View Full Version : Boring Pulleys

12-13-2004, 08:52 PM
Being a new machinist I need to bore some Alum toothed pulleys , with and without flanges. Need to bore them to 12mm. Pulley sizes are 30mm and 90mm. I do have access to a Mill.


1. What is the best method to hold the pulleys in a 3 jaw chuck so it doesn't get damaged and secure.

2. Need to fit Keyways. Don't have a broaching set. What other methods could I use. Could I use an End Mill and then square up the slot with a file or as someone suggested putting a piece of tool steel in the lathe tool post and take incremental cuts for the keyway.

3. Last question. On a 12mm shaft what would the max size I should make the keyway. Would 1/4 inch be too big?...

Any other suggestions or advice appreciated.



12-13-2004, 09:19 PM
The best method to hold your pulleys is to machine soft jaws to about .005 smaller then the size you are holding, or same size.
If you have no soft jaws, I would use some brass shim's on your jaws and clamp very lightly, don't take heavy cuts.
As for putting keyway in, I used to put a HSS partoff blade in the tool post and slotted the keys this way.[Before I had my Slotter] You might have to grind it first to the correct size..about .0005 undersize, make sure, the blade sits nice and parallel, dial it up with a indicator, you can tilt the blade in such a way that you have clearance to the back.
Take about .003 at the time, use some tapping fluid and at the end of the stroke, move the tool away from the cut, before you travel back.
It looks like, a 1/8" keyway is about the right size.

12-13-2004, 09:31 PM
Thanks for your quick reply Konrad.

How do you machine soft jaws. Are they made from Alum?... Do they replace existing Jaws or do they fit over the existing jaws.

1/8 keyway.. I'll get some keyway that size.. thanks.

For the slots. Could I use an 1/8 square tool steel, appropriately sharpened?...

12-13-2004, 10:26 PM

As a shortcut method to protect your pulleys, measure the outside diameter of the pulley surface and the width between the flanges. Then, bore yourself a little ring with that width and inside diameter. Turn the outside of the ring in the same setup to ensure concentricity.

Then, take your hand hacksaw, and saw the ring into three segments. With a bit of juggling, (you may want to evolve a couple more arms, first :D) you can nest the three segments in between the pulley flanges and get the whole mess in the chuck.

If you want to make it really easy, you can start with a larger piece of stock and machine your ring (before you cut it) with a flange on the outside that will nest against the face of your jaws. This helps take a little bit of the guesswork out of the setup.

I might also recommend that you just go with a setscrew for your pulleys. The keyway is liable to end up a bit sloppy or misaligned (which means you need to file the slop into it to get it together :D). Mill a small flat spot on the shaft where the setscrew will bear.

A beefier setscrew than normal will drive all that you can torque through a little shaft. Locktite is your friend for permanent assembly, too.

12-13-2004, 10:31 PM
Not to take away from Konrad's excellent advice but since he is not on-line at the present time. :)

Lather turn and bore the jaws from a piece of aluminum with the internal dimensions as close to the OD of the gear as you can, the OD of the soft jaw is not critical but large enough to offer support while tightening the lathe chuck jaws and to clear any flanges. After you have that done cut it into three equal segments and then place them over the gear and space the lathe chuck jaw center on each piece and tighten.

12-13-2004, 10:37 PM
Ok Hu, so you are fast, big deal :D

12-13-2004, 10:58 PM
If you have a one piece jaw system, then you are out of luck, because these jaws are hard thru out. Soft jaws are made out of mild steel and mounted, [screwed] on top of your base jaws.
Then I would go with a split ring system, like hufludung mentioned.
1/8 square tool bit might be too flimsy to use, it should be just about the with of your hole, otherwise too much flex...on small size hole like this it's a bit of a bit.h..can be done..but might be better if you could give it to a local machine shop and just broach it thru with a 1/8 braoach, if not suggesfull, go with a couple of setscrews, and have a small flat machined or filed on [shaft], where the screw head makes contact, that way you ensure no slipping and you can allways dissemble it
with ease.
If you are going with key, practice first on a "dummy" piece...practice makes the master!

12-14-2004, 12:21 AM
Thanks everyone...... wilth all this advice I'll soon become a master....(not).

Also I didn't mention that the pulleys have a flange on the bore housing.. this is about 7mm long... I suppose I could chuck this into the 3 jaw if I do it carefully.

I think I'll go with trying the Set screw option first..(thanks HFD) and put a small flat on the shaft. I can do that on the Mill. I also have a bottle of the Loctite High Strength Retainer compound which I can use too. If I use the set screws and the Loctite hopefully that'll be enough. (I know Ynneb used superglue on his and it held without set screws... sorry for telling your secret Ynneb...) :)

Once again you guys came up with the goods... thanks...
now I can finish my X drive... Log should be updated this Sunday.

Then I'll only need to finish the wiring...eeeeekkkk.. hang around guys.... I may need you...


12-14-2004, 01:04 AM
One more advise on that loctite,..only use it if absolute necessary and probably not needed, if you have a good fit, it's just down the road, if you have to take things apart...it's going to be a Bit.ch.
If needed, then I would do it only after you have the machine going to your likings...then your know, that it's going to be the last time!

12-14-2004, 10:25 AM
Konrad is right :) Don't use high strength loctite until the machine is already working, and thus the assembly can be trusted as being the last. If you must anyway, use a grade that is not so high strength, so that you can remove screws etc. It takes a lot of heat to make the good stuff let go of its grip.