Broaching deep square holes

[SGropp]

As part of a door hardware project, I need to make an accurate 5/16 square hole through the length of a 1'' diameter bar, 1 1/2'' long. The material is 1018 CR mild steel. I actually only need the square hole to size in the middle 3/4'' of the piece. I plan to bore out the bar to the recommended 21/64'' pilot size and relieve each end to whatever the diagonal measure of the 5/16'' square is. I ordered a Dumont 5/16'' square broach with the intent of using a 3 ton arbor press or a 15 ton H frame hydraulic press to push it through.
Am I on the right track with this? Should the broach be lubricated ? When I've needed to do this in the past, I subbed it out to a machine shop, but I no longer have easy access to that resource. I only need to make 2 pieces for the current project, but this is a recurring need ,so I want to get set up to do it right in house.
Thanks in advance for any help. This site is a great resource of information.

[John B]

That should be OK, when I had a similar problem, but only for a one off, I used an old square file of the right size, cut off the tang, forged it to a longish taper at the front, and cut teeth into the taper, heat treated it and pushed it through with a press.

Just make sure it is vertical to the axis when you push it through

[irnsrgn]

Broaches for deep holes are very long and tapered compared to a normal keyway broach and they are usually pulled thru, Be very careful as when pushing any deviation from square will break the hard brittle broaches. I broached with a hyd press for the larger sizes and used an 8 ton Arbor press for the smaller sizes. After shattering several broaches, I learned to push aways (about an inch), then let the pressure off to correct any side deflection. I never broke another broach doing that. Just remember you are going to need at least 4 times the force it takes to broach a keyseat as you will be cuttinng on 4 sides instead of just 1.

The dark thread cutting oil, Buttercut or tap magic should work for the lubricant.

[irnsrgn]

I needed a similar piece many years ago and instead of broaching or farming it out, I bored a hole big enough to allow a piece of 3/8 square keystock to just slip into the hole and used a piece of shaft a bit bigger than I needed and heated the short shaft up, inserted a piece of 3/8 keystock in the hot piece and using a swage of the proper size, swaged the inside hole square and then finished it by filing for a slip fit and then squared the ends in the lathe then turned the OD to size between centers in the lathe. FWIW

[SGropp]

What would be the process on pulling the broach through ? There is a small center hole in the pilot end of the broach but I can't imagine what could grip and pull the tool through. Someone also suggested that I fully anneal the the material before I attempt to broach the hole.
The specs that came with the broach gives the minimum Length Of Cut as 3/8'' and the max as 1''

[devon blacksmith]

We make small square holes through round bar for door latches we just drill and drift to the right size cheap and quick.if the out side neads to be acurate as well I would turn them down to size after.

[medieval]

Look at Reid supply co. (reidsupplydotcom) I bought some pieces from them to use as a die hilder for a square shafted touchmark. I don't know what term they use, but I got 3 sizes. You can then cut a piece 3/4" long and put it into the bored hole of your piece and plug weld from the outside. Grind the welds flush and you can't tell how it was done. Their phone # is: 800-253-0421. They are located in Michigan. ;)

[mcraigl]

If none of that works out for you, go see your local waterjet guy with a chunk of 1 1/2" plate and tell him what you want. Take a 6 pack and show up at 4:30 on a friday and you might just get it for free! Usually works for me anyway.