Can one of you machinists maybe help me out?

Eric Patterson

Eric Patterson

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I'm restoring a vintage Powermatic drill press and have run into a problem. One of it's variable speed pulleys has a worn keyway. One solution we came up with was to rebroach it to 7/16". I'd post pics but the parts are at a machine shop now. The difficulty I've run into is my machinsist (two man operation) doesn't have a 7/16" broach. His Dumont Minuteman set only goes to 3/8". Dave McCann suggested I find machinist who uses newer wire cut technology. Before I take that more expensive route I thought I'd see if any of you machinists have a 7/16" keyway broach with a 1 3/8" bushing I could borrow for one keyway. It may be a long shot but I figure it's worth a try before I go shopping for another machinist since this guy is reasonable and will take walk-ins unlike the rest of the machinists around here that work for Gov big dollar missile contracts.

Thanks.

Eric Patterson
 
I can't believe that a muckity muck like you can't take it down to the company shop where they make those missles that knock on your door..tell the inhabitants.."Pizza"..then fly in and blow the snot out of them..and have one of the company machinists whip it out for you.(And charge it off to the gubmint)
 
Lee

Unfortunately I'm too far removed from the hands-on machinists guys or I'd ask for a favor. We do computer network and comms testing where I work now. No more stuff that blows up and no trips to the missile range these days. A lot of the prototype/test work is done in smaller machine shops and they just don't cater to the public. One machinist told me to head to Birmingham if I wanted a general machine shop. You know what, it just occured to me one of my best friends works for an outfit that has an in-house machine shop. Maybe he can lend a hand.
 
couldn't you use an end mill to widen the slot? That's what I'd probably try to do (and maybe bugger it up good in the process)

Remember, I'm NOT a machinist so take this with a grain of salt.
 
One simple solution that I have used many times is just to recut the same size keyway 90deg from the orginal. This is particularily useful if you can't or don't want to recut the shaft keyway. Based on the configuration of your pulley of course.
Good Luck
 
just broach a new key way 180 degres from the last one, the same size that's on your shaft, or just cut a new 3/8" key on your shaft and broach your pulley 180 degres at 3/8"
 
Found a couple pics.

repair.jpg



drivensheave.jpg



The above pics may help see what I'm trying to do. One half of the pulley slides up and down and is locked in position to the other half with two pins in the keyway. The holes that accept the pins have been reamed out over the years. So I have a worn keway, worn pins that need to be replaced (no biggie there, just a little lathe time on some keystock), and reamed out pin holes. These can create slop, noise, and vibration. Yes, I could bore new pin holes 90 degrees and cut a new keyway. Maybe that is the easiest solution but I really hate to start poking new holes and taking out more metal if I can help it. A 7/16" keyway on top of the worn out 3/8" keyway seems clean and simple, if only I could find a broach set to do it.

Thanks for the input. I will give it some thought.
 
Eric is into hand carved decoys and hand built boats, why not a hand cut keyway. Can't be that much different than hand cut dovetails.

BWAAAAAAAAAAAAAAAAAAAAAAAA
 
Dave

Check your messages. By the way, I measured the wall thickness and motor shaft protrusion into the pulley. Looks like there is room and meat for your extended pin solution. Thanks, you've given me some good options.
 
Eric, I'll check tommorrow, I have some tools and may have something that big. Don't panic there is a ton and a half of talent here.
 
Lee, I don't know anyone that has the equipment to do stuff like this except for where they work. If I did they might not answer the phone when my number showed up on caller ID!

Ken, those keyways are looooong and the fit needs to be pretty accurate or you'll get binding or slop. I don't think I could do it with a file and keep it in spec.

Wicker, thanks. I think the tougher creature to find is the 1 3/8" bushing for a 7/16" broach. They make them for a 3/8" broach and only cost about 12 bucks so I could buy one, have it milled out to 7/16" and then do the rebroach job. If you've got the broach let me know. Thanks!
 
Eric, The best suggestion would be to cut another 3/8" key slot 180 degrees from the original key slot. This will keep your pully sheath balanced when it is rotating.
 
Eric, No luck on the broach, I have a set with a 1 3/8 pilot but only goes to 3/8 broach. Good luck with your project.
 
Eric,

Just my .02 cents but how about having a machinist take an oversize dowel and grind flats to fit the keyway dimensions. Then have a pressfit hole drilled into the shaft to accept the dowel.

Good luck,

Ed L.
 
Ed

The shaft is hollow so you can't just press pins in or they will fall through. The head is the biggest dimension. Dave had an idea along those line where you make the pins long enough to reach the other side and counter bore them in. I pretty much have a solution with the 7/16" braoch barring anything unforseen. I borrowed a 7/16" broach and will tailor a 1 3/8" bushing for this job. Should be straightforward now.

Thanks, and welcome back.
 
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