Need Keway Broached

[lesrhorer]

There are videos on you tube broaching on a lathe or mill.
Mr Pete, and Kieth Appleton to name a couple.
What machines do you have or access to? What material is pulley?
What does this pulley do? Pics would help too.
Chuck

I should have mentioned from the outset it is Aluminum. It's for my mini-lathe. I am replacing the stock 750W brushed motor with a 1200W brushless motor. The tiny V-belts that currently drive the spindle are too frail. I've owned it less than a month and one of the V-belts shredded itself. They are also quite expensive and hard to find, being something of a specialty item. I am replacing the 2-step V-belt pulley system with a single flat timing belt.

I already had a friend broach one of the pulleys with a 5mm HSS bar using his lathe. The results were not very good.

 

[lesrhorer]

Yep, that's the way I broach. Tightly tape 3 good 32 tpi hacksaw blades together for an 1/8" broach in a pulley then dress it up/tweak it with a small triangle file. For a wider keyway just tape together more hacksaw blades. I've tried never tried to do a timing pulley though. That would complicate things.

You mean because of the thin lips? Well, maybe. Certainly the thin lips can't be held very tightly in a vice. A shim on each side a little deeper than the depth of the lips will protect them from the holding force, no matter what sort of clamping method is used. That, or one can clamp the pulley along the spin axis, rather than on its edge.

 

[ErichKeane]

I should have mentioned from the outset it is Aluminum. It's for my mini-lathe. I am replacing the stock 750W brushed motor with a 1200W brushless motor. The tiny V-belts that currently drive the spindle are too frail. I've owned it less than a month and one of the V-belts shredded itself. They are also quite expensive and hard to find, being something of a specialty item. I am replacing the 2-step V-belt pulley system with a single flat timing belt.

I already had a friend broach one of the pulleys with a 5mm HSS bar using his lathe. The results were not very good.

So the one thing people don't really mention with the lathe method: you're basically making it a shaper, and need to use shaper tools. So it comes down to the grind!

Even on a large machine, a 5mm wide cut would turn out awful chatter wise. You basically should have a RH and a LH shaper tool plus a rougher (or a flat face tool thst is narrow to do all 3).

This becomes tougher on a large, since I think you don't have enough axes to do it Right.

 

[lesrhorer]

Yep, that's the way I broach. Tightly tape 3 good 32 tpi hacksaw blades together for an 1/8" broach in a pulley then dress it up/tweak it with a small triangle file. For a wider keyway just tape together more hacksaw blades. I've tried never tried to do a timing pulley though. That would complicate things.

Interesting. If I can find the right thickness blades, this could be done pretty easily on the lathe. I am a bit leery of a purely hand based approach. Since this pulley will be under significant loads and spinning in both directions, the keyway needs to be pretty accurate.

Right now, I am leaning towards using a 3mm end mill and moving the mill bed 1/2mm each direction. Getting rid of the 3mm radius on both sides won't be difficult using a file. I can pretty easily clamp the pulley flat on a pair of parallel bars.

 

[ErichKeane]

Interesting. If I can find the right thickness blades, this could be done pretty easily on the lathe. I am a bit leery of a purely hand based approach. Since this pulley will be under significant loads and spinning in both directions, the keyway needs to be pretty accurate.

Right now, I am leaning towards using a 3mm end mill and moving the mill bed 1/2mm each direction. Getting rid of the 3mm radius on both sides won't be difficult using a file. I can pretty easily clamp the pulley flat on a pair of parallel bars.

If you rough it out with the mill, the lathe shaper thing should go way easier for pulling out the corners too, in car you wanted to indicate it in/get it quite accurate.

 

[lesrhorer]

If you rough it out with the mill, the lathe shaper thing should go way easier for pulling out the corners too, in car you wanted to indicate it in/get it quite accurate.

That's a great idea. I think I will try that.

 

[lesrhorer]

I have been thinking about how to locate the bar in the lathe so it is dead center off the pulley axis. I have a QCTP, which makes things easier, but how to measure dead center? There are a number of easy ways to determine when the top of a tool is dead center, but for this application, the center of the bar needs to be dead center on the part. I am going to bore out a piece of round stock to the same diameter as the diagonal of the tool bar. (5.66mm 7.07mm, respectively for the 4mm and 5mm keyways.) I can then tweak the height of the bar until it slides perfectly into the hole bored in the round stock. The center of the bar will then be dead center on the spindle axis. Replace the round stock with the pulley in the chuck, rotate the tool holder a few degrees to give it some clearance, and viola! A poor man's keyway broach. I just hope I have better results than my friend did. I think with a preliminary 3mm rough cut on the mill it will do just fine. 'Fingers crossed.

Now I just need to figure out a good way to lock the lathe spindle so the part doesn't accidentally rotate.

 

[lesrhorer]

I'd have to build a tool for it, but I could do it on my shaper depending on the shape/vice-hold-ability of the pulley.

That sounds rather expensive, not to mention a bit of work for you. Of course, a shaper would work quite well, as long as one has a good way to center the pulley on the shaper's thrust axis.

 

[ErichKeane]

That sounds rather expensive, not to mention a bit of work for you. Of course, a shaper would work quite well, as long as one has a good way to center the pulley on the shaper's thrust axis.

I've actually got most of the parts around... I am going to use a spare 5c collet block and weld it to barstock to hold in the tool holder, just never got around to it (and may have re-used my bar for something....)! As far as centering the pulley on the shaper's axis, thats a pretty common task. You set the pulley so it sits 'straight up' in the vise, then run a square bottom tool so it touches on both corners, thus you are reasonably well centered.

Either way, total is about an afternoon to get it setup and cut.

 

[lesrhorer]

I've actually got most of the parts around... I am going to use a spare 5c collet block and weld it to barstock to hold in the tool holder, just never got around to it (and may have re-used my bar for something....)! As far as centering the pulley on the shaper's axis, thats a pretty common task. You set the pulley so it sits 'straight up' in the vise, then run a square bottom tool so it touches on both corners, thus you are reasonably well centered.

Either way, total is about an afternoon to get it setup and cut.

Well, OK. How much do you want to do two pulleys, one with a 4mm keyway, and one with a 5mm keyway?