Not really a big deal. Unlike a servo that I can switch over to constant torque mode I have to be able to detect that the stepper motor has stalled with a specific power setting. If the stepper driver has resistors for setting current then it's pretty easy to use a relay to switch them based on the motor direction. 18 ft-lb for tighten. 20 ft-lb for loosen.Nope. Unless they started opening on weekends again :-(
No. I don't have 5mm metric in stock. I have lots of Philips Pan head and the bolt diameter is large enough to clear the socket. Plus I might still mount a flat slotted encoder disk there instead of mounting an encoder on the back of the stepper motor.no recess to use socket-head cap screws?
Going down this route soon.I found in the drawings/XAxis folder all sorts of drawings and photos I had done a few years ago. Working with ordering parts from AliExpress for the Robot Arm I realized I should get after getting ball screws. The thing that put that project #42 on hold was not knowing whether to use a 16mm, 20mm or replacement 2505 sized ball screw to replace the 1" ACME 0.2" pitch screw.
I had a photo of the screw nut and where it went when I had the table off a few years ago.
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But I really couldn't tell from those pictures whether the much larger ball nut and holder would fit. So first step is remove the RH side plate, wind the lead screw all the way over so the edge of the table lined up with the frame section in the photo above. Dangled a square over to measure to the screw center line.
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Well lots of measurements. Sketches, then CAD drawings and finally taking the original ACME screw and nut assembly drawing I did in 2017 and adding it to the two parts I drew today.
Here's a perspective view.
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So similar end view with the ACME screw centered on the X axis.
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Looks like there will be plenty of room for a larger ball nut holder. Why not just go with a 16mm screw? Well the pulleys and bearings and spacers etc are all sized for the current 1" ACME screw. The cost of a 25mm over a16mm isn't that high and the rounded ends then match all my bearings and the pulley.
All I need to do is cast new end plates with the hub in line with the new ball screw center line. Easy to do since it was a two part pattern. Just move the hole up and use some wax to plug the old one.
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All for now. Time to download the 1" double ball nut step file and model it with the parts done here.
I'm finding it invaluable this time to do all the CAD up front. To make sure things fit. I know on the island if the mill is disabled there are a few people close by who can make some chips if I make a mistake. But I'd rather not have the mill that disabled.Going down this route soon.
For me the plan is some maintenance to see what wear hard CNC is causing and plan mitigation. Measure up and design mounts for the ballscrews. Assemble and continue work will setting up for next retrofit (without glitches one hopes).I'm finding it invaluable this time to do all the CAD up front. To make sure things fit. I know on the island if the mill is disabled there are a few people close by who can make some chips if I make a mistake. But I'd rather not have the mill that disabled.
Spent some time thinking about how to mount the CUI or US Digital Encoder on the back of the stepper motor. Turns out the issue is mounting holes as there aren't any. Not like the SteppersOnline motor that I wish I had ordered.And just for general interest. The 3D parametric CAD drawing took less than 10 minutes. The CAM using AlibreCAM took about 25 minutes which includes generating and zipping the G-Code .ngc files.
I'm not suggesting anyone use the files but if you are interested in what I did.
How I would use them would be to:
1. 0.042" aluminum sheet a bit larger than the diameter placed onto scrap plywood or MDF and held in the corners. Ensure that the center point sits over a T-Slot.
2. Run the G-Code that cuts out the middle hole.
3. Hand drill through the plywood and with a large fender washer and a bolt anchor down the middle.
4. Next run the G-Code that does the center drilling for the mount holes and encoder holes.
5. Run the G-Code that does the 4 mounting holes.
6. Screw self tapping screws into the wood through the 5mm mount holes.
7. Run the G-Code to drill the encoder holes.
8. Finally run the G-Code to cut out the outer perimeter.
9. Remove the outer clamps, screws and bolt.
10. use a deburring tool to clean the perimeter if the edge is ragged. Same with the 14mm center hole.
11. Depending on the state of the encoder holes deburr from the rear with a hand tool.
12. Mount to adapter.
There. A 12 step program...
That was the original idea. But a plate that can take either threads or countersunk for a screw or threaded insert raised the plate enough that the encoder disk locking screw is just on the edge of the shaft. Not the longest shaft. Same issue with the CUI holder. If I'd restarted this project 3 days earlier I could have added a StepperOnline motor with all the AR3 Robot Arm motors and reduction drives etc. But a single motor at $33 with the holes already there along with $32 shipping all US $ turns into about $100 Cdn.
Does it have to have the square hole?I have a problem and I'm not sure how to solve it at the moment. The knee shaft has the usual square end. The pulley is not keyed but has the two set screws on the shoulder.
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I can't just run the set screws down to press on the flats because if there is some sort of over torque event the screw part that sticks out bends. I've been using some brass pins pushed down by the set screws but ultimately it's the same issue. Some sort of sudden load and the pulley turns a bit, the brass pins are bent a tad and my Z axis has changed position slightly.
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If I make a 25mm bushing with a 14.14mm square hole and then slice it into key like pieces I could then jam them down with the two set screws as long as the screws went into a dimple in the insert.
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Alternatively put a flange on the insert with the square hole. As long as the set screws enter a dimple in the bushing it won't twist. I suppose it would be better if the bushing were keyed to the pulley.
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Does it have to have the square hole?
Seems to me that a round bushing with bore that clears the corner-to-corner dimension would support the majority of the grub screw stickout.
What about increasing the grub screws diameter and adding two more on the two other fl