GT2 pulley, 20 tooth (part # S3023) are a tight fit!

Assembly questions and answers for the Shapeoko 3 CNC Mill
kristenanne77
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GT2 pulley, 20 tooth (part # S3023) are a tight fit!

Post by kristenanne77 » Tue May 12, 2015 12:42 am

The four GT2 pulleys (part # S3023), the ones with the larger center hole, are a tight fit going on to the motor shaft.
Real tight. I am afraid I might damage them while trying to push them onto the motor shaft.
Are the supposed to be this tight?

K

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Re: GT2 pulley, 20 tooth (part # S3023) are a tight fit!

Post by WillAdams » Tue May 12, 2015 12:53 am

Better tight than loose.

Try putting the motors somewhere cool for a while, then put the pulleys in hot water, retrieve one motor, carefully dry one pulley, then try putting things together (use pliers or some other suitable tool to ensure you don't burn or scald yourself).
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Joe_C
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Re: GT2 pulley, 20 tooth (part # S3023) are a tight fit!

Post by Joe_C » Tue May 12, 2015 1:20 pm

K; I would advise you be careful and not force anything to fit. You might damage the bearings in the motor. Besides, you might have to remove or adjust it later. I had the same tight fit pulley. I carefully enlarged the pulley opening with a small round jeweler's file. Being careful to file flat and even. (I make machinists cringe!) I should have contacted Carbide support but by that time, I had 'Go!' fever.

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Hans
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Re: GT2 pulley, 20 tooth (part # S3023) are a tight fit!

Post by Hans » Tue May 12, 2015 2:14 pm

In an industrial setting, most things that are supposed to go on a shaft and then not move are an interference fit (need to be forced on or heated to install). This give the best straightness and concentricity of mounting, and helps keep things from spinning on the shaft that shouldn't. Where I work, they have bearing heaters which are essentially a hot plate with a stepped cone instead of a flat top. 6061-T6 starts to lose its temper around 275 F making it weaker, but that's not really a problem for you since even in its annealed T0 state the aluminum is far stronger than the belt teeth. The bore will increase in size by .001" for every 325 F you increase the temperature by, given a .25" bore. The amount of interference is almost certainly less than .001". The temperature drops quickly especially once you start fitting the pulley on the shaft, so get it in place quick.

You can also press the pulley on with an arbor press or even a clamp if you support the back end of the shaft so you're not pushing on the bearings. Don't use a hammer, though.
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cvoinescu
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Re: GT2 pulley, 20 tooth (part # S3023) are a tight fit!

Post by cvoinescu » Tue May 12, 2015 3:15 pm

The pulleys have set screws and I don't think they are intentionally interference fit. They are supposed to be easily removable, without being too loose either. Judging by the aluminium pulleys I've seen, they're probably just machined inconsistently. Even with American-made pulleys from SDP/SI, I've had about one complaint per three hundred pulleys of them not fitting on the shafts (and it was the pulley, not the shaft). In one case, it was obvious from the tool marks that the tool had seized in the bore and the pulley had slipped in the chuck; in another case the pulley looked fine, but the bore was a little too small, so maybe they skipped a final reaming step on that one.
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Hans
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Re: GT2 pulley, 20 tooth (part # S3023) are a tight fit!

Post by Hans » Tue May 12, 2015 4:01 pm

I just mean it might not be so bad if they're tight, and they can still be put on if somebody wanted to go down that road. We don't have the benefit of an industrial assembly department, though. If they won't slip on and the set screws aren't in the way, then you can probably get a replacement because it is a manufacturing defect, even if they're technically usable.
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kristenanne77
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Re: GT2 pulley, 20 tooth (part # S3023) are a tight fit!

Post by kristenanne77 » Tue May 12, 2015 7:53 pm

All these useful tips. Great.
I should be able to get the pulleys on easier.

Which raises another question....
How would I get the pulleys off if I needed to?



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newtothis
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Re: GT2 pulley, 20 tooth (part # S3023) are a tight fit!

Post by newtothis » Tue May 12, 2015 8:18 pm

I back out the set screw, for the tight ones I cover with a random wide strip of rubber to protect them and use a pair of pliers with just enough grip to hold - then pull. Most of the time, they slide off with finger pressure and a light tug. I've tried swearing at them but it doesn't work.
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Hans
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Re: GT2 pulley, 20 tooth (part # S3023) are a tight fit!

Post by Hans » Tue May 12, 2015 9:00 pm

They're supposed to come off easily after loosening the set screws. Press-fit and shrink-fit components are properly removed with a bearing puller. You can find cheap sets at Harbor Freight and Amazon, for example. Pliers, hammers, etc. work but it's undesirable to pull on the motor shaft very hard (you're mainly worried about damaging the ball bearings in the motor).

I'll have to buy a puller if I ever want to change my pulleys... I superglued them on when the set screws were slipping :mrgreen:
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veng1
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Re: GT2 pulley, 20 tooth (part # S3023) are a tight fit!

Post by veng1 » Tue May 12, 2015 9:29 pm

Consider filing a flat on the shaft and use thread locker on the set screw.

In a pinch, you can use a drill press or arbor press to remove the pulley. Support the pulley and press on the shaft.

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