# PM-728VT CNC Conversion Instructions



## chipinator (Aug 27, 2022)

Hello all...I hope everyone is staying well.  I would like to convert my PM-728VT to CNC.  I've searched around on the interwebs, YouTube, etc..., and I can't seem to find detailed instructions on how to do this, from the electrical to the mechanical, everything.  Going into it blind is not something that I relish doing.  Would anyone happen to know where I might find detailed instructions on this conversion?  Thanks.


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## chipinator (Aug 29, 2022)

With no answers, apparently there aren't any instructions for this conversion.  That's too bad.  I'm sure there is a market for instructions such as this.  There are likely a lot of people that would like to know how.

Maybe someone can answer this question associated with this post then.  I was sourcing AC servo motors for my PM-728VT mill and I was asked how much torque was needed.  Seeing I'm no CNC machinist, yet, would anyone be able to provide a torque value I would need?  Any suggestions would be helpful.  Thanks.


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## Firebrick43 (Sep 1, 2022)

There are no step by step instructions, as what every individual wants/needs/budget is different.  

There are pleanty of "guides" on youtube and the web to wire and set up individual components.  Its up to you to research and decide what components to use.  

Your AC servos is a perfect example.  With non ground ball screws and the typical support bearing quality/housing design that most of these machines use, AC servos provide little advantage except fast rapids.  And I question the "need" for fast rapids in such a small machine and the detriment to the plain ways that they can cause.    But some feel that they need them, and thats ok.  Life would be dull if everyone did the same thing.  

Steppers, especially the closed loop ones with encoders provide higher slow speed torque and can provide more accuracy than the mechanical components can provide.


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## 7milesup (Sep 1, 2022)

@chipinator I don't mean to be rude but aren't you the guy that did not want to fix the one shot oiler system? I believe you said you weren't a milling machine mechanic. As @Firebrick43  just pointed out it is a large process to convert a mill and there are no step by step instructions to my knowledge. You will have to completely disassemble the mill for the most part to put in ball screws etc etc.


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## chipinator (Sep 1, 2022)

@Firebrick43    Thank you for taking time out to respond.  I appreciate it.  AC servos vs. steppers is noted.  A nice bit of information to have.

@7milesup    I'm not a milling machine mechanic which is why I didn't want to disassemble my mill to try and find a leak that was an issue from the point of purchase.  Why should I be responsible for an issue that I didn't cause on a brand new item and why should I be the person to have to fix it when it's under warranty?  Just like my car analogy...I'm not a car mechanic so when something happens to it I take it to the stealership to get it fixed, and I'm willing to pay.  Maybe not your cup of tea but it's mine just fine.  As @Firebrick43 stated above, "Life would be dull if everyone did the same thing."  Cheers!


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## 7milesup (Sep 1, 2022)

Well, good luck.


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## chipinator (Sep 4, 2022)

That's why I like instructions.  I would like to do it right the first time.  I did find this site on the interwebs, https://cncproprietary.com/buy-pm-728vt-cnc-conversion-guide/, that purports to sell a conversion guide but I can't find a place on the page to purchase it.  Odd.


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## sunrise305 (Sep 15, 2022)

Did you end up starting this conversion?


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## chipinator (Sep 17, 2022)

@sunrise305    I haven't started yet.  I've been sourcing all of the components at a snails pace it seems.  For instance, I'm interested in DMM AC servo motors but I just found out a few days ago that the mounting holes in the NEMA23 motors are not straight through, they are oblong.  DMM does have an 8mm thick mounting bracket in case the mounting holes of the motor don't align with the holes in the mounting bracket for the motors that attach to the mill.  I want to make sure I'm purchasing correctly the first time as these are high dollar items.  As well, I'm trying to find all of the companies that produce/market/sell AC servo motors so I can make comparisons.  I called Precision Matthews and asked if their precision ball screws were ground as @Firebrick43 mentioned above and they are not ground.  I haven't found any precision ball screws for this machine that are ground.  If anyone finds precision ground ball screws for this machine, I would be interested in receiving that information.  That's kind of where I'm at.  Once I find really good AC servo motors, I can move forward a little further.


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## sunrise305 (Sep 17, 2022)

chipinator said:


> @sunrise305    I haven't started yet.  I've been sourcing all of the components at a snails pace it seems.  For instance, I'm interested in DMM AC servo motors but I just found out a few days ago that the mounting holes in the NEMA23 motors are not straight through, they are oblong.  DMM does have an 8mm thick mounting bracket in case the mounting holes of the motor don't align with the holes in the mounting bracket for the motors that attach to the mill.  I want to make sure I'm purchasing correctly the first time as these are high dollar items.  As well, I'm trying to find all of the companies that produce/market/sell AC servo motors so I can make comparisons.  I called Precision Matthews and asked if their precision ball screws were ground as @Firebrick43 mentioned above and they are not ground.  I haven't found any precision ball screws for this machine that are ground.  If anyone finds precision ground ball screws for this machine, I would be interested in receiving that information.  That's kind of where I'm at.  Once I find really good AC servo motors, I can move forward a little further.


Thanks for your response.  I have seen numerous threads about PM-728VT owners heading down this path, a conversion that is of interest to me and many others, but never any reports of the final outcome.  I posted a question on this forum months ago asking for feedback on how those conversions turned out but received rzero response.


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## chipinator (Sep 17, 2022)

Feel free to reach out to me as I go down this path.  I foresee this taking some time sourcing everything though.


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## 7milesup (Sep 17, 2022)

chipinator said:


> I haven't found any precision ball screws for this machine that are ground. If anyone finds precision ground ball screws for this machine, I would be interested in receiving that information.


You will not find ground ball screws that are anywhere close to what you want to spend.  For example, the precision ground ball screw for my Sharp mill is $2000, which is ONLY for the x-axis.  Generally, for a mill the size of the 728 you would be looking at $1500 for the x-axis and probably $900 for the y-axis.  That will get you started.


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## chipinator (Sep 17, 2022)

@7milesup    Thanks for posting.  Ouch!  That's a good amount of money that I'm not willing to spend for precision ground ball screws.  Maybe I'll just go with what PM is selling and be gentle with them.


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## 7milesup (Sep 17, 2022)

At one point, I was looking at converting my 833T to a CNC machine.  I looked around quite a bit for "good" ball screws, but it seemed like it was an uphill battle.  *Here is one place* that I was looking at.  Also*, this place. 
https://www.automation4less.com/ballscrews.htm*
Here is a thread I ran across.  It is old but still has some useful info in it.* Benchtop-machines ball screws quality choice mapping.
This thread is even older but provides an overview of ball screws.*


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## Firebrick43 (Sep 18, 2022)

chipinator said:


> @7milesup    Thanks for posting.  Ouch!  That's a good amount of money that I'm not willing to spend for precision ground ball screws.  Maybe I'll just go with what PM is selling and be gentle with them.


As 7milesup stated, ground ball screws are very spendy. The reason I mentioned them was not for durability/strength but precision. Many have the idea that ac servos are more precise, and they can be, but only if they have ground ball screws and Abec 7 super precision support bearings to match. If you have a limited budget as many hobbiest do, your limited to rolled ball screws and abec 3 bearings. Not to mention very few have precision ground spacers between the support bearing.  And so your accuracy is limited and therefore why use ac servos over closed loop steppers?  Accuracy is only as good as your weakest link.


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## chipinator (Sep 19, 2022)

I'm not cheap but I'm not rich either.  I would like good accuracy but I don't know how accurate a closed loop stepper motor can be.  Anyone have any really good brands/companies for closed loop stepper motors I can research?  Of course I'm looking for NEMA23 for the X and Y axis, and NEMA34 for the Z axis with a spring set brake/electronic brake.


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## JimDawson (Sep 19, 2022)

You might take a look at the Automation Direct LS servo line, comparable to DMM with better documentation and better setup software.  I have used these on one project and was happy with the result.  https://www.automationdirect.com/selectors/ls-servo

The other option is the slightly more expensive SureServo2 line.  I have one of the 7.5kW units on my lathe spindle and am quite happy with it.


			https://www.automationdirect.com/selectors/sureservo2
		


I have also used DMM servos on a number of projects, they work OK. A bit of a PITA to tune and adjust.  I do have 4 of their 1.8kW units on my lathe.


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## chipinator (Sep 20, 2022)

@JimDawson    Thank you for the reply.  I'll have a look.

Then there's the software option.  I have a dedicated computer and monitor specifically for this build.  I would like to use a conversational software package, however, I emailed the Mach4 developers and they stated it was not conversational software.  Aye yie yie!  Anyone know of a good conversational software package I can use as well as use CAD/CAM?


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## JimDawson (Sep 20, 2022)

chipinator said:


> Anyone know of a good conversational software package I can use as well as use CAD/CAM?


Centroid Acorn Pro version has full conversational programming, in addition to normal G code. And will work with any of the above servos or steppers.





						Acorn CNC controller, Step and Direction 4 axis CNC Control board with ethernet communication.DIY CNC kit
					

Acorn Do-it-Yourself CNC control board for Mills,Lathes,Routers,and other Machine tools.  Mach3 replacement CNC controls for new machine tools as well as Retrofits for older NC machinery



					www.centroidcnc.com


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## chipinator (Sep 20, 2022)

@JimDawson    Thanks again for the reply.  I appreciate it.  Looking back over which motor to use, I looked at the SureServo2 line you suggested.  The page for the SureServo2 is asking for Torque Required from the Motor.  For a mill such as mine, how much torque would you suggest?


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## JimDawson (Sep 20, 2022)

chipinator said:


> @JimDawson    Thanks again for the reply.  I appreciate it.  Looking back over which motor to use, I looked at the SureServo2 line you suggested.  The page for the SureServo2 is asking for Torque Required from the Motor.  For a mill such as mine, how much torque would you suggest?



Assuming a 5mm pitch ball screw and direct drive, the 400W units would be fine for the X & Y axis, and the 750W would be OK for the Z axis.

Also rather than a brake on the Z motor, an air spring would be my first choice to counterbalance the Z axis.  Most likely less money than the brake, certainly not more.  An air cylinder, small air tank, and a regulator.


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## 7milesup (Sep 20, 2022)

@chipinator   Have you *seen this video? * It is a PM727 but might give you some ideas.


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## Firebrick43 (Sep 20, 2022)

Certainly Jims suggestions and even the clearpath SK would work well but so would some nema 23 or 24  closed loop ~4nm  steppers would work with x and y 

Amazon 4 NM closed loop stepper

I would use a nema 34 6nm or 9nm with the Z axis.  

I also agree with Jim Dawson about either an air cylinder or even a counterbalance that will work well on a 727.  The brake is a safety if you loose power.   Most commercial vertical CNC mill have either a nitrogen charged counterbalance cylinder or actual counterbalance weights (especially on older machines)  If you get the weight close to being balanced you won't need a brake, and there will be less wear and tear on you screw and on the ways of Z.


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## JimDawson (Sep 21, 2022)

@chipinator it can be a bit overwhelming trying to spec and design a CNC system.  There are really very few guidelines out there to help with the decision making.  I hope that this will be of some help.

I have pretty much stayed out of this discussion on purpose, because I have no experience with benchtop machines, and haven't researched the parts.  I normally work on commercial equipment, but the same general principals apply.  I had a bit of time and took a look at what others have done on similar machines.  I also actually have a benchtop CNC machine but it just sits on the shelf because I have no need or room on the floor for it right now.  It uses NEMA 23 and 34 stepper motors.  I'll do a controls retrofit on it someday.... Maybe.

Ignoring budget constraints, the three most important factors to consider when purchasing parts is quality, documentation, and support.  In most cases if the documentation and support is there, quality will be there also.  In other words, purchase from known trusted vendors that have a North American telephone number and email address.  You pay a bit more for hardware purchased with good documentation and support, and it's worth every extra penny.  This also applies to the software and controller.

*Accuracy. Repeatability. Resolution.

Accuracy:* If you tell the table to move 6.00001'' then if the machine is accurate it will move 6.00001'', no more, no less.  In a perfect world it would hit that target, but the world is not perfect so there is always going to be some error in the move.  To get the error smaller the cost of the hardware goes up exponentially. A common accuracy for hobby class equipment is +/- 0.002'' over 12''.  Or maybe a bit better.

*Repeatability:* More important than accuracy is repeatability.  Will the machine move to the same place every time?  You can compensate for accuracy errors if the machine will repeat.  I expect that repeatability should at least be in the +/- 0.0002'' range if you have enough resolution.

*Resolution:* The smallest unit that your system is capable of measuring/moving.  The more steps or encoder pulses per revolution of the ball screw the smaller division the system will measure.  Normally you want the resolution to be at least 10X the target repeatability.  So let's take a 5mm pitch ball screw and a 200 step/revolution stepper.  I'm going to use metric measurements here.  1000 microns = 1mm or 0.001mm = 1 micron =0.000039'' .  So 5000 microns/200 steps = 25 microns or about 0.001'' per step.  So reasonable resolution will be in the range of 2.5 microns or about 0.0001'' or better.  I use 1 micron resolution scales on my machines, and expect repeatability of +/- 0.0001'' or better.

Having said all of that, there are many other factors that enter into the overall tolerance and what you can expect out of the machine. 

*Mechanical:* There is no substitute for a tight machine with no backlash.  Just like perfect accuracy, 0 backlash is not going to happen, but you can most likely get it close to not measurable with tools normally found in most shops.  The backlash can come from not only the ball screw but also the thrust bearings as well as flex in the overall system.  The ultra precision ball screw kit from Precision Mathews would probably be my first choice.  It comes equipped with double nut ball screws and looks to be just a simple bolt in installation, as well as being designed to exactly fit your machine.  It doesn't get any simpler than that.  Looks like it could be installed in a day.  $1200 for the complete kit seems reasonable.

*Axis Motors:*  There are two types of motors that are in common use today; steppers and BLDC (Brushless DC).  The BLDC motors are commonly called ''servo motors'', but that is not technically correct.  The marketing department of the various vendors have muddied the waters with their own naming conventions. A servo system is any closed loop system, so any motor that operates with a closed loop is a servo motor.  Your home heating system is a closed loop servo system, as is your car a multi axis system where you are the controller.

*Stepper Motors:*  This is the low end of the axis motors.  Cheap and easy to set up.  Normally limited to Step & Direction open loop control. Can easily lose position if over torqued by missing steps, or just completely magnetically decouple and quit turning while growling at you.  Open loop only.  Base resolution of 200 steps per revolution, but normally operated in half or quarter step mode for 400 or 800 steps/rev.  Steps/rev can be set higher at some cost to performance, normally up to about 56,000 steps/rev.  Rated torque is holding torque at 0 RPM.  Torque drops off rapidly as RPM increases.

*Closed Loop Steppers:*  A small step up from a standard stepper, the difference being that they hung an encoder on the back of the motor then feed that encoder signal to the drive to compare the actual position to the commanded position, and make small adjustment if needed.  These are still stepper motors and subject to the same performance limitations as normal stepper motors.  These are a closed loop servo system with the loop closed at the drive, but with no possibility of feedback to the controller.

*BLDC Servo Systems, or more commonly called servo motors:*   More expensive than steppers or closed loop steppers.  Generally much higher performance.  The torque curve is normally flat from 0 up to near the motor rated speed, with 2x to 3x short duration overload capacity in the low to mid speed ranges. They will not ''lose steps'' like a stepper.  Most modern drives can be controlled by your choice of Step & Direction, Analog torque or speed signal, or direct communication using some derivation of a ModBus protocol. Depending on your choice of control, the loop can be closed at the drive or the controller via the drive encoder output or an external encoder.  All commercial machines use these systems today. There are probably 25 or 30 servo system manufactures.  Prices range from affordable for the hobbiest to crazy prices.

*Controllers

Motion Controllers:*  The motion controller handles the trajectory planning for the desired move.  You tell the motion controller where to move to in any number of axes, give it the speed and acceleration and the Go command.  It figures out how to make the move so the tool follows the desired path to get to the target point.  The moves are only straight lines, arcs are generated by very short straight line moves, so small that you can't see them.  This target position could be only 0.001'' or less from the current location or it could be several inches to the target position.  In the case of a closed loop system, the drive or controller is tightly monitoring the tool path and is making adjustments as needed, normally with a few microsecond update rate.  In addition the controller needs to perform PLC type functions like being able to turn on coolant, maybe controlling a VFD for the spindle and other peripheral functions.

Gone are the days of the parallel port machine control used the old Mach3 systems.  It's pretty hard to even find a modern PC with a parallel port.  Most systems today use USB, Ethernet, or PCI card to interface with the PC.  Ethernet and PCI cards are the most robust systems.  USB systems can be sensitive to electrical noise.  Many of the cheap ''motion controllers'' sold on eBay and Amazon are not actually motion controllers, but rather just breakout interface between the PC and the world. A hardware motion controller is a computer dedicated to the machine control duties and uses real time control.  They communicate with the PC, but they do the heavy duty math thus relieving the PC from those duties.

I am only going to address the systems most commonly found in the home shop here, there are many others available.  Mach3/4 use the PC as the motion controller, Centroid Acorn?, Centroid Oak, Dynomotion, CamSoft, and others use hardware motion controllers.

*Open Loop Systems:* The cost for these systems is generally less than a full closed loop system.  Mach3, Mach4, Centroid Acorn, and Dynomotion Kflop are all open loop step & direction systems, there is no provision for position feedback to the computer/controller.  The computer/software just assumes that the motors are doing what they are being told to do, and for the most part this works just fine.  If the loop is closed at the drive level then these CNC systems work good, but keep in mind that the DRO display shows where the controller thinks the position is, not necessarily where it actually is, but for the most part the displayed and actual position agree.  CamSoft can be used as open or closed loop because they use a Galil Motion Control controller that has the capability of both step & direction and full closed loop analog control.

*Closed Loop Systems:* Centroid Oak, Dynomotion Kflop/Kanalog, CamSoft, and others close the loop at the controller. All of these use a dedicated hardware motion controller. The DRO display is the actual position based on the encoder feedback from the motors or external encoders.  It is my preference to close the loop at the controller level, and use external encoders for position feedback, although I have used the drive encoder output as the feedback encoder with good success.  My prefered encoders are 1 micron resolution linear magnetic scales.  With linear encoders you pretty much take mechanical ball screw/backlash errors out of the system and directly read the table position.  But there is no substitute for a tight mechanical system.

*CNC software:*  Mach3/4 is CNC operating software of course.  Dynomotion, Centroid, CamSoft and others all come with their own CNC software.  I have not used any of them, but they all work and have various levels of user friendliness.  You mentioned wanting conversational programming.  I have used that before and found it to be more trouble than it's worth.  CAM software is so much easier to use, I even use it for quick jobs like facing off a part.  No way I'm going to stand there and punch commands and numbers into the computer when I can generate the same thing with a few mouse clicks.

*CAD/CAM software:*  There are so many options available that I'll only touch on a couple that I use.  Prices range from free to only SpaceX can afford it.  Today Fusion 360 is my go to CAD/CAM software. Free to hobbyists, although the free version is somewhat broken, but what do you want for free.  It still works and has mostly full functionality but a few limitations.  I used to use AutoCAD and let that license expire when I bought a Fusion 360 license, but for a substitute I use NanoCAD V5.0 (free) which is virtually an AutoCAD clone.  For CAM software CamBam is a good value with a short learning curve.  It has some rudimentary CAD functionality. At $150 for a lifetime licence it is a good value and I sometimes still use it.  They have a very generous trial period program.

*Electrical:* Once you decide what hardware you want, you are going to need to stuff it in a box and wire everything together.  Buy all of the components that you need, lay it all out on the table, then buy the enclosure 20% larger than you think you need.  Nothing worse than running out of panel real-estate. You want to generally follow NEC, UL, and OSHA guidelines, however for home shop use, strict adherence to any of those is not required.  But you want to keep things safe and not burn down your shop.  This means using proper components, fusing, and wire sizing.  In addition proper safety shutdown circuits.  Automation Direct is my go to vendor for all things electrical panel related, however I am not opposed to buying enclosures and other non-critical parts from eBay or Amazon.  Do not buy circuit breakers from anyone but known vendors, there are a lot of fakes out there that look like breakers but are in fact just cheap switches.

As far as electrical diagrams, there is no generic diagram for a CNC machine, they are all different.  There are however some generally accepted circuits for power handling, control power, and E-stop circuits. The hardware will come with wiring diagrams.

I am tired of typing now so I think I'll go make some chips. I hope this helps.  I'll be happy to try to answer any questions.


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## koenbro (Sep 21, 2022)

sunrise305 said:


> Thanks for your response. I have seen numerous threads about PM-728VT owners heading down this path, a conversion that is of interest to me and many others, but *never any reports of the final outcome*. I posted a question on this forum months ago asking for feedback on how those conversions turned out but received rzero response.



I have completed a conversion with Clearpath and Acorn with MPG and probe, power draw bar, Z-axis brake, enclosure and coolant (using mist now).

Works well, am happy with it. Not sure what else to report. There is a build thread under my name.


Sent from my iPhone using Tapatalk Pro


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## chipinator (Sep 21, 2022)

@JimDawson    Wow!  Jim...Thank you for taking the time to write all of that information.  I don't know what to say but thank you.  Too bad I don't live in your area.

I was looking at the SureServo2 motors last night.  I see that they have Auto Tuning.  Seems to be a nice feature to have when you don't know what you are doing.  It looks like these motors need proximity switches though.  

I thought I read somewhere that AC servo motors don't need proximity switches although I'm not sure if that is true or not.  

Centroid/Acorn is in the running for controllers and software.  The AcornCNC board looks nice but I"m sure there are plenty more controller boards on the market.  I did see a C82 dual port multi-function board from CNC4PC but I didn't see a brand name.

Oh to make the right choice.


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## JimDawson (Sep 21, 2022)

chipinator said:


> @JimDawson Wow! Jim...Thank you for taking the time to write all of that information. I don't know what to say but thank you. Too bad I don't live in your area.


My pleasure. 


chipinator said:


> I was looking at the SureServo2 motors last night. I see that they have Auto Tuning. Seems to be a nice feature to have when you don't know what you are doing.


Very handy under some conditions, especially when using step & direction control with the loop closed at the drive. I think most servo systems have auto tuning.  I have only used the auto tune on the one ClearPath installation I did.  The rest I just manually tuned to my control and machine.  Last week I manually tuned some DMM units over the phone working with a guy getting his mill retrofit done.  Pretty easy really. I was giving him numbers to plug in and just asking what was happening.  Almost like I was standing in front of the machine, not the first time I have done this.   Tuning is just a matter of tightening up the action of the system with the PID values until the machine goes unstable, then back off a bit.



chipinator said:


> It looks like these motors need proximity switches though.  I thought I read somewhere that AC servo motors don't need proximity switches although I'm not sure if that is true or not.


Proximity switches?  Servo motors don't require any switches except maybe to turn them on and off, you could use a wall light switch.  I guess they might have forward and reverse limit connections, but any switch would work, including but not limited to prox switches.  Normally the limits are connected to the controller rather than the drive.  But I guess there is no reason you couldn't connect to both for a redundant system.


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## 7milesup (Sep 22, 2022)

@JimDawson Thanks for that write-up.  I was trying to wrap my head around CAM and post processing for my Sharp mill with a TRAK Prototrak AGE 2 system.


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## JimDawson (Sep 22, 2022)

7milesup said:


> @JimDawson Thanks for that write-up.


My Pleasure!



7milesup said:


> I was trying to wrap my head around CAM and post processing for my Sharp mill with a TRAK Prototrak AGE 2 system.


The TRAK Prototrak AGE 2 system is about as convoluted as the Anilam M system that I used to have on my mill.  I guess I would consider an upgrade to a more modern system.  I mean, floppy drives? Really? However the manual does allude to being able to use a Fanuc 6 post processor to generate G code.


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## JimDawson (Sep 22, 2022)

chipinator said:


> Centroid/Acorn is in the running for controllers and software. The AcornCNC board looks nice but I"m sure there are plenty more controller boards on the market. I did see a C82 dual port multi-function board from CNC4PC but I didn't see a brand name.
> 
> Oh to make the right choice.



In your case, I would recommend the Centroid Acorn system.  It's is simple, inexpensive, well documented and supported.  There is also a large user base to draw knowledge from.


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## chipinator (Sep 22, 2022)

@JimDawson    I'm definitely leaning towards the Centroid Acorn and software.  I thought I remember reading something to the effect that their G code may be a little different.  I can't remember where I read it though.  Anyway...  In my previous post, I meant proximity switches (limit switches) for the X, Y, and Z axis' so an accidental programming error doesn't cause the motors to crash the table.  That would be nasty and likely expensive.  Now I just have to narrow down which motors.


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## JimDawson (Sep 22, 2022)

chipinator said:


> @JimDawson    I'm definitely leaning towards the Centroid Acorn and software.  I thought I remember reading something to the effect that their G code may be a little different.  I can't remember where I read it though.


Fusion 360 has a Centroid post built in.  There are no two software brands that use exactly the same G code.  The basics are the same across the board, but some of the canned cycles can be different.  For the most part, the primary codes that are used are G0, G1, G2, G3, and G81.  You can make any part that your machine could possibly cut with only those codes, in fact, you really could cut any part only using G1, which is just a straight line cutting move.



chipinator said:


> Anyway...  In my previous post, I meant proximity switches (limit switches) for the X, Y, and Z axis' so an accidental programming error doesn't cause the motors to crash the table.  That would be nasty and likely expensive.  Now I just have to narrow down which motors.



I figured that's what you meant.    A lot of machines do use prox sensors, but it's my preference to use normal limit switches for this purpose.  From a controls perspective, it really doesn't matter what type of switch you use as long as they work.  Crashing a machine can really ruin your day.


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## chipinator (Sep 23, 2022)

@JimDawson    In a perfect world, and you had precision ground double-nut ball screws, which motors would you use/prefer if you had my mill?


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## JimDawson (Sep 23, 2022)

chipinator said:


> @JimDawson    In a perfect world, and you had precision ground double-nut ball screws, which motors would you use/prefer if you had my mill?



I think I would go with the Automation Direct LS servo motors.  400W for the X & Y and 750W for the Z.  These are the same motors I would use on my machine.  I'm a little undecided on the need for the Z brake, I'm thinking a counter balance would be the better option.


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## chipinator (Sep 23, 2022)

@JimDawson    I looked on the Automation Direct website and found the following servo motors -

APMC-FBL04AYK-AD  [400W]
APMC-FCL08AYK2-AD  [750W w/integrated brake]

I couldn't find a NEMA number on either of the motors.  If the 400W motors are NEMA23 and the 750W is NEMA34, I'm good.

I know you aren't interested in an integrated brake, however, I had seen a couple of Tube videos with counterbalances and one with the integrated brake.  I think I will try the integrated brake first and see how that performs.  I do understand the counterbalances though.

Do you think the servos I listed above are ones that you would use or would you have different motors in mind?


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## JimDawson (Sep 23, 2022)

chipinator said:


> @JimDawson    I looked on the Automation Direct website and found the following servo motors -
> 
> APMC-FBL04AYK-AD  [400W]
> APMC-FCL08AYK2-AD  [750W w/integrated brake]
> ...



Yes, that would be the correct motors.

They are not exact NEMA frame size equivalent. You would not know it unless you had them sitting side by side with a NEMA frame motor.
The 750W motor (80mm frame) has a slightly smaller face than the NEMA 34 frame, and has a 19mm shaft vs. the 1/2'' shaft of the NEMA 34.
The 400W motor (60mm frame) I'm not sure about yet.  It does have a 14mm shaft vs. the 1/4'' shaft of the NEMA 23 motor.

I'm trying to get accurate dimensions but Fusion 360 is not cooperating tonight, having some file upload problems.  It would be a simple project to make adaptor plates to fit the NEMA mounting brackets.

EDIT:  The 400W motor face is just slightly larger than the NEMA 23 face.


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## chipinator (Sep 24, 2022)

@JimDawson    Thanks for that Jim.  I appreciate your insight.  This is very helpful.

When I first looked at the DMM AC servo motors, I noticed that their NEMA23 motors didn't have straight through mounting holes.  The company kind of oblonged the holes I guess in an effort to allow them to mount easier.  DMM emailed me that they have an 8mm adapter plate for those as well.  When those motors were mounted, standing in front of the mill, instead of looking like a square with the flat sides at the cardinal points, the 90 degree edges of the motors were at the cardinal points, kind of in a star mounting position.  Not a big deal I guess. 

For the PM's ultra precision ballscrew kit, https://www.precisionmatthews.com/shop/cncballscrewkit-pm-728vt-up/, it looks like the provided couplers wouldn't work for the Automation Direct motors.  I don't know if there are couplers that are made that would fit the Automation Direct motor shafts to the ballscrews given their size.  I wish this were easier!  I know, nothing in life worth having is easy.


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## JimDawson (Sep 24, 2022)

chipinator said:


> @JimDawson    Thanks for that Jim.  I appreciate your insight.  This is very helpful.


Thank you



chipinator said:


> When I first looked at the DMM AC servo motors, I noticed that their NEMA23 motors didn't have straight through mounting holes.  The company kind of oblonged the holes I guess in an effort to allow them to mount easier.  DMM emailed me that they have an 8mm adapter plate for those as well.  When those motors were mounted, standing in front of the mill, instead of looking like a square with the flat sides at the cardinal points, the 90 degree edges of the motors were at the cardinal points, kind of in a star mounting position.  Not a big deal I guess.


It's pretty common to make motor adapter plates, and the normal way of doing it is to rotate the motor to get hole clearance.



chipinator said:


> For the PM's ultra precision ballscrew kit, https://www.precisionmatthews.com/shop/cncballscrewkit-pm-728vt-up/, it looks like the provided couplers wouldn't work for the Automation Direct motors.  I don't know if there are couplers that are made that would fit the Automation Direct motor shafts to the ballscrews given their size.  I wish this were easier!  I know, nothing in life worth having is easy.



You buy the coupler pieces separately.  Yes, there are couplers that will fit.

EDIT:
X & Y axis
10mm


			https://www.automationdirect.com/adc/shopping/catalog/motion_control/drive_couplings/jaw_coupling_hubs_-a-_spiders/sjc-25c-10
		


14mm


			https://www.automationdirect.com/adc/shopping/catalog/motion_control/drive_couplings/jaw_coupling_hubs_-a-_spiders/sjc-25c-14
		


Spider for above


			https://www.automationdirect.com/adc/shopping/catalog/motion_control/drive_couplings/jaw_coupling_hubs_-a-_spiders/sjc-25-bl-sleeve
		


Z axis
10mm


			https://www.automationdirect.com/adc/shopping/catalog/motion_control/drive_couplings/jaw_coupling_hubs_-a-_spiders/sjcb-40c-10
		


19mm


			https://www.automationdirect.com/adc/shopping/catalog/motion_control/drive_couplings/jaw_coupling_hubs_-a-_spiders/sjcb-40c-19
		


Spider for above


			https://www.automationdirect.com/adc/shopping/catalog/motion_control/drive_couplings/jaw_coupling_hubs_-a-_spiders/sjc-40-bl-sleeve


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## chipinator (Sep 25, 2022)

@JimDawson    Jim...Thank you so much for your kindness in helping me.  It truly doesn't go unnoticed.

I'm typically a person that tries to look far enough down the road to take into consideration issues that may arise.  For instance, if a motor for some reason stops functioning and your CNC is now down.  Have you ever seen a shaft coming out the back of these types of motors so that mill crank handles could attach?  At leaset you would have manual control at that point.  What do you think?


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## JimDawson (Sep 25, 2022)

chipinator said:


> @JimDawson    Jim...Thank you so much for your kindness in helping me.  It truly doesn't go unnoticed.



My pleasure to help out where I can. 



chipinator said:


> I'm typically a person that tries to look far enough down the road to take into consideration issues that may arise.  For instance, if a motor for some reason stops functioning and your CNC is now down.  Have you ever seen a shaft coming out the back of these types of motors so that mill crank handles could attach?  At leaset you would have manual control at that point.  What do you think?



A subject that is near and dear to my heart   I have hand cranks on my machine and can operate full manual, 2 axis CNC with manual quill, 3 axis CNC with manual 4th axis, or full 4 axis CNC.  All with change over in seconds. (Ok, it takes more than a few seconds to set up the 4th axis    ) If I could only have one CNC machine in my shop, this would be the prefered system.

I have never seen a dual shaft servo motor.  There are dual shaft stepper motors available, and I have seen handwheels attached to those.  Not the best IMHO.  The better way to do this is to offset the motor from the ball screw and drive the ball screw with timing pulleys.  Then attach the handwheels directly to the ball screws.  There are hundreds of machines out there configured like this.

Here is a picture of my machine showing the X and Y drives with the offset motors.  The exact motor placement would be a bit different on your machine due to the different frame design.  But maybe easier because your motors would be much smaller, my motors are about 12'' long and about 4'' diameter, old school brushed DC motors.  Where your motors would be about 2.5'' square and 4'' long






The down side of this is that the standard CNC kit would need to be modified a bit to accommodate the changes.  Not really a big deal but would require a bit of engineering and fabrication.  The extra parts and modifications could easily be done on the machine, before starting the installation of the new CNC conversion hardware.


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## chipinator (Sep 28, 2022)

@JimDawson    If you were to have to use stepper motors for a machine like mine, which brand and model would you use that's able to accommodate mill crank handles?  I'm interested mostly out of curiosity.  Thanks.


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## JimDawson (Sep 28, 2022)

chipinator said:


> @JimDawson    If you were to have to use stepper motors for a machine like mine, which brand and model would you use that's able to accommodate mill crank handles?  I'm interested mostly out of curiosity.  Thanks.


I would probably go with Automation Technologies products, they have several dual shaft NEMA 23, and NEMA 34 motors available.





						NEMA 23 Stepper Motor |
					






					www.automationtechnologiesinc.com
				




Not better products than eBay or Amazon, at least they are a stocking USA distributor.  And the one time I did have a problem with one of their products they were very responsive and sent a replacement with no hassle.


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## 7milesup (Sep 30, 2022)

@chipinator  I would consider servo motors if you want to maintain manual functionality.  Stepper motors have a certain degree of "cogging" to them when rotated by hand.  This is inherent in all stepper motors, but it does vary with the size of the stepper, and I also believe the manufacturer, although I do not have first-hand knowledge on that aspect, but rather, only from what I have read.  
My mill and Jim's mill both have servo motors that are connected to the ball screw via timing belts.  This system works very well and allows for easy manual control.  One safety item I should mention is to purchase cranks that have the handle stow away.  I feel that this is very important for a machine that has both manual and CNC capabilities.  You don't want that handle sticking out when the axis activates.  
Also, counterbalancing the Z-axis, in my opinion, would be important because when power is taken away from the servo motors, they are free to move, so your Z-axis will self-lower until it gets to the table.  
The picture I have included shows the servo motor at the left end of the x-axis and the y-axis at the front,
	

		
			
		

		
	






	

		
			
		

		
	
 but it is mounted low nearer the base.  The handles are stow-away type.  (This is a picture from the day when I brought it home)


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## akschu (Oct 1, 2022)

I followed koenbro's thread when I converted mine.  Bought the same acorn and clearpath servos.  It's pretty decent.  The clearpath stuff is fast and accurate, the PM precision ballscrew kit mounted with little trouble, and the acorn stuff has been great.  After backlash adjustments I'm within .001.

schu


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## chipinator (Oct 2, 2022)

@7milesup    Thanks for the picture; very nice acquisition.  I have a cousin who's been a machinist/tool and die maker for a lot of years and he mentioned the same about timing belts.  He told me that direct connects do not have the fidelity that timing belts do.  In my case, without doing a lot of designing and fabricating, it looks like at least for now I'll have to stick with direct connect.

In the beginning, which is where I'm at, I just want to make sure I'm making all of the correct decisions up front.  I'm not one that typically steps out immediately on a high dollar purchase - I mull it over for a couple of months going back to what I've decided on again and again until I feel I've made all of the best informed decisions.


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