# PM-940M-CNC



## fritts (Feb 3, 2019)

Got on one the last 940M-CNC's that PM produced.  Its an all options unit with the 4th Axis, VFD, and auto oiler.  Unit also came with a small coolant reservoir, pendant, and R8 drill chuck and shell mill,  woohoo.

Used a friends bobcat with forks to move the large crates off the semi trailer and get them inside the building.  The mill comes in a vary large wood pallet/box and is awkward to move.





After removing banding and wood boxing, I used a large engine hoist to move the units to the floor.  Both stand and mill had a very large amount of rust preventative grease.  Also were very dirty with dust, grit an saw dust.




A few of the accessories.






In order to get the mill into the machine side of the building I had to remove the table.  Once had started the process I realized very quickly that these mills are absolutely filthy.   Grease, grit, dust, paint, machine chips, and saw dust were everywhere.   I highly suggest complete disassembling and cleaning absolutely everything.  On top of that A large percentage of the fasteners were hand tight or loose.




Mill is in its final home now but still requiring cleaning and reassembling.




Electronics appeared very tidy.   Though will most likely replace the NMotion control with an Acorn out of the gate.

I have already purchased a 1700 ozin and an addition 1200 ozin stepper to get the X and Y up to 1200 ozin and the Z at 1700 ozin.  Not sure if I should have gotten a brake for the Z yet though.


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## phazertwo (Feb 10, 2019)

Interesting how different your cabinet layout is over mine.  You're on the right track, toss that nMotion in the trash before you even try it.  Where did you purchase the new steppers from?  I've been thinking about doing the same thing... Shouldn't need a brake with a stepper, they hold position.

I'd also ditch the e-stop.  It's a Normally open switch, which is a huge no no for an estop.  Also, double check all the connections on the mill, I found about 15 loose wires...

Super fun mill, with an awesome work envelope.  You're going to love it!

PZ


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## B2 (Feb 14, 2019)

Hi guys, 

It is nice to hear from folks who bought the same machine as I.  I finally have had my machine up and running now for about a year, but given that this is the first mill I have ever used and I have been kind or busy with other stuff I am still learning my way.  It would be nice to hear from you about the performance of the machine so that I can determine if mine can do better or not.   Without other experience, I really do not know good from bad.  I do think the machine is pretty accurate with limited run-out and backlash.  

Fritts, your machine via your pictures looks just like mine except for the electronics layout and maybe the interface box between the nmotion controller and the stepper drivers.  My electronics are probably more like Phasertwo's and he noted the layout difference.  I have not changed my machine at all, still using the nmotion and the original steppers, however, I have often wondered if the mill would run more smoothly with a different set of control electronics. Anyway, I wanted to give the nmotion etc a chance before I make that drastic a change.   I have attached three photos.  1) still ion the shipping pallet.  2) Inside the electronics box.  3) After mounting the stand on a dolly, moving the electronics box to the right side (considerable effort, but nice to have), and full install into my basement(I had to bring it through the basement door in pieces and reassemble after in place).  I noted that they moved the transformer to the bottom in your electronics and so took it off the heavy back plate.   

I used the mill will still on the pallet to drill the many holes I put in the steel plates I use to make the dolly.  It seemed to worked fine, but I noted that if I lost power or turn off the machine without locking the vertical clamps the head would slowly sink and crash the tool into the work.  I was pretty disappointed that the z-stepper would not hold the weight. I then measured the repeatability and found that the stepper was slipping all of the time.  I just ran it up and down an inch several times and then measured to see if it came back to where it started.  It was way off.  Since that time I have measured that head weight, including a chuck and gear oil to be at about 240 to 280 pounds.  That is a lot for the little stepper, however, when I lifted the mill I found the lock washers and nut for the vertical lead screw to be laying under the mill on the pallet.  I also found the the vertical manual crank and gear rattles a lot when the stepper is driving vertically up or down.    After I had the electronics box removed I could put the lock washer and lock nut back on the lead screw/bearing and this plus adjusting the way friction I managed to get the z-axis stepper to hold just fine. Vertical repeatability with or without powering down is about 0.001 or better (my measurement accuracy).  Clearly, though the head stock is just too heavy and so will probably cause way wear.  I have thought about counter balancing it with a weight or spring off the back,  but since it all works ok I have not done so.  Having the electronics box on the side provides nicer access to the back of the vertical post, better access to the electronics and now I can push the mill closer to the wall.   However, I had to reroute the wires out the cabinet which required some new holes.   Anyway, I had to take the electrical box off the back and the x-axis table off to get the machine through my doorway(s) so I could get at the lead screw from the back to put the washer and nut back on and properly adjusted.  

There is another forum discussion about this z-axis nut falling off so mine was not the only 940M where this happened.  You can see this nut from the bottom of the mill if you want to pick it up and look up.... with a mirror.  Otherwise, take off the electrical box and you will have an access hole in the vertical post.  By the way, the loaded electrical box is heavy too!  I could not pick it up by myself and it was load for two.   In addition, to the heavy transformers there is a thick steel plate at the back that everything is bolted to.

 I also find that there is some electrical surge when powering up and so on occasion the stepper breaker throws, but this is only after it has been powered down for along time.  I have not figured this one out yet, but it is only a minor nuisance.  

The worst think about mounting the cabinet on the right side of the mill head post is that the left cabinet door now bangs into parts of the mill when opened.  I have a fix for that, but it is not high enough on the list.  

Because I was such a newbie I had assumed that with the variable speed motor I would be all set to do power tapping.  How little I knew!  I have a tack so I measured the spindle speed vs what is programmed.  It is only about 90% accurate.    Also, the motor/electronics has a  lot of inertia/delay and so does not start turning immediately when a command is issued.  Not good for power tapping.  So I keep thinking about attaching my forth axis stepper via timing drive belt directly to the spindle (at the spline) and fixing it so that when I want to do tapping I can just use it as the spindle drive.  It turns out that when you switch between the low and high speed gears there is enough room between the gears that for a short distance the spindle is free.  The normal drive motor does not engage to the spindle.   Hence, I think that one could connect a stepper directly to the spline shaft and get good enough speed control to do power tapping.  Maybe...!

Lastly, if you do not have a spline wrench you will want to get one.  I had no way hold the spindle from turning when changing tools.  I live in Pittsburgh, and so I went back to Precision Matthews and they happened to have one that Matt let me have.  You can see it, a little, in my photo.  It is laying in the stand tray on the left hand side.  

By the way, if you would like to share contact info I am willing.  

Dave.


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## fritts (Feb 22, 2019)

So I now have a 1700 oz in on the Z and 1200 oz in on the X and Y.   I removed the manual quill drive and will be removing the manual Z axis gear.   The only movement I seem to have in the Z is with power off.   When I remove the manual Z gear I'm sure it will drop more.

I have run a couple of programs now.  The steppers are rather loud at low speed.   So may change the micro stepping on the drives and adjust my Mach 3 settings.

The pendant has been working off and on.  Sometimes only the Z will move as well.

The other issue I have run into is that I need to purchase the full license of Mach3.   At $175 for a license I am questioning just going to the Centroid Accorn.  Wondering if anyone has had long term success with the NMotion controller?  From the looks of it probably not.

I purchased a some TTS tooling and will be looking into a probe soon.  I purchased a spline wrench at the same time as I noticed I did not have one.

One item I'm still trying to figure out is how I'm going to fabricate a chip tray for the unit and how to attach it.  would like something similar to the Tormach but want it to be a bolt on affair.


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## B2 (Feb 22, 2019)

Hi Fritts,

I had z-axis dropping problems until I properly tighten the lock nut on the bottom of the z-axis screw and then tightened the ways a bit.  The nut and washers had actually fallen off and the end of the screw was vibrating jerking on the stepper.  There was a discussion about the lock nut:  https://www.hobby-machinist.com/threads/pm-940m-cnc-z-axis-bearings.59538/    would even fall when the power went off.  I figured it out finally.  The nut was mising.  So the screw would flex due to the weight of the head, when it flexed it would jerk the stepper from the cog position to the next causing the screw to flex back the other way and then repeat.  So for each flex/bend of the screw the head would woble on the ways a little etc.  This all set up a low freqency mechanial resonance and the head would just slowly drop down.  The same effect would sometimes cause the stepper to even miss steps on the way up or down when the power was on!   The head is really too heavy for the small stepper, but I suspect that the holding force of the stepper is the really issue.  It needs to be a lot larger or the head need to be lighter weight or better still counter balance (someday).  I actually do not think the stepper is too small for the over all job.  A couple of times I have forgotten to release the vertical lock on the head and yet the stepper can run the machine up and down accurately even with it locked!!!

On the pendent issue, I found that the vertical wiring tray on the right side of the control cabinet was bending the serial connector coming from the pendent making the connector contact perhaps intermittent. It had even bent the pins of the connector.     My nMotion box was mounted right up to the wiring tray leaving little space for it. Here is the picture of the nMotion location in the control box:  https://www.hobby-machinist.com/attachments/imag0477-jpg.287754/   I cut some of the wiring tray away and now the connector is plugged in properly.  Anyway, my pendent now seems to work cleanly and repeatably.  I use it all of the time.  

I do not seem to have problems with the nMotion.   At least I do not notice any problems.  I purchased the Mach3 lic. out right and it came with a set of wizards which are very useful, but not well documented.   Later, by error, I went back and purchased the wizard package ($50) which will run out side of Mach3 to generate G-code.  This wizard software is set up a little different and has a different interface, but mostly does the same functions.   Being a newbie to G-code I found the wizards to be handy at providing examples of G-code of how to get the machine to do various things.  I figured out details from the arc wizard and then could join various arcs to make a curvy shaped object.  I also found the drilling of holes space around a circle to be handy for generating the G-code which I then can quickly modify.  

 I suggest that you go through the machine and make sure all of the wiring connectors are tight.

Chip tray.... I have no suggestions on this, but look forward to your solution.  I also need to come up with a way to fix the end of the x-stage oil drain hose.  It commonly comes loose at the mill stand oil tray and drips to the floor!  

Dave


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## fritts (Feb 28, 2019)

Decided to just go Acorn after some more weirdness.  Pulled the Nmotion and its power supply.  Had enough room to put both the Acorn board and relay board in its place.  Used some 1 in nylon spacers and 6-32 screws.  Also while I was at it pulled the cabinet off the column and relocated it to the wall.  Ordered some wire and nylon coated steel conduit (Electrotek on amazon).  Will try and get some of it rewired this weekend.  Also thinking about putting the power switches on the front of the spindle , purchased a NC E-stop as well to convert over to all NC limits and homes.  The control box arm may get re purposed for mounting my laptop.  






Still having problems getting the manual Z axis bracket off.  The upper thrust washer won't come down any further and so I can only lift the Z ball screw/motor assembly so far.  Any help?


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## fritts (Mar 11, 2019)

Got the Z axis thrust bearings off.  They were a light press to the shaft.   Not sure why that was done.   Removed the lower Z axis mounts.  Pressed out the shaft reinstalled with new thrust bearings.   Locations is quite right looks like I need a spacer in order to get it to tighten on both thrust bearings.
	

		
			
		

		
	





Started the re wiring and running corrugated hoses.   I'm using eletroduct 1/2 PVC coated steel corrugated conduit.  works pretty well in place of the 12mm conduit.   Had to drill out a few of the covers to allow it to fit.  Amazon link.    https://www.amazon.com/gp/product/B07DX9JLGY/ref=ppx_yo_dt_b_asin_title_o00_s01?ie=UTF8&psc=1





Started adding conduit boxes from the main electrical and lengthening wires.





Created a new front panel for the switches as well.




Also received a probe from Drewtronics.


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## phazertwo (Mar 12, 2019)

Wow, this is really looking good.  I like how you removed the old switch control setup, I think it causes more vibrations issues than it's worth hanging off the side of the column.

PZ


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## macardoso (Mar 12, 2019)

Is that a wireless probe? How much did it cost?


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## fritts (Mar 12, 2019)

No its the wired unit $170 from  Drewtronics


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## fritts (Mar 17, 2019)

Finally got the fine feed plate covered.   Working on the conduit movement for the control wires.   Also need to add the electronic port for the probe and mounting points for coolant and air nozzles.


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## phazertwo (Mar 17, 2019)

Man, you're not messing around!  That looks pretty good!

PZ


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## phazertwo (Mar 26, 2019)

I forgot to ask, and maybe you already answered it, but how is the 1700oz-in Z motor working out for you?  What kinda of speed and accel are you getting out of it?

PZ


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## fritts (Mar 27, 2019)

Sorry Phazer I have not had a chance to complete all my conversions yet so I haven't been able to try it out.


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## markf3x (Apr 17, 2020)

fritts said:


> Decided to just go Acorn after some more weirdness.  Pulled the Nmotion and its power supply.  Had enough room to put both the Acorn board and relay board in its place.  Used some 1 in nylon spacers and 6-32 screws.  Also while I was at it pulled the cabinet off the column and relocated it to the wall.  Ordered some wire and nylon coated steel conduit (Electrotek on amazon).  Will try and get some of it rewired this weekend.  Also thinking about putting the power switches on the front of the spindle , purchased a NC E-stop as well to convert over to all NC limits and homes.  The control box arm may get re purposed for mounting my laptop.
> 
> View attachment 289159
> View attachment 289160
> ...




Hi, I am stuck in the same spot you were when you posted this.. I'm trying to remove the manual Z axis and crank, but scratching my head...  Looks like I need to remove the large locknut at the bottom of the lead screw, correct?  Doesn't look like a regular socket works, correct?  It needs to be a spanner pin type socket?  Any idea what tool removes this hard to reach (or see) locknut?


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## szenieh (May 17, 2020)

markf3x said:


> Hi, I am stuck in the same spot you were when you posted this.. I'm trying to remove the manual Z axis and crank, but scratching my head...  Looks like I need to remove the large locknut at the bottom of the lead screw, correct?  Doesn't look like a regular socket works, correct?  It needs to be a spanner pin type socket?  Any idea what tool removes this hard to reach (or see) locknut?



I managed to remove the worm gear drive end that attaches to the manual crank shaft. I only wanted to eliminate the annoying sound from that useless manual crank when the z-axis is moving. So, I did not touch the ball screw. I went in from the front under the head (after lifting the head up and supporting it with 2x4's so it doesn't come down crashing on me), and I removed the allen screw holding the worm gear. I then "walked" that gear out by turning it in place- as it turned, it advanced forward sliding on the shaft as the key was gone so was the allen screw. I remember that I removed a key to allow it to rotate. It came right out disengaging from the driven worm gear which I left in place on the ball screw. I kept the face plate of the crank in place also as it keeps that hole closed. Noise from that gear is now gone.

Hope this helps. Please ask if anything I wrote is not clear. It would help to look at the two pictures by fritts posted on March 11 2019 when he said he managed to remove the manual crank. He did a full removal; I only removed that small gear shown on the left picture, as I was only interested in getting rid of the annoying gear noise. It is tight in there- so expect few scratches as you use your fingers to turn that gear to slide it out of the shaft.


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