How to cut a square hole?

[auto.pilot]

I would like to replicate a drum key like what is shown below. The hole is approximately 1/4 inch square and 3/8 inch deep. I have a small metal lathe and drill press. Material will be brass. The hole shown in this picture is very square, but slightly rounded inside corners would be acceptable. Can this be done?

Thanks

jim

 

[7HC]

I would like to replicate a drum key like what is shown below. The hole is approximately 1/4 inch square and 3/8 inch deep. I have a small metal lathe and drill press. Material will be brass. The hole shown in this picture is very square, but slightly rounded inside corners would be acceptable. Can this be done?

Thanks

jim

View attachment 41754

You could drill an appropriate size hole, then file it by hand. A little laborious, but it is brass so it's pretty soft going.
Or you could mount it in the lathe chuck, then grind a tool to shape and plunge it in and out in the manner of a shaper. If you grind the tool with sharp square edges you could get square corners that way if you wanted.
Finally, if expense is no object you could do it in a couple of seconds with a rotary broach, but you could probably buy a hundred drum keys for the cost of the broach and holder.


M

 

[Hawkeye]

I would drill a 1/4" hole into the end of the blank (Do this step first so as not to waste the other steps if something goes wrong.), then push (hammer) a tool into it to chisel out the corners. The tool is made from a piece of 1/4" square HSS such as is used for a lathe tool.

You can grind the end so that the corners come to sharp points of 4 or 5 degrees. Make sure to remove the tool frequently so that it doesn't get jammed in the hole. Don't use regular cutting oil. Kerosene would likely be better for brass.

You might have to use a file to start the corners so that the broach will enter the work.

 

[GK1918]

That a boy Hawkeye, thats how I do squares on anything. Anyone happen to see how sockets are
made, Discovery channel red hot blank, and the male shape is pressed in. All my boring bars
cherry red HSS blank pressed right through, brass not problem.

 

[AR1911]

You could drill an appropriate size hole, then file it by hand. A little laborious, but it is brass so it's pretty soft going.
Or you could mount it in the lathe chuck, then grind a tool to shape and plunge it in and out in the manner of a shaper. If you grind the tool with sharp square edges you could get square corners that way if you wanted.
Finally, if expense is no object you could do it in a couple of seconds with a rotary broach, but you could probably buy a hundred drum keys for the cost of the broach and holder.
M

I think I'd do this, but I'd have only one corner of that cutter sharp, with lots of relief.
I would set up the spindle so I could index it at 90 degrees. Do 1 corner at a time, then do the flats as a 2nd op.

 

[Tony Wells]

Well, if I were to home-brew any sort of volume method, I'd drill the hole O/S, leave the OD larger, then with a square punch of the appropriate size, push it through a tapered ID of some hardened tool steel in a press to swage it down around the square and leave the OD round. Of course, it would have to be configured to have a withdrawal means to avoid getting the punch stuck. Brass isn't very springy, so chances are it would be tight after pushing through the forming die. And the OAL would increase as the swaging took place.

It would take some calculation and experimentation to get everything to come out just right, but it would be the quickest way other than a rotary broach, I believe. Or maybe the old fashioned way would be to rotary forge it down against a square mandrel.

 

[8ntsane]

You should be able to do it all in the lathe. If your lathe has a 4-jaw chuck, use that to index every 90 degrees. Just stick it in the lowest gear you have to keep the chuck from moving on you. You could also put the chuck key in , and a bungee cord to take up any slack in the setup.

Use a HSS tool bit , and grind to suite, and wheel the cariage back and forth like a shaper. Do one corner at a time, then rotate 90o till you have a sqaure.
hole.

You may be able to do 2- corners at once, then just roll the chuck 180o and do the last two. Being your going into a blind hole, and with hit bottom, the use of the carriage stop would be helpfull too.

 

[jerryhawthorne]

Bearing in mind that I'm a total dummy in machining, could you please explain what a "broach" is and how turning this devise in a lathe will make a 90 degree angle. Never understood this.
Thanks, the dummy in this forum.
Jerry

 

[7HC]

Bearing in mind that I'm a total dummy in machining, could you please explain what a "broach" is and how turning this devise in a lathe will make a 90 degree angle. Never understood this.
Thanks, the dummy in this forum.
Jerry

For want of a better expression the broach, which is in the shape you wish to cut, 'climbs around' inside the hole, cutting as it goes.

Here's a video of a rotary broach being used in clear plastic: http://www.youtube.com/watch?v=BhvNU2E_x_Y


M

 

[lohring]

If it's not too big of a square you can grind a tool bit to size and press it straight through in one pass. I do this with mild steel for the square drive for a 3/16 flexible shaft. The tool needs a little relief, the start hole needs to be bigger than the across flats dimension, and a generous chamfer helps. My square is .153 across the flats with a .170 chamfered pilot hole. I press the bit through with my milling machine vise for an accurate alignment.

Lohring Miller