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My PM-940 CNC Modifications

cut2cut

Active Member
Active Member
#1
I've been slowly making modifications to my turnkey Precision Mathews PM 940 CNC mill with the Variable speed motor option since it arrived in January 2017

So far I don't have a lot of time testing the changes I've made, so I can't say for certain if they are wise or not, but a number of people have been asking about various things so I thought I'd start a separate thread rather than Hijack the other one.

Ok, so here she goes with just the bare facts which I'll outline in further detail later on and update this post as more things are changed out or modified.

1 ) Spindle, drive train and Motor "upgrade"
Removed Spindle Gear Box completely
Replaced with Belt and Pulley
Replaced Spindle Motor ( has encoder built in )
Requires Better spindle bearings

2 ) Control hardware and software
Removed the nMotion USB controller
Replaced with the Mesa 7i76E ( E stands for Ethernet ) controller
Replaced Mach 3 with Linux CNC control software ( required with Mesa controller )

Future :
3 ) "Power" Drawbar

4 ) Servo motors

5 ) Enclosure

6 ) Other cool stuff, hopefully ! lol

Each section will have a parts list and links to where I got them.

Cheers,

Jake
 

cut2cut

Active Member
Active Member
#2
Part 1 ) Spindle , Gear train and Motor "upgrade"

I used quotes around the word "upgrade" because I have yet know if its an vertical move, or lateral ! :)

For instance, the Motor probably doesn't produce more HP but it appears to be better quality and also has an encoder for better speed control with an appropriate VFD. Depending on the speed control ( VFD ) the encoder can be used as feedback for the VFD to help maintain speed more consistently, and also should maintain better torque. I believe the Delta VFD-E that comes with the PM940 CNC VS has this capability with an optional card, but I am not sure. I also bought , but have yet to use, a Durapulse VFD with a feedback card. So far, its collecting dust due to time constraints mostly. The Delta seems to be working pretty well after someone on this forum suggested settings that match this particular motor better than the default settings that the VFD comes with.

april 15 2017 edit
[ So, I should go into more detail about the spindle bearing upgrade. You need a large press to remove the spindle bearings and put it all back together with the new AC bearings, Also, you need a bearing puller to remove the standard bearing race(s) (this is a tricky step because there isn't much lip for the puller to access).
The AC bearings do not have a separate bearing race like the standard bearings, so when you assemble it, it has to be pressed into each part in a logical order or it will put stress / harm the new ball bearing and/or races. The upper bearing on the inner bearing surface (of the spindle itself) can either be cooled and the bearing warmed to allow the bearing to be seated, OR you can do what I did which was create a slip fit for the inside of the upper bearing by turning the spindle on a lathe with a bit of sandpaper to buff it down a small amount. The problem with this approach is you could introduce some runout by creating too much of a slip fit. Also if you aren't consistent you may make your spindle "seat" out of round. My greatest worry is that I'd take too much off and certainly this would result in increased runout. Even a slight amount of heat (created by the sanding process) would throw off the measurement and could cause you to keep sanding due to heat expansion. If I were to do it again I'd have some way to cool the spindle after each session of sanding it ( with 1000 grit sandpaper and slightly warm the bearing before testing bearing fit after each attempt at sanding more off. Its a bit tedious but worth the extra concern, imho. ]

There is more detail needed and I will add more detail but don't have time right now. ZZZZ... sleep is calling me. However I am providing a parts list for those that just don't care about details and live dangerously :) Note that items with double asterisk ( ** ) need and will get more detail.

Here is the motor I used:
http://dealerselectric.com/145THTR15540.asp

The AC bearings for the spindle :
qty 1 - VXB Brand 7207C P5 High Precision Angular Contact Bearing 35x72x17 ABEC-5
qty 1 -VXB Brand 7206C-P5 7206C P5 High Precision Angular Contact Bearing 30x62x16 ABEC-5

Pulley ( 2 to one ratio )
**qty 1 : 5.6 inch 10 groove J - Profile pulley
http://www.ebay.com/itm/291936349578?ul_noapp=true
( requires some of the head case to be modified for this pulley to fit inside the gearbox cavity )
** Taper bushing not listed yet... it depends on your motor shaft size ...)
** 2.8 inch 12 groove J profile PULLEY
http://www.ametric.com/p-18443-12j281108.aspx

** taper bushing for 2.8 inch pulley for 28mm spindle ID
http://www.ametric.com/p-13391-110828.aspx
( requires some thin shim as spindle OD is slightly less than 28mm )
( requires a key to be fabricated to go in spindle grooves so Pulley isn't only a friction fit )

** Ametric brand BELT -10 ribs Micro V J groove
http://www.ametric.com/p-30298-260j10.aspx
( the Ametric belt is what I used, but I believe an 8 groove GoodYear brand one is better after some people on this forum suggested the good year brand over Gates, which I think is what Ametric sells, possibly ) McMaster Carr has GoodYear brand :
** 9003K89 Ultra-Flexible J-Section V-Belt 8 Bands, Trade Size 260J8, 26.3" Outer Circle
( could be a bit bigger than the Ametric one... hard to say if its too large. I have one coming so I'll be able to try it and update this )

Cheers,
Jake

note, the motor mount plate is just temporary, something sexy will be made when I decide on how to configure a double pulley arrangement.
IMG_1525.jpg IMG_1881.jpg
 
Last edited:

rodjava

Steel
Registered Member
#8
Jake,
For servos, check out DMM Technology at http://www.dmm-tech.com/

This a true plug and play, complete servo system and the pricing is not bad.

I have the 4 axis AC servos on my cnc router and they setup and work perfectly.
You can ask and read more at cnczone.com.

Btw, thank you for sharing your upgrades. I might do the same in the future.


Rod
 

cut2cut

Active Member
Active Member
#9
Jake,
For servos, check out DMM Technology at http://www.dmm-tech.com/

This a true plug and play, complete servo system and the pricing is not bad.

I have the 4 axis AC servos on my cnc router and they setup and work perfectly.
You can ask and read more at cnczone.com.

Btw, thank you for sharing your upgrades. I might do the same in the future.


Rod
Hey Rod,
I am considering the Clearpath servos but I'll check these out too. Thanks ! I really really like that my pulley and belt spindle is whisper quiet now... would be cool to have the benefits of a closed loop and also they are whisper quiet too !
And while we are on the subject of quiet, one of the reasons I switched out the motor was the one I got doesn't have a fan at all and doesn't need one either !, so its way more peaceful when the machine is on, but not cutting.
Cheers,
Jake
 

phazertwo

Active Member
Active Member
#10
Any more updates on this? I'm very interested in the spindle motor setup, mine makes enough noise to drive you nuts while it's running.

PZ