Cutting/ Broaching inner keyway on a lathe

danleereed

danleereed

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Hello gang, I had a part I needed to have done today. I needed to get a 3/16" keyway into a 3/4" diameter hole, 1.25" deep. I had a piece of 3/16" square tool steel and guessed at how it should be ground. I used a 1/2", 90 degree boring bar to hold the cutter. I took about .005" per cut until I got it to .090" cutout.

The issue I had the most trouble with was deep chips. I bored the hole to .75" and 1.375" deep. The 11/16" pilot hole drill went about an 1/8" deeper to let the key cutting tool go deep enough. As I went through the many cuts I couldn't remove some of the chips at the end of the cut. My keyway ended up being only 1.125" deep when I finished.

Is the only way to get the full key to the end to bore more depth for the build up? Or is their a better way to grind my tool to make the chip come out? I thought about moving the saddle back every pass or two in order to break chips at the end, but that would add a considerable amount of time to the job.

Here are a couple of pictures of the tool and the end result.

phone 0916 452.JPG phone 0916 453.JPG phone 0916 454.JPG
 
Looks like a great job, and you ground that tool just like I would have. But I'm not sure what to do about the chips in the bottom. Lighter cuts maybe and reach in and break them off? :dunno:
 
A relief cut at the end of the bore or grind a tool to cut the chips out. Just feed the tool in at the end of the keyway and back the carriage to break the chip.
 
Used to have to do this at a place I worked years ago. We would drill a hole through the side of the part at the bottom of the bore. I like the under cut idea. Wouldn't have to be very wide.
 
Paul in OKC said:
Used to have to do this at a place I worked years ago. We would drill a hole through the side of the part at the bottom of the bore. I like the under cut idea. Wouldn't have to be very wide.
Click to expand...
I thought of the relief cut (like for internal threading) but was a little concerned about weakening the part as it would have to go 360 degrees. I luv your other idea about drilling a hole. You can always put a setscrew in the hole if the part has to be sealed.
 
I am intrigued by your ability to create a square key-way with your lathe, but am having problems wrapping my head around the concept. Were you moving the carriage in and out or the cross feed?
 
Pontiac Freak said:
I am intrigued by your ability to create a square key-way with your lathe, but am having problems wrapping my head around the concept. Were you moving the carriage in and out or the cross feed?
Click to expand...

Yes, to both Pontiac. I manually moved the carriage in and out of the hole to make the cut and moved the cross slide back about .005 per entry or cut until I had reached the proper depth. I had the lathe set in a very low gear to lock the head so the chuck wouldn't spin. It seemed to go very well.

I like the idea of a drilled hole for relief. Also if the part was large enough diameter I would maybe consider the relief groove/ cut at the end. I was also thinking it may weaken smaller diameters to cut the relief.

I have 1 more to make this week so I can finish this project. I am going to drill a little deeper and get more clearance so I can get the key as deep as I need it regardless of the chips that stick in the end. Also I have a pick to try to work some of them out before they build up to thick. I wasn't really expecting to deal with the unbroken chips the first time around.

Dan Reed
 
Very well done. I have one suggestion on the tool grind. The chip breaker you have is a tad deep. It caused the chip to curl rather than break I'll bet. Shallower would have caused the chip to break at rock bottom. Just a thought for next time.

"Billy G"
 
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