Tool closed-cell foam with router?

It’s Christmas evening and the day’s visitors are gone, the food is put away, and I slipped into the workshop and fitted a light to a compass. Both were gifts. The fit is pretty good and I think I am really going to enjoying using this compass while paddling in the dark. The light protrudes from the bottom of the compass. It is sticking out by less than a sixteenth, but that’s gonna make the unit rock when it is bungee-corded on my deck.

I want to fit a little “coaster tray” of closed-cell foam under the compass. I’ll hollow out the spot where the light protrudes.

Is it possible to work foam with a router? I’d like to carve a groove in the foam to mate it with the bottom of the compass. A router would be an ideal tool if I was working with wood. Will it work on foam?


Just a guess, but
I think the high speed of a router would be way to much and just melt the foam

I would try a variable speed Dremel and experiment with various bits

Jack L

You can do a lot of shaping with a serrated kitchen knife and sandpaper.

Danger, the router will just pick up the foam and throw it at high speed, then you’re left with a router running in the air. Don’t try it.

Bill H.

Depending on the size of the grooves and hollows, you can use a variable speed drill and woodshaping bits to rough out your minicell.

Jack’s suggestion of a Dremel is good if you have one, but my knock-off only has quite small burrs, therefore my suggestion of a drill.

If you can hold, vice, or jig it in a stand, you can put a decent-sized woodshaping bit on a drill and move the minicell to shape it rather than a more cumbersome drill being used. That’s the advantage of a Dremel-type tool.

Grayhawk also has a good point: you can rapidly and fairly easily rough out minicell with a serrated blade. Cut larger sections with a saw or longish bread knife, rough shape with a shorter serrated steak knife, shape shape with a rasp, finish with sandpaper.

Good luck with you compass+light stand!

May it point the way in the darkness as you


-Frank in Miami

industrial fabrication
would use a router type operation or a laser. there is a $pecific bit type

a router’s rotation speed with small bites both on bit and on material prob eliminate saw type tearing.

new xacto or utility knife blades cut V’s well or use a variety of fine toothed rasps see Macmaster Carr…you can email M Carr.

Hollow out the space then fill/shape with silicon goo for a final mounting pad…

try Utube

I used a router to make a foam seat
It worked fine on the 2" stiff gray foam. After routing I used s shur-form (sp) rasp for the final shaping. It should work if you start on one corner of a large piece, a small piece could be dangerous trying to hold in position.

Good Luck


within reach

– Last Updated: Dec-26-15 9:56 AM EST –

2 foam mincell blocks cut from horsecollar pdf retrieved from the Andrea Doria

holding Momo boat tweeters fitting into windshield corners/dashtop.

cut with hacksaw, gouged with utility knife for tweeter bottom.

handling the block, not the freshest minicell in the area but still flexy, instant comparison is with balsa.

slide mouse pointer to bottom screen

after sawing ? maybe…

Might try
putting the foam in the freezer for a while before attempting to work it. I’ve used this technique for cutting other types of foam with saws and sanders. Don’t know if it’ll help with all kinds of foam, but its worth a try and can’t hurt anything.

Yes it works
I got back in the shop this morning and tested working the foam with the router. The router carved a nice groove in the foam. I was afraid it would just melt into goo. The groove isn’t completely clean, there’s a bit of fuzz on one side wall. I think I could easily sand off the fuzz, but it isn’t going to hurt anything to leave it there and may actually help by offering more purchase for glue.

Specificaly what I am doing is using a quarter-inch, straight-plunge router bit to carve a quarter inch deep dado into the foam.


Glad you gave it a try
I router foam quite a bit. Never been a problem. Would have responded sooner but I just saw the post.


I see
You got it figured out. I use a router or a hot knife when working with foam/ccf

Helpful video -

– Last Updated: Dec-30-15 6:50 AM EST –

I came across this video on the youtubes:

Is there any option to use without cell?

1 Like

I have no idea what this means. Use what? and what do you mean by cell? This is a 4 year old post.

Same user made a nonsensical remark to my post about my Werner Cyprus. Maybe a language barrier? Or a chatbot?