Precision Matthews PM-728VT CNC conversion

Two more photos of the geared mechanism.

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I used to have a encoder hooked up but kept breaking small taps. I blamed the motor with bad low speed control an poor stopping and reversing power. I told myself I wouldn't try again until a motor upgrade but it might have been my setup. let us know how it works for you.

I am also curious about the 4th axis you are planning/working on. I made mine from a lathe headstock and it works great. I am running tiny parts on it right now. I designed a pneumatic brake for large part indexing and off center drilling and it works fantastic, without a harmonic drive its the "secret sauce". If you want more info just let me know.

 
koenbro said:
As always, you guys are great -- thanks for the practical discussion.

I went ahead and ordered the LMS 4" precision rotary table that @jimrk linked to above. The reason I went with the LMS rotary over the PM BS-0 dividing head, as I initially intended, is the z height. The PM solution has the clear advantage of angular adjustment but am not convinced that with my z-axis limitations that's worth it. Also ordered the tailstock matching this table, and the 3-Jaw 3" lathe chuck. Have never used a lathe chuck (or a lathe :) ) so I am very excited to try it/them out. Wanted to also get the compatible dividing plate set but they are out until late January.


Am very tempted by the elegant, self-contained and stand-alone solution @Cletus has shown above, because I think I can use it as a welding positioner as well. What motor and controller are you using, @Cletus ?
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Hi @koenbro

Can you share your experience here? How did your CNC rotary table work for you?
 
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Loftfan said:
Hi @koenbro

Can you share your experience here? How did your CNC rotary table work for you?
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The stepper motor will depend on the size of the rotary table, the mounting arrangement and the required torque.
This is the stepper driver I used along with a 20V power supply from a laptop

Twotrees Stepper Motor Driver, TB6600 4A 9-42V Nema 17/23 CNC Controller Single Axes Hybrid - Upgraded Version: Amazon.com: Tools & Home Improvement

Twotrees Stepper Motor Driver, TB6600 4A 9-42V Nema 17/23 CNC Controller Single Axes Hybrid - Upgraded Version: Amazon.com: Tools & Home Improvement
www.amazon.com
The stand-alone control unit is Arduino based running some code I found on the net, which I modified a bit. The rotary table can be run off the CNC controller on my CNC modified Grizzly mini-mill effectively making it a 4-axis Mini VMC or can be controlled independently by the stand-alone Arduino control unit, and I use this a lot on my PM935 mill.

As far as a rotary welding positioner is concerned, I bought this unit for my TIG welding bench. I also find it useful for all sorts of stuff around the shop. (I beefed-up the ground arrangements some too)

This "Retort Clamp" I find useful to hold the torch when doing MIG pipework
Hope this helps -- Cheers!
 
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Any update on 4th axis @koenbro? I was looking at your rotary encoder and I'm wondering why you didn't use a belt? Seems like that would be much quieter and even more accurate.

Any thoughts on upgrading the motor? The unit seems to be solid enough to do aluminum work quickly except for the slow spindle speed.

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akschu said:
Any update on 4th axis @koenbro?
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Sorry nothing new to report, will restart the project once the weather cools down.

akschu said:
I was looking at your rotary encoder and I'm wondering why you didn't use a belt? Seems like that would be much quieter and even more accurate.
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Agree. I already printed timing pulleys, and got a timing belt. Will design and make the housing next. You are totally right the two geared interfaces are annoyingly noisy.

akschu said:
Any thoughts on upgrading the motor? The unit seems to be solid enough to do aluminum work quickly except for the slow spindle speed.
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I would very much like to upgrade the motor. Do you have any suggestions for 1 to 1.5HP motors that would be suitable?
 
I don't have any thoughts. I've mostly followed you because I needed to get this going quickly to make some parts I needed. Once my huge project is done I hope to build a housing around it, add cooling, add 4th axis, power draw bar, and a better motor.
 
koenbro said:
I would very much like to upgrade the motor. Do you have any suggestions for 1 to 1.5HP motors that would be suitable?
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@mcardoso on this forum has had some very good suggestions on spindle motors for me. I haven't made a move on those yet, but It will likely happen at some point.

I'm in the middle of my own 4th axis motor retrofit project here. I'm expecting the servo motor to arrive tomorrow.
 
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