Routing 2" wide grooves in foam

[bhoza01]

I'm sure this question has been answered before. However, I've scoured the threads and can't seem to find it.

I will begin construction on a 5x8 foam trailer shortly. I know my way around a shop, but this will be my first trailer build. I plan to use the 2" Foamular 250 panels for the walls and roof. I have never worked with this material before, so I don't know the best way to approach it.

I plan on inserting 1"x2"s into grooves cut into the foam. They will provide support and as studs to drill into. What is the best/easiest way to cut 2" wide grooves into the foam? I've kind of talked myself out of using a heat knife, because it's a new method and it doesn't look super foolproof or accurate. I just know I'm the kind of guy that would either burn himself or make awful messy cuts. But I'm open to suggestions. I would prefer to use a router, but how does the foam hold up to routing with regular woodworking bits? I know it's got to make a mess (foam-dust everywhere), but do regular router bits make clean cuts? If so, I'm eyeing a pretty sexy 2" wide surface planing bit. I think the bit is 1/2" deep, so two or three deepening passes ought to get it to the right thickness. However, the bit is around $50 delivered, so if it's not going to work I'd rather save the cash and look at other methods.

I'm leaning on y'all for your hard-earned experience. You're awesome!

Ben

[ghcoe]

KC will probably chime in here for the routing question. He has done quite a bit of routing of foam with his build. Yes, expect the foam blizzard unless you have a real good dust collector.

Me I like the hot wire. Nice clean cuts, no dust. Gravity feed is the way to go.

Cut

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[KCStudly]

Yup, KC here, routing is the most accurate IMO. Use the same techniques as wood except your depth and feed rates can go up exponentially. Rig up a shop vac to your router shoe to get the worst of it and keep your tool path from clogging.

I prefer carbide bits, just keep them clean and they will cut and last for ever. No need for a special 2 inch wide bit, just set up some temporary guide rails and sweep between them. I have a couple of longer 1/2 inch diameter bits that will easily do 1-1/2 deep (or 2) in a couple of passes; maybe one if pushed to the limit. Actually, it is probably more of a factor of what the shop vac can suck away w/o clogging at the router base; smaller chips suck up easier.

What I did find was that the foam dust tended to clog the fine vac filters pretty quickly, so I made a cyclone separator out of another old/dead shop vac. That solved the problem of clogged vac filters.

I have to admit that I am impressed with the hot knife techniques and accuracy that ghcoe has achieved, and if you decide to try that I highly recommend that you look through his posts (even if you don't it's a good read). I have tried my hand at a few hot wire jobs with varying degrees of success, but just decided that I could get a better result quicker using the router, rather than trying to perfect those techniques by my own hand.

Table saw is also a good option if you have dust collection well sorted.

I was also able to rip relatively small strips and shapes using a double fence on a small table top band saw, just start and pull the spaghetti thru; rips as fast as you can pull.

[bhoza01]

Thank you both for your advice. Those are some sexy hot knife cuts. I may end up trying my hand at the wire of death after all. Haha

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[lthomas987]

Ghcoe's sexy hot knife cuts are what put me in that direction as well. Mine were far less beautiful. But worked fantastically none the less.

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[ghcoe]

The best way to run a hot wire is just enough heat to cut and use gravity to control the cut speed. Gravity and low heat make a nice clean cut that you see above. If your wire glows it is too hot.
https://youtu.be/1h8EGYTb7rc

[Tempest]

Very slick setup!

[GPW]

Seeing that video is so wonderful ... what a Great idea !!! However maybe it’s time to take it to the next level ... how about replacing those hot pencils with a nice inexpensive ceramic resistor ( dollar , thirty ) much smaller ,neater , safer... https://www.tubesandmore.com/products/r ... D10%20Watt

[ghcoe]

Seeing that video is so wonderful ... what a Great idea !!! However maybe it’s time to take it to the next level ... how about replacing those hot pencils with a nice inexpensive ceramic resistor ( dollar , thirty ) much smaller ,neater , safer... https://www.tubesandmore.com/products/r ... D10%20Watt

I did away with the pencils. I still use a pencil to wrap the wire around to make a nice wire coil. I found that then I can just bend the wire, once coiled, over and stick the end into the holes I drilled for the pencils. Works great that way. The wire only gets hot between the connectors so you do not have to worry about the coiled wire getting hot in the wood.