foam glue

[dan_nelson]

I want to do some test cuts on pink or grey foam from a big box store. the model is 4 " thick . I could slice the model and do it that way, but for this one I would like to glue up the pieces first and then cut. what glue to use? how will it eat up the bits? feed rate on foam ? this is a large crown moulding so I am usind a .50 ballnose for the rough 25% stepover and a .25 ball for the finish. Thanks Dan and Bridget Nelson

[bleeth]

You can cut as fast as your machine will cut and use a low RPM. Solid carbide bits last a long time with that stuff.
For a PRS standard you can cut 4+ips and bit speed around 8k.

Start there and move up as you can and listen to your tool. It's almost like moving through air-you just want to keep the router/spindle speed low enough not to melt the material.

On adhesive Randy is correct that contact cement is best but will eat the foam. Wilsonart has a low VOC cement that has a high tack and will probably do a better job than the "usual" high styrene sprays. The water bases take too much pressure for what you are doing. If you are only doing a fairly small quantity the stuff you pick up at big orange, etc or 3-m spray 90 in a spray can will work. What I have done is shake the can while spraying so what I get is a "web" of adhesive instead of a lot in one spot.

[CNYDWW]

To find a glue that wont gum up your bits is going to be hard. Usually extruded polystyrene is glued with a spray contact adhesive. During my days as a mold and pattern maker, we didn't find any alternatives. This may gum up your bits a little but you can use it sparingly and it wont be too bad. Just use acetone to clean up your bits. When using the spray adhesive, make sure to lightly spray both surfaces and let them dry completely before you stick them together. Also be cautious of the propellants in the spray, they can eat the foam. Less is more in this case.

Regards
Randy

[scottbot]

I've used Gorilla Glue before. It doesn't gum up your bits or dissolve the foam but it is expensive.

Scott

[dan_nelson]

Thanks I have gorilla glue on hand I will try it this afternoon

[paul_z]

Gorilla glue is a polyureathane glue. It uses water or water vapor to cause the glue to set. If you put it together quickly in a dry environment, the glue might not set (as in never). The instructions should have something about wetting a surface before putting the pieces together. Wood has some moisture content and it is usually enough to cause the glue to set. Still, it's probably a good practice to wipe one side with a damp cloth.

You may also want to put something rather heavy on top of the stack to keep the glue from creating gaps between the sheets as the glue foams up.

Once the glue is set, it should machine quite nicely.

Try a small piece first.

Please let us know how this works out including pictures if possible.

Paul Z

[scottbot]

What Paul says is very true as you may already know.
I use a spray bottle full of water and mist the foam before I glue it.
Works like a charm.

Scott