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Old 11-16-2013, 05:29 PM   #11
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Chuck, Looks really good so far. I was wondering, have you thought about what you will be using the mill for? From what I've seen on your Z work, it appears you were not planning to use a ball screw. If you want to do any 3D work, you may wish you had spent the time. Just a thought. Keep up the good work.

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Old 11-16-2013, 07:05 PM   #12
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Chuck, Looks really good so far. I was wondering, have you thought about what you will be using the mill for? From what I've seen on your Z work, it appears you were not planning to use a ball screw. If you want to do any 3D work, you may wish you had spent the time. Just a thought. Keep up the good work.

maury
Thanks, Maury. I do plan to do some contour work which will require the Z-Axis to work with minimal backlash. The quill is spring loaded and I can increase the tension on it if I need to. If that doesn't work, I can always go back and change it although I expect that would take an inordinate amount of effort.

This morning I finished the Z axis mounting bracket.







I would liked to have done it on the Tormach down at the TechShop, but I'm still struggling with getting a drawing processed all the way through FreeMill, the free CAM program I'm using for the moment. So, I just machined it manually. Boy, you're right about the axes unwinding on you if you don't have the locks clamped down nice and tight. Even with a 3/16, 2 flute endmill running at pretty high RPM I could see the slot beginning to creep sideways on me.


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Old 11-17-2013, 01:08 AM   #13
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I'm pairing 20 tooth with 48 tooth pulleys on the X-Y Axes. I need a smaller pair for the Z axis and happened to have a 15 tooth pulley for the motor so to keep the ratio the same as the other axes, I needed a 36 tooth pulley. I know it's not necessary to have the same gear ratio on all axes, but I like consistency. I didn't have a 36 tooth pulley on hand and I didn't want to pay the outrageous price for one, so I decided to make one. Here's a picture of the blanks I turned.



I already had a cutter I had made a number of years ago from a 1/8" slitting saw. I had beveled the edges to the proper angle and used it once before to make another pulley. Here it is chucked up in the mill, teeth already cut. I'm using my Arduino powered dividing head to index the blank as I gut the gulleys.



Unfortunately, I cut two of the gulleys twice as deep as they should be. I had forgotten that my ball screws move the axes twice as far as before! Made the correction and cut the rest of the teeth. I don't think it was make much difference.
Here's the (nearly) finished pulley.



Still need to bevel the edges of the teeth and bore out the hole in the center to the correct diameter.
I also just realized that the electronic dividing head will make a nice 4th axis when I everything up and running. Guess that 4th axis on the G540 will come handy after all!

Chuck
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Old 11-19-2013, 11:02 PM   #14
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Got the X-Axis motor bracket nearly finished. Here's the part that attaches to the mill table, with clamping screws drilled, tapped, and mounted.



And here it is with the motor attached.



Will trim off the bottom part of the motor bracket later when I get closer to finished with the project.

Chuck
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Old 11-24-2013, 07:15 PM   #15
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Still plugging away on this thing. I've spent the last few days experimenting with a couple of new Y-Axis bearing blocks. I'm not happy with either one, so I'm back to using the original casting. I am, however, replacing the two thrust bearings with somewhat larger angular contact bearings, back to back, to handle the side thrust from the belt tension. Won't receive those until Tue or Wed, so I've been filling in with other parts.

Here's a picture of the Y-Axis motor mount (so far). Still have to make the part that attaches the motor to the arm.



Some folks on the CNCZone forum have expressed concern about the size of my steppers. Hopefully they will be beefy enough if I don't try to coax too much speed out of them. Otherwise, I may have to move up to Nema 34 motors with a higher torque rating.

Chuck
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Old 11-24-2013, 08:13 PM   #16
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Some folks on the CNCZone forum have expressed concern about the size of my steppers.

Chuck

The guy's at the zone expect results like a real production machine. Just get the best rear ratio physical size will allow. Put the biggest gear on the screw as you can and not hit anything, and put the smallest pulley on the motor as you can. That will give maximum torque. you wont have big speed for rapids but you will have the torque for cutting. Your not making 1000 of anything so who cares.

If I remember correctly you have Gecko drives so if you want to post up the motor specs I can calculate the best input voltage to your drives, for your motors based on the inductance of the coils. Thats if you haven't done it. That will also improve torque through out your RPM range. The higher the RPM the greater the benefit.
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Old 11-25-2013, 02:24 AM   #17
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If I remember correctly you have Gecko drives so if you want to post up the motor specs I can calculate the best input voltage to your drives, for your motors based on the inductance of the coils. Thats if you haven't done it. That will also improve torque through out your RPM range. The higher the RPM the greater the benefit.
Thanks, Steve. The motor inductance is 6.8 mh per phase, 1.6 ohms resistance and are rated at 3 amps. The holding torque is 280 N cm which converts to about 396 oz in. I bought a 24v, 15 amp power supply specifically for this application, but could buy a different if there would be a significant performance boost. The driver is a Gecko G540 and will handle up to 50 volts DC for the motors.

As you said, speed is of little consequence to me. I have 20 tooth pulleys for the motors and either 48 or 60 tooth pulleys for the ball screws.

Here's the Y-Axis motor mount. It will be attached to the mounting arm with two 5/16" bolts through the 1 5/8" long slot. The bolts will be 3/4" apart which will give me 3/4" belt adjustment.



I realize this could still slip, but with two bolts holding it, it should be much more secure.

Chuck

Last edited by cfellows; 11-25-2013 at 02:29 AM.
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Old 11-25-2013, 03:54 PM   #18
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Excellent work...I've been hemming and hawing over CNCing my busy bee 1997 mill...don't suppose you have any saved drawing's you'd care to share?
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Old 11-25-2013, 07:16 PM   #19
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I think I will be able to use the MDI functions in the MACH3 Demo to move the axes around manually.
Mach 3 has a nice jog mode, just tap your tab key and it will come up
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Old 11-25-2013, 09:08 PM   #20
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Chuck, that is good placement for your "Y"motor. Good thinking. On my conversion the pulley for the "Y" limits the travel a little, making parts with just over 8" in the "Y" impossible.

You may want to also check out the pulley size for the "Y" so this doesn't happen to you. You will want all the "Y" you can get.

maury


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