[Jim27]

For machining a sheet metal punch I plan to put some taper on the face to reduce force needed. Overall size is 8 x 8 Since it's a shallow taper - about 0.1" in 4" - I am wondering if a corner radius end mill might be better than a ball end mill. And some strategy for a path that follows the outline of the shape (planning to taper the female section so as to not distort the desired interior piece although with the shallow taper it may not be a big deal which side is tapered). If I make the path centered on the die edge the scallops would be away from the edge. Seems like cutting it with a ball will be a lot of cutting near the center vs. the corner rounding that will be cutting on the tip - much more wear on the center of the cutter and smaller/deeper scallops from the ball end mill. And cutting from deepest to shallowest depth would have the cutting at the tip although I have to ramp down at some point to start the cuts. What's the best way to do this? Material is 4140PH and will be doing this with carbide end mills.

[Jim Dawson]

Can you post a drawing or even a rough sketch of what you want to do? I'm having trouble getting my head around what you are describing, maybe not enough coffee yet.

[Jim27]

It's a punch for 0.027 aluminum "coil stock" that is fairly soft. Wanting to vary the height around the lip of the female die section to reduce force needed. Thinking about 3 - 4 times material thickness which results in 0.075 to 0.100". Corners are highest and will engage first. Looking at my sketch I am thinking I may make the whole bottom high and have 3 high sections rather than 4 - seems better since I have limited distance across the bottom.

Typical way to contour is a ball end mill but since the sections have very low slope an end mill with small radius at the tooth tips seems like it would be better than ball end. Most of the cutting would be at the tooth tips rather than the center where surface speed is near zero. And the cusp height would be less for the same number of passes. At least that's my thought.

Then there is the issue of tool path. Thinking if the tool center follows the edge of the opening there will be no cusps along the die edge. And any cusps will be on the scrap outer section of material. I can try some tool path options in my CAM (Fusion 360).

Main question is ball end mill or corner radius end mill. Any thoughts are appreciated.

[Jim Dawson]

If I understand correctly, a ball endmill might be the best choice for this operation.

[Jim27]

I probably didn't explain it very well. I just found this page that talks about the subject although their presentation and calculators could have been clearer IMHO.
https://www.villamachine.com/ball-en...ulator-how-to/

And here is something on some limitations related to ball end mill profiling. Just trying to understand the trade offs better...
https://www.harveyperformance.com/in...trategy-guide/

[peteeng]

Hi 27 - Usually a punch/die is polished to reduce the chances of pickup. Especially with "soft" aluminium. How many parts are expected from the tool? If its a production tool then grinding/polishing is recommended. The higher the polish the less the tool force required as well.... Peter

[Jim27]

Hi 27 - Usually a punch/die is polished to reduce the chances of pickup. Especially with "soft" aluminium. How many parts are expected from the tool? If its a production tool then grinding/polishing is recommended. The higher the polish the less the tool force required as well.... Peter

You are talking of polishing on the sides of the punch? I can do that and good to know but that's not what I am asking about. The face of the punch will be flat so no issue with milling that. The milling I am asking about it is the face of the female part of the punch and the piece that part touches is scrap.

[deadlykitten]

pfff, i know someone that does punch press similar operation, into 50-60hrc sheets, like 1mm width, area similar to 8x8 square inchi ... but i won't meet him soon

however, there is much more into this than the punch tool edge taper ( if allowed ) and the tool used to make it, but the fixture of that tool, heat treat, dimensioning, sheet fixtureing before punching ( is a 2 step process, thus the mould has 2 consecutive contacts, one to secure the sheet, 2nd to cut it )

unfortunately, now, i have no idea what to tell you

[Jim27]

Found this page that deals with wood routing but the basics are the same. Shows radius end mill is much better for low slopes with milling path up and down the slope.
https://community.carbide3d.com/t/ba...finish/24272/7