Cutting Pulley Keyways - Without a Broach

[savarin]

I've cut keyways in aluminium with a sharp honed HSS tool bit it worked ok, mounting in the tool post, setting the pulley so the cut is at 90'.
By sliding the saddle up and down the bed and moving the cross slide towards me it slowly cut the slot.
Its not fast but a couple of thou at a time and it got there.
I made the tool bit approx half the width of the slot I needed so it was easier but had to cut it twice to get the width.
A broach would be way quicker but how much use would it get.

 

[nnam]

How about these two ideas. One is very basic, cut with a scroll saw using a modified/appropriate blade, then dress it up with a file.

Another is using a round rod. Drill and tap at the end to keep the cutting bit secured. Near the end of the rod, on the cylinder surface, drill a hole across the diameter through the center, then make a cutting bit from a same size drill bit's mounting end. The initial bit would have reliefs made to help cutting. The 2nd bit would be made without the end relief to have a flat final surface. The rod has the same diameter as that of the hole where the keyway is cut.
If the rod is big enough, tap a set screw at the other side of the bit holder hole to adjust the depth of cut.

I plan to make one using the second idea. What do you think? It appears to be very simple. I used the same idea for making scribe tool.

 

[yendor]

I have seen a guy who used his MILL to do this. He set up the pulley flat in a vise and used a small diameter 1/8" End Mill to cut a Round Bottom Keyway then moved over to the lathe and used the method you described to finish it up square.

 

[macardoso]

I have purchased one off broaches for a reasonable amount of money. Like you said, you will rarely use the set. I do not own an arbor press, but you can use your lathe carriage to push the broach through. Can't be a huge broach, but I've done a 5mm keyway in aluminum on my 12x36 lathe and 1/8" in steel no problem (both 1" or more deep). put the part in the chuck (preferably backed against a shoulder or backing plate and push the broach in using the flat side of your toolpost. Just don't go nuts on the force you exert.

 

[Earl]

I have purchased one off broaches for a reasonable amount of money. Like you said, you will rarely use the set. I do not own an arbor press, but you can use your lathe carriage to push the broach through. Can't be a huge broach, but I've done a 5mm keyway in aluminum on my 12x36 lathe and 1/8" in steel no problem (both 1" or more deep). put the part in the chuck (preferably backed against a shoulder or backing plate and push the broach in using the flat side of your toolpost. Just don't go nuts on the force you exert.

This is the cutter that I used. It is 1/2 inch boring bar with a 3/16 HSS tool bit. Too much flex in the bar even with minimal stickout from the tool holder. The pulley was for a 5/8 shaft so I could not use a larger bar. I started with a much shallower cut. (about 2 -3 thou) I even tried using the opposite side of the bar and pulling it thru the pulley. I used wd40, tapmatic, and every other cutting oil that I had. Broches are cheap!!!

 

[SLK001]

What you did should have worked - and rather quickly. My only observation is that your tool might have too aggressive of an angle at the front and was therefore digging in - especially in aluminum. If it was digging in, then the depth of the tool would have to be continually adjusted (deepened) because the boring bar was being pulled down onto your part (dragging).

 

[Earl]

What you did should have worked - and rather quickly. My only observation is that your tool might have too aggressive of an angle at the front and was therefore digging in - especially in aluminum. If it was digging in, then the depth of the tool would have to be continually adjusted (deepened) because the boring bar was being pulled down onto your part (dragging).

I re-ground that bit of hss 3 times during the experiment. (I have to call it that because it didn;t work for me) In the beginning there was almost no rake. I kept increasing it until it is what you see in the pic.

 

[Suzuki4evr]

Feeding a thou at a time using the cross slide actuating the compound by moving myself side to side worked very well and it turned out to be a surprisingly easy operation

And by the sound of it, good exercise.

 

[Lo-Fi]

It wasn't as bad as a thought it would be driving it mandraulic! I did work out that almost zero back clearance was key to stopping it digging in while maintaining a positive cutting rake. I also ran it through with a half width tool before going for the full profile which helped immensely.

 

[Jim F]

View attachment 351857
This is the cutter that I used. It is 1/2 inch boring bar with a 3/16 HSS tool bit. Too much flex in the bar even with minimal stickout from the tool holder. The pulley was for a 5/8 shaft so I could not use a larger bar. I started with a much shallower cut. (about 2 -3 thou) I even tried using the opposite side of the bar and pulling it thru the pulley. I used wd40, tapmatic, and every other cutting oil that I had. Broches are cheap!!!

The grind on that will cause it to dig in the deeper it goes.
It should be square at the front, with a relief on the side facing the work.