4th Axis Backlash

harris cue comp said:
if you run a direct drive in mach 3.you can run the 4th axis at max of 168000 and 50000accelerations. this will allow you to do engraving in record time as the a drive moves like the other 3 axis.
any a driver that has a ratio seriously slows down your indexing and your production time.
there have been some good advice here in this thread but a direct drive indexer is by far the best way to go.
thanks
Robert Harris
Click to expand...

?

As in a 1:1 ratio? With a stepper motor? You might have better resolution on an etch a sketch

Would love to see a video of this.
 
LGSM3 said:
?

As in a 1:1 ratio? With a stepper motor? You might have better resolution on an etch a sketch

Would love to see a video of this.
Click to expand...

I was looking at a 6:1 belt drive and thought that might even be to low. What is recommended? This would be for indexing only and not a spinner
 
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Some great info here for sure.
One more question on the harmonic drive, what is the holding force like for keeping position ? Not for cutting wood , but for milling high tensile Ali or Free machining steel ?
For myself I will need 2 setups, one as a spinner, so will most likely use a belt setup,The other an indexer, I will most likely go with a harmonic drive, but need more info about them 1st, that's why so many questions. In my case the indexer needs to be one that can use a face plate or other attachments be placed on the unit,not just a chuck.
Neil
 
Neil - I can hardly rotate the chuck by hand with power off. Once powered on, that 50:1 ratio works in favor of the motor holding torque and there's no way I could budge it without concern of damaging the chuck jaws. I believe they would have broken before the chuck would have moved.

Here's a pic of the faceplate with the chuck removed. If you want specific measurements, PM me and I'll take more exact measurements for you.

Best,

mac
 
Neil

Scratchy's remarks are consistent with my findings.

I don't have one in a full 4th axis setup, but I do have a very small one, just the harmonic part. It's only about 1.250" in outside diameter, and that's the housing. It was originally built into a small servo motor.

It's difficult to make the input shaft spin by turning the output shaft. It's much more stiff than I had expected.

There's also no detectable backlash. I haven't built an actual drive from it yet, but expect to soon. I may just opt to buy one from ebay though as they look cheap enough. I'll trash that motor and chuck though for sure.


Royce
 
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etch a sketch

i dont how long you have been running cnc mills and programing them in the fourth axis. if you are doing programs that are wrapping you need as much speed as your mill can generate. i appreciate you thoughts as you probably know the mill time for generating fourth milling.
thanks
robert Harris
(thanks tw)
 
I had a miserable time doing wrapped inlay work until I learned how to use the "Use Radius for Feed Rate" and the "Radius Correct" functions in M3. Once I had those setup, axis rotations take place at more or less the same general rate as the linear moves. This function setting tells M3 to adjust the A axis feeds based upon the radius of the work to achieve essentially a linear feed rate at the surface rather than typically much slower angular rates.

I am doing inlays with pretty small cutters, though, and don't need real high feed rates, typically running around 10 - 20 in/min for my maximum rates.

mac
 
That looks a good find for what I am needing in a 4 axis to make some parts with.
I will need to do more research myself before buying , but that is a very good start for me.
Do they have a tail stock/ support at the same center height to suit?
Thanks.
Neil
 
Neil I have not seen a tailstock for it. I know you can find a Chinese one fairly cheap and adjust the height as needed. You think the 6:1 ratio would be ok for inlay work?
 
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