Precision Matthews PM-728VT CNC conversion

[koenbro]

SPINDLE CONTROL
Meanwhile I replaced PM's 0-10V factory spindle control board with a KB ELECTRONICS KBSI-240D signal isolator. The PM factory board was not giving a linear spindle response, at least not with the Acorn. As I tested it with a voltmeter, Acorn's output was nicely linear in the desired speed range. The spindle response was higher but not with a constant rate, and the board does not have a pot to fine tune. Now I get decent reponse to spindle speed g-code.

 

[Weldingrod1]

You need cross braces!!! X the back (top to bottom) and run an brace across the right and left sides. Think about an X brace under your shelf too.
For an X, it can be flat bar and doesnt need to be super huge or thick. 2"x1/4" will be verging on overkill. 1/8" thick.is.probably plenty too. A single cross bar wants to be able to be pushed on, so consider squate or rectangular tubing for that. Bolting the braces will add some damping, but however you attach it, get it solid. If its bolts, torque it like you mean it!

Fyi, open sections like angles and channels are MUCH easier to twist than closed ones. Your router table was a better design for stiffness!

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[macardoso]

Thanks for that tip and the McMaster link. Which item did you choose? (perhaps you have the item # 4138Txx?). I will probably go that route too.

I'm not 100% sure since it was a good few years ago, but I think it was 4138T61 with a 50 lbf gas fill. My G0704 has about 9" of usable Z travel with the way covers installed so 10.24" of stroke would have covered it.

 

[koenbro]

Making slow progress. Have replaced the PM 0-10V spindle speed controller (which I couldn’t make work and is not tunable) with a proper isolator KBSI 240D isolator which works well.


Then started work on the enclosure:

It’s made of 1010 and plan to use slide in panels on the back, curtain-like strips on the sides to allow full movements in the x axis ( and accommodate long stock), and even plan to enclose the top. As for the front, am thinking a hinged door that swings upwards.

Its overall outside dimensions are: 48"W x 31"D x 28"H. Looking at the 8020 catalog now to decide on the hinge, slide-in panels, and locks (if any). Then the hard part of making a tray comes next.


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[koenbro]

 

[pdentrem]

I would do a sliding front door. Either one piece or split left and right. A lift door is a head banger.
Pierre

 

[rwm]

I agree. Add 1010 strips to the front top and bottom and use dual sliding doors.
Robert

 

[jlchapman]

Nice progress on the enclosure!

What did you get for backlash on your 3 axis?

 

[koenbro]

Nice progress on the enclosure!

What did you get for backlash on your 3 axis?

I don't know how to properly test backlash, but would like to measure it. Do you have a method you recommend?

 

[jlchapman]

I don;t know how to properly test backlash, but would like to measure it. Do you have a method you recommend?

I’ll send you a link when I get home. Marty did an awesome write up