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Posted by pdrahn@coinet.com on October 16, 2008, 11:39 pm
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I think what you are doing is "pinning" the tube to the gear/shaft. I
think the pin will quickly enlarge the hole in the tubing. At any
rate, you will want the hole in the aluminum to be smaller than the
pin, so it is a press fit. That means initially drilling the whole
assembly with a drill bit slightly smaller than your final size. Then
remove the aluminum tube and drill the gear and shaft to your final
size.
Also, the size hole made by your drills will be slightly larger than
your drill bit. Otherwise you could not get the bit out of the hole!
That is why you should get a reamer for the exact final size you want
and use it after drilling. This lets you use a regular smooth pin. A
"roll pin" should be used if you cannot ream the hole. It will shrink
to fit the hole and expand to hold tightly.
Good luck,
Paul
> As you might know, I'm fitting an aluminum tube (6061 .065" wall
> thickness) over the gear sticking out of a motor shaft. It fits
> perfectly IMO. So now I either glue it or key it (if "key" is the
> right terminology). I'm confident that my glue will do the work, but
> I'd like to key it to make removing and replacing the aluminum tube
> easier.
>
> The motor and its gear have been pressed and glued against a 2 x 4
> so that it is secure during drilling.
>
> I need to know what size hole. I plan to drill with a cobalt bit and
> then fashion the shank of an inexpensive equal size bit for the key.
>
> I'm planning to go all the way through the gear/shaft/gear so that
> the key will stick out from both sides and the aluminum tube will be
> torqued on opposite sides.
>
> By the way. Would there be an issue with just drilling a shallow
> hole into the motor gear and using a key to turn the aluminum tube
> from one side only? Does that throw things off balance? The motor
> will be spinning at 5,000 to 10,000 rpm.
>
> The motor shaft diameter is 1/5". The gear diameter is about 1/2".
> The gear length is .3".
>
> Should I use a 5/64" or 3/32" drill bit? I might be able to do the
> drilling with a smaller 1/16" bit, but is a 1/16" key diameter
> big enough to turn the 6061 .065" wall thickness aluminum tube?
>
> Will that drilling risk loosening the gear on the motor shaft?
>
> Thanks.
>
> --
> the key will be flush with the outer surface of the aluminum tube
> on both sides and it will be covered by the inner race of a ball
> bearing that goes around the aluminum tube so the key cannot come
> out (it will probably be glued too)
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> thickness) over the gear sticking out of a motor shaft. It fits
> perfectly IMO. So now I either glue it or key it (if "key" is the
> right terminology). I'm confident that my glue will do the work, but
> I'd like to key it to make removing and replacing the aluminum tube
> easier.
>
> The motor and its gear have been pressed and glued against a 2 x 4
> so that it is secure during drilling.
>
> I need to know what size hole. I plan to drill with a cobalt bit and
> then fashion the shank of an inexpensive equal size bit for the key.
>
> I'm planning to go all the way through the gear/shaft/gear so that
> the key will stick out from both sides and the aluminum tube will be
> torqued on opposite sides.
>
> By the way. Would there be an issue with just drilling a shallow
> hole into the motor gear and using a key to turn the aluminum tube
> from one side only? Does that throw things off balance? The motor
> will be spinning at 5,000 to 10,000 rpm.
>
> The motor shaft diameter is 1/5". The gear diameter is about 1/2".
> The gear length is .3".
>
> Should I use a 5/64" or 3/32" drill bit? I might be able to do the
> drilling with a smaller 1/16" bit, but is a 1/16" key diameter
> big enough to turn the 6061 .065" wall thickness aluminum tube?
>
> Will that drilling risk loosening the gear on the motor shaft?
>
> Thanks.
>
> --
> the key will be flush with the outer surface of the aluminum tube
> on both sides and it will be covered by the inner race of a ball
> bearing that goes around the aluminum tube so the key cannot come
> out (it will probably be glued too)