4th Axis Build

4th Axis Build

Postby AlbertaClipper » Tue Mar 07, 2017 4:19 am

I have it in my head that I need to build a 4th axis for my machine. For you that have one can you answer a few questions for me, please.

1. I have a Nema 23 motor I would like to use. Does it have sufficient holding power (torque) for a 4th axis? Workpieces no more than 4"-5" in diameter 36" long.
2. Can I direct connect the motor to the chuck/spur, at 200 steps/rev, or do I have to need a reducer/pulley arrangement?
3. Do you recommend a chuck or will a drive spur and tailstock be ok to hold/turn the workpiece?

TIA

Mike
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Re: 4th Axis Build

Postby IslaWW » Tue Mar 07, 2017 6:06 am

Mike...
You don't say what the holding torque is for that motor, but for 4-5" material, my opinion is that even the 570 ozin NEMA 23's are too weak for a diameter that large.

You will need some sort of mechanical reduction. I recommend 2:1 for each inch of desired diameter. Example 3" diameter = 6:1 reduction.
With direct drive and 200 steps per revolution your step resolution would be near .078" at 5" diameter totally unacceptable. At eighth steps it would still be over .009" which is still poor. With 6:1 reduction and eighth steps resolution is around .0015. Assuming a commonly used .006 to .008 stepover with nicely detailed 3D files you want to have a minimum of 3-4 steps to get to your required stepover to not induce rounding error distortion.

Chucks seem to perform the best, but they must have a setscrew to prevent winding off, if threaded on. If used gently for on center 3D machining a spur may also work.
Gary Campbell
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Re: 4th Axis Build

Postby ozymax » Tue Mar 07, 2017 6:38 am

I have a home built 4th axis of my own design.
I use a 280oz Nema 23, that I purchased from Probotix. I run through a 6:1 belt reduction and have a max dia of 90mm stock.
I run the driver at 1/8 stepping and it has worked fine for what I do. I've done some lengthy, approx 4hrs, carving jobs without any loss of position etc.
I simply have a 90mm face plate to which I mount either 3 or 4 angles. The stock gets screwed to the angles and the angles kind of self centralise. It's basic but for me, I feel it's better than using a chuck.
The chuck would add more weight and give me less length along the axis.

The axis doesn't live in this position all the time. I have dedicated mounting lugs in the table surface and an offset position in Mach3 for my rotary work.

Belt drive cover.jpg


Test stock mounted.jpg

This was my very first test piece. Nothing fancy, just testing the concept.

Test 01.jpg
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Re: 4th Axis Build

Postby highpockets » Tue Mar 07, 2017 6:48 am

Like your design.
Where did you get your 6:1 pulleys and belt?
I have a Nema 24 with 8mm shaft.
John
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Re: 4th Axis Build

Postby ozymax » Tue Mar 07, 2017 7:31 am

highpockets wrote:Like your design.
Where did you get your 6:1 pulleys and belt?
I have a Nema 24 with 8mm shaft.


https://shop.sdp-si.com/catalog
I just wished they were next door to me.
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Re: 4th Axis Build

Postby highpockets » Tue Mar 07, 2017 7:36 am

ozymax wrote:
highpockets wrote:Like your design.
Where did you get your 6:1 pulleys and belt?
I have a Nema 24 with 8mm shaft.


https://shop.sdp-si.com/catalog
I just wished they were next door to me.


Thanks, great source.
John
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Re: 4th Axis Build

Postby AlbertaClipper » Tue Mar 07, 2017 7:11 pm

Thanks Gary and Ozymax. Ozymax your build is exactly what I had envisioned. Thanks for the supplier link!
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