# Pm727 Cnc Conversion Experience



## thebeerbaron83 (Dec 31, 2016)

So, here is my PM727 CNC conversion experience.  I got a lot of info from Youtube and the forums, so hopepfully someone can benefit from my experience.  It is not quite done yet and I need to clean up the wiring, but so far so good.

I ordered my PM727 from Precision Mathews on eBay and it was to my house in two days!  Pretty impressive.  While tinkering with the machine I noticed the spindle was getting pretty hot.  With no load on it I was getting temps around 107 in the high speeds after only a few minutes.  Matt has excellent customer service and explained 107 is not that hot and told me to get in touch with him if temps get into the 150-160 deg range.  I have also read from others that the spindle will get hot during the first several hours of operation.  

So I began ordering parts for the conversion.  Here is a list of what I used
- 1605 Ballscrews with milled ends and double ball nuts from eBay (800mm for the X axis and a 700mm that had to be cut down for the Y axis)
- BF12/BK12 Bearing supports from eBay
- 1605 Ball nut Housing (28mm) eBay
- 425oz Nema 23 motors eBay
- Gecko G540 Drive with 400watt power supply
- Wood enclosure for G540 eBay (seller jusharrjust)
- DB9 motor cables with motor end connector eBay (seller len1007).  These cables are great!
- Aluminum heatsinks for G540 eBay
- x3 - 15 tooth XL (.200") timing pulleys (SDP/SI online)
- x3 - 30 tooth XL (.200") timing pulleys (SDP/SI online)
- x3 - 53 tooth .375 width XL (.200") timing belts (I am using a 3" center distance) (SDP/SI online)
- Spindle light Amazon (this thing is pretty amazing)

I made some motor brackets out of 1/4" aluminum plate I had lying around.  They do flex a bit, but nothing that affects the operation of the machine.  I would probably use steel if I did it over, but its not really worth changing them.  These work fine.  
I had to do some fitting and fabrication to swap out the old lead screws for ballsrews.  The Z axis was pretty easy to do.  What I'm milling does not require more than a couple inches of commanded Z travel, so I attached the Z axis motor to the fine adjustment wheel instead of messing with the Z axis lead screw.  
Setting up Mach3 was pretty easy.  I used the .xml file from Gecko's website, which sets up the ports and pins.  I did have to change a couple things to get the touch probe to work.  be sure to go into your computer BIOS and set the parallel port to EPP mode also.  There are plenty of write-ups on setting up Mach3 so I won't go into the details.  
I also downloaded the Hoss Machining Touch Probe screenset.  I haven't had time to really test it out yet, but it is the best auto-zero strategy I have seen so far.  I can't wait to start messing with it.  
So far I have tuned the motors and ran some GCode to make sure it moves how it is supposed to.  tomorrow I will Clean up the wiring and run some milling strategies.























Like a boss.


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## jbolt (Dec 31, 2016)

Looking good! 

Post some video when you are fully up and running.


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## thebeerbaron83 (Dec 31, 2016)

Thanks! I have it running now. I've added a coolant system and I'm trying to figure out how to connect a spindle control relay to the existing pm727 wiring. I'm also adding a gas strut to the quill to get rid of some of the backlash, but I'm running code and making chips!


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## thebeerbaron83 (Jan 1, 2017)




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## thebeerbaron83 (Jan 1, 2017)

Here are some more photos. I should have taken some pictures as I was doing to conversion, but I didn't think about it.


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## rdean (Jan 1, 2017)

A suggestion only.
You may want to switch your drive and driven belt pulleys on each axis to gear down and not gear up each motor.  It looks like you have a 2 X 1 gear up ratio from the pictures. The result would be more torque and more accurate positioning.

The 1605 screw makes about 5 turns per inch so the way you have it the motor would only turn about 2.5 revolutions for 1" of movement.  If they were swapped the motor would then make 10 revolutions per inch and have 4 times the power it has now.  Your rapids speed would still be close to 100" per minute which is more than enough.

Ray


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## jbolt (Jan 1, 2017)

Looking good. 

If you don't already know the BK bearing blocks can be a little sloppy and they usually install the AC bearing in the wrong order. I did a little write-up in my build log on how to tune them up, set the pre-load and remove the slop. http://www.hobby-machinist.com/threads/pm932-cnc-build.21442/#post-192473


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## thebeerbaron83 (Jan 1, 2017)

rdean said:


> A suggestion only.
> You may want to switch your drive and driven belt pulleys on each axis to gear down and not gear up each motor.  It looks like you have a 2 X 1 gear up ratio from the pictures. The result would be more torque and more accurate positioning.
> 
> The 1605 screw makes about 5 turns per inch so the way you have it the motor would only turn about 2.5 revolutions for 1" of movement.  If they were swapped the motor would then make 10 revolutions per inch and have 4 times the power it has now.  Your rapids speed would still be close to 100" per minute which is more than enough.
> ...


That does make a lot more sense.  Unfortunately I will have to buy new pulleys because the shaft diameters are different.  I'm sure there will be plenty of things I will decide to change as I go along here.  Thanks for the advise!


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## thebeerbaron83 (Jan 1, 2017)

jbolt said:


> Looking good.
> 
> If you don't already know the BK bearing blocks can be a little sloppy and they usually install the AC bearing in the wrong order. I did a little write-up in my build log on how to tune them up, set the pre-load and remove the slop. http://www.hobby-machinist.com/threads/pm932-cnc-build.21442/#post-192473


Nice write up!  I will check them out and get them tuned up.  This is why I love the forums!  Thanks!


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## HEAVYMETAL87 (Jan 14, 2017)

Sort of a dumb question- by running the motors off to the side of the ball screw like that- if I was to leave enough clearance for the hand wheels could I still use them with the motors hooked up with out much head ache? 
I was thinking of using servos- and since they have their own encoders couldn't that also double as a DRO for the mill? 

Thanks!


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## thebeerbaron83 (Jan 14, 2017)

HEAVYMETAL87 said:


> Sort of a dumb question- by running the motors off to the side of the ball screw like that- if I was to leave enough clearance for the hand wheels could I still use them with the motors hooked up with out much head ache?
> I was thinking of using servos- and since they have their own encoders couldn't that also double as a DRO for the mill?
> 
> Thanks!


You can certainly add hand wheels, but you wouldn't be able to use them unless the power to the motors was off.  I don't know enough about servos to tell you if manually turning them would cause damage. I've never had a problem with manually turning steppers while they are off.


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## HEAVYMETAL87 (Jan 14, 2017)

Also, forgive my ignorance on this one- do you have a Z axis motor on the actual ball screw- or is that the fine feed for the quill that is handling that for you?


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## thebeerbaron83 (Jan 14, 2017)

I have the z axis connected to the fine feed for the quill.


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