Machining a Pulley for a Drill Press

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.

Karl

I use one of my boring bars to scrape keyways in bores . Which one depend on key size , one bar holds 3/16" cutters , the other 1/8" .

Giving the Devil his dues, I suspect that there is a reason the motor shaft is keyed. Like maybe they tried the cheap-charley set screw and it wouldn't hold.

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 later.

jsw

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You can buy a 5/8"-bore keyed step pulley for $14.09 plus shipping:

or $13.39: Two hits from google for 5/8 step pulley

I agree.

Making this sort of stuff is always more expensive than buying. The only question is how many times more expensive.

i

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 visualize everything.

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 diameter.

Thanks everyone.

Darren Harris 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 DC motor.

Rebuilding pulleys, or replacing pulley/belt systems, isn't an upgrade. If you must redesign or rebuild, make that effort count.

Oops!

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 (4-40 IIRC.)

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 to use.)

Good Luck, DoN.

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.

jsw

564

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.

If you have a faceplate or can attach a plywood disk to the spindle maybe you could screw the pulley onto it. Start by truing up the seating surface with the pulley on a 1/2" shaft.

jsw

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Don't they all? :-)

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?

Good Luck, DoN.

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.

It would seem that I would have to

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.

meter with small

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.

Darren Harris 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 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.

[ ... ]

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 bushing.

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?)

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.

Good luck, DoN.

That ebay auction says the pulley is a spindle pulley; ie the upper end of the drill press spindle goes through it.

Actually I was referring to the *practice* itself of filing free hand to create such a condition.

=A0 =A0 =A0 =A0 =A0 =A0 but if I made a jig to

*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.

the motor shaft would be a

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?

Yes.

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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Yes, there is enough. (But of course this requires some thought on how to work hold again).

Ha! If I could only figure out where the "right place" is. :-)

Actually the auction says "spindle pulley", so I guess it would be a lost cause either way.

Thanks.

Darren Harris Staten Island, New York.