# PM 728 Mill- Issues and upgrades.



## rwm (Aug 18, 2020)

After waiting for the DRO to become available I pulled the trigger on a PM 728.







I made a stand to get one of my cabinets under it.






Engine hoist in my crowded little shop:





And finally home:





There are a lot of nice things about this machine. The tram out of the box was pretty close.





A few bumps with a dead blow and it was right on. The motor and variable speed control are awesome and very smooth.
The table motion is reasonably smooth with minimal backlash.

The only issue so far is the fine feed for the quill. The fine feed turns a worm that engages a worm wheel that runs on the quill feed shaft. On my machine, the fine feed knob binds considerably at one segment for every rotation of the worm wheel. There seems to be an engagement error. I have worked with tech support at PM and they are sending me a new worm wheel to try. Hopefully that will solve the issue.

Robert


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## rwm (Aug 18, 2020)

Some upgrades:

Chip shield





Work light





Speed handle









I will keep you posted on the fine feed issue.

Robert


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## sycle1 (Aug 19, 2020)

Looks like a sweet new mill! (just slightly envious)
May your chips be easy and many!
Cheers


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## rwm (Aug 19, 2020)

The other really annoying thing about this mill is the power board beeps for 10 sec after you turn it off. I presume it is alarming for power failure? Not a helpful feature. There is no way I can live with that.  I suppose I will open up the board and remove the piezo speaker. Kind of like my Schnauzer does with stuffed animals?
Robert


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## Skowinski (Aug 19, 2020)

Congrats, nice machine!  Let the chips fly!

I was looking at that exact mill for a week or two, almost bought one, then decided to go with the idea that you need to get something bigger than you think you will need, ended up ordering a 833TV.


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## rwm (Aug 19, 2020)

Trust me; I would have gone bigger if I had the space. There is a BP in my future with this machine becoming CNC. Charlotte real estate prices are the limiting factor.
Robert


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## MtnBiker (Aug 19, 2020)

I like the chip shield. That's a great idea!


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## matthewsx (Aug 19, 2020)

Looks like some extra space in the front room there


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## GunsOfNavarone (Aug 19, 2020)

Awesome man! Machines in the house? H3ll yeah! I'd stick our bed in the garage if my wife was cool with the equipment in the house. You should have seen her face when she came home and the GSXR600 was in the living room.....actually it wasn't funny at all.


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## rwm (Aug 20, 2020)

New speed control knob. Much better look, although my knurling is not what I would like to be.






You may have noticed I flipped the face plate around so I am just using the bare metal side. I like the look much better. If you can't figure out what the buttons do without the labels you probably should not be using power tools.
Robert


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## GunsOfNavarone (Aug 21, 2020)

It's funny man, we both have the "same" avatar, we both have PM-72x's, we gotta have the same hand guns/rifles/knives....hay...what's your wife's name?.....


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## rwm (Aug 21, 2020)

Great minds think alike! 
R


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## rwm (Aug 27, 2020)

Next plan:
Hand cranking the Z axis is a workout. I want to automate it. Rather than go with a geared DC motor, I would rather get part of the way to CNC and put a stepper or servo on the Z axis. Then I can build a primitive board to step it. 
I have no idea how to attach the motor to the Z. I have no idea what size or type of motor. I have no idea how to build the control circuit. I definitely know that I will figure all this out with the expertise available here! 
I would invite any comments or suggestions at this time as I plan this. I will also review the many threads here to see what others have done. This was discussed in a PM727 thread but I am not sure the Z axis looks the same.
Robert


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## GunsOfNavarone (Aug 27, 2020)

Yeah, I posted similar questions. Always a bit surprised that there a X axis power drives but not Z except for bridgeports etc. Perhaps it's the weight, but my Z isn't that much harder to turn than X. A stepper would be nice as you could set simple increments. You thinking direct gear drive or belt?


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## rwm (Aug 27, 2020)

I was thinking direct. Not sure how much torque that would take? The side handle is geared down about 4:1. When these machines are converted to ball screw they are typically direct drive and the ball screw has a greater pitch. Shooter I believe used a NEMA 34 on a PM 272 with ball screw?
Robert


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## GunsOfNavarone (Aug 27, 2020)

Maybe for holding power that NEMA 34 would be a good choice. So, a spline to whatever size shaft is on the 34...7mm? Then a bracket to mount motor to column. I think a potentiometer would be cool to control it, but you're thinking moving towards a single axis CNC?


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## rwm (Aug 27, 2020)

I have already got a lead from Jim Dawson on something like this:









						DC 5V-12V 2-phase 4-wire Micro MINI Stepper Motor Driver Speed Controller Module  | eBay
					

If a limit stop is required, the upper limit switch can be connected to P3. [Power reverse connection protection] yes. Adjust Speed We afford all cost if it's our fault. Working mode.



					www.ebay.com
				




Yes I am headed toward Z axis automation with a plan to totally convert in the future.

Robert


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## GunsOfNavarone (Aug 27, 2020)

I played with the idea, I think our gear drive versus belt drive for spindle was a bit of a roadblock. There is a guy on YT that did get past that. I'll see if I can find him.


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## rwm (Aug 27, 2020)

I was going to take off the side handle and try to mount direct to the Z lead screw. I believe it is a keyed shaft. I could use a double ended stepper for so I could move the head (at least a little) if the system failed. I suppose you could mount the motor on the side and drive the horizontal shaft. 
Robert


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## GunsOfNavarone (Aug 27, 2020)

This guy does a great job at the conversion, maybe you'll get some ideas...
PM727 CNC conversion


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## rwm (Aug 29, 2020)

I just went and measured the actual torque required to raise the head of my mill. I used a 5" lever arm on the shaft and measured just under 5 lbs of force to lift it. So this equates to 25 in-lbs or about 400 oz-in torque. That would be the upper limit of most NEMA 24s but a powerful one might work.
Robert


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## GunsOfNavarone (Aug 29, 2020)

I would give yourself some cushion not to mention rapid versus a slow movement would require more.


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## rwm (Aug 29, 2020)

That is an excellent reminder. I did not figure in any inertia. Duh.
Robert


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## JimDawson (Aug 29, 2020)

rwm said:


> I just went and measured the actual torque required to raise the head of my mill. I used a 5" lever arm on the shaft and measured just under 5 lbs of force to lift it. So this equates to 25 in-lbs or about 400 oz-in torque. That would be the upper limit of most NEMA 24s but a powerful one might work.
> Robert
> 
> _I have gotten some input from others who have done this and they concur about the NEMA 34 with about 1000oz/in torque. I am confused about how to drive this? Those low power controllers on eBay are obviously designed for a much lower power motor. I would need a high power driver for this application. Outside of learning to program an Arduino is there an easy way to accomplish this? Could is use the controller you suggested above to provide logic input to a high power controller?_



Just to maintain continuity the italic text above is from a PM with Robert.

The stepper system normally consists of 3 main parts, the controller, the driver, and the motor.  You can use any controller that outputs a 5 volt step & direction signal.  The driver is the high power handling device that accepts the 5 volt input signals from the controller, and translates this into a high power 2 phase output to the stepper motor.  

An example of a driver https://www.ebay.com/itm/LeadShine-...859435?hash=item3658f7a82b:g:AaMAAOSwzL9d4MWT

You will want to size the driver to the motor, the higher the voltage the better, but the maximum amperage output is the important number.  You want the driver to be able to meet or exceed the motor rated amps.  The amp output on all of the available drives is adjustable to match the motor, you can always adjust it down.


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## rwm (Aug 29, 2020)

Jim- thanks for chiming in. I am now understanding this in much greater detail.

It looks like something like this would work for single axis control.








						Motor Pulse Signal Controller Generator Stepper Motor Driver PWM Speed Regulator  | eBay
					

Find many great new & used options and get the best deals for Motor Pulse Signal Controller Generator Stepper Motor Driver PWM Speed Regulator at the best online prices at eBay! Free shipping for many products!



					www.ebay.com
				




The output of this would feed the driver.

Robert


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## JimDawson (Aug 29, 2020)

Yes, that would work.  I have some experience with those and the one thing to note is that you need to set the speed pot to zero or near zero before you press the go button, then turn up the speed.  The output does not ramp up to the set frequency, but rather just applies the set frequency instantly, and at higher settings can cause the motor to decouple and just sit there and growl at you.  Won't hurt anything, but the motor doesn't rotate under that condition.  In other words, it tries to accelerate the motor faster than is mechanically possible.


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## GunsOfNavarone (Aug 29, 2020)

And I realize you're kind of freestyling this, but if you were going with the end goal of CNC, why would you not use a conventional stepper driver? Keeping in mind I'm new to the CNC stuff, I am in no way criticizing...


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## rwm (Aug 29, 2020)

Guns- I am glad you are commenting. I AM using a conventional driver module. This board would be the controller that would operate the driver. I do not want to spend the money or time on a 3 axis controller that requires computer input.
Jim- I can see that frequency issue! Also that module would be a little sketchy since it has no indicator (that I can see) to tell you which direction it was set to move! It needs a forward/reverse light. After looking around eBay it seems that most or these small boards have an integrated driver for small steppers. This was one of the few that have control only.
Robert

Edit: I just realized I could hack the board and add an led indicator on the direction output pin to indicated forward/reverse. Also the enable pin for that matter. This might be the ticket!


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## JimDawson (Aug 29, 2020)

Something like this might be better, you can add your own buttons and speed pot on a small panel.








						DC 5-32V Stepper Motor Speed Controller Driver Servo PLC Control For Industrial  | eBay
					

Input and Output: all input is optocoupler isolation, while output the negative pulse. The low level signal is valid. Start the motor and it will be in forward rotation again on and on. Then it automatically starts to reverse and won’t stop until it touches the REV limit.



					www.ebay.com
				




Here is one I did a few years ago.  Speed, For/Rev, Stop, and Run


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## rwm (Aug 29, 2020)

Ordered! That's exactly what I want to do.
My Chinglish is a little weak though. By "public side" do they mean ground? By "forward limit" and "reverse limit" do they mean when those terminals are high that determines the direction?
Thanks for you help on this.
Robert


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## rwm (Aug 29, 2020)

I keep meaning to post this. I made my first cuts in aluminum recently and I was very impressed!







The stock is 3/8" 6061. I used a 2 flute end mill and I did the slots as full thickness passes. The mill handled this easily. I am very pleased with this so far. This plate will be used to mount a small rotary table. 
Robert


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## GunsOfNavarone (Aug 29, 2020)

I was originally planning on selling my 727m once I got the Tormach, but it is nice to quick, one and done stuff on it, not to mention the ample work envelope. That Z Mod would sure sway me, I have had so many machine projects the last few months (projects FOR the machine) that I just want to get to real projects.


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## rwm (Aug 29, 2020)

I hear you! Its crazy how much time I spend making tools instead of actual product!
Robert


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## JimDawson (Aug 30, 2020)

I think ''public side'' means common.

Not sure what Forward Limit and Reverse Limit do.  Just set it up on the bench and connect per the drawing one at a time and see what happens.


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## rwm (Sep 2, 2020)

These are cool! Works very well...






Robert


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## GunsOfNavarone (Sep 2, 2020)

I have that same one too man! This is getting weird....


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## GunsOfNavarone (Sep 18, 2020)

How the Z axis coming along? @rwm


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## rwm (Sep 19, 2020)

Sorry. No progress. Life got in the way. I did acquire a Dell Optiplex case that could mount the electronics!
Robert


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## rwm (Jan 27, 2022)

I have discovered that my DRO is not working correctly on the Y axis. I could not figure out why I was getting errors on this axis until I played around with it today. I am finding that my Y read head, which is mounted on a long steel arm has enough flex to vary by .007 inches. If you manually push on the read head, and watch the DRO it will deflect as expected. The problem is that it does not come back to zero! This creates an uncertain error of up to .007". I have checked all the mounting screws and everything is tight. This error has already unknowingly caused several problems (in retrospect- I initially thought I made a math error. Now I realize it was the DRO!) Is anyone else seeing this on their machines?









						PM 728 Y axis DRO problems
					

I am posting this as a new thread hoping that other PM728 owners will chime in here. My Y axis DRO is malfunctioning. It is mechanical, not electronic in nature. Basically I have about .007" of play/backlash in the arm that supports the read head. If I manually deflect it, it does not return to...




					www.hobby-machinist.com
				




Robert


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