Square hole in round piece?

Jason snipped-for-privacy@removethisshaw.ca

wrt 1/8 cable to 7/16 square shaft coupling

Perhaps most importantly what you're asking is how to make a 7/16 square blind hole, 3/8 deep.

It always depends on the tools at hand. (I'm thinking that if you drilled through the center of the coupling blank 1/8, and then had a 7/16 counterbore with a 1/8 pilot for the start of the square-hole end, etc.)

But, drill a 7/16 bore on the end that's to be the square end by locating the hole with prick punch and then center punch, then drilling there first w/ a drill bit that will follow the center punch mark, and then enlarge with a 7/16 bit. File or chisel (with a cold chisel) the corners square (relatively), and you have it. At least that's one way.

If you get frustrated with filing to finish a blind hole, you could make a through hole in a 3/8 wide disk, and then solder/weld/screw it onto another part that would have the 1/8 bore for the cable.

You're ptobably going to need setscrews for both ends of the coupling. FM

Buy a socket and weld it on. YOu can also buy a sleeve with a square internal hole. YOu could drill out the square hole round and cut out the corners with a small chisel or broach. YOu could make it oversize so the square fits in the round hole and heat it red hot and clamp it in a big vice or press with the proper external size two piece round die. Or buy the part from the factory.

John

Jason wrote in news: snipped-for-privacy@removethisshaw.ca:

punch broach? Take a square tool bit (hss) the appropriate size and grind a concave in one end. Drill the part to at least the diameter of the square, a bit more if the application allows. Use your press and press the tool bit down through the hole to broach it. Be careful, the bit can shatter. Might be best to encase it in a piece of tubing if you can fixture the part up.

I have had a number of occasions when a hole other than round was required, usually square or hex. What has worked for me is to machine a broaching tool.

The workpiece wil have a hole drilled as large as possible without intruding on the finished space. e.g. for a 1/8", square, drill a 1/8"D hole

The tool will be turned from drill rod to a diameter corresponding to the largest radius. e.g. for the above, 1.414*0.125 or 0.177 with a short region at the end turned down to form a pilot. In this case,

The necessary shape is then milled on the larger part. For squares, hexes etc. I use an inexpensive spin index and a 5C collet to hold the work piece.

This part is hardened and tempered and pressed into the work piece to cut square corners into the drilled round hole.

Ted

This is a typical application for an EDM machine!

I was gonna say, jobs like this one make our little solid-state unit back in the corner look pretty good.

If I had one, I might go that way but am I correct in assuming that the electrodes are usually graphite? That is trully nasty stuff to machine, at least to clean up afterwards.

Ted

You can use a die-sinker or a wire-machine. With the wire-machine you'll need typical brass-wire, well you won't get exact sharp inner edges, only an edge with the wire radius (+gap of last impulse setting) but this is often enough. With the die-sinker, graphite is only one type of electrode material, you could also use for example copper....

Not *THAT* big of a deal. I cut them daily. It's very hard on tooling however, since it's so abrasive.

Jason:

You could machine it like you suggested yourself, and then just plunge straight down in the corners (carefully - slow feed), to get rid of the end mill radius. The smaller the end mill you use to machine the pocket, and relieve the corners the more "flat area" you'll have to locate on the square shaft.

Unless there's some particular reason for absolutely square corners, you could do it like people used to and relieve the corners with a larger diameter end mill. It cuts down a smidge on the contact area of the square, but not very much. Much easier than trying to mill a .0125" R corner 6" deep ....