I decided to get back to putting together an old table top drill press
that had never been used. I proceeded to connect the AC and the pulley
to the motor shaft, only to find out that the pulley has an I.D. of
1/2" and the motor shaft has O.D. of 5/8". (This explains why the
previous owner never finished it).
Outside of trying to find another pulley set I was wondering if I
should look into machining the present motor pulley by boring the
1-1/2" I.D. long from 1/2" diameter to 5/8" diameter.
Also, the pulley has a set screw, and the motor shaft has a key-way.
The problem is that the set screw *may* be too small for the key-way,
in which case I'd also have to re-drill for a larger set screw.
And all this after I figure out whether this would be best done on a
lathe or a mill, and then how to work hold for both operations.
I'd appreciated any advice on whether a project like this is
plausible, or should I just keep my eyes open for a pulley set that
Staten Island, New York.
boring a pulley out from 1/2 to 5/8 is a nice little lathe project.
Work holding can be easy or a bear depending on your exact pulley. I
generally use soft jaws (to get a large clamp area and not mash the
pulley) and clamp to the O.D. of the whole thing if the pulley isn't
huge. This one shouldn't be. Use of softjaws also guarantees your
pulley is dead nuts on center.
Use your favorite boring bar to bore pulley to size. Go maybe 2 thou
over so the pulley will slide right in place. You don't want a press
fit. I often use a piece of shaft the same O.D. as the motor shaft to
test the fit.
Before I bought a broach set, I often did the keyway right in the
lathe. (This little project needs more description than I'm giving
here) To do this, you mount a lathe tool bit the same size as your key
right in the lathe tool holder. Mount it so the bit points straight
into the bore and is on center. All you need for bit grinding is a
back rake right on the end of the bit.
From there, with the lathe off, start running the carriage in/out by
hand to slowly cut the keyway. Take a few strokes, then advance the
cross slide. Machinery Handbook has a nice table to tell you the
dimension from top of keyway to opposite side of the bore so you know
how much metal to remove.
There are other methods, this is just one good one.
If you have a big enough lathe it isn't hard. I'd put the pulley on a
short 1/2" rod, center the rod and turn the pulley OD concentric, then
chuck the pulley by the turned surface and check that the rod is
centered. Then bore it out to slide onto the motor shaft with no more
than finger pressure. You can use the inside and outside jaws of
calipers as a transfer gage, or turn some scrap to measure the same
diameter as the motor shaft.
Jamming a setscrew into the motor shaft keyway will cause damage
that's hard to repair. You can rough out a keyway in the pulley with a
scroll or saber saw and files, then finish it smooth and parallel on
the lathe as mentioned. That method is very slow so you want to rough
out as much metal as possible. The pulley keyway can be roughed deeper
than necessary since the setscrew pushes the key into the shaft.
If you accidentally rough the keyway too wide, mill a custom T-shaped
key. The proper key should work until the drill press jams, then the
poorly supported key might roll.
The simplest way to attach the pulley is to grind a flat for the
setscrew on the opposite side of the motor shaft. If you don't the
raised burr will gouge the pulley bore when you HAVE to remove it
On Tue, 15 Feb 2011 22:42:57 -0800, Searcher7 wrote:
You can buy a 5/8"-bore keyed step pulley for $14.09 plus shipping:
<(Amazon.com product link shortened)>
or $13.39: <http://www.acehardwareoutlet.com/ProductDetails.aspx?SKU "837>
Two hits from google for 5/8 step pulley
Are you related to my better half? You might as well sell your mill if
you're only going to make stuff that can be cost justified.
This looks like a perfect oportunity to practice boring to size and
making a keyway.
That's what I was thinking. (Though being a novice I may be in over my
head). I'll have to save and re-read all the suggestions until I can
In the meantime since I have to drill a lot of 1-1/4"" holes in
plywood, laminated MDF, and plastics(Delrin/Nylon) I assume that I
should be looking for a single step pulley in the area of the larger
Staten Island, New York.
You needn't consider the motor at hand, then; either find a
suitable one from a supplier of such things, or from your pile of
scavenged units, or from a buddy's pile of scavenged units.
Heck, offer the unsuitable motor for swap on craigslist...
Or, consider upgrading to a nice speed and torque controlled
Rebuilding pulleys, or replacing pulley/belt systems, isn't an
If you must redesign or rebuild, make that effort count.
That is awkward. I've made sleeves to *increase* the diameter
of a motor shaft, with a T cross-section key to fit both the keyway on
the shaft and that on the larger pulley. (And, the key is held in place
with a couple of counterbored holes for small Allen head cap screws
The main problem to my mind is whether you have a large enough
lathe chuck to grip the pulley. I would suggest soft jaws, turned to
fit the V-groove of the pulley as being more likely to hold the pulley
securely for the boring without damaging the flanges. Just grip on the
OD of the flanges. and you will make nicks which will probably cut or
fray the belt over time.
You want the setscrew to bear on the key -- not the bottom of
the keyway. So -- you'll want some way to cut the key slot in the
pulley after boring.
The common way is to use a DuMont key broach of appropriate
size, with an appropriate bushing to guide it..
But for that -- you will need an appropriately sized press,
which I don't think that you have.
And -- I'm pretty sure that you don't have a shaper, which is
another tool often used for the purpose.
So -- the best bet is -- *before* you remove the bored pulley
from the lathe chuck:
1) Lock the spindle against rotating -- engage direct drive and
back gears at the same time.
2) Set up a boring bar in the lathe carriage, with
a bit ground to cut the proper sized keyway.
3) Feed it in the full depth with the carriage -- at first barely
scraping. Then feed out with the cross slide and repeat.
Keep going until the depth of the cut is a little more than half
the width (as the key has to fit into the motor shaft, too.)
For the boring -- best on a lathe.
For the keyway, there are keyseating heads available for serious
sized Bridgeport mills (a vertical shaper) -- but not for anything which
you can get up to your apartment. So use the stroking approach in the
lathe. You should be able to find better descriptions of the process by
those who have done it -- since I have not.
How many steps on the pulley? How widely spaced are they? Can
you be sure that the replacement pulley will have the same spacing?
(And, of course, the size of the V-grooves depends on the belt you plan
I have, to shape a cylinder with a protruding tab. Unless you can
adjust the carriage hold-down clamps for minimal play it will tilt
from the misdirected cutting pressure. The carriage feed doesn't have
anywhere near the mechanical advantage of an arbor press, so the chip
has to be very thin and the job goes slowly That's why I suggested
sawing out most of the keyway. I used a Sears/AA lathe that has a
handwheel on the 16TPI leadscrew and IIRC couldn't take much more than
0.001" per pass in aluminum.
On Thu, 17 Feb 2011 00:08:00 -0800 (PST), Searcher7
Measure the diameter of each step on each pulley. The ratio between
the one the drill press pulley and the motor pulley is perfectly
adequate to calculate spindle RPM from the constant motor RPM.
If the front pulley step is half the diameter of the mating step on
the motor pulley the spindle will turn at twice motor RPM.
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.
O.K. This measurement would have been easier to get using
calipers -- vernier, dial or digital.
The flange spacing is only important in terms of finding the
right belt to fit it.
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.
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.
You need something to spread the grip out a bit -- you want to
grip both of the largest diameter flanges.
The pulley setscrew is seldom on the smallest step for this
reason. The setscrew should line up with the keyway in the pulley.
3/16" deep? It has a 3/8" width? That is a big keyway for that
small a pulley.
Go to a larger step -- closer to the center of the key. Drill
and tap for a new setscrew.
Just one -- on the middle step -- should suffice.
That could work.
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?
I don't know how much of an issue that would be but if I made a jig to
keep the file perpendicular to the axis of rotation it would eliminate
any concentricity problems. (But machining the motor shaft would be a
last resort anyway).
Yes. I just have to dig them out of the deep box they're sharing with
a ton of other tools. :-)
Yes. I actually did all these measurements for just in case I'd come
across a match somewhere.
Yes. It is the 4-jaw I was thinking about.
Yes. maximum surface/clamping area is what I'll aim for.
The set screw on this pulley is located in the second smallest step,
and there is no key way.
Yes. That's what I was thinking. (Another reason why this motor is too
big for this pulley). :-)
That would be the middle step.
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).
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. (?)
Thanks for all the advice.
Staten Island, New York.
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.
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.
How long is the motor shaft?
How does that compare to the maximum distance between centers on
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.
[ ... ]
They are one of the tools which you should keep near the
surface. They are very useful for quick measurements.
[ ... ]
O.K. Including people might read the list and think "I have a
pulley about that size." (However, *I* don't.)
O.K. More comments when I get down to the URL posted.
[ ... ]
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
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
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.
[ ... ]
Well ... used motors from the right place can be very cheap.
It may be an idler pulley, made for two ball bearing assemblies
to be pressed into to allow it to spin freely.
Actually I was referring to the *practice* itself of filing free hand
to create such a condition.
*If* the file is straight and kept perpendicular with some sort of
support(that would also eliminate bouncing) the same amount of
material taken off when the file hits the lip will also be taken of on
the opposite lip as it comes back around. As a result the depth of cut
at both sides of the "canyon" would have to be equal.
Without taking it apart I can't say, but the shaft protrudes 2-1/8"
out of the motor housing.
Hmmm. I just looked and apparently the shaft ends at the fan inside
the housing. Ok. That's about 9-1/2". I didn''t measure but the promo
for this lathe says that the distance between centers is 14". But I
assume that with the proper collets and the spindle pass through it
shouldn't be an issue either way, correct?
I just checked and the answer to that is yes.
Even though I'd only have to machine 2-1/8" of the shaft, considering
the size of it's key way, machining the cheaper pulley would probably
be a better way to go, correct? (I've never taken apart a motor
before, so I'd have to be meticulous in documenting dis-assembly).
Yes. :-) I'm in the middle of a major reorganization and I'm *finally*
getting all my tools into a single room that I'll use as a workshop.
So I have unboxed and put everything in their place yet.
I measured the depth of the bore at 1-3/8" which is why I concluded
that a hole for a set screw can be put in the middle pulley step which
is within that distance.
Ok. About the bushing. I also initially assume that that was a
bushing. But that may not be the case. I subsequently concluded that
it is just part of the pulley that isn't painted black...
Looking in from the large side I see nothing to suggest a separate
piece. Nevertheless, if that portion *is* removed the 5/8" bore
criteria would be satisfied.
I'm having a difficult time putting the set screw back in. (I probably
have to pick up a better set of Allen keys)..
"Key stock". Is that what it's called? (I thought that I'd just have
to get some square rod and mill it down).
The motor was attached to the base when I got it. Only the motor
pulley and belt needed placement after I connected the AC. The belt is
tension is adjusted by pivoting the motor until proper tension is
achieved. This is done with a screw below the belt-guard housing.
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