Cutting Foam

[steve_g]

Wow... recommendations all over the place! And all from folks who are or have been cutting foam. My previous experience with foam would suggest that what works is what works for you (me in this case). I want Monty's down cut bit strategy to work even though it goes against all we teach about cutting plastics. I don't have vacuum and expect that tape will become difficult the nastier my work environment becomes. I hope that Monty's 1/2" bit recommendation allows chips to flow and not re-weld. Most are suggesting that higher flute counts work well... The most flutes I have on hand (I need to start cutting tonight) is three. A 1/4" 3 flute up cut and a 1/2" 3 flute down cut rougher / finisher. I'll be experimenting...Randy, thanks for the heads up on the 3M #74 glue

Steve

[MogulTx]

Steve,

Note that I DO edge clamp. (And occassionally eat an edge clamp if I am sleepy!) I use the Irwin clamps that are available at HD. I assume every Shopbotter has a couple sets of those! The necks are plastic so they fail quickly if you miscalculate on the location of the cutting path!! And you don't lose the bit that way!

Monty

[knight_toolworks]

ok a quick test with cutting. all at 18k and I tried upcut 4f and downcut 2f. between the two I did not see a difference. what made the difference was the cut speed. 6ips is not bad it is the one in the middle of the 3. 2ips are the top and bottom one upcut one downcut. no real difference. climb cut is on the right the top one all chewed up. the bottom one is 6ps with a 2f downcut.
So the conclusion is 18k and 2ips upcut or downcut and a normal cut not a climb cut.

[stump]

Thanks for sharing the photos. It really helps to have a visual to refer to.

[steve_g]

Steve

You have put all questions and speculation to rest! Thanks so much for taking the time to do the testing. If you don't mind, I'll add the info and picture to the "router bit basics" article I'm wrapping up.

Thanks again for incontrovertible proof!

Now ... The person who was to approve my drawings did not do so. I'll lose tonight for cutting.

Steve G

[MogulTx]

Steve, Steve, Steve,

I can not believe it! You took a look at my info, ( and many others') and in lesss than a day, you have improved on what I have been doing for months! I feel like such a neophyte!

I went out tonight and cut 6 sheets of foam(3 of 3/4 and 3 of 1/2") and they ALL turned out far better than the stuff I had been doing.

Although I responded thinking I was helping YOU, it turns out that I was the guy getting assistance. You really ROCK, you know that? The differences? Exactly what you said... I was specific about the direction of cut and I amped up the speed to 18K.... ( I DID keep my IPS. I am doing packing materials, so I don't need "perfect". I need good edge protection...)

I remain humbly in your debt.

Thank you Obe Wan Kenobe.

MGM

[knight_toolworks]

I was twiddling my thumbs today so I figured I would check it out. I had been cutting too fast myself though the results are not terrible. but looks like I wasted money on the two 4f bits I got from mcmaster for my upcoming job. I was surprised the downcut worked fine. but I can't find long enough 1/4" downcuts so I may not go that way.
I have 20 to 30 sheets of gater foam to cut this week if they ever get me the files.

[steve_g]

I just wrapped up my foam cutting job... Steve Knight's sample cuts yesterday saved me lots of time. Here are my observations after the fact...

1. I used a down cut bit and as expected my bottom face was not as smooth as my top face, a compromise I was willing to make.
2. I had some acute angles where ramping brought my speed down so slow the foam melted on the bit... Rather than read up on ramping commands, I set the speed slower than I wanted and used the [shift] + [>] key sequence to raise the speed with out recalculating the ramping.
3. On some parts I V-carved an outline to aid the scene painters... My 120° bit doesn't seem to care at all what speed it's run at. I tried every thing from 1ips to 4ips. all were acceptable.

Thanks again to all who contributed here
Steve G

[knight_toolworks]

glad to hear on the v bit I have not used one on foam yet.

[steve_g]

Addendum to observations...

4. The puzzle cut worked very well for assembling sections without needing additional alignment methods. I cut both male and female sections without adding any "clearance" into the toolpathing. My expectation was a joint with an interference fit. What I got was a very smooth slip joint. Note to self... foam needs no allowance for joints to fit well.

Steve