How to profile crown dies for air hammer

[territorialmillworks]

When I made the fuller portion of my combo dies, I mounted the stock off center in the 4 jaw chuck......swinging that much weight caused some scary vibration,but it worked(without injury to me or the lathe LOL... Now I want to make crown dies but haven't figured how to profile the long radius. Any ideas on doing this on the mill...I have a rotary table but it doesn't have any t-slots. Suppose I could drill/tap some holes. Thought I would free-hand the side radius with flap sander to avoid buying a speciality end mill...THX for any and all ideas...Keith

[bigfootnampa]

Keith mine have no crown on the long axis and I like them that way. I frequently feed my material at an angle and the angle can vary depending on what I need to clear the hammer body... so, much crown along the width of my dies would be undesirable. I have softened the corners slightly and that seems to work well. I just used a flap sander as you are planning. I use the flap sander to resurface the dies on occasion too... they get a little wear at the radiused corners. My dies are just nicely rounded along the corners with flats in the center still. I like the texture that they produce... essentially indistinguishable from my hand hammered textures. I find that I can easily vary the texture depth by hammering either more or less aggressively. If you really want crown along the long axis though I would certainly do that with my flap sander as well. You could use a template to mark a line along the sides and to check the profile as you grind. Amazing what you can do with a flap wheel! I keep three grinders at the forge... one with a coarse flap wheel, one with a cut-off disc, and one that has a wire brush in it.

[Mainely,Bob]

A few quick questions as I have no idea what type of machines or tools you have access to;
Do you have access to a shaper?
Do you have access to a heavy duty disc sander?
How many of these type of dies do you plan to make?This last question is so I we know how much time you may want to spend on a jig.

[dkunkler]

You could rough out the long radius while still chucked in the lathe, checking it with a template as you go, then finish it with flap disks.

[monstermetal]

I have done several sets, all just by hand with a grinder... Its not that hard to do and I really dont think you could do it much faster any other way... for the crown dies what I did was make cardboard templates (although thin wood would be better) of one quarter section of the die... then used those to check each opposite or adjacent quadrant. The ones I made where not yet heat treated so I roughed them out with a 9" grinder, then went to a hard wheel 5" grinder... then 24 grit fiber disks and finally finished with a hand held belt grinder (Dynabelter) It took maybe 3 hours to do both dies...

[territorialmillworks]

I have everything mentioned except for a shaper & horizonal mill (we wish!!) I suspect that I'm over engineering things once again. This would be a one-off situation. A template and patience should get me there. Guess I'll p/u some flap discs and get after it...THX guys........

[Mainely,Bob]

Easiest way to produce most profiles for me would be to make a pattern out of scrap plywood that had the radius that I wanted on it.Cut another scrap of ply wide enough to clamp the die onto one end and hang several inches off the end of the table for the disc grinder on the other.Clamp or screw the pattern onto the overhang so it will ride against the edge of the table.When you swing the piece thru the arc limited by the pattern attached to the board which is attached to the die then when the sparks stop you will have your die ground to the exact radius of the pattern.
Leave a way to make small adjustments but the distance from the pattern edge to the final height of the die should be the distance between the table edge the pattern bears on and the surface of the disc.
That`s how I grind stuff like that.Hope it helps.
BTW-That same jig assures consistent results if you either need to dress that die or make another to replace it.