Precision Matthews PM-728VT CNC conversion

[koenbro]

Hello everyone, I have an order on a PM-728VT and is due to deliver within a month. I will do a CNC conversion (with the PM mechanical kit), and will document it here, while also posting the myriad questions that are certain to come up. I am planning to weld up a base for it that will incorporate a toolbox that I already have. I am garage hobbyist and plan to mill aluminum and mild steel mostly.

My experience is with an Avid CNCRouterParts 2x4' extrusion based router that I built, using a 2.2kW air cooled spindle driven by a Delta VFD. The motors are NEMA23 and the controller is a Warp9 ESS; I got the electronics boxes already assembled by Avid. Then I added a THC and a Hypertherm PM-45XP with a water table. I use Fusion 360 and Mach4 with SheetCam for plasma.

For the mill, I have already bought an Acorn with their CNC12 software (paid version).

 

[koenbro]

Here is my first question: What motors to choose and how to size them? The CNC conversion kit specifies NEMA 23 for axes x and y, and NEMA 34 for axis z. The ballscrews have a 5mm pitch, the axes lengths are: x-axis = 28”, y = 9”, z =16”, and the diameter is (I think, not sure) 12mm.

I am in touch with Teknic to select the ClearPath servos and they need to know speeds and acceleration (worst case moving load weight) on each axis.

Can somebody help estimate these? Or anyone who has a done a 728 conversion pitch in with their experience and advice? Much appreciate any help.

 

[shooter123456]

I have a PM-25 which is similar in size. I use CPM-SDSK-2321S-RLN for the X and Y and CPM-SDSK-3421P-RLN for the Z. The table with 3 vises mounted will move at 400 IPM and the head does 300 IPM. The head has an air cylinder and heavier motor as well, so it should be a pretty close comparison if the 728 is slightly heaver.

 

[koenbro]

That is plenty fast movement! It is this real-life experience that I needed. Thank you much for your reply.

What materials do you mill? How does this setup perform with (mild) steel?

 

[Teknic_Servo]

Hi koenbro,

I'm the Teknic applications engineer you've been working with. After coming across this post, I'd like to clarify the specifications that will allow us to recommend the best ClearPath motor for you.

In addition to the screw specifications you've provided, it's helpful to know what you'd like for a maximum load speed (for example, 500 IPM) and how fast you'd like to accelerate the load (for example, 1/4 G). With this, we can recommend the optimal ClearPath and provide the specifications needed for the Acorn controller (i.e. steps/sec and steps/sec^2).

Please give me a call at 585-784-7454, or fill out our contact request form at https://www.teknic.com/contact/ if you have any questions.

-Ian R., Teknic Servo Systems Engineer

 

[koenbro]

In addition to the screw specifications you've provided, it's helpful to know what you'd like for a maximum load speed (for example, 500 IPM) and how fast you'd like to accelerate the load (for example, 1/4 G). With this, we can recommend the optimal ClearPath and provide the specifications needed for the Acorn controller (i.e. steps/sec and steps/sec^2).

Hello again Ian, and thanks for your dilligent support. As you see, I am trying to do my homework. Based on the CNC experience with my 48x24" router/plasma, I think a rapid of 400ipm is more than adequate, and that is before considering the vastly smaller envelope of the mill compared to the plasma table. As for acceleration, I can only guess -- and your starting value of 1/4 g seems ok. Can you please recommend the NEMA 23s for x and y and NEMA34 for z with these parameters?

Second, can we turn the problem on its head? Others seem to have been satisfied with CPM-SDSK-3432S-RLN for the z axis and CPM-SDSK-2321S-RLN for x and y. Can you run the simulation on these and tell me the rapids and accelerations? I am looking for the enhanced feature set for all three motors.

Thank you kindly.

 

[Teknic_Servo]

Hi koenbro,

After doing some research into the PM-728, I have estimates for the typical load weight and cutting forces for each axis. For a "typically-loaded" PM-728, variants of the ClearPath motors that shooter123456 recommended (CPM-SDSK-2321S-RLN for the X and Y and CPM-SDSK-3421P-RLN for the Z), are a nice fit, depending on your motion goals. These motors will easily provide 600 IPM rapids and 1 G of acceleration on the X and Y axes. The Z will realize 500 IPM rapids and 1/3 G acceleration.

Based on your comments, the specific motor part numbers you may want to consider are CPM-SDSK-2321S-ELS for the X and Y, and CPM-SDSK-3421P-ELS for the Z. There are two differences in these part numbers as compared to those provided by shooter123456.

• The E (Enhanced) instead of the R (Regular) option provides higher commandable machine resolution (0.00003" vs. 0.00025", respectively) and a wider RAS selection (a jerk and jerk derivative smoothing algorithm in ClearPath). For high-precision milling (when paired with good mechanics and a capable controller such as the Acorn), the E option may enable an increase in part accuracy and edge quality.
• The S (additional shaft sealing) versus the N (standard shaft sealing) option provides a second seal for additional protection against the environment. If the motor shaft is exposed and the particulate created in the machining process is abrasive, this Viton seal will protect the motor's bearing for the life of the machine.

I'm confident these ClearPath motors will work well with a PM-728 mill. In fact, ClearPath's onboard diagnostic tools allow you to measure on-machine performance, ranging from actual torque usage to tracking accuracy during a cut. Here's a helpful video which goes into greater detail on ClearPath's software oscilloscope capabilities.

Using this tool, you'll know if my motor selection is correct for your specific use case. And if it turns out that the needs of your machine are unique or you'd prefer different motor performance characteristics (such as higher RPM), Teknic offers a 90 day return period during which, if the motors are over/undersized for your needs, you can return them for a full refund through our webstore.

Please let me know if you have any questions.

-Ian R., Teknic Servo Systems Engineer

 

[7milesup]

Thanks Ian for being on the forum and giving your insight.
I have, what is most likely, a dumb question. Can you use the ClearPath servos with Linux controls and software?

 

[koenbro]

Hi koenbro,

After doing some research into the PM-728, I have estimates for the typical load weight and cutting forces for each axis. For a "typically-loaded" PM-728, variants of the ClearPath motors that shooter123456 recommended (CPM-SDSK-2321S-RLN for the X and Y and CPM-SDSK-3421P-RLN for the Z), are a nice fit, depending on your motion goals. These motors will easily provide 600 IPM rapids and 1 G of acceleration on the X and Y axes. The Z will realize 500 IPM rapids and 1/3 G acceleration.

Based on your comments, the specific motor part numbers you may want to consider are CPM-SDSK-2321S-ELS for the X and Y, and CPM-SDSK-3421P-ELS for the Z. There are two differences in these part numbers as compared to those provided by shooter123456.

Thank you Ian, I placed the order in the Teknic online store. I hope I ordered all the right cables with it; I have emailed you the order # in the hope you'd look over the list and let me know if I left anything out. Once I receive the ClearPath package, I will set up the system on the bench with the Acorn prior to mounting it on the mill. Will document my progress here.

Once again thank you Ian @Teknic_Servo, @jimrk, @kiloseven, and @shooter123456 (hope I did not forget anyone -- apologies if I did) for the advice along the way -- it helped tremendously.

 

[Teknic_Servo]

Thanks Ian for being on the forum and giving your insight.
I have, what is most likely, a dumb question. Can you use the ClearPath servos with Linux controls and software?

Hi 7milesup,

Controllers that output 5-24 VDC step and direction commands are compatible with ClearPath-SD. Therefore, if your specific Linux controller outputs digital step and direction signals (see page 152 of the ClearPath user manual for specifications), then it should work well with ClearPath-SD.

FYI, we've had a number of customers successfully use the LinuxCNC controller with ClearPath SD motors.

-Ian R., Teknic Servo Systems Engineer