Milling deep pockets for vacuum forming mold

[smokediver576]

Hey CNC Zone Crew,

What are folks doing when you need to mill deep (say 2 to 3 inches) into a mold cavity that has 1/16" radius parts of the wall and pocket. Right now I'm using Fusion 360 to do a 3D adaptive roughing with a 1/2" and 1/4" but I'm unable to get into the tight little corners and such. Lucky for me this is all in PVC plastic because they are just test molds.

Where can I get long 1/8", 3/16" and 1/4" ball nose end mills that are say in the 4 to 6 inch overall length. Not too worried about tool deflection since A: it's in PVC plastic and B: this will be for finishing passes with very little meat in the cut.

Just curious what folks thoughts are.



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[SCzEngrgGroup]

A 4" long 1/8" endmill? You'd have a hard time milling a marshmallow with that! I've use 1-1/2" 1/8" endmills, and they are so flexible they are almost unusable on any kind of metal, even with extremely light cuts. I don't know what the answer is, but I'm pretty darned sure it isn't a 4-6" long 1/8" tool. I think you need to re-think your fixturing, and figure out how to get a more substantial tool in there - the cutting end may need to be 1/8", but if you come in from a different angle, you should be able to use something with a larger shank so you're not trying to machine with the stiffness of a piece of al dente pasta.

Regards,
Ray L.

[smokediver576]

A 4" long 1/8" endmill? You'd have a hard time milling a marshmallow with that! I've use 1-1/2" 1/8" endmills, and they are so flexible they are almost unusable on any kind of metal, even with extremely light cuts. I don't know what the answer is, but I'm pretty darned sure it isn't a 4-6" long 1/8" tool. I think you need to re-think your fixturing, and figure out how to get a more substantial tool in there - the cutting end may need to be 1/8", but if you come in from a different angle, you should be able to use something with a larger shank so you're not trying to machine with the stiffness of a piece of al dente pasta.

Regards,
Ray L.

Sorry... should have corrected myself on that one. The 1/8" would be 3" at most.

I agree, I think I'm going to work on changing how I set the molds up and what radius I put in them.

[SCzEngrgGroup]

Sorry... should have corrected myself on that one. The 1/8" would be 3" at most.

I agree, I think I'm going to work on changing how I set the molds up and what radius I put in them.

And maybe consider a 4th axis, which would let you use a much shorter tool. Or even tilting the whole thing 30 degrees might be enough to make the difference. Even a 3" long 1/8" tool would be like a piece of spaghetti.

Regards,
Ray L.

[LeeWay]

You might be able to use a longer bull nose cutter with a radius on the ends.
For just one off molds though, I think I would stand the part vertically with a little wider billet. Then machine it down with large bull nose tools. Then face off as a second op to end up with what you have there.
Probably get the job done in 1/4 of the time.
No little tools at all that way.

[Uman]

Since it is PVC and a test mold; Mill the part in two separate pieces and glue/screw the pieces together. The flat shoulder looks like a good parting line.
A 3D-printer is also an interesting option.

[smokediver576]

Since it is PVC and a test mold; Mill the part in two separate pieces and glue/screw the pieces together. The flat shoulder looks like a good parting line.
A 3D-printer is also an interesting option.

We will be testing some 3D printed options this week. We have a much larger mold (15" x 15" x 4") that we will be working on in the coming weeks that we're testing a method where we "sliced" the buck up like a loaf of bread and printed it. I'm going to be real interested in how this works on the time to print vs cut.

[NIC 77]

What are folks doing when you need to mill deep (say 2 to 3 inches) into a mold cavity that has 1/16" radius parts of the wall and pocket. Right now I'm using Fusion 360 to do a 3D adaptive roughing with a 1/2" and 1/4" but I'm unable to get into the tight little corners and such. Lucky for me this is all in PVC plastic because they are just test molds.

Where can I get long 1/8", 3/16" and 1/4" ball nose end mills that are say in the 4 to 6 inch overall length. Not too worried about tool deflection since A: it's in PVC plastic and B: this will be for finishing passes with very little meat in the cut.

Have you tried searching for tapered bits? 4 to 6 inches is quite a reach, but may available in either a tapered bit or a bit that has a large shank for most of the length and a small bit at the tip. For a normal 1/8" bit, 4 inches long, I think you'd snap it like a twig on the first pass. As someone said, I wouldn't mill a marshmallow with one.

I found this after a minute of searching. It may take you longer to find exactly what you want if it exists in those lengths. That's just an example of a tapered bit. I believe this is what Lee was referring to.

2Pcs Tapered Ball Nose End Mill 1.5MM Tip H-Si Coated 6mm Shank For Wook Working | eBay

I've never actually used one. Perhaps someone who has experience with them can give you better advice.

It will be interesting to see if there is anything a mill can offer in a situation like this that a 3D printer can not do better. Of course, that's just for plastic. You mentioned this is a test mold. What will the final version be made from?

[Jim Dawson]

That looks like a job for a bull nose endmill. Machine vertically. Looks like you could use a 1/2 endmill. With no dimensions it's hard to tell what sizes would work.

[smokediver576]

That looks like a job for a bull nose endmill. Machine vertically. Looks like you could use a 1/2 endmill. With no dimensions it's hard to tell what sizes would work.

The fillets were set to 1/8" radius in the inside.

[smokediver576]

Have you tried searching for tapered bits? 4 to 6 inches is quite a reach, but may available in either a tapered bit or a bit that has a large shank for most of the length and a small bit at the tip. For a normal 1/8" bit, 4 inches long, I think you'd snap it like a twig on the first pass. As someone said, I wouldn't mill a marshmallow with one.

I found this after a minute of searching. It may take you longer to find exactly what you want if it exists in those lengths. That's just an example of a tapered bit. I believe this is what Lee was referring to.

2Pcs Tapered Ball Nose End Mill 1.5MM Tip H-Si Coated 6mm Shank For Wook Working | eBay

I've never actually used one. Perhaps someone who has experience with them can give you better advice.

It will be interesting to see if there is anything a mill can offer in a situation like this that a 3D printer can not do better. Of course, that's just for plastic. You mentioned this is a test mold. What will the final version be made from?

Hey Nic
Thanks for the link. I ended up ordering some ball nose EM's from CarbideDepot.com. We'll see how these work with some pattern modifications as well. The issue with the tapered ones is that I have a straight wall next to that fillet. If I only had a 5 axis machine......

[SCzEngrgGroup]

Hey Nic
Thanks for the link. I ended up ordering some ball nose EM's from CarbideDepot.com. We'll see how these work with some pattern modifications as well. The issue with the tapered ones is that I have a straight wall next to that fillet. If I only had a 5 axis machine......

If you simply tilt the part (make one of the short ends higher than the other - e.g. - mount it on a sine vise), you will no longer have a straight wall, you can get by with a much shorter tool, and you won't need a 5-axis machine...

Regards,
Ray L.

[IMT]

The fillets were set to 1/8" radius in the inside.

Any reason you can't stand it up on end and use an end mill with a 1/8 corner radius (as Jim and others suggested)? Like this one 1/2 SE 4 Flute EXT LG Corner Radius 0.125 Solid Carbide End Mill - End Mills - Cutting Tool - Products

[IMT]

If you simply tilt the part (make one of the short ends higher than the other - e.g. - mount it on a sine vise), you will no longer have a straight wall, you can get by with a much shorter tool, and you won't need a 5-axis machine...

Regards,
Ray L.

Then you can profile it with a tapered ball end mill, .125 or small tip radius that tapers to a reasonable shank diameter.

[C*H*U*D]

It's hard to tell with no dimensions, but I would be inclined to stand it up on end like others have said, and use a bullnose. If the part was stood up vertically, how long would an 1/8" bullnose have to be? Even with draft in there, it would be easier to do than laying flat the way it's pictured.

[AUSTINMACHINING]

Harvey tool makes long, reduced shank, small cutters. They key is having a short flute length to maintain stiffness over the length of the shank. Still 3-4" is going,to cut like a rubber stick. PVC machines damned easy, but I would look for an extended reach holder using a standard tool if geometry allows it.

[CadRhino]

Good suggestion on the sine vise

If you have one of the tilting 4th axes rotary tables you should be able to mount the part in a 4-jaw chuck at the angles you need with standard tool lengths to do the job.

Nathan

If you use.
simply tilt the part (make one of the short ends higher than the other - e.g. - mount it on a sine vise), you will no longer have a straight wall, you can get by with a much shorter tool, and you won't need a 5-axis machine...

Regards,
Ray L.