3/8 square broach in an arbor press?

I have a part that will need a 3/8 sq x 1/2" long in mild steel. 20-40 parts every 4 months or so. Figure I could do 'em myself. Looking at a Dumont broach. Calls for a 25/64 pilot and about 3700lb of push. I have a 2 (or 2 1/2?) ton press. Will she do it? Or do I need an 4' cheater bar? Ideas? Good, bad and the ugly?

I think I would be looking for a hydraulic press. They are not terribly expensive. I just bought a Dennison 4 ton for $500.

I would try it with your present arbor press. I did 1/2 square holes in about a thousand pcs of 3/4 inch long bushings when I was young and had no trouble. With 1/2 length you will have only a few teeth engaged at any one time and probably less that advertised push will be required.
Working in another shop we used an Enerpac hydraulic ram in a shop built press and it was a pain to stack up spacers with the short (4 inch) stroke. If you get a longer stroke and can do the whole thing in one shot it would not be so bad.

I have done 1/2" sq. thru 1/2" ss304 with my Dake 1 1/2 arbor press.

The arbor press will do the job. You will have to do about 2-3 passes depending on the accuracy that your looking for. We use a 3/8 dumont key cutter to cut bevel gears in three passes, the last pass is .015 to hold tollerance. The problem you will run into is the broach will want to pull into the material, as soon as you feel the broach get tight stop and tap it back a little. Then use a quick short stroke to break through the build up and it will go back to normal. You will sweat but it will work out for you if your only doing 40 pieces.

Should work, proper cutting oil will make life a LOT easier....

Practical question for the experts: An arbor press typically has a flat surface on the bottom of the ram. Pressing the broach through requires that it be centered. Do you use a holder fitted to the end of the ram to hold and center the broach? It seems to me that with a hard flat surface on both the ram bottom and the broach top, and cutting oil, it would be awfully easy from the broach to slip or get mis-aligned.

david n said:

I have a part that will need a 3/8 sq x 1/2" long in mild steel. 20-40 parts every 4 months or so. Figure I could do 'em myself. Looking at a Dumont broach. Calls for a 25/64 pilot and about 3700lb of push. I have a 2 (or 2 1/2?) ton press. Will she do it? Or do I need an 4' cheater bar? Ideas? Good, bad and the ugly?

Click to expand...

in a pinch and if only needed every once in awhile....I use the Bridgeport or some mill...put a tool bit in square collet holder and align with indicator square...and then just lightly push the quill down and up taking about .003 grand with each pass....move in X or Y as you go...use oil....you can go pretty darn fast when ya get good at it...damn near speed of a broach but nicer and straighter key IMO if the broach has a centering problem as you speak of

bosleyjr said:

Practical question for the experts: An arbor press typically has a flat surface on the bottom of the ram. Pressing the broach through requires that it be centered. Do you use a holder fitted to the end of the ram to hold and center the broach? It seems to me that with a hard flat surface on both the ram bottom and the broach top, and cutting oil, it would be awfully easy from the broach to slip or get mis-aligned.

Click to expand...

It has been 35 years since I did that job. I was working as a temp and the only machinist in a sheet metal shop. They did the initial set up, but I do not remember any special alignment used. Probably dropped the bushings in pocket in a fixture and eyeballed the broach straight. If I was doing this in my own shop I would probably use a conical socket on the ram to line it up straight,as well a pocket in a plate to line up the bushings. I know from experience that a key way broach can lean and make a crooked keyway.
I am fairly sure it was a Dumont broach and only one pass was needed. The shop was in Phoenix the press was outside under a shed roof and I do not remember dying of heat stroke, it could not have been too bad.