[Jim27]

I am looking at milling some parts for an aluminum sheet metal punch out of mild steel or something slightly harder and need some longer end mills. Largest end mill I can chuck is 1/4" which happens to be the smallest radius I need to cut so that works out fine - I drew out the shape so the smallest radius is as large as possible to maximize end mill diameter and minimize flex.. I have some 2 flute carbide end mills but they are a bit short - cutter length of 3/4". I need at least 1" and maybe a bit more and see that 1-1/8 and 1-1/2 seem to be standard for "long" end mills. Since they are long I am concerned about flex and think 4 flute would have less flex and chip clearing shouldn't be an issue as the chip load is small.

Trying to plan the best way to do this. Shape is basically a tube with some detail on the inside of the die and outside of the punch - main concern is the die piece. Currently thinking - drill a 1/2" hole, then mill out the shape. Should I start with a shorter end mill for what it can reach and then go to the long end mill? That would reduce the chance of breaking the long end mill.

On the bottom side of the die the pocket tapers a bit so I can use the shorter end mill without concern for the shank rubbing above the cutter length and some small steps aren't an issue (although I could use a ball end mill to minimize steps in the walls).

Any other suggestions? How concerned should I be with flex and long end mills?

[Jim Dawson]

Given that the die is only cutting in the top 0.010 or so, cut the profile on the top of the die maybe 1/4 inch deep on size. Then flip the die over and cut the profile 0.020 or 0.030 oversize on the bottom side. This does two things, it solves your depth of cut issue, and it gives clearance for the slugs to drop out but still has plenty of support for the cutting edge.

I also use solid carbide router bits from my local hardware store. They work fine.

[Jim27]

I should have explained the part details better... I want to include a guide above the cutting surface so I can mount this in a regular arbor press without a die set. That's the main reason I need more end mill cutting depth. The parts will look like the radius die shown here:

Special Punches and Dies

With perhaps a bit taller lead in on the die so it doesn't disengage with pulled up.

I had posted in the die area a slightly different construction

http://www.cnczone.com/forums/diemak...punch-die.html
but it would require a die plate and I think also some plates on the sides of the top to control rotation. Would like to reduce the parts count if possible.

[Jim Dawson]

In re-reading your other post you are needing to corner round up to 0.040 material. This really means that you only need about 0.100 total travel to accomplish the job. I would make a retract stop that clamps to the ram that limits the up travel on the arbor press. That way the total working die/punch length only needs to be about 0.250 or so and the punch doesn't disengage from the die on retract.

[Jim27]

Good suggestion but I would still like to know more about deflection concerns for future projects.

[Jim Dawson]

I normally run a finishing pass(s) at about 0.005 or so. That pretty much eliminates any effect of deflection. Any end mill will deflect somewhat, even one > 1 inch dia, so you have to run finishing passes for maximum accuracy. Sometimes this requires a couple of finishing passes at 0.0000 step over.