Cutting foam & tearing foam

[dubliner]

I wonder if anyone could look at this file & see what I'm doing wrong, I'm cutting blue foam, and what happens is the spindle will move slowly around a corner or curve & leave a great finish but then accelerate very quickly on straight sections or reasonably long curves & seemigly just push the bit , tearing the foam. I think its at 6 IPS, @ 15k rpm, 1/2" 90dg. Oops file is too big, any ideas? I could email the file.

[Brady Watson]

Neville,
Since the lighter foams (1-4# density) are a bit 'squishy' you really need a little more cutter dwell time - meaning that even though the foam is easy to cut without breaking a bit, you need a very light chipload to get a clean cut. If you were to look at the cutter where it meets the foam with a magnifying glass, you'd see the foam spring back and forth when the cutting flute sheared the foam. 2-flute tools have too much 'pull' causing chunks to pull out. If you want a super clean edge, use a 4-flute end mill & 18,000 RPM. Give it a whirl and you'll see the difference.

-B

[dubliner]

Hey Brady,
Yes thats the effect I got when it moved slow enough to actually carve the groove, but what I was perplexed by was that it would lurch through a section then move slowly through another. I got both good & bad cuts within the same file - so I naturally assume I did something wrong.As always thanks for your time Brady.

[dubliner]

4457
As you can see hopefully, the tears are the result of moving so fast it didnt have time to carve. I thought it might be due to tuning the cars up as thats been what Ive been working on, but it seems like its in the file as I watched it and it did the same thing in the same locations when re-cutting the file. Second pic was too big, but perhaps you can see it in the cut just above the"Thi"

[Brady Watson]

Nev,
The reason your tool goes slow around the corners and quick in the straights is a function of your move speed & VR settings. You might want to adjust some of the ramping settings for a less aggressive ramp to minimize some of the effects. This will keep the tool at a more consistent speed. Optimize your speeds to get a clean cut at full move speed (straight sections) then you will be good in the corners as it is pretty darn tough to melt blue foam.

-B