Cutting Foam

[steve_g]

We have the maxim that "all ShopBot owners are sign makers" if not now... soon! I think another may also be true... All Bots will cut foam for a school or church production requiring scenery... eventually.

I haven't been paying attention to foam cutting postings because in another life I was plant engineer at a foam processing plant and learned to detest the static charged, in your nose and in your clothes stuff!

I just learned that my wife volunteered me to help with a project at her school... She knows that I need to be diverted from the failed craft fair market! Sooo, I have some questions...

1. I'll be cutting 1" pink extruded Styrofoam, are smoother cuts realized by using a onion skin strategy and making the final cut a conventional cut?

2. Is the dust collector of any use or should I open the doors and make generous use of my compressed air ?

3. Has anyone tried using a puzzle joint to assemble sections too large for the Bot?

4. What's the glue of choice for laminating... I'll be gluing up an 8' X 12' X 12" thick arch using 1" material because that's all HD carries in Texas

Thanks for any insight you have to offer!

Steve

[knight_toolworks]

I don't usually use the brush on my dc as it tends to vac parts off the table. but it will get some of what flies around. but the brush may damage the face. I don't see a problem with puzzle pieces. Use a 4 flute upcut bit and cut it at 18k and as fast as you can that will keep the pieces in place.

[myxpykalix]

I can't tell you why this happened because i haven't cut alot of foam but what happened the last time i cut foam i found that the cut particles were hot coming off the part and would wrap around the bit then harden back up around the shaft.

I guess maybe my rpm was too high and the speed too slow?:confused:

[steve_g]

Any chance It was a down cut bit?

Steve

[knight_toolworks]

I can't tell you why this happened because i haven't cut alot of foam but what happened the last time i cut foam i found that the cut particles were hot coming off the part and would wrap around the bit then harden back up around the shaft.

I guess maybe my rpm was too high and the speed too slow?:confused:
I got that cutting 2" deep with a 1/4" bit that had about 1.5" cut depth. I cut it in two passes and sometimes the foam would melt. but if I cleaned it off it would then be fine. cut a whole sheet it was fine the second sheet did it several times then stopped.
with a 4f bit I like to cut at 6ips and 18k and I get a pretty clean cut but sometimes the parts don't stay in place.

[steve_g]

Steve

Do you see any difference cutting climb or conventional?

Steve G

[knight_toolworks]

I don't remember if I tested them both. a regular cut does pretty well if you use a 4 flute bit. that seems to make a big difference. but I will test a climb cut next time.
this last job was for a friend who bought a shopbot. people bug him to do things and he does not have time so I get most of his work. I was going to trade him some welding to cut these foam letters for a friend. no bigge but he realized he did not have time to pack and ship them the next day as they had to get there the day after. so he gave me 200.00 to box them and drop them off at fedex. I had a bunch of different sized foam letters trying to box them using paper to hold them in place and get them to fedex early enough to get there the next day. three boxes that weighed more then the contents and just in time. took mroe effort to find boxes and pack them then it took to cut them. but I did not have any jobs that day so it was ok.

[CNYDWW]

First off i would suggest expanded polystyrene if you can get it. Then again, i hate the extruded stuff. I have not used puzzle joints for foam but i have inlayed pieces together and it shouldn't be too much of an issue. I would use 3M Foam Fast 74 Spray adhesive. Coat both surfaces and let tack up. Keep in mind once they touch, that's it. If you can, don't cut the laminated pieces. You can imagine the mess the contact cement makes on bits. More flutes on your bit the better. I always use 4 flute upcuts at low rpm. 2 ips cut speed. Since you have the adhesive already, you can lightly spray the back of the material and let it tack up then use it to help hold the foam down in the machine. The light coating shouldn't cause an issue with your bit unless you're cutting deep into your spoil board.

Regards
Randy

[MogulTx]

Steve,

I cutt his stuff ALL the time. I use a Whiteside RD5200 ( 1/2" 2 flute, DOWN cut, Spiral. This pushes the foam back onto the table.) I edge clamp it, as my vacuum is not set up ( draws too many amps that I don't have). Woodworker's Supply has a comparable bit for less money, but it is a shorter cutting length. ( Should not matter for what you are doing).

I zero to the surface then raise it about .015-.02 and re-set the zero there. That almost always leaves just the film on the second surface ( With this bit, and as long as my table is flat and clean).

I cut it printed side down, so i get the pattern I am looking for without any printing on it. I use 3.5IPS w 1.5 plunge, and full depth up to 3/4"(the thickest that the local HD sells). At 12.6K RPM, it clears a lot of the curlies that then get caught by my DC yet it STILL makes a horrific mess. Use it anyway, it will be that much less that you have to clean up later. If you have a dust mask, you might want to use it. I get that foam in my eyes, nose, mouth ( hair, skin, clothes)... I hate that part of it!

And if you need a bit, I have two new on shelf- but I don't know when I will be in Dallas area. Probably not for a couple weeks...

Thank you again for the use of that cane design. It makes me smile every time I see my nephew use it. He graduates high school next month!

Monty

[Brady Watson]

4 flute end mill + Crank spindle/router all the way up + Limit MS to 2 IPS or less.

See how that grabs ya...

-B

[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.
http://i154.photobucket.com/albums/s266/knighttoolworks/posting/8adc799b.jpg

[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

[jhedlund58]

I cut foam... mostly for H.S. drama club... very light and the drama director loves it... maybe cause i do it for free...

on the chip out... i have found that that happens to me when last pass is very shallow... i use aspire... and they allow u to change the depth of the passes on profile cuts... i made my last pass deeper... .2 or even .25.. and the chip out went away... i was having the problem with wood too. and this approach has been very satisfactory

[steve_g]

Jeff

I did my 1" foam cuts all it one pass... how deep are you cutting per pass?

Steve

[jhedlund58]

i cut conservatively at .125 per pass... which is why i try to get my last pass to .2 or so... i sure there are others that wood not agree with this thin of a pass... time is no issue for me... and i like the results. maybe it is my buddy48 with the 2.2 spindle.. i use the chip calculator and keep rpm between 12000 and 14000... then adjust the speed accordingly