PM30 Owners - Need Some Dimensions

[mikegiraud]

I recently received a new PM-728VT which is a somewhat new offering from Precision Matthews. I knew that no CNC kits existed for it yet, but want to see if any of the PM30 ball screw mounts will align with the PM-728VT. Can anyone out there with a PM30 tell me the dimensions between the hand wheel mount screws? I suspect that Precision Matthews would commonize some generic components like cast hand-wheel mounts to save tooling costs, so the PM30 kit's mount may very well line up. The ball screw lengths won't work due to the larger travels on the PM30, but buying mounts alone from Dave at ArizonaVideo would save a couple weekends of design and machining along with the confidence of a proven design.

These are the dimensions that I need. Also to anyone considering a new small machine, the PM-728VT is excellent. The build quality is exceptional. 100% Taiwainese, and it shows. The dovetails are the best that I've seen on a small import machine.




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[currinh]

Mike:

The PM728VT looks like a great machine for a CNC conversion. I'm very tempted to get one for this.

I think it is closer to the PM727 machines than the PM30. At least the table sizes are real close. I found a set of ball screws for the PM727 at:

https://www.ebay.com/itm/3-ball-scre...-/254036726285

Their page gives dimensions for those screws. Since you have a PM728VT you might see if these will work. If you do please let me know either way.

Likewise you might look into the end plates for the 727 retrofit kits.

Thanks.

Hugh

[mikegiraud]

Hugh,

Thanks for the reply. I've already designed and ordered all the items needed. I appreciate your response regardless. The PM-728VT is a great machine. Its the highest quality small machine that I've seen thus far. The ways are impeccable with very consistent hand scraping on the slides. Oiling system is pre-installed, even though I had to cut oiling grooves in the gibs. The quality is so nice that I had to increase my budget on the CNC conversion to make this machine realize its full potential. I'm doing C5 grade ground ball screws, 25mm for Z, and 20mm for X/Y, Nema 34 750W servos on DYN4 drives, power drawbar with 3-stage cylinder, and 2.2KW 12k rpm AC Servo Spindle. Spindle servo weighs 60lb so a counterweight riding 15mm linear rail on the back of the column, supported by #35 chains. I'm using the TTS tooling system already so staying with the stock spindle. The stock spindle is really decent, with AC bearings rated to 7800rpm as far as I can discern. I won't take it beyond that to start but will eventually swap out the bearings and have it balanced to 12k rpm. My hope is to cut aluminum at 50ipm reliably. I recommend this mill.

-Mike

[CL_MotoTech]

50ipm in aluminum is no issue with even steppers. With a three flute 3/8" end mill that is basically standard feed. You can go much faster if you want, I've run 4 flute .5" at 90ipm. That said, I've only ever run my spindle up to 8k. Recently, as my belleville stack has grown, I limit to 6k because I find there's just too much vibration to deal with. I think the easiest method to reduce vibration at this point would be to significantly add mass to the head. I have no idea how you would balance a spindle, draw bar, and belleville stack, it seems impossible with the bellevilles moving around. Running without a PDB and belleville stack my spindle is perfectly vibration free. I'm on a G0704, with TTS, and ATC. That said, you can certainly get away with less collet throw if you are manually placing tools, and that means a shorter and less vibration prone belleville stack.

[currinh]

Mike:

Sorry I couldn't respond earlier, but just found your thread. Glad you've gotten it worked out. I would not have thought you could get ball screws that large in. Great to know.

I would sure be interested in your design if you are willing to share. Did you have the ball screw ends machined or are you doing this yourself? What supplier did you use for your ball screws? Would love to see progress and/or the finished machine.

My conversion would/will be simpler than yours, likely stay with steppers. It'll be a hobby mill so primarily runs of one or two parts. With this, fast motions just scare me. Likely stay with the stock spindle and motor. Also probably use LinuxCNC with Geckos and a Mesa card. I'm likewise using TTS tools on my knee mill conversion, just right for me.

Thanks.

Hugh

Thanks for the reply. I've already designed and ordered all the items needed.

[arizonavideo]

If you guys want I can just make a few mounts and screws up for the 728.

I dont think much will fit from the 30 or 727. If they used RF-45 mounts then some of the PM-25 will fit.

The Y is the easiest, what is the bolt spacing and the bolt offset from the bearing zero?

[currinh]

Dave:

I may be interested in a cnc kit for the PM728. I don't have the machine yet so can't measure the end plates for you.

I really do want to extend the X and Y motors towards the machine rather than sticking out. Yes, space is that tight. But also for less interference with the Y motor doing set-ups etc. Something like this on a knee mill or what Peter Homann did with his bench mill (posts 87 & 109). Also see this post.

Please let me know if you develop a kit for the PM728. Thanks.

Hugh

If you guys want I can just make a few mounts and screws up for the 728.

I dont think much will fit from the 30 or 727. If they used RF-45 mounts then some of the PM-25 will fit.

The Y is the easiest, what is the bolt spacing and the bolt offset from the bearing zero?