WARNING ! on topic post : broach questions

This may help

. I have a Dumont metric and inch broach set and not all require shimming, the smaller sizes can cut the slot in a single pass, whereas larger sizes may have one or more shims depending on the keyway depth.

standard keyway dimensions. Dumont may have the shim pack details on their site, I haven't looked.

Broaches are brittle and likely to break if not pushed straight in, or if the work shifts on a less than ideal support. I prefer to use an arbor press because it gives more feel.

The shims extend the cutting depth of the broach by allowing multiple passes. You can make shims from sheet metal if you don't have the "right" size, but you can also custom-fit the key to whatever slot depth the broach gives you. I've had good luck with tee-shaped keys when I didn't have a broach the size of the shaft slot. A key that's a snug fit in either the shaft or the hub slot is less likely to fall and get lost during disassembly. If the shaft runs in bearings I make the other side a sliding fit to avoid having to pound on the assembly. A little clearance in slot depth helps avoid the key jamming from setscrew burrs.

I bought import broaches from Enco and make the guides and shims as needed.

-jsw

Whenever you buy a single broach or a set all the shims neded should be included. The larger size broaches require more passes, hence more shims. An arbor press is good for broaching One thing to watch out for when broaching is the broach getting crooked. Because the broach is tapered in steps the teeth will sometimes dig in and the back of the broach will start to come away from the bushing. So when you first start the broach press it in a little and the relieve the pressure so that the broach can spring back if need be. You will either need to but a bushing for your part or make your own. I have made lots of custom bushing for broaching. For odd size holes and for tapered holes. Eric

Yes -- with a caution: Every quarter inch or so -- back up the press and restart to allow the top end of the broach to re-center properly. If it walks too far off center, you will break the broach.

You need a plug which fits into the hole with an external keyway to guide the broach, and a shoulder to keep the plug from falling through the bore on the workpiece.

Depends on size -- ranges from zero to three shims supplied with the broach in the storage tube. Yes, your first pass is with no shim, then add shims until you have all of them used. Having the shims means that the broach does not have to be so long that the hydraulic press will have to be reset several times to accommodate the whole stroke.

I've not used them on either brass or aluminum. I think that with brass you can get away with no lubes. With aluminum, I would spray it with WD-40 or Kerosene which usually make good cutting lubes on aluminum.

Good Luck, DoN.

So that's why they sometimes shift when I release pressure on the arbor press handle. I thought it might be the random scrap that bridged the opening in the press bed.yielding a little. I don't risk my best straight bar stock for that.

-jsw

art

I have cut one keyway on the lathe and understand not wanting to do that ag ain. But you inspired me to search the internet for a better solution. And I th ink I found one. If you search on " Slotter keyway cutter for minilathe " you should find an article from Model Engineering which is close to good. Basically it is a ram that mounts on the cross slide and is manually operat ed. Still a fairly slow process, but it looks like it would be fairly simp le to make the ram operated by air and retracted by a spring. With a simp le circuit to activate the ram , you could probably get one stroke per seco nd. Then you could use a stepper motor to move the cross slide, but that w ould probably not worth doing.

I am not planning on actually making such a kludge. I don't have a need ri ght now. But it is fun to think of projects like that.

Dan

Well that would beat the way I've been doing it . I've been using my small boring bar set dead on center (vertically) and moving the entire saddle assembly with the hand crank , advancing with the cross slide for each stroke . Done it vertically with a cutter held in the spindle of the mill too ... but decided that's a bit too rough on the pinion gear setup the moves the quill up and down .

I did that when I made an L00 mount for metal spinning chucks and it worked but I wouldn't want to do it again in a hurry. Most of the material was milled out but I still had to square it up to fit the L00 nose key.

That is how I did it. Moving the entire saddle assembly makes it slow.

Dan