Thread: Broaching a Key into a blind hole

I've got a project that it would be nice if I could broach a key into a blind hole. Shaft/hole size is 3/4"

Any "poor boy" ways someone can hint at for me. Depth maybe 2" Maybe broaching of some sort is not the approach at all, let me know if there's a way.

I always just broached thru holes like nothing, but this is different.

Thanks,

Richard

Richard, poorboy method. Chuck it in a lathe and use a boring bar with a bit ground to the width of the key. Run the carrage back and forth and use the cross slide to advance the tool. Not good for a production run, but ok for 1 or 2 pieces. I've done this before and it works well. If you have a Bridgeport Shaping attachment, that will work also. Good luck. Bill

GREAT METHOD

BUT, It's too big to put into my lathe, and probably any lathe within 50 miles of me!

Thanks, and I'm still waiting for my magic answer!

Richard

Richard
Just follow this link
http://bbs.homeshopmachinist.net//Fo...ML/000549.html
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Or use a bridgeport either puttint the tool in the spindle and runnining the quill up and down .....or putting the tool in the spindle or clamp to the head in some other way and run the knee up and down...or run in and out on either the x or y axes....

Also if you can stand a thru hole just in the area where the keyway is ,you can broach through that.

If you have access to a sinker EDM, that would work great, but I assume you don't or you would've already thought of it.

How about mortising like they do in wood ? You'd need a piece of tool steel, hard enough to cut the material, the size of the key and ground more or less concave at the cutting end. Then drill a hole the depth needed for the key, diameter about equal to the key width. Next, drive the tool into the same path, cutting out the corners ... oops, better put some clearance on the side of that cutter or it's never coming out again.

Just a wierd, poor boy amateur idea.
Den

Poor boy method would be to chip it with a cape chisel and finish with a file. 2" should be no problem.

You can make an end cutting broach. Basically just a hardened piece of tool steel the exact profile you want to cut. with the end ground off square or hollow ground to give some rake. Takes a lot of force to push. I think that the cheap socket sets have the hexes broached this way. There is always the sheared off metal pushed into the recess of the socket.
Maybe make up several sizes to remove metal gradually.
Piece of round stock dia. of hole, cut keyway, place lathe bit in keyway, etc.

Hope this helps.

Richard:
what you want to do is easy with a little tool from National Machine Tool Co. in Cinn. Ohio.
The tool is placed on a drill press chuck and run at approx 900 rpm . As the chuck turns , it rotates a cutter to plow out your keyway. I use one for 5/8 inch bore to cut a keyway in a blind hole approx 1 3/4" in length at a size of 3/16 x 3/32. I also have a 1" cutter for 1/4 x 1/8 keyway. The tools cost about 500-600 dollars but they might be able to let you know if any of their customers in your area can do it for you. Their # is 1-800-528-6682. The e-mail is nmtco@eos.net and the web address is www.keyseaters.com This company has been around since the early 1900's and their service is great. I have been using their tooling for the past 5 years for cutting blind keyways .

Richard,could you possibly use a round key instead of a square key? Plug the 3/4in. hole with a short steel dummy shaft and drill a hole half in the shaft and half in the material you want to broach. I've seen the round keys used several times and they seem to stay put.

another variation of the round key idea especially if the shaft keyway has closed ends for a feather key is to use an endmill or slotdrill to cut the internal keyway and just go that little bit further and then make a key to suit with a round top and a flat bottom to suit the shaft,or for a light drive you can just file the corners of a standard key.

If you have the room, undercut(recess) the hole so when you put it on a Bridgeport with a shaper (or any single stroke shaper) the broached material will break out and not be hammered into the bottom of the hole. Slater tools makes a rotary broach, but I don't know if that tool would handle this heavy of a cut. They have a web site.

Hi Richard, if your blind hole has relief, you can use our broaching tools on your cnc lathe or cnc mill to cut your internal keyways, check out our site Broaching Tools for CNC Lathes and CNC Mills to Broach Internal Keyways or our YouTube vid
broaching keyway on cnc lathe with inserted broaching tool.mov - YouTube