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Discussion Starter · #1 ·
They sell this rasp file set on Amazon. I THINK I can modify the center round rasp file to make the 6" rotary rasp tool I need to carve into foam. The RPMs don't need to be excessive, and it is just foam. so the side cutting force will be minimal. The bit just needs to plunge as much as six inches into the foam, and then move SIDWAYS. All of the other rotary rasps I found have five inches of smooth round steel shaft with a cutting bit at the end. This will not work, to cut sideways through foam. I ordered two of these sets, to see if I can make this work. If not, they aren't very expensive.

Joe

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They sell this rasp file set on Amazon. I THINK I can modify the center round rasp file to make the 6" rotary rasp tool I need to carve into foam. The RPMs don't need to be excessive, and it is just foam. so the side cutting force will be minimal. The bit just needs to plunge as much as six inches into the foam, and then move SIDWAYS. All of the other rotary rasps I found have five inches of smooth round steel shaft with a cutting bit at the end. This will not work, to cut sideways through foam. I ordered two of these sets, to see if I can make this work. If not, they aren't very expensive.

Joe

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Personally, If you're planning on trying to make that rasp work in a router, I wouldn't want to be anywhere near it when you fire it up.
 

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Discussion Starter · #3 ·
Personally, If you're planning on trying to make that rasp work in a router, I wouldn't want to be anywhere near it when you fire it up.
Thank you. I am not planning on spinning it at thousands of RPMs. It is only cutting foam, after all. I would think that the speed of a cordless drill (400 RPM?) is all that would be required to carve foam out of the way. Well, they arrived in my mailbox today! So on with the experiments!

Joe
 

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Discussion Starter · #5 · (Edited)
I want to be able to carve as much as six inches deep into a block of sign foam in a single pass, to remove much of the foam from a cavity. Then a simple final pass with a 1/4" ball end router bit, also slowly, and with a very short step over, to clean up the final interior surface.

A shop vac will remove the foam bits, and the router only need to spin as the speed of a cordless drill after all, because I am carving FOAM. So I do not believe I need to worry about the bit flinging out from centrifugal force due to not being perfectly balanced. I seriously doubt the router RPMs will change at all, or even notice that it is cutting something.

I am not building a piano! This is for foam Halloween props. This experiment will be to do a negative carve of a bust, for the purpose of making the creepy Disney style busts that watch you as you pass by. You've probably seen them. It is an optical illusion. It looks like a regular bust, but since it is carved into material rather than protruding forward as a normal bust would, and it is lit from behind, your brain plays tricks with your eye, and it appears that the bust rotates and stares at you, no matter which direction you look back at it. This particular bust is only 4" deep into the material.

The shaft is .293" in diameter, so I may need to turn it down on a lathe to fit a 1/4" collet. Alternately, I could drill out an aluminum collet just a hair.

No one MAKES a bit to do this, so I had to think outside of the box ... just a "bit." 😆 The pointy aggressive profile of this rasp is spiral, so the teeth rotate UP like a barber pole. I am anxious to try this experiment!

Joe

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