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10th Sep 2021, 07:24 AM #1Diamond Member
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Anyone used Power Feed setup for CNC?
Factory neighbour has a large Hafco mill (BM-40 or 30) that he has asked about adding some CNC abilities to. He is not real computer savvy, so I will be looking for a non-PC based solution. Maybe a tablet, or LinuxCNC on an embedded device.
The easy way would be to add big stepper motors and some toothed belts, but that prevents manual use unless they are disconnected again.
I'm looking at the Power Feed motors, and DRO scales, and wondering if LinuxCNC could be configured to use these already attached motors instead of steppers?
(I know real CNCs use DC servos, and high end ones also have additional closed loop feedback, but has anyone ever heard of one without direct feedback from the screw motors?)
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10th Sep 2021, 09:06 AM #2Most Valued Member
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I can’t see that being possible - backlash and lack of ability to control small movements would be the killer.
While it may be possible to control large movements with feedback from the scales, I can’t see it working with the relatively large on/off movements from a typical feed motor.
Aside from the technical challenges, there would be a huge time investment to get a DIY machine to the “unskilled operator” level.
If you didn’t get it all the way there, you would be supporting it forever.
Personally - I wouldn’t touch it with a barge pole!!
Proper conversion with ball screws etc for your own shop - maybe, but definitely not for a customer.
Steve
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10th Sep 2021, 10:07 AM #3Most Valued Member
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As Steve said, without knowing either how many steps the motors are doing or having any way to repeatably and controllably energise them like a servo or stepper you can't make anything remotely functional. Even if you have the positional feedback from the scales.
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10th Sep 2021, 10:09 AM #4Diamond Member
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Thanks Steve. Backlash is indeed the issue with existing (Acme thread?) screws.
(and "hunting" would be the issue with scale based closed feedback)
Some of those power feed enclosures have speed control levers, instead of the old left/off/right lever.
I'm not sure any of the free software supports speed control, plus backlash compensation, plus closed feedback, though
The only CNC machining actions he asked for are milling circles and rectangles. Which is why I considered the hackiest solution.
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10th Sep 2021, 12:03 PM #5Most Valued Member
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Milling an accurate even accurate ish circle is the hardest part of a 3 axis cnc machine. All the early point to point machines that still used trapezoidal screws could do lines and pockets okay a lot of them used multiple electronic clutch packs to take the drive from a single DC servo. Moving multiple axis simultainiously was impossible. To avoid hunting the clutches released very quickly triggered by the control. They also had hydraulic axis clamps that clamped all the non moving axis.
I suspect with your proposed idea entering corners of pockets would be a regular hand grenade experience of smashed endmills and he would be having to manually lock all the non moving axis all the time.
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23rd Feb 2022, 09:05 PM #6Diamond Member
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As a follow up, I opened up one of these drives this week:
I thought the forward/reverse lever was just a switch, but on this model, they are also a lever that engages the motor shaft with the small bevel gear. (i.e. the clutch, so that you can manually turn the mill axis handle without driving the power feed motor as well.)
This means effectively the forward & reverse is electrical, but the on/off is both mechanical and electrical.
Not easy to interface to - would need to mechanically lock the direction lever in one direction, and then override all the electronics to get fwd/rev.
Possible, but not worth the time. Removing/selling the power drives, and adding steppers, will be much faster/easier
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