collect information and share ideas. I'm sure he and I have slightly different end goals in mind, so I will try to keep this generic.

*Background:* Anyone who has converted or built a benchtop CNC (up to RF45/PM-940 size) is likely aware of the extreme limitations of spindle options out there. In fact, the spindle is almost always the limiting factor in custom built designs. There are a couple of categories that we can group the available spindles into:

*Stock Spindle*: These are the machine running the original spindles that came with the machine. While this doesn't add much to the cost, these spindles are often limited in speed and torque due to a gear head design and brushed or brushless DC motors. Speed control from the CNC controller may be difficult without special interfaces.
*High Frequency Spindle*: There are a ton of router type machines running water or air cooled high frequency AC spindle motors coming from China at relatively low prices. For general machining work, the 18-24k rpm spindle is too fast and the extremely limited torque and rigidity limits their application to light cuts with small tools.
*AC Induction - Belt Drive*: Many hobbyists opt for an open loop AC induction motor run on a VFD. The cost of this setup is often significantly more expensive than the aforementioned options, however it offers great torque and control over the motor speed. Hobbyists are usually limited by the size and weight of the motor, as well as the cost. Speed is limited without special considerations to 7200rpm (2x motor nameplate) and torque falls off rapidly above 3600 rpm. Rigid tapping is possible with special considerations.
*Servo Spindle - Belt Drive*: Typically seen on the high end hobby builds, a servo spindle offers a flat torque profile across the entire speed range and precise control of velocity and position. Rigid tapping is easily accomplished with this spindle configuration. Hobbyists are often limited by the cost of these systems and the maximum speed of the lower cost models (3000rpm). Servos rated for 5000 rpm are available up to 2.5HP but may be difficult to find.
With these options in mind, we look at some features which an ideal spindle (again, for a high end hobby class machine) would have:

*8000-12000 rpm*: Higher spindle speeds offer cutting performance for tools 3/8" and under.
*3HP*: Roughly the maximum single motor rating before 3 phase power is required.
*Substantial low end torque (>30Nm)*: Allows use of larger diameter tools, facemills, and improved performance in steel.
*<75 dBA Noise*: Comfortable to work around.
*Thermally stable*: <130*F at 100% duty cycle.
*Quick Change/ATC Compatible*: Pneumatic/Hydraulic tool release  
*Low TIR*: .0002-.0001 TIR at spindle taper
*Closed Loop*: Encoder Feedback of spindle position for speed control and rigid tapping
*Common Taper*: R8/BT/CAT taper, minimal tool change height is ideal due to limited travel in hobby machines
*High Spindle Rigidity*: Thick spindle walls and large bearings for improved cutting performance
*Tool Compatibility*: Tooling system equipped to hand tools up to and including 1/2" shank. Options available for larger tools if needed.
*Cost*: Cost should not exceed $1-2000 over the purchase price of the machine.
In upcoming posts, I'll try to dive into research I've done on each of these topics and how we might achieve them. Please join in and share your ideas or let me know if any of the requirements should be tweaked.

-Mike


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## macardoso (Jan 14, 2020)

*Discussion about target spindle speed*

Many of the benchtop machines which hobbyists target for CNC conversions come from the factory with geared head spindles with a top speed of 2500-3000rpm. These sppeds are suitable for manual machining with HSS and drilling, but is far from ideal for dynamic (trochoidal) machining with smaller cutters. A machine the size of a G0704/PM25 seems to be best suited for using 3/8" endmills in aluminum and 1/4" in steel (full flute length 10-40% engagement), while a machine the size of a RF45/PM940 would be suited for 1/2" endmills in aluminum and 3/8" in steel. Larger cutters may be used but rigidity is very limiting. Likewise, small cutters are acceptable, but productivity is extremely limited by spindle speed.

Using modern carbide tooling (seemingly commonplace among serious hobby CNC users) the allowable spindle speeds for tooling is very high. Far beyond the 3000rpm limitation of the stock spindles. It is for this reason that we would want to consider a 8-12k rpm spindle, especially for aluminum.

Having recently installed a 5000rpm servo spindle on my G0704, I can confidently say that I still feel limited by my top speed, especially when using tools under 1/4". My 3/8" aluminum specific carbide endmills recommend 10-12k rpm in their speeds and feeds. A higher speed would go a long way in making these machine more productive in finishing operations with small tools.

*Spindle Options*

Unfortunately reaching these higher speeds presents a real design challenge that goes against many of the other design criteria listed in the first post. The first challenge is that there are not many motors capable of providing 8-12k rpm directly. Gearing up the speeds is feasible but presents a large number of challenges specifically with noise, efficiency, and torque drop. Standard gearing available at the hobby level cannot cope with the increased speed and stresses. Belts perform poorly when the driven pulley is much smaller than the driver. Direct drive attachments limit access to the spindle for drawbar usage. Finally, built in spindle motors require extensive machining and engineering, and I have never once seen one used in a hobby machine.

From my design analysis, belted connections to a motor with a very high name plate speed is the best option, reducing the ratio which must be introduced to reach the final target speed. The easiest motor to use would be an inverter duty induction motor, giving a running speed of 7200rpm. This configuration would necessitate a 1:1.38 gearing ratio to hit the 10k rpm mark.

A better solution would be to use a purpose built spindle motor (such a a Fanuc a2, A06B spindle motor) which comes ready to run at 8-10k rpm. In real Fanuc CNC machining centers, these motors are belted to the spindle and provide power and torque very effectively. I have been scouring for used ones and have seen them listed for $500-1000. This motor could be geared 1:1 or a small increase ratio which would be very acceptable. Purpose built spindle motors have a constant blower fan to maintain cooling in low rpm high torque applications.

If servo motors are preferred there are a few high speed options available in the 6000-8000 rpm range from Siemens, Kollmorgan, and perhaps others. These tend to be lower power, low inertia units which may not be favorable for a spindle motor with medium inertia.

*Transmission*

As suggested above, it seems that at these high speeds, you are limited to direct drive or carefully engineered belt drive transmission systems. Gearing is used in industry, but requires hardened and ground gears in special high speed gearboxes. It is my opinion that this is out of reach for the hobbyist.

From my experience, timing belts are not necessary when the belt transmission is appropriately designed, and at higher speeds, they are a significant source of running noise. Air is sucked into the teeth and tightly compressed as the tooth rotates around each pulley. The compressed air then snaps out the other side creating a lot of noise. My current CNC timing belt spindle design operates comfortably at 5000rpm, but would not be suitable for higher speed applications.

Poly-Vee belts are marketed as the preferred solution for high speed applications and have been proven throughout the industry, both in machine tool and automotive applications. The thin profile of the belt reduces the size requirements of the pulleys.


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## macardoso (Jan 14, 2020)

*Discussion about HP*

This is a fairly easy one. We would like to have the most horsepower available at the tool (within reason). The machines this spindle is being designed for will have significant rigidity limitations so it is unlikely that you would be able to take advantage of a 5 HP spindle. Furthermore, most VFD manufacturers switch to 3 phase input above 3HP, marking it as a good upper bound.

My current G0704 has a 2.25HP spindle and I am hard pressed to use more than 40-50% of its capacity while milling, due to rigidity limitations. I am able to get close to 100% in drilling operations. 

If a hobby machine were suitably constructed to handle the cutting forces, and the user was willing to install a rotary phase converter (or oversize their VFD for single phase derating) then a larger spindle motor could be considered.


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## Boswell (Jan 14, 2020)

Macardoso, I appreciate your thoughtful discuss on these topics. I have PM45-CNC and have often thought about what it would take to increase the maximum RPM.


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## macardoso (Jan 14, 2020)

*Discussion about low end torque*

In a milling spindle, there is a unique range of applications, from large drilling and facemilling, to micro tooling. The high spindle speeds typically do not require substantial torque, however the tools running at lower speeds do. A motor which has been geared up for high speed use will perform quite poorly when using larger tools in steel or using facemills.

My current design, for reference, uses a 1:1 servo motor with 11Nm of torque at 100% continuous, with momentary spikes to 300%. This is plenty sufficient for milling aluminum and steel at 5000rpm, however it is quickly used up when using larger cutters (>1/2") or facemills. I would suggest a minimum of 30Nm for acceptable performance in the <1500rpm speed range.

It becomes quickly apparent that this is likely not able to be achieved with a single gearing ratio, and a belt change or back gear would need to be employed.

*Transmission*

I haven't done the most research into the design, but Fadal, a CNC machine manufacturer, has a really neat pneumatic belt change system. It has multiple belts on a step pulley system, but only 1 can be in contact with the pulley at a time. They are switch by a pneumatic system which engages or disengages an idler pulley. Perhaps this system could be integrated into out high performance spindle to give multiple speed and torque ranges.




The alternative option is a classic step pulley which would require the user to stop the machine and change the belt. I believe this is what Tormach went with on their new 1100MX mill with a 10k spindle.


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## macardoso (Jan 14, 2020)

*Noise*

I may have more sensitivity to this issue than others, but my hobby shop is in my basement of a 120 year old house. The walls and floors are very thin and my wife doesn't appreciate a lot of noise when I'm working in the shop. In addition, I find the machine much more pleasant to use if I can be around it comfortably without damaging my hearing.

The design limit I set when building my current CNC was 75dBA motor idle noise at 5000rpm (doesn't count the cutting sounds of endmill on workpiece). To accomplish this, I had to carefully select a profile of timing belt for high speed applications and totally enclose the transmission in a thick walled airtight housing. The final sound level ended up at 68dBA as measured by my ultra accurate iPhone app at 1' from the front of the machine

I believe that designing this high performance spindle in a similar way from the beginning would be important. The higher speeds present a ever greater challenge than I faced. Here are some design factors I think will play the most into the audible noise:

Quality spindle motor with good bearings. Should be very quiet during a bench test.
Smooth running and balanced spindle with correctly installed spindle bearings.
Selection of a non toothed Poly-Vee belt. No cogging noise like a timing belt.
Sealed transmission enclosure, limits emitted noise, safety. Downside, difficult to access for manual belt changes. Great for automatic belt change
Low TIR (<0.001") of driver and driven pulleys
Minimal unsupported span of belt between motor and spindle
Easily adjustable spindle belt tension. Adjustment screw would be great here
At the end of the day, the spindle will still be noisy, but careful design will minimize this. A built in blower fan will add a good chunk of noise that we cannot control.


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## macardoso (Jan 14, 2020)

*Thermally stable* 

I have not done much/any research into this, however the spindle bearings on my 5000rpm spindle do tend to get to 120/130*F during prolonged running at full speed. The bearings are safe to around 250*F, however this is way too hot and the grease will drip out of the bearings long before this. 

Carefully set preload of the spindle bearings can minimize heat, however at 8-12k rpm, the heat generated may be more than passive cooling can handle. A simple water cooling jacket around the spindle bearings and perhaps the head casting itself would do a lot to help stabilize the spindle temperature, however it does add a lot of complexity.

Thermal management is also important for accuracy. On an RF45/PM945 machine, starting the spindle from room temp (70*F) and allowing it to reach 130*F (assumption, constant temperature all the way to the column) would cause the tool to move 0.0029" in the negative Y direction. No hobby CNC control that I know how has thermal compensation in it, so this error will throw your parts out of tolerance.


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## macardoso (Jan 14, 2020)

*Quick Change/ATC Compatible *

Since most serious hobby CNC users will be using preset tools and maybe even an ATC, the spindle must be able to automatically clamp and unclamp the tool. The exact mechanism will vary depending on if you are using a BT taper with a pull stud or an R8 taper and Tormach Tooling System.

The tool retention force must be sufficient to handle the cutting forces of this spindle, and the throw of the drawbar must be great enough to fully unclamp the tool.

My current R8/TTS system retains the tool with 1800lbs of force, however I have had a couple incidents of tool pullout, so I would consider a system closer to 3000lbs. BT30/40 tapers have different requirements which I have not researched.

Typically the hydraulic or pneumatic cylinder is located directly above the spindle, so having the spindle motor off to the side with a belt allows access for this.

The mechanism should not place the compression forces across the spindle bearings.

EDIT: A properly designed tool clamping mechanism should have feedback to ensure tool clamping and separately feedback to ensure the cylinder is not in contact with the spindle during rotation.


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## RJSakowski (Jan 14, 2020)

FWIW, I measured the sound levels from my Tormach 770. At maximum speed the motor generates 90-92 dB @ 3ft.  With the spindle in the high range, it goes up to around 95 dB while the spindle in the low range, it is around 92 dB. I suspect that most of the noise is due to the integral fan in the motor.  There have been a number of mods to the Tormach's removing the internal fan  and replacing with an external fan.  While this was done for improved cooling at lower speeds, it would cut the noise quite a bit.


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## macardoso (Jan 14, 2020)

RJSakowski said:


> FWIW, I measured the sound levels from my Tormach 770. At maximum speed the motor generates 90-92 dB @ 3ft.  With the spindle in the high range, it goes up to around 95 dB while the spindle in the low range, it is around 92 dB. I suspect that most of the noise is due to the integral fan in the motor.  There have been a number of mods to the Tormach's removing the internal fan  and replacing with an external fan.  While this was done for improved cooling at lower speeds, it would cut the noise quite a bit.



Yikes! That is a lot louder than I imagined it would be. Thanks for sharing! Maybe my suggested requirement is too tight then?


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## macardoso (Jan 14, 2020)

*Low TIR* 

I think the golden standard is to have your entire tooling assembly below 0.0003" TIR. Since most tooling will tend to add at least 0.0002" TIR, the spindle must be very accurate to avoid tolerance stacking. 

Ultra precision spindle bearings are *very *expensive so I have long considered hard turning the spindle taper in place on the machine to be a viable option. The bearings would still need to be very high precision, but maybe you could sneak by with something less than ABEC9/ABEC7.  

Spindle repair companies will sometimes hard turn a commercial VMC spindle in place so this seems reasonable to me. 

Belt vibrations and pulley concentrically will play into the runout at these levels so the transmission systems needs to be well balanced.


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## RJSakowski (Jan 14, 2020)

My machine is directly under the living room and the better half is sensitive to noise from below.  However, I find the the noise due to machining far exceeds that of the motor and spindle.  Because of this, I find myself running less aggressively than I might otherwise.


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## macardoso (Jan 14, 2020)

RJSakowski said:


> My machine is directly under the living room and the better half is sensitive to noise from below. However, I find the the noise due to machining far exceeds that of the motor and spindle. Because of this, I find myself running less aggressively than I might otherwise.



Sounds very familiar    Funny how engineering requirements come from all over the place


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## macardoso (Jan 14, 2020)

I'm going to call it a day for putting ideas up here, hopefully give @shooter123456 a chance to share some of his design as well. I'll follow up with some of the other topics perhaps tomorrow.


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## RJSakowski (Jan 14, 2020)

One of the issues with the Tormach design was a increase in spindle length due to frictional heating.  One approach has been to use Belleville or wave spring washers to control the bearing preload.  Perhaps a better way would be to use opposed angular contact or tapered roller bearings at the bottom of the spindle and a third bearing that has axial play to control runout at the top.


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## ACHiPo (Jan 14, 2020)

Interesting thread!


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## spumco (Jan 14, 2020)

Macardoso,

You know I've been on the same hunt for about 18 months as I plan my upgrade from R8 to BT30...

There is a guy who has replicated the Fadal 2-speed poly-V system.  There's a quick Youtube video of it working, and more on his instagram posts.  He's using air instead of hydraulics but it looks sweet.  That system give you so much more flexibility with motor & spindle selection.






Do want. Not so sure I want to go through the hassle of building one, however.

I started off with a huge "3HP" 1110mm frame BLDC on my mill from the factory.  Pathetic, proprietary driver would cut out, no low end torque.  That spindle motor & drive are probably what killed Mikini more than anything.  Figured I had a motor good for scrap only - who wants to pay $900 for a Tiawan BLDC drive on a suspect motor?  Motor is the same thing (more or less) as on the Tormach 770.

So I switched to a 2HP induction motor with encoder feedback to the VFD and motion controller.  Works very well, but is simply too big & heavy for my mill at about 80lbs.  Can rigid peck-tap despite 1:1.56 ratio because there is an index sensor on the spindle to trigger the Z/spindle synchronization.

I am about to get started on a servo upgrade to cut down on weight and provide C-axis positioning.  Originally got a Parker Gemini drive & servo which would get me to about 8kRPM with some belt ratio.  I was prepared to live with (some) lost low end torque.  Got tired of waiting for Ebay to cough up an A06B-0853 2.2kw 10kRPM from a Chiron for under $500. 

As you mentioned most 240-1P drives top out about about 8-10 amps, and there are a few at 10-12. Getting a 5kRPM servo and driving it at 1:2 means your little 1.5HP motor is going to be a dog drilling steel at low speeds.

_*But...*_  I read an old post on the 'Zone about servos & BLDC's recently, and discovered that some of the old 'analog' servo drives had some serious amps.  Jim Dawson is probably responsible in some way for that thread...

AMC, Copley, and others made 'generic' drives which top out at 20A continous - now we're talking 5hp servos!  They take 0-10Vdc analog input for velocity control.

However, most servos for sale on Ebay are resolver types, not encoders with halls.  And quite a few have proprietary encoder or resolver outputs (Fanuc, Yaskawa, Kollmorgen (some)).  No-go on the drive to motor communication - playing mix-n-match with servos & drives is not for the faint of heart.

So...enter CUI Devices (and others).  Programmable commutation encoders with auto hall phasing.  Find a motor with speed rating and continuous amps at the max of your drive and just replace all the proprietary signal components with a $40 CUI commutation encoder.

Now you can get a cheap old analog drive, and a big 130mm frame 5kRPM servo and have a 10kRPM spindle with positioning capability.  And because it's 1:2, you don't need a separate spindle encoder (if using timing belts) - just tell the controller you've got a 2x encoder count with 2 index pulses per rev.  And the servo should still have home shop grunt at low RPM.

Or duplicate the Fadal thing like Mr. Genius above and now you've got *proper* low-end torque and whatever top end you want.  I think a 4HP servo running a facemill at a 2:1 reduction would push the limits of a BT30 spindle.  Definately need the drive dogs for that one.

OR...  _and this is what's sitting on my bench at the moment_... I'm going to try taking that huge BLDC and fit it with an encoder. Then drive it like a servo with a Copley XTL-230-40 20A drive. The Copley has auto phasing, and auto hall alignment to boot. I hope & suspect that the old 'dog' BLDC will perform rather well and it's got a 6kRPM mechanical rating. We shall see. The Copley fell in to my lap, so to speak.

If not, I also scored another Gemini & a 4kRPM rated speed 3KW servo for a silly price.  One of them will go on the mill, and the other will go on a to-be-designed CNC lathe.

Summary - VFD & induction motor (get a sheet metal one, not cast-iron) is inexpensive and easy.  Otherwise one can probably piece together a servo system with some patience.

I will report back on the BLDC to servoectomy experiment shortly.

-Ralph


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## shooter123456 (Jan 15, 2020)

The spindle I am working on has slightly different design goals, but the majority is similar to what macardoso posted above.  The overall goal is to come up with a spindle design that is smoother, quieter, and faster than the stock design, that can be made for reasonable cost using machines available to hobby users.  I don't love outsourcing the work to professionals because then I have a nice end product without the pride of making it.

My goals for the spindle are (at the moment):
1. A smooth 10k RPM
2. Rigid tap capable
3. ATC ready
4. 2-3 HP 

For the taper, I am going with BT30 for a number of reasons.
1. Tooling is readily available and inexpensive (TTS is restricted to Tormach and a few knockoffs of questionable quality)
2. Tooling is more likely to be sharable with future machines
3. Substantially more variety available for tools
4. Better retention with a pull stud (compared to TTS using R8 collet and 3/4" shank)
5. Much easier to implement an ATC
6. Fits well for the size of the machine

I would like to be able to fit the spindle on the machine with minimal permanent modification to it. The biggest restriction there is going to be the bore that the outside of the housing needs to fit into (2.36" on my machine).  That restricts the size of the upper bearing slightly as well as the spindle wall thickness.  The alternative is either making a new head for the machine (Either with welded steel or aluminum screwed together), which is a possibility, but one I would prefer to avoid if there isn't a significant gain in performance.  However, the way the head separates from the Z slide, a new one would not be out of the question.

Right now I am looking at using a matched pair of 7007 bearings on the bottom and a single 6906 bearing at the top.  The reason for this selection is largely size and cost.  If I decide to go ahead and make a new head for the machine, I can fit a larger set.  The lower bearings are the same size as the current lower bearing (though now there is only 1) and the upper bearing is slightly larger (30x47mm vs 25x47mm).  A matched pair of 7007 bearings is relatively inexpensive and they are easy to find.  I have found quite a few match pairs for under $150 that will work.  Stepping up in size to a 7208 would also be possible as those aren't prohibitively expensive, but that would need a new head to make it worthwhile.

The top bearing would be free to float axially to allow for thermal expansion while the bottom pair will be fixed.  

I have a few pictures of my current design compared to the stock spindle.  I am still early in the planning and designing process so everything is still open to suggestion and change.


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## bakrch (Jan 16, 2020)

Very exciting thread. 

My home shop/garage is pretty far away from the house ... not terribly concerned with noise levels.

I am far from a formally educated engineer, but if I can lend a hand in any way I will do so. 

Pending approval from management, I have access to a fully equipped machine shop for personal projects (manual and CNC). This includes ovens for heat treatment that are large enough to fit anything we can dream up. Precision grinding would be my limitation, absolutely none of that equipment in our shop.

I know we want to keep this in the realm of a hobbyists ability to produce, but I do not mind prototyping.


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## macardoso (Jan 16, 2020)

spumco said:


> You know I've been on the same hunt for about 18 months as I plan my upgrade from R8 to BT30...



I forgot all about that but yes! Never knew details of what you were looking for.



spumco said:


> There is a guy who has replicated the Fadal 2-speed poly-V system. There's a quick Youtube video of it working, and more on his instagram posts. He's using air instead of hydraulics but it looks sweet. That system give you so much more flexibility with motor & spindle selection.



I've seen this one and it is awesome! Bit noisy, but otherwise really clever. Exactly what I'm thinking of. 



spumco said:


> I am about to get started on a servo upgrade to cut down on weight and provide C-axis positioning. Originally got a Parker Gemini drive & servo which would get me to about 8kRPM with some belt ratio. I was prepared to live with (some) lost low end torque. Got tired of waiting for Ebay to cough up an A06B-0853 2.2kw 10kRPM from a Chiron for under $500.



They're always on my watch list. So expensive though 



spumco said:


> I started off with a huge "3HP" 1110mm frame BLDC on my mill from the factory. Pathetic, proprietary driver would cut out, no low end torque. That spindle motor & drive are probably what killed Mikini more than anything. Figured I had a motor good for scrap only - who wants to pay $900 for a Tiawan BLDC drive on a suspect motor? Motor is the same thing (more or less) as on the Tormach 770.



I thought all the Tormachs were AC induction motors. Huh. It's amazing how much Tormach did right from the get go - even with all the issues they've had. Nobody else has been able to stick in that market.



spumco said:


> So I switched to a 2HP induction motor with encoder feedback to the VFD and motion controller. Works very well, but is simply too big & heavy for my mill at about 80lbs. Can rigid peck-tap despite 1:1.56 ratio because there is an index sensor on the spindle to trigger the Z/spindle synchronization.



That's amazing. What controller are you running? 



spumco said:


> Getting a 5kRPM servo and driving it at 1:2 means your little 1.5HP motor is going to be a dog drilling steel at low speeds.



My 1:1 11Nm 2.25 HP servo hits 100% on a mildly aggressive 1/2" drill through aluminum. It still has some significant overload reserves though. Steel is a different beast.



spumco said:


> So...enter CUI Devices (and others). Programmable commutation encoders with auto hall phasing. Find a motor with speed rating and continuous amps at the max of your drive and just replace all the proprietary signal components with a $40 CUI commutation encoder.



I've seen their stuff and it looks great! Always have gone with US Digital for low cost encoders.



spumco said:


> OR... _and this is what's sitting on my bench at the moment_... I'm going to try taking that huge BLDC and fit it with an encoder. Then drive it like a servo with a Copley XTL-230-40 20A drive. The Copley has auto phasing, and auto hall alignment to boot. I hope & suspect that the old 'dog' BLDC will perform rather well and it's got a 6kRPM mechanical rating. We shall see. The Copley fell in to my lap, so to speak.



Can't wait to see how that works out. Hopefully the BLDC is up to the task here. Gave the Copley a quick look over. Nice drive. It can do BLDC motors?



spumco said:


> I will report back on the BLDC to servoectomy experiment shortly.



Can't wait to hear!


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## macardoso (Jan 16, 2020)

shooter123456 said:


> The overall goal is to come up with a spindle design that is smoother, quieter, and faster than the stock design, that can be made for reasonable cost using machines available to hobby users. I don't love outsourcing the work to professionals because then I have a nice end product without the pride of making it.



I totally agree with you on that one. Also because of the cost. I just don't know how I could go to a grind shop and have them do it for less than the value of the entire machine. I see the prices we pay at work and it is crazy stuff. I think you could probably start with some pre-hard material and do all the turning on a hobby lathe (not that 7x12 stuff though). Bet a 12x36 or 13x40 would handle it.



shooter123456 said:


> My goals for the spindle are (at the moment):
> 1. A smooth 10k RPM
> 2. Rigid tap capable
> 3. ATC ready
> 4. 2-3 HP



Sounds reasonable! Are you considering any kind of low gearing? Do you do any work with steel?



shooter123456 said:


> For the taper, I am going with BT30 for a number of reasons.
> 1. Tooling is readily available and inexpensive (TTS is restricted to Tormach and a few knockoffs of questionable quality)
> 2. Tooling is more likely to be sharable with future machines
> 3. Substantially more variety available for tools
> ...



I've long considered this, but the cost of the tooling is driving me away. I've invested a few hundred in Tormach TTS and have a lot of holders to show for it (28 of them actually). They're almost always loaded up and ready to go. At $100 each from Maritool, I don't see how I could afford BT30. Are there cheaper suppliers that are decent?



shooter123456 said:


> I would like to be able to fit the spindle on the machine with minimal permanent modification to it. The biggest restriction there is going to be the bore that the outside of the housing needs to fit into (2.36" on my machine). That restricts the size of the upper bearing slightly as well as the spindle wall thickness. The alternative is either making a new head for the machine (Either with welded steel or aluminum screwed together), which is a possibility, but one I would prefer to avoid if there isn't a significant gain in performance. However, the way the head separates from the Z slide, a new one would not be out of the question.



This is a really important point. If we had the room, the easiest option would be to buy a finished Tormach spindle cartridge rated for 10K. 



shooter123456 said:


> The top bearing would be free to float axially to allow for thermal expansion while the bottom pair will be fixed.



That's a really solid idea. Building your own design certainly would give you the flexibility to place the bearings in the most ideal locations.


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## macardoso (Jan 16, 2020)

bakrch said:


> My home shop/garage is pretty far away from the house ... not terribly concerned with noise levels.



Hopefully one day for me.  I'd even settle for a ground level shop right now. Basement makes it difficult sometimes.



bakrch said:


> Pending approval from management, I have access to a fully equipped machine shop for personal projects (manual and CNC). This includes ovens for heat treatment that are large enough to fit anything we can dream up. Precision grinding would be my limitation, absolutely none of that equipment in our shop.
> 
> I know we want to keep this in the realm of a hobbyists ability to produce, but I do not mind prototyping.



That's a really generous offer! Hopefully one of us will be in a place to need that soon! I need a new mill before I can really get a dog in this fight. Everyone cross their fingers and do a rain dance for me that I can get my hands on a RF45 sized mill that I've been stalking.


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## bakrch (Jan 16, 2020)

I've been leaning toward a PM940 for my next build, but RF45 size is plenty big enough for me if it means I can participate in this effort.


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## macardoso (Jan 16, 2020)

bakrch said:


> I've been leaning toward a PM940 for my next build, but RF45 size is plenty big enough for me if it means I can participate in this effort.



I was hoping to keep this generic. I have a G0704 (hoping for a BF46 Vario), shooter has a PM-25, I'm blanking on @spumco 's machine. I think they're probably all more similar than different. I think the spindle is often the most difficult part of a CNC conversion and it's fun to toss around ideas.


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## bakrch (Jan 16, 2020)

macardoso said:


> I was hoping to keep this generic. I have a G0704 (hoping for a BF46 Vario), shooter has a PM-25, I'm blanking on @spumco 's machine. I think they're probably all more similar than different. I think the spindle is often the most difficult part of a CNC conversion and it's fun to toss around ideas.



Definitely keep it generic. Much of what I am throwing out there is just to put all of the cards on the table so-to-speak. This way we can all plan our moves, or at least I can.

I'm fairly flexible right now and have no real timeline (my PM-25 is plenty sufficient to get me by for now).

I've read somewhere (not sure how true it is), that the G0704 and PM25 have the same head, but when you get to the rest of the castings everything is more or less different.  If we all have that to start with, we should definitely exploit that.


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## macardoso (Jan 16, 2020)

I think in size and features, the G0704 and PM-25 are pretty similar. In construction, the PM 25 has some real advantages, especially that the column mounts on top of the base (G0704 bolts to the back - very hard to adjust). The spindles seem identical? I bought a CAD model of the PM-25 to help me design and all the parts of the G0704 spindle seem to fit exactly to the CAD model. General fit and finish of the PM-25 is better too. My G0704 has kinda poor fitting gibs and ways. I'm sure Shooter can elaborate here better than I can.

I started with the G0704 because it was all the rage 8 years ago in the wild west days of Hoss Machine. I really didn't know much about anything (had just started college) and I don't think Precision Matthews existed. I certainly wish I had bought a bigger machine, but it was the right call at the time and I've had a blast with it!


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## shooter123456 (Jan 16, 2020)

macardoso said:


> I totally agree with you on that one. Also because of the cost. I just don't know how I could go to a grind shop and have them do it for less than the value of the entire machine. I see the prices we pay at work and it is crazy stuff. I think you could probably start with some pre-hard material and do all the turning on a hobby lathe (not that 7x12 stuff though). Bet a 12x36 or 13x40 would handle it.


Yes, cost is another obvious factor.  Material cost should be reasonable but I imagine that professional work would be at least $1000.  Material selection is something I have not yet figured out.  I am also not sure about hardening or grinding afterward.  I think a toolpost grinder could do the trick, though I know a lot of people won't grind on their lathes.  I have not decided how I feel about it yet.  



macardoso said:


> Sounds reasonable! Are you considering any kind of low gearing? Do you do any work with steel?


I am not sure.  I was considering a 2 step pulley, but I don't do much work with steel.  I have done maybe 3 small parts in steel on the machine in the 2 years I have had it.  My motor is 6000 RPM, so maybe a high range bumping up to 10k, then a low range gearing it down to 3k.



macardoso said:


> I've long considered this, but the cost of the tooling is driving me away. I've invested a few hundred in Tormach TTS and have a lot of holders to show for it (28 of them actually). They're almost always loaded up and ready to go. At $100 each from Maritool, I don't see how I could afford BT30. Are there cheaper suppliers that are decent?


I have the same problem, but I keep thinking that if I ever get a larger machine (and I really hope to some day), I will be buying all of that tooling anyway.  There are a lot of machines that I have my eye on for one day in the future that are BT30 spindles (something like a robodrill or Syil tapping machine) which will mean purchasing all of the tooling anyway.  There are a ton of suppliers for BT30 tools that are less expensive than Maritool, but I don't know about quality for all of them.  Like anything else, there is the option to have less expensive tools where they will be sufficient and purchase the better ones for the important stuff.  For example, drill chucks and roughing tool holders can be on the lower end and finishing tools one the higher end.  I know of at least these suppliers that should have decent stuff though:

Tormach - $50-60 for set screw or collet chucks
Shars - $50 - 60 for set screw holders (They also have a set of 4 that comes to $35 each)

You also need to factor in a little bit more for the pull studs, which will add maybe $10 to each tool.  There are some import tools for as low as $15 each.  Quality will be a question, but like the cheap TTS tools you found, at $15 each, it may be worthwhile to buy several, measure them, and use the best ones or return the ones that don't meet their specifications.  It would be a hassle, but an option.


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## bakrch (Jan 16, 2020)

macardoso said:


> I think in size and features, the G0704 and PM-25 are pretty similar. In construction, the PM 25 has some real advantages, especially that the column mounts on top of the base (G0704 bolts to the back - very hard to adjust). The spindles seem identical? I bought a CAD model of the PM-25 to help me design and all the parts of the G0704 spindle seem to fit exactly to the CAD model. General fit and finish of the PM-25 is better too. My G0704 has kinda poor fitting gibs and ways. I'm sure Shooter can elaborate here better than I can.
> 
> I started with the G0704 because it was all the rage 8 years ago in the wild west days of Hoss Machine. I really didn't know much about anything (had just started college) and I don't think Precision Matthews existed. I certainly wish I had bought a bigger machine, but it was the right call at the time and I've had a blast with it!



On paper the PM-25 certainly has advantages. I can confirm the dovetail and gib fitment is very good on my machine, seems to be the common opinion. The column however, even with the better design it was poorly executed on my particular machine. It takes .02 in shimming to get the X square, but only .004 for the Y/nod.

I'm not sure what is typical, but needing .02 for X is very unacceptable to me.

I'm getting off topic here, so I'll stop now ..haha.


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## macardoso (Jan 16, 2020)

Thought I'd try to get a couple more posts on the topics in the first post as promised.

*Closed Loop*

Accurate control of speed and position (indexing & tapping) requires encoder feedback. The encoder can be mounted to the motor (either integral or external) which is good, belted to the spindle - also good, or directly attached to the spindle - best. The encoder should have an index channel.

One issue with the spindle encoder is the speed. Very few encoders are rated for speeds above 6-8000 rpm, and the receiving circuitry is usually not fast enough to track these signals. Special encoders must be purchased and the number of counts per rev (PPR) is typically much smaller than an axis motor to limit the output frequency.

Mounting the encoder to the spindle is also tricky as the pneumatics for tool release is positioned above the spindle tube. A hollow bore encoder might be considered here. Heidenhain for example makes a high speed hollow bore encoder specifically for machine tools. No price though 









						NEW Encoders for High Speed Spindles - HEIDENHAIN
					

HEIDENHAIN ERM 2400 encoders are ideal for applications that offer little space and yet require a relatively high accuracy of angular measurement.




					www.heidenhain.us
				




The encoder needs to be relatively immune to vibration, contamination, and temperature leaning us towards a magnetic encoder over optical.

Differential outputs and a differential receiver would be a big plus.


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## macardoso (Jan 16, 2020)

*Common Taper* 

As discussed above, the spindle should have a common taper to allow for easy access to tooling. This selection is critical as it determines tooling cost, accuracy, rigidity, and tooling vendors.


R8: Not ideal due to long tool change length and balance issues. Tooling is widely available and inexpensive.
R8/TTS: Quick change Tormach Tooling offers moderate stability, limited but low cost tooling options, and a short tool change length. Most of us already own a lot of TTS tooling.
BT/CAT/ISO 30: Greatly increased stability. Toolholders balanced to 10k rpm. Lots of tooling vendors. Slightly longer tool change height than TTS. Moderately expensive
BT/CAT/ISO 40: Too large for a benchtop machine.


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## spumco (Jan 16, 2020)

macardoso said:


> What controller are you running?


Software: UCCNC
Controller: UC400ETH
BOB: PMDX 126 w/107 0-10v spindle board



macardoso said:


> Gave the Copley a quick look over. Nice drive. It can do BLDC motors?


_EDIT - don't go searching Ebay and snapping up all the drives I just discovered!_
The XTL (and some others in the Xenus line) can do halls, differential encoder w/ halls, and diff encoder w/o halls.
The XTL-/S model can do analog encoder or analog halls /digital encoder
the XTL-/R model can do resolvers
Control signals: analog 0-10v, pwm, step/dir, external encoder for gearing/camming, CANopen, ASCII

Also has a secondary input for a load encoder (dual-loop)



macardoso said:


> buy a finished Tormach spindle cartridge rated for 10K.



Or a 12k version.  Tormach is chinese after all..
https://www.aliexpress.com/item/323...chweb0_0,searchweb201602_4,searchweb201603_55



macardoso said:


> get my hands on a RF45 sized mill that I've been stalking.



Um...
https://cleveland.craigslist.org/tls/d/euclid-cnc-vertical-mill/7045473138.html



macardoso said:


> I'm blanking on @spumco 's machine.


Mikini 1610L.  About halfway between a 770 & 1100 Tormach in size.  Linear rails & steppers (for now).



macardoso said:


> Mounting the encoder to the spindle is also tricky



Offset the encoder and drive it with a timing belt right off the spindle main pulley.  Drive it at some sane ratio (1:1, 2:1, etc.) and adjust the PPR in the controller.  This method has been used on plenty of lathes (Omniturn & other 'factory' retrofits).

Stolen off the 'net:



Determine your desired resolution needed for a spindle/C-axis (can't be that small, right?) and get one with a PPR that doesn't blow the optocouplers away on the BOB or drive. 

A 1024 line encoder is 4096cpr in quad.  So lets say a 5kRPM motor at 1:2 (for the magical 10k spindle) and a 2:1 reduction to the encoder.

4096cpr / 2 = 2048cpr at 10k spindle rpm.
2048 * 5000 /60 = 170khz.  This is do-able most low-end BOBs which seem to all be using the same 200kHz optos.

And 2048cpr gives you 0.176 degrees per encoder count resolution.  Not great for a 4th axis, but would be fine for a spindle to position a broach or line up for an ATC.

This also means you don't need to use a timing belt from the spindle motor to the spindle - any poly-V belt slip will be taken care of by the direct connection from spindle to encoder.  Quieter belt drive at the expense of higher belt tension and top/motor bearing radial loads.  You can get a cheapo USDigital, CUI, or import with whatever output style you want and not spend a fortune on a SICK or Heidenwhatever.

Most hollow-bore encoders I've seen top out at about 32-50mm bore - they aren't really suited to installation over a spindle.

-Ralph


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## spumco (Jan 19, 2020)

*Interruption for Public Service Announcement*

I (re)discovered the forum thread describing the two-speed pneumatic belt selector construction.  It's from a German hobby CNC forum - must use Google Translate.  Great thread, but the belt thingie starts about page 20.

https://forum.zerspanungsbude.net/viewtopic.php?f=50&t=26643&start=190

Even some of the little details are interesting - check out the shaft locks he's using to mount the pulleys.  I'd not seen those before and they look extremely useful.

Might be helpful - something like this opens up many options for spindle motors.  As previously mentioned, one can either spend huge money on a high-speed (10Krpm) motor, or run a 1:2 (or whatever) ratio and live with reduced torque at low RPM.  Meaning you'd need to over-size the motor 2x to make up for lost torque.

Sure you can fit a 6"-8" frame motor that takes 30A @320vdc to run, but what amplifier will drive it off 240-1P?  The absolute max amplifier I can find is 20A/40A continuous/peak off single-phase - and that's with _big_ heatsinks and fans.

With the above belt selector you can go with a smaller, lighter motor that takes fewer amps and still have plenty of low-end torque.  Less money, less weight for the head to move.

EDIT: found his Instagram site:

__
		http://instagr.am/p/Bn4JWudgR2f/

*End PSA*

Still waiting for some stupid Wago connectors to test out the Copley drive.  Hoping my 'Lego' servo motor/drive plan works out:

1. _*Any*_ motor with the desired speed & amp rating
2. Ditch the factory feedback for an AMT or US Digital commutation encoder
3. Drive it with a 'generic' amplifier.

Should open up many, many possibilities on the used servo market.  Fingers crossed.


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## macardoso (Jan 20, 2020)

spumco said:


> EDIT - don't go searching Ebay and snapping up all the drives I just discovered!



I would never I have a sizable supply of AB Ultra 3000's hanging around for my needs. I'm always worried when I tell people about my secret suppliers that they'll go grab it all!



spumco said:


> Also has a secondary input for a load encoder (dual-loop)



You should *definitely *use that.



spumco said:


> Or a 12k version. Tormach is chinese after all..



OK, wow. I honestly hadn't thought of that, but this seems to make a lot of sense. a BT30 spindle built from scratch would cost roughly:

$200 in AC and radial bearings
$150 in stock
$100 for pulleys
$100 for a drawbar and belvilles 
Some amount for a gripper for the pullstud
So maybe $600 and then you need to actually machine it to tolerance. I mean if that's what you're looking for then perfect, but I'm more open to an out of the box option. The 90mm diameter is pretty big and the $1000 takes a big bite out of the $1-2000 budget... but it is a fully complete spindle cartridge.

Do any of you have experience buying from AliExpress or Alibaba? I have always gone for the Chinese sellers on eBay, but I'd love to have another option. Are you protected as a buyer? 



spumco said:


> Um...



Nice find. I'm still holding out for HGR to dump a mill in my lap real cheap. It's actually quite a bit bigger than an RF45. I keep lowballing them, and I'm pretty sure people are going to snatch up the last couple, but I can't help get my hopes up. When I'm done crying over those when they're all gone, maybe I'll go look at that one.



spumco said:


> Mikini 1610L. About halfway between a 770 & 1100 Tormach in size. Linear rails & steppers (for now).



Cool! Have you been happy with it? Guessing you did some serious modifications.



spumco said:


> I (re)discovered the forum thread describing the two-speed pneumatic belt selector construction. It's from a German hobby CNC forum - must use Google Translate. Great thread, but the belt thingie starts about page 20.



God that awesome. Will be reading it today.



spumco said:


> Sure you can fit a 6"-8" frame motor that takes 30A @320vdc to run, but what amplifier will drive it off 240-1P? The absolute max amplifier I can find is 20A/40A continuous/peak off single-phase - and that's with _big_ heatsinks and fans.



You can oversize most 3 phase drives and derate them 0.578 for single phase operation. Hypothetically you could run a 100HP motor on single phase, but you'd need a 175HP 3 phase drive. It gets expensive doing that, and you have to check with the MFG to see if they officially support it.


A big downside of the franken-motor idea is that you lose special information about the motor that helps the drives run them really well. For example, on my AB drives, it expects you to be able to enter the flux saturation ratio of the windings at various current output levels and you also need to know the thermal resistance and capacitance. The drive uses these values to generate field weakening and correctly model the thermal loading of the motor. 

I've done exactly what you're describing, but I've never had a company willing to share that information with me about their motors.


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## spumco (Jan 20, 2020)

macardoso said:


> Cool! Have you been happy with it? Guessing you did some serious modifications.



Happy?  Yes, but it's been more of a learning experiment than a useful part-producing tool.  It met all the requirements I had at the time - cheap, single-phase, can still (barely) move it without paying riggers, and no gibs/ways to deal with.  No mechanical conversion issues.  Came from the factory with ballscrews & HiWin rails.

Modifications? Mechanically, sort-of.  Electrically, yes.  It currently has the original Nema34 steppers and drives, but everything else electrical has been replaced.  I made a kludged-up PDB because the induction motor I have is too big to fit a normal PDB multi-stage cylinder, and I built the 4th axis discussed before.  But no _serious _mechanical mods.

And those will be gone soon, too.  As I mentioned I have a BT30 spindle, DMM 750w servos, PDB, and a new motion controller & BOB to throw in.  I'm setting it up to eventually get an ATC.  Sadly, the head has to come off as my R8 spindle is 80mm and the BT30 is 90mm.  Boo.



macardoso said:


> You should *definitely *use that.


No point on a spindle motor, right?  But for the next build (lathe?) I'll probably do it.



macardoso said:


> Do any of you have experience buying from AliExpress or Alibaba?


Not directly.  I bought it from an importer.  Its all about risk-tolerance.



macardoso said:


> you lose special information about the motor that helps the drives run them really well.


I suspect you're right.  However, my current project as proof-of-concept is to take a really, *really* obscure motor with very little available data and see if the Copley will make it sing.

When I say little data - I know the pole count and the _advertised_ power & continuous amps + DC bus voltage. That's about it. Mikini was painfully secretive about technical specifications: no motor plate, all electronics painted black, part numbers ground off the chips, etc. All I have to go on are some bits of info they let slip years ago in the 'Zone forum. They even had the nerve to call thier BLDC spindle motor a "servo" - I guess technically hall feedback counts, right? /snort/

Anyway, the Copley manuals and videos indicate their drive & software can figure out all the variables needed to make it work.  They even have a 'nameplate' tuning calculation mode where you can bypass all the fussy values and just enter rated speed, amps, torque and power and it'll do the magic.  Watching them do coarse positioning with halls only, and no-halls commutation (wake-and-wiggle) is pretty cool.

If the drive can figure this particular BLDC motor out, it should have no problem with a brand-name Baldor, Parker, Siemens, ABB, whatever where I have all the motor data needed.  If I can get 80-90% of the performance of a matched-pair from an OEM ($$$) from the Franken motor approach, I'll be happy.

Or some smoke will come out.

_*And I was wrong earlier about the Tormach 770 - it is an AC induction motor, not a BLDC.  I was confusing it with some of the other smaller mills - memory failing.*_

Hope I'm not hijacking the spindle thread too much.

I figured any spindle discussion needs to start (or be closely followed by) with a motor discussion.

Since, as you said earlier, the spindle is the heart of a machine tool - how do you drive the spindle?  I'm perfectly happy with induction motors but you can only get so much power on top of a hobby-class/size machine before the motor weight becomes an issue.  On a lathe, who cares?  The spindle motor just sits there - go get the biggest motor & VFD your power company will let you have.

On a mill, however, a 3HP sheet-metal motor seems about the limit.  I ran across what's termed a 'feather picker' motor - it's a Nema 56C framed 3P induction motor that's a bit longer than the typical 2HP version.  That coupled with a VFD that does homing (Hitachi) and a spindle encoder could be a decent combination.  Problem is that it weighs 60lbs, and a new motor & VFD & good cables will get you close enough to $800-$1000 to start thinking about a PM motor.

That's why I've been going down the AC servo/drive rabbit hole for the past year trying to find something cheap and less weight/size than an induction motor.

Another option is to use a built-in ATC spindle (S30?) for a router.  Expensive, but so much easier to install or integrate than a separate spindle/motor/gears or belts.  I just wish the folks making router spindles would get the word that a low-speed spindle - say 8/10kRPM - would be a winner.  Some of us want to make holes in steel, and I can't interpolate a 2" deep 3/8" hole with an end mill.  Not happening, and running that 3/8" drill at 6kRPM is a good way to experiment with friction-stir welding.

-Ralph


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## macardoso (Jan 21, 2020)

spumco said:


> Sadly, the head has to come off as my R8 spindle is 80mm and the BT30 is 90mm. Boo.



So you did buy that spindle cartridge? I'm super interested to hear what you think of it!



spumco said:


> No point on a spindle motor, right?



No, not really. But it would help a lot on an axis motor with linear scale feedback.



spumco said:


> Not directly. I bought it from an importer. Its all about risk-tolerance.



I'd be really interested in hearing more about that process if you don't mind. You can PM me if you don't mind sharing.



spumco said:


> I suspect you're right. However, my current project as proof-of-concept is to take a really, *really* obscure motor with very little available data and see if the Copley will make it sing.



I think it will work just great! Wasn't trying to suggest that your setup won't work, but rather to warn others that trying to mix and match servos can be really difficult unless you know what you're doing.



spumco said:


> Hope I'm not hijacking the spindle thread too much.



Not at all. Very interested to hear about all of this. Didn't really have a direction in mind for this thread, more of an open discussion board for all things spindle related.



spumco said:


> That's why I've been going down the AC servo/drive rabbit hole for the past year trying to find something cheap and less weight/size than an induction motor.



It is tough. There are only a few options out there that are really good. Still not ideal though. AC servos have a huge benefit for size and weight. My 2.25HP 5000rpm servo is only 85mm square and weighs 10lbs. That size induction motor would weigh 60lbs or more.




spumco said:


> Another option is to use a built-in ATC spindle (S30?) for a router. Expensive, but so much easier to install or integrate than a separate spindle/motor/gears or belts. I just wish the folks making router spindles would get the word that a low-speed spindle - say 8/10kRPM - would be a winner. Some of us want to make holes in steel, and I can't interpolate a 2" deep 3/8" hole with an end mill. Not happening, and running that 3/8" drill at 6kRPM is a good way to experiment with friction-stir welding.



God I wish someone would have a metal cutting spindle offering. I always cringe when I see the router guys trying to get through steel at 18krpm on one of those little water cooled spindles.


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## jbolt (Jan 21, 2020)

Great discussion! I went down this road a few years back for my PM932 conversion. In the end I decided it was not worth the blood & treasure for a hobby mill. 6K is fast enough for what I do which is mostly one-off parts. I look forward to seeing what comes of this.

There are metal cutting spindles out there but not something for the hobby market. When we built the CNC router for cutting aluminum plate up to 1/2 thick for the high school robotics team I spoke with manufacturers all over the world to find a spindle that met our requirements and budget. A lot of interesting things out there you won't find on a website. 



macardoso said:


> I always cringe when I see the router guys trying to get through steel at 18krpm on one of those little water cooled spindles.



Hey! It wouldn't fit on the mill!!!


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## spumco (Jan 22, 2020)

macardoso said:


> So you did buy that spindle cartridge?


Yes, I bought it.  It's not very interesting, but here's the deal:

The Mikini is/was the predecessor to the SkyfireCNC VM2 (big one).  Same designer.  Mikini was imported by some guy in California, and he specified all the electronics (I think).  So there is some commonality of mechanical parts (ish) between the Mikini and the Skyfire.

I saw that Skyfire was selling their BT30 spindles, so I got hold of their US importer buy that didn't work out.  So I tried their Canadian distributor and he got the spindle and PDB imported for me.  I got spanked on duties (twice) but the spindle is nice.  I haven't installed it...

Because it turns out Skyfire modified the original head castings in a few important ways.  I knew before I bought it that the new spindle was 90mm (vs 80mm), but the head is also now taller by about 3/4" inch and has a few other changes.  So fitting this thing is going to be a chore.  I have to make a top adapter plate as the new spindle is also taller.  The Skyfire head is open on top - mine is not - so I've got to cut the top open and make sure the adapter plate is also a reinforcing/structural item.

Sigh.  That's why I'm hunting for the 'perfect' motor.  I'm not going to do such massive surgery (including pulling the column to fit a new Z-servo) and not put exactly the spindle motor I want on it.  And adding the two-speed belt drive selector discussed earlier would be a royal pain - half the spindle pulley (HTD-5m) is down inside the head.

So I'm on the hunt for a massively oversized servo that I can drive at 1:2 and get 8-10kRPM and still drill or face-mill steel.  I've got 20A continuous to play with and that gets me in the 3-4kw neighborhood.

But it all depends on whenther this franken-motor experiment works.  If it does, I'll invest in a big servo and have a go.


----------



## spumco (Jan 26, 2020)

Franken motor experiment successful!

1. Ripped off the old Hall sensor and installed an AMT-312D (differential A/B/Z + Halls) on the motor.
2. Used the CUI/AMT phasing software and it auto-phased the Halls to the windings.  Sweet.
3. Soldered up an encoder cable from the AMT to the Copley drive.
4. Plugged in the drive & went through the Copley auto Hall phasing, motor tuning, and so forth.

The old BLDC is now spinning like a grown-up servo.  With the OEM Hall-only BLDC drive it would hunt +/- 200RPM without a load - and cut out randomly above 3500RPM.  You could stop it with your hand below 1500RPM.

Now I can run it at 50RPM and the leather glove test indicates it has gobs of torque even at standstill.

It can also ramp up from 0-6kRPM in a blink.  Need a braking resistor to stop it that fast, but that's down the road.

More importantly, it can now be driven in positioning mode just like a 'real' servo.  Watching it whip back and forth was very satisfying.

So...  this opens some doors for used motors being retrofitted as spindle drive motors.  No more 'treadmill' motors or insanely heavy induction motors. 

PM servos all the way now for me - even if they show up with some odd-ball resolver or proprietary encoder signal, the encoderectomy plan will take care of that.

There are plenty of ABB, Kollmorgen, Siemens, Baldor, and other PM servo motors with max speeds well in excess of the DMM Tech 1.8kw servos I've seen some folks using.  If you can find a 2 to 4kw servo with a top mechanical speed of 5k-8kRPM you no longer need to gear it to the point where there's no low end torque.

The AMT encoders are programmable, so you can set the resolution to avoid overwhelming your controller max input speed.

I'm going to shoot for about 1:1.6 and a 8k+RPM spindle top end, and trying for about 10Nm of continuous torque.

Good luck, let me know if anyone has questions about this setup.  Remember - I'm not an expert.  I just got lucky poking away at this thing.

-Ralph



View attachment 20200125_125710 (2).mov

View attachment 20200125_124855.mov


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## shooter123456 (Jan 30, 2020)

I have been trying to decide if BT30 would be affordable/practical with the price of tool holders.  

Comparing cost, I quickly noticed that there are a million BT30 options out there which makes it a little bit difficult to compare apples to apples.  With TTS, which BT30 holder is comparable in performance?  It is also tough to compare because there are few details about the TTS holders.  What are they made of? They only say alloy steel, which could mean a wide variety of materials.  Where are they made?  Mine don't say made in the USA so it is probably a safe bet they are made overseas.  So a direct comparison is difficult, to say the least.

Some of their prices at the moment are:
Set screw holders - $22 
ER20 holders - $45
Boring arbor - $49
Face mill arbor - $80

Their set screw holder prices dropped recently.  I recall them being about $35 when I checked last and I am not sure how long they will stay at that price.  Might be worth grabbing a few before they go back up. 

For BT30 holders, the hardest part is just determining which holder would have roughly equal performance with all other factors not considered (ie BT30 spindle being better than R8)
On Amazon I found some of the following prices:
Tegara BT30 1/8" set screw holder - pack of 2 - balance to 20,000 RPM - $42 each
No name import BT30 ER16 holders - advertised .0001" TIR - pack of 4 - $22 each
ZXHAO ER16 holder - No details - $31 each

With various other options ranging from $20 - $200 each, there are a lot to choose from.  A nice side note is that if any of them don't meet the advertised specifications, returning to Amazon is easy.  

Tormach has the set screw holders for BT30 around $50 each, which is significantly more expensive than their TTS products.  For the ER20 holders, they are slightly more expensive at $55 each.  

That also does not take into account the pull studs needed for an ATC.  Those add anywhere from $7-$20 to each tool holder.  

That also ignores the fact that many people already have TTS holders.   Starting from nothing, it may not be quite as bad tooling up for BT30, but having a significant investment in TTS holders already would certainly make it more difficult.  

At this point I am still leaning toward BT30 because I think the performance will be better and I like the wide range of tooling available.  Being able to share tooling with future machines is also a plus in my mind.


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## macardoso (Jan 30, 2020)

That was my concern with tooling for BT30. It is attractive, but I have a far amount of TTS at this point. Probably $500 into it. Would suck to just walk away from that investment. Measuring tool offsets offline with BT30 is tricky too.


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## spumco (Jan 30, 2020)

macardoso said:


> Measuring tool offsets offline with BT30 is tricky too.


Haven't tried it yet, but I'm not so sure about that.  I think I'll turn a chunk of steel to have a BT30 ID taper and face both ends.  This goes on the surface plate with the socket taper facing up.

Stick a tool holder in the spindle and get the difference between the spindle face and the holder tip.  Then put the holder in the socket on the surface plate.  The difference in the length betwen your socket face and the tip is the other value.

The difference between values is the offset you apply when you measure all other tools.  Zero on the socket face, measure the length of the tool, and add/subtract the offset.

Or you could face the socket incrementally until it measures exactly the same as your spindle.  Now you don't have to worry if your socket/fixture taper is perfect  - just as long as a tool/holder resting in it on the plate is the same length as when its installed in the spindle.



shooter123456 said:


> At this point I am still leaning toward BT30 because I think the performance will be better and I like the wide range of tooling available. Being able to share tooling with future machines is also a plus in my mind.



This, plus no pull-out.  Even with as few paying jobs as I get, I can buy a lot of tool holders if I scrap a part from pull-out.  I don't want to have to baby-sit the machine and feed-hold the instant I hear chatter.

TTS works great and is cheap.  I've pushed it pretty hard with no issues - but the minute there is some squealing or chatter I get some pull-out even with my drawbar torqued well above the Tormach recommendations (plus clean taper, fresh Bellevilles, and light lube on the sliding surfaces).


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## macardoso (Jan 31, 2020)

spumco said:


> Franken motor experiment successful!



That's seriously awesome! Great work. Really opens a lot of doors. As a motion control guy, I've watched how all the companies take really drastic efforts to make their motor to drive interface proprietary - even on "open" networks. This circumvents that.


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## spumco (Jan 31, 2020)

It appears that the next hurdle in the 'Ralph Hijacks This Thread" saga is that the Frankenservo has a strange 18mm stepped shaft.

A QD bushing to fit 18mm doesn't exist on this planet.  Mount 14mm QD bush lightly snug in pulley, pulley in the 4-jaw, indicate the taper and have a go?


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## Yukonjack (May 3, 2021)

Any more updates? I'm working on a a PM-940 to CNC


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## spumco (May 3, 2021)

We've sort of continued the conversation on the other thread.  Due to a number of delays, I'm just getting back to sorting out my spindle motor...  nothing set in stone quite yet.


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## macardoso (May 4, 2021)

spumco said:


> We've sort of continued the conversation on the other thread.  Due to a number of delays, I'm just getting back to sorting out my spindle motor...  nothing set in stone quite yet.


https://www.hobby-machinist.com/thr...mill-spindle-and-axis-motor-performance.90490


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## Yukonjack (May 4, 2021)

Thanks for the link. Seems a lot of threads end, right when they're getting to the good part


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