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View Full Version : Replacing motor on small harmonic drive ?



fabhund
20-12-2014, 07:10 AM
Dear Forum.

I'm getting warm on the idea on getting a 4.th Axis for my diy machine.
Primarily wood routing.

I found this kit on eBay:
http://www.ebay.co.uk/itm/CNC-Router-Rotational-4th-Axis-A-axis-3-Jaw-100mm-Chuck-Gear-Box-1700-Tailstock-/261583773351?ssPageName=ADME:X:RTQ:GB:1123

However the motor fitted is a 2-phase stepper NEMA23.

My machine is build up using 3-phase steppers NEMA23, and I already have the drive and motor in spare.
So I wanted to replace the motor on the harmonic drive.
Don't know much about alignment and harmonic drives, but from the picture "it seems" fairly easy.
Is there any alignment/adjustment involved in this, just so I don't start out breaking the wave generator or flexible gear.?

1. Alternative could be getting a 2-phase driver, but that adds to price, as I already have motor and driver.
2. Alternative Getting a belt driven instead, but I like the high torque from this, If one day I would expand with a 5.axis.

Best Regards, Bo Andersen.

johnsattuk
20-12-2014, 10:14 AM
I have done a similar thing ie:- changed a 2ph motor for a 5ph motor.

Motor needs to be accurately centered, are the spigot dia's the same, are the shaft dia's the same. I did enlarge the bore of a wave generator, needs to be accurately centered and absolutely free of swarf, dirt.

The wave generator is usually only held on with grub screw, before you remove it measure the distance from the flange of the motor and make a note of it, this controls the depth of engagement into the flexspline.

When reassembling it is very easy to engage the generator one tooth out (eccentrically) because of the very fine pitch, make sure it turns nice and freely before tightening the bolts.

fabhund
22-12-2014, 09:56 PM
I have done a similar thing ie:- changed a 2ph motor for a 5ph motor.

Motor needs to be accurately centered, are the spigot dia's the same, are the shaft dia's the same. I did enlarge the bore of a wave generator, needs to be accurately centered and absolutely free of swarf, dirt.

The wave generator is usually only held on with grub screw, before you remove it measure the distance from the flange of the motor and make a note of it, this controls the depth of engagement into the flexspline.

When reassembling it is very easy to engage the generator one tooth out (eccentrically) because of the very fine pitch, make sure it turns nice and freely before tightening the bolts.

Thanks for the heads up on the details.
Both motors are NEMA23, with 8mm Shaft. So I would assume it's a match.
Did contact the eBay seller, and they (of course) say the warranty will be void if I open up the gear. Never the less, the freight cost to China is so darn expensive that
I never would return it anyway.
Best Regards, Bo Andersen.

EddyCurrent
22-12-2014, 10:30 PM
This any better ?
http://www.aliexpress.com/item/100mm-CNC-4th-Axis-Tailstock-CNC-dividing-head-Rotation-Axis-A-axis-kit-for-Mini-CNC/2025750866.html

Jonathan
22-12-2014, 10:50 PM
Search for the harmonic drive datasheets and you'll find notes about assembling them properly.


This any better ?
http://www.aliexpress.com/item/100mm-CNC-4th-Axis-Tailstock-CNC-dividing-head-Rotation-Axis-A-axis-kit-for-Mini-CNC/2025750866.html

No, it's a lot worse due to the lack of harmonic drive.

EddyCurrent
23-12-2014, 11:28 AM
Buy two and make one of these; https://www.youtube.com/watch?v=_aLqeVJC7Ak