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I'm hoping to use a DC motor to drive a cog bar horizontally along a track. AFAIK, I'd need to install a (plastic) cog on the motor shaft, which itself grips on the (plastic) cog bar. Does anyone know how to prevent the cog from shifting on the shaft? The shaft is 10mm long and I'd like to make sure the cog cog sits at 5mm, where the cog bar is.

Any help will be appreciated.

Thanks

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  • $\begingroup$ There are a few different techniques for attaching gears to motor shafts and different gears tend to be designed for a specific technique. A picture or link would help. $\endgroup$
    – hauptmech
    Dec 23, 2015 at 10:53

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If the pinion will be close to the gearbox plate, use a washer or thrust bearing between the pinion and plate. The washer can be made from teflon or polyethylene sheet, or you could use thin steel washers. Shaft collars also can be used to keep the pinion from shifting in and out, but a pinion with a setscrew (as pictured below) would be more compact. An N20 gear motor apparently has a 3 mm diameter shaft; one of the shaft collars below is 3 mm. The pictured thrust bearing is 2.5 mm bore.

enter image description here

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The term I'd use for cog-bar and cog is rack and pinion.

Plastic pinions are usually press-fit if they are very small or use set screws if they are just small.

I assume you are asking the question because the pinion is sliding on the motor shaft. Use epoxy. Use one that takes some time to cure so that you can position the pinion without worry.

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  • $\begingroup$ Thanks. Apologies for the misuse of terminology. Usually, should a pinion like this be used which has a screw hole? Should the smaller end be pushed all the way to the inside end of the shaft? If so, wouldn't the pinion rub against the gearbox plate? $\endgroup$
    – Kar
    Dec 23, 2015 at 17:22
  • $\begingroup$ A pinion with a set screw like you show should work fine. Your bigger challenge will be to mount the motor pinion assembly so that it remains aligned with the rack. $\endgroup$
    – hauptmech
    Dec 23, 2015 at 20:58
  • $\begingroup$ Could the pinion touch the outside of the gearbox or should there be a gap? Indeed, is there a standard approach to aligning the rack with the pinion? $\endgroup$
    – Kar
    Dec 23, 2015 at 21:00
  • $\begingroup$ No gap will be OK but watch out for friction from the pinion touching the motor frame. There is not really any standard approach. $\endgroup$
    – hauptmech
    Dec 23, 2015 at 22:11

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