Fabricating a broaching die

[fortcollinsjerry]

I'm trying to figure out how to make a broaching die that will cut the spiral pattern seen in this picture. It is the tip of a ram rod made in Germany about 1750. I have a lathe and a mill/drill to work with. I suspect it was made with some kind of spiral cutting tool such as the long bench rifling tool that put rifling in barrells. This thing is only about 3" long. Other than laying them out and cutting them by hand any ideas?

[2ManyHobbies]

What about knurling? It would almost look like straight gear cutting on your die, but you could tilt the axis about 20 degrees and be close to what you have pictured there. If your die were cut from decent steel and you were using it to work brass, you might not need to bother with heat treating.

Here is one hand powered:
http://bbs.homeshopmachinist.net/showthread.php?t=41517

And here is only one of the ones that Frank Ford has built and posted:
http://bbs.homeshopmachinist.net/sho...ighlight=knurl

[oldbikerdude37]

What about knurling?

2ManyHobbies has the right idea, you can get knuling wheels of any type and make you own for short runs in soft metalfrom 4140 or some drill rod.

If you make a home made cut knurling wheel it dont need to be very wide, maybe .125" wide and not even machined just laid out and made with a die grinder. Im cheap but get what I want done.

Engineering is economics so dont spend $100 on a $10 problem so I say 2ManyHobbies is right on the money.

[loose nut]

If you have the equipment the best way would be to use some form of rotary fixture (horizontal rotary table, dividing head, spin indexer) set up horizontally on a mill with a gear train (or a chain and sprocket drive) connecting it to the table leadscrew. The gear ratio would have to calculated to give the right rate of twist on the part to be machined and then use a form tool to mill the grooves in the part. As you turn the lead screw the rotary devise will also turn and it will mill a spiral on your part. Clear as mud right.

[dp]

A rotary broach and a slanted orientation dog would do the trick.

http://www.slatertools.com/video_orientation_dog.htm

[JoeCB]

How many do you intend to make? if just one or two, perhaps just lay them out and file as you suggested. If several, your thought about the rifling tool should work. Make a spiral guide, 1/2 " square stock twisted (simple blacksmith task). Cutter would be a hollow tube with (I think) three adjustable form cutters set 120 deg apart. Tool to be drawn over the work piece, indexed etc etc

Joe B

[Tony Ennis]

The original looks to be hand-engraved.

[Toolguy]

It would be a simple matter to knurl that with one angled knurl of a diamond set of two. You could even choose which way the spiral goes by which of the 2 knurls is used.