Re: Machining a Pulley for a Drill Press

On 2011-02-17, Searcher7 <Searcher7@xxxxxxxxxxxxx> wrote:
On Feb 17, 3:29 pm, "DoN. Nichols" <BPdnichol...@xxxxxxxxxxx> wrote:
On 2011-02-17, Searcher7 <Search...@xxxxxxxxxxxxx> wrote:

[ ... ]

I was tempted to just power up the motor and use a file on the
spinning shaft. :-)

        Likely to wind up eccentric.  Every time the shaft brings the
keyway around, the file will drop and cut a little deeper for the first
part of the other side of the keyway.

I don't know how much of an issue that would be

The shaft eccentric would mean that the pulley would be
eccentric, leading to *lots* of vibration as you ran it, not to count
the periodic tightening and loosening of the belt as it rotates.

but if I made a jig to
keep the file perpendicular to the axis of rotation it would eliminate
any concentricity problems.

I don't think so. With a 3/8" wide keyway, the diameter would
drop as the key passed under the file every rotation, starting it down,
and then cutting a bit more metal from the other side of the keyway.

(But machining the motor shaft would be a
last resort anyway).

How long is the motor shaft?

How does that compare to the maximum distance between centers on
your lathe?

Do you have a live center for the tailstock?

Does the motor have center holes in both ends of the shaft?

If so -- you disassemble the motor -- taking careful note of
how the centrifugal switch goes together, and put just the rotor and
shaft between centers -- and use the lathe to turn the diameter down.
This will eliminate the eccentricity problem suggested above.

[ ... ]

        O.K.  This measurement would have been easier to get using
calipers -- vernier, dial or digital.

Yes. I just have to dig them out of the deep box they're sharing with
a ton of other tools. :-)

They are one of the tools which you should keep near the
surface. They are very useful for quick measurements.

[ ... ]

        O.K.  Now -- the pitch diameter only becomes important when you
are calculating belt ratios, not while you are trying to machine the
pulley to a larger hole.

Yes. I actually did all these measurements for just in case I'd come
across a match somewhere.

O.K. Including people might read the list and think "I have a
pulley about that size." (However, *I* don't.)

As for holding the pulley. If a 4" chuck isn't big enough the 5" I
have might be.(Of course I wouldn't be able to take *full* advantage
of such a chuck on my mini lathe).

        Are you talking about a 4-jaw chuck, or a three-jaw chuck?  The
jaws in the 4-jaw should be reversible, so you can grip a larger
diameter using the largest step.  And that would give you the ability to
center the pulley well -- plus the flanges of the pulley would seat
against the next step down on the jaws, to get it close to plane.

Yes. It is the 4-jaw I was thinking about.

O.K. More comments when I get down to the URL posted.

[ ... ]

The set screw on this pulley is located in the second smallest step,
and there is no key way.
http://i290.photobucket.com/albums/ll257/Statenislander/Tools/Pulley1.jpg
http://i290.photobucket.com/albums/ll257/Statenislander/Tools/Pulley2.jpg

Looking at those -- it *looks* as though the pulley is a rather
rough casting, bored out somewhat large, and then a bushing pressed in
from the big end. (And that hollow at the big end may limit where
you can put your setscrew. Measure the depth there vs how far to the
center of the pulley grooves.

Dig out the caliper, and use the inside jaws to measure the step
above the shaft mounting bore on the small end. That *may* be close
enough to your needed shaft diameter to be usable. (Or, it may be a
near metric size. Let's see -- 5/8" is pretty close to 16mm -- actually
15.88 mm, so if the pulley bore is actually 16mm, you would have too
lose a fit -- by 0.12mm or about 0.005" -- so get some 0.0025" shim
stock and wrap it around the motor shaft before sliding on the pulley
after pushing out the bushing.

Probably the threads of the setscrew engage both those on the
pulley and on the bushing, to keep the bushing from spinning in the
pulley. You would have to remove the setscrew before pushing out the
bushing.

                   I'd have to dig to find my micrometer with small
enough anvils to accurately measure the O.D. inside the smallest step,
but going by my initial and of course inaccurate size of 0.95492",
which I think I can assume should be about 1", I came up with the
following.

The motor shaft is 5/8"(.625") in diameter.
The motor shaft key way is 3/16"(.18750") deep/square.

        3/16" deep?  It has a 3/8" width?  That is a big keyway for that
small a pulley.

Yes. That's what I was thinking. (Another reason why this motor is too
big for this pulley). :-)

Well ... you could take some 3/8" key stock, and mill it to make
a 'T' shape -- with perhaps 3/16" width where it protrudes above the
motor shaft. And you could adjust the extent to minimize the needed
depth of the keyway in the pulley.

Note, however, that this motor may be just plain too big for the
drill press. Too much torque, likely to make the belts slip every time
you turn it on. You really need to find a more appropriate sized motor
for the drill press. (Have you checked whether the holes in the motor's
base even line up with the holes in the motor mounting plate on the
drill press?)

So if the key must be equally seated into key ways located in the
shaft *and* the pulley then the set screw would sit in a wall that is
less than 3/16"(.18750") thick.

        Go to a larger step -- closer to the center of the key.  Drill
and tap for a new setscrew.

That would be the middle step.

If there is meat on the inside all the way down to the shaft.
Seeing how much of a cavity is in that pulley makes me doubt it.

[ ... ]

That said. Someone is sending me a couple of small single step pulleys
that I *might* be able to use until I can set up and machine the one I
have.

        I hope so.  You know of course, that you could keep the same
speeds with a larger pulley if you got a lower speed motor. (But you
don't want to buy a new motor anyway -- right?

Unfortunately my finances won't allow any "major" purchases for a long
time.(My employer has kept me out of work for two months so far).

Well ... used motors from the right place can be very cheap.

BTW. I see a similar pulley on eBay: 380210297514

Not that I'd buy it, but I'd have to make a collar. (Which I think
might be easier than boring if I found a tube with the right I.D.).
And it is larger than the pulley I have. Also, it has no key way or
set screw. (?)

It may be an idler pulley, made for two ball bearing assemblies
to be pressed into to allow it to spin freely.

Good luck,
DoN.

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