Precision Matthews PM-728VT CNC conversion

Here is a good video on Overall Ratio Calculator: https://centroidcncforum.com/viewtopic.php?f=61&t=1449&start=10

Here is the backlash information: https://centroidcncforum.com/viewtopic.php?f=63&t=1801

Backlash is the very last post, but the whole topic is a good read.

All these adjustments are necessary and alot easier to do before everything is enclosed.

I had on the x-axis almost .009 thousandth before I made my adjustments down to .0010 to .0013. The article also tells how to compensate in CNC12 for up to .0015 backlash.

Have you used your KP-3 yet? I almost pull the trigger everyday but I wanted to wait and get the machine setup properly first. I have a Haimer, but until I really know CNC12 and the commands, I wont use it. To easy to break probes and expensive to replace.
 
koenbro said:
Yeah it does not seem to struggle or anything. When you power it off, it tends to come down though, so I put a piece of 2x4 underneath. A pulley and weight seems reasonable, just not sure how I can hide it. Is there some off the shelf hydraulic system one can add, or is that overcomplicating things?
Click to expand...
A couple of weeks ago Marty (of martyscncgarage) posted a video on YouTube showing how to install a z-axis electric brake. This is a device that goes between the servo and the ballscrew and is locked when in a power-off condition. With a signal from the CNC board, it unlocks the z-axis.

This seems like a pretty good solution for the problem of the machine head coming down when the z-axis servo is powered down. It won't provide assistance to the servo motor during normal operation though, but you noted that the motor is powerful enough.

I enquired with Teknic support and Teknic will be offering this product as an OEM in a few weeks. It is currently available direct from the manufacturer.
 
Sakumar, I watched the video and called Teknic also. They sent an email to the manufacturer for me, but I havent heard from them. I think I'll wait until Teknic is carrying it. Nice solution, but expect it to cost around $350.
 
I have removed the enclosure to fix the base and check the backlash as recommended above. Am getting some 22GA steel sheet later in the week to make a tray. What kind of drain and diameter do you recommend? Will 1" be enough, or should I go for a shower-style 2" drain?

What coolant do you recommend for this application?

Still figuring out what kind of 8020 components I need for the sliding door. Thinking about this one (and its corresponding upper) versus the dual roller wheel assembly, or combining them: roller assy on top, and track on bottom?

2221_photo_2.png


2753_photo.png
 
Last edited:
jlchapman said:
Here is a good video on Overall Ratio Calculator: https://centroidcncforum.com/viewtopic.php?f=61&t=1449&start=10

Here is the backlash information: https://centroidcncforum.com/viewtopic.php?f=63&t=1801

Backlash is the very last post, but the whole topic is a good read.

All these adjustments are necessary and alot easier to do before everything is enclosed.

I had on the x-axis almost .009 thousandth before I made my adjustments down to .0010 to .0013. The article also tells how to compensate in CNC12 for up to .0015 backlash.

Have you used your KP-3 yet? I almost pull the trigger everyday but I wanted to wait and get the machine setup properly first. I have a Haimer, but until I really know CNC12 and the commands, I wont use it. To easy to break probes and expensive to replace.
Click to expand...
That is very useful, thank you, I will test the backlash and report back.
 
jlchapman said:
Sakumar, I watched the video and called Teknic also. They sent an email to the manufacturer for me, but I havent heard from them. I think I'll wait until Teknic is carrying it. Nice solution, but expect it to cost around $350.
Click to expand...
jlchapman, I finally heard back from the z-axis brake manufacturer (Newstart Motion). They quoted $400 -- including shipping from China.
 
sakumar said:
jlchapman, I finally heard back from the z-axis brake manufacturer (Newstart Motion). They quoted $400 -- including shipping from China.
Click to expand...
I very much doubt that I'll ever spend 400 dollars on a brake when I can just slip a piece of wood under the head.
 
koenbro said:
I very much doubt that I'll ever spend 400 dollars on a brake when I can just slip a piece of wood under the head.
Click to expand...
You're probably right. I worried about scenarios where there's a power failure and the self-lowering head gouges through a part, or the table or worse. Or if I forget to place the wood and it breaks a KP-3 probe or perhaps a Haimer tip. Definitely an expensive solution though but since Teknic are going to OEM it, I feel reassured about the quality.
 
I'm going to wait and see if teknic carries the brake. Will have to be cheaper to get me interested.
 
GREAT Thread!!! I am working on the conversion of my PM728VT as well. It has stopped for the moment because I can't get it done and tested in time to make some parts needed by mid-May. I will have to make those parts manually instead of CNC.

I will post some pictures and such later. I really appreciate learning from others!
 
You must log in or register to reply here.
Back
Top