Turning down stepper shaft

**twistedfuse** · 1st November 2012, 08:57 PM

Hey All,

Got a random question for all the mechanical minded out there. I recently got myself a good deal on a low backlash Parker Bayside planetary reducer to replace the pulley and belt system. Although it has minor backlash (<10arcmin - although most say measurable is <6arcmin), it takes up less room behind the gantry and fun to try something new...and the major manufacturers can't be wrong in using them. Calculated resolution is still very low and i doubt noticeable unless i decide to machine aluminum production molds...lol.

Anyway, the reducer i bought is for a Nema 34, however the clamp on spur pinion for the motor is only .375" inner bore. This is both supplied and documented. Now the thing is, and most would already have picked it, all the standard nema 34 motors, at least the ones i have/come across, are all 0.5"+ inner bore.

I know its a hot topic about how bad it is to disassemble the motors so does any have any detail or knowledge on reducing the shaft diameter of a motor as i would prefer to use a motor i have laying around here rather than having to buy one with custom modification costs and shipping from a manufacturer. I am intending to run a single shaft motor but any information may be useful for both single and double shaft motors.

Daniel

**twistedfuse** · 1st November 2012, 08:59 PM

P.S Also if anyone does know how or knows someone who can it would also be very helpful.

*** EDITED - Just found that they do sell a second mounting pinion for .5" shaft motors. Just wasn't obvious on the site i was browsing. Still be interested in if it is possible though.

**Bob Willson** · 2nd November 2012, 12:55 AM

HiDaniel

I found after the Brisbane floods when I had to fix up my motors that there is nothing wrong with disassembling and reassembling the motors so long as you put them back together in exactly the same way as you took them apart.
Mark the cases to ensure this and you should be fine.
It is justthat they have very little clearance and almost no tolerance for error in their assembly.

**Malibu** · 2nd November 2012, 03:19 PM

G'day Daniel

Never having tried to turn a shaft down, I have drilled and threaded the end to have a locking screw in it, I can tell you they are HARD!
I'm not a machinest, but I can do a bit of turning... I would think the only way would be to grind it to size, but that would take a serious turner to get that done right.
I'd be inclined to bore out the pinion if there was enough meat on the shoulder to be able to.

I'll second Bob's comment on pulling the motors apart. I've pulled several down and as long as there's a bit of care taken and the end shields are marked, there shouldn't be any problem. Just work in a clean area without any iron swarf around because those magnets are strong and will pick up every piece you never thought was there!
Oh, and watch your fingers when inserting the rotor back into the stator housing!

**twistedfuse** · 3rd November 2012, 10:27 AM

Thanks Bob and John,

Was curious about whether the steppers would have a problem, after all the steppers are assembled by hand at the factories so it is good to know. Might look at pulling one apart one day just for the fun of it to try it for myself. I know the shafts are hardened so i expected grinding the shafts to be the best option. Spoke to the rep for parker bayside and told i can get many different sizes but when i got the pricing was a bit shocked at $150 ea. Might see if i can bore out the pinion but in the mean time ill have to save.

Daniel

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