# Cutting/ Broaching inner keyway on a lathe



## danleereed (Sep 16, 2014)

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.


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## JimDawson (Sep 16, 2014)

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?


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## Malave16 (Sep 16, 2014)

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.


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## PatMiles (Sep 17, 2014)

Just what I needed... last week. I'll be putting one of these together... next week.

Pat


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## Paul in OKC (Sep 22, 2014)

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.


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## epanzella (Sep 22, 2014)

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.


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.


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## Pontiac Freak (Sep 23, 2014)

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?


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## danleereed (Sep 24, 2014)

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?



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


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## Bill Gruby (Sep 24, 2014)

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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