Forrest Addy
Diamond
- Joined
- Dec 20, 2000
- Location
- Bremerton WA USA
Ever shape a wide keyway? This is how it's done.
YouTube
Note how the gentleman in the video cuts the center from the wide keyway he layed out in the hub. Then he uses a full width tool to cut to width. Thus he stages the cut limiting the thrust required. This is fully in line with the way I was taught 50 years ago and 7000 miles away. Small world.
Shapers and slotters have limited thrust. Form tools require thrust out of proportion to the section of the chip because the necessary force for penetration has to be summed with the resistance of the chip section. A keyway tool is a form cutter in effect even though the cutting edge is straight.
Another point is the top angle. Too shallow and the tool tries to spring away. Too acute and the tool tries to dig in. Different materials and heat treatments require different top angles if you want to be extra fussy but 4 degrees positive is a good starting point. If the tool deflects away from the cut, increase the top angle.
Be careful with the tool width. The keyway width will be almost exactly the tool width. Good luck if you finish a bit undersized and try to sideshift to remove the last couple thou. The attempt will drive you nuts. Keyway slotting tools are skinny in the Y direction and easily deflect to the side in an unbalanced cut. Both sides of the tool have to be engaged if the keyway sides are to be parallel and straight. A one-sided skim cut will inevetably bellmouth. The best solution for a slightly undersized keyway is a sharp on-size slotting tool. If that's not possible, you're better advised to hand-work the last couple thou. A dress with the belly of a sharp 3 square file will take less time than preparing an on-sized shaper tool.
This is all lore I gained from my mentors in 1965.
Personally, I prefer to broach keyways. Broach sets may be expensive but it's a once in a life time buy. Most small shops will have to buy them only once. Doc Mortenson gave me his Imperial set when he retired and he stole it when he was an apprentice. That makes it at least 70 years old. I replaced some lost shims, the 1/4 broach and made some bushings to time double keys, bushings for tapered bores, etc but otherwise it's good for another 70 years of once a month use. Come to think of it, I haven't used it it ten years. I'm 78, the age I should search for a successor.
YouTube
Note how the gentleman in the video cuts the center from the wide keyway he layed out in the hub. Then he uses a full width tool to cut to width. Thus he stages the cut limiting the thrust required. This is fully in line with the way I was taught 50 years ago and 7000 miles away. Small world.
Shapers and slotters have limited thrust. Form tools require thrust out of proportion to the section of the chip because the necessary force for penetration has to be summed with the resistance of the chip section. A keyway tool is a form cutter in effect even though the cutting edge is straight.
Another point is the top angle. Too shallow and the tool tries to spring away. Too acute and the tool tries to dig in. Different materials and heat treatments require different top angles if you want to be extra fussy but 4 degrees positive is a good starting point. If the tool deflects away from the cut, increase the top angle.
Be careful with the tool width. The keyway width will be almost exactly the tool width. Good luck if you finish a bit undersized and try to sideshift to remove the last couple thou. The attempt will drive you nuts. Keyway slotting tools are skinny in the Y direction and easily deflect to the side in an unbalanced cut. Both sides of the tool have to be engaged if the keyway sides are to be parallel and straight. A one-sided skim cut will inevetably bellmouth. The best solution for a slightly undersized keyway is a sharp on-size slotting tool. If that's not possible, you're better advised to hand-work the last couple thou. A dress with the belly of a sharp 3 square file will take less time than preparing an on-sized shaper tool.
This is all lore I gained from my mentors in 1965.
Personally, I prefer to broach keyways. Broach sets may be expensive but it's a once in a life time buy. Most small shops will have to buy them only once. Doc Mortenson gave me his Imperial set when he retired and he stole it when he was an apprentice. That makes it at least 70 years old. I replaced some lost shims, the 1/4 broach and made some bushings to time double keys, bushings for tapered bores, etc but otherwise it's good for another 70 years of once a month use. Come to think of it, I haven't used it it ten years. I'm 78, the age I should search for a successor.
