So, where I work, we have this arcade game, which is a classic claw machine. IN order to raise the claw up and down the machine makes use of a worm gear, like so: enter image description here (although for the meticulously curious, this is actually the drive that moves the trolley the claw rests on back and fourth but it is almost identical to the part in question.)

I noticed that the gear seems to be on little grooves here. On one of our machines , the gear has actually come off of the grooves on the horizontal shaft. This has been causing the gears to slip whenever the motor tries to rise the claw. I assume this can happen because the vertical gear puts friction on the other gear that makes it tend to slide in the direction of rotation along the shaft, so my question is this:

Is this gear on the horizontal shaft held in place by friction (if I slide it in place until it is hard to move from pressure between the shaft and diameters of the gears, am I good) or do I need to clean the shaft and apply some adhesive in order to expect it to stay? It works okay now, but I didn't exactly test it extensively.

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    $\begingroup$ Neither. Usually by a positive mechanical means - splines, a keyway, or a grubscrew. You can see splines here. $\endgroup$ – Brian Drummond Jan 4 '17 at 13:01
  • $\begingroup$ That's what I mean.. it slid off the splines. Is just sliding it back going to fix it? This is a good example, not the gear in question. $\endgroup$ – user1833028 Jan 4 '17 at 13:02
  • $\begingroup$ If it can rotate on the splines it's too badly worn.. If it's loose enough to slide back on but not rotate, adhesive may be OK. After cleaning, there are grades of Loctite for the job. $\endgroup$ – Brian Drummond Jan 4 '17 at 13:05
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    $\begingroup$ I don't know if those are splines or just upsets to allow press-fitting. $\endgroup$ – Ethan48 Jan 4 '17 at 16:26
  • $\begingroup$ The horrible black goo on the gear wheel and the worm drive probably started off as nice clean grease, before it picked up a few decades worth of dust and dirt. If you clean all that off and apply a bit of new grease, it will probably be OK for the next few decades. The easiest way to clean it properly might be to remove the "claw" shaft completely. $\endgroup$ – alephzero Jan 4 '17 at 17:40

it appears the spline-like grooves pressed into the shaft's surface are upsets, which are there to derive an interference or press fit between the shaft and the gear. this is intended to fasten the gear onto the shaft so hard that it will not come loose, but if too much torque is applied to the gear by the worm drive, it will shear loose from the shaft and spin. glue would not help since the strength of the press fit is derived from the shear strength of the stuff the gear is made out of, which is probably greater than that of any glue you might try. if this is a common problem, then the assembly method of the gear on the shaft probably needs to be revisited.

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  • $\begingroup$ +1, I agree. At first glance it looks like a spline but it is indeed a deliberate surface deformation very like a deep knurl. A knurl can be used to increase the effective diameter of a cylinder. It is also possible that this method was used instead of a shear pin as a kind of "over-torque valve" for want of a better term. I'd say this machinery was definitely built down to a price! $\endgroup$ – user6335 Nov 23 '17 at 8:06

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