[oakleigh]

Im a self taught machinist using alphacam to cut mainly 2d profiles for foam inserts for cases.

i muddle through reasonably successfully but my latest insert is going to cause me headaches!!

On the attached image the arrow is pointing to an area i know is going to be tricky i think this area will pulll over the material and cut through the wall.

So my questions are.

how do i machine this successfully without it pulling over and cutting through the wall.
Do i use a 12mm tool or a 6mm ?
how many cuts? any suggestions for feed speed?

the depth of the foam is 75mm
Im using LD18 Platazote Polyethelene high density foam.
The thickness of this wall is about 12mm
im running at 24000 rpm
When im machining foam i always leave 2mm to pull out the insert later this allows me to machine finer wall thicknesses.

i need this to be as efficient as possible as i know i will be making a few of these.

[christinandavid]

You could initially leave that top area enclosed ie leave a 'bridge' to retain strength. Finish the enclosed areas above and below the 'bridge' then nibble that 'bridge' at the death either by incremental 'chain' plunging, alternating above/below, or peeling it away with a scallopy trochoidally motion.

Sorry about the poor vocabulary - I've just finished work and I'll be up in 5hrs to return - my brain's a bit fried (flame2) I have no idea about machining foam so that strategy may be total crap.

Goodnight!

DP

[oakleigh]

Ive just made a sample before reading your post and that was the only area that failed.

The bridging idea is great, with two sections should sort it out. im going to try that now.
im just going to make the bridging section share the same geometry so hopefully i will be left with a wafer thin foam that i can just pull out afterwards.

Thankyou for your suggestion
have a good sleep!!

[xy_eezy]

If you look at the problem area as a basic three sided shape, would it not be possible to go around two sides of this shape(in either direction you choose), then simply finish the remaining side, coming from the other direction, thus completing the cutout of that small area stress free? Have to admit, I've never cut foam before, though.