Will drilling through extruded foam board (running feeders) cause the foam board to melt. Up until now I have been tapping holes with a nail and thought a drill would get the job done much more efficiently.
NO
An awl works well for this.
nickl02,
I just rotate the drill bit manually with my hand. If you do use an electric drill, just run it slowly. It won’t take much pressure to cut through it.
Tom
I bought a drill bit with an extra long shaft and I just push it down through the foam until it hits the plywood underneath then I turn on the drill.
Just use a slow speed and you should be fine. Slow as in not full speed. I don’t mean barely turning. I never had a problem with melting foam from drilling myself though. I think because it is not a ‘dense’ foam the same way styrene is. Styrene has melted on me, but insulation foam never has even on jobsite sites.
So yeah, I would say go for it, it won’t melt. Have fun. 
I’ve never seen a drill melt foam, and I’ve dropped hundreds through the stuff for feeders. Just how fast are you running your drill?
I use a cordless drill and small bits, something near 1/16-1/8", and have never felt that I was even heating the foam let alone melting it. You will be fine.
You will be fine with a drill…but don’t drop a soldering iron on it… it will melt the foam and cause some funky smells… don’t ask how I know
While very new at model railroading, I have had occasion to make holes in different types of foam and thin wood before, and my perfered method was to chuck a nice straight nail ( with the head cut off ) in the drill. Give the point more of a chisle shape & some seration with a file, and it works just fine, at any speed.
If your foam is really thick, cut a piece of coat hanger (longer than the thickness of the foam of course), and use that in your drill bit. It works.
… and if you are cutting a hole under a throwbar for that tortoise wire, a leather punch (3/8" or 1/2" diameter) works great. It will remove a neat core.
Karl
The nail or awl or scriber for that matter works well for most holes. I have a section where I needed to go through 6" of foam and used an extension drill 1/8"d. They are available 6", 8" and 12" long from various suppliers. If you have trouble feeding small wires through the foam, use a piece of brass tube that fits the hole, push it all the way through and then feed the wire through the tube removing the tube from below afterwards leaving the wire in place. Hope that helps. J.R.
I use a long drill bit and push it through the foam to the plywood base and then turn on the power-never had a problem with the foam melting and its a little neater.
A long thin-bladed screwdriver works well for this, too. Once I get the hole all the way through, I push a drinking straw down into it. This makes feeding wires a lot easier. For really thick foam areas, I made a tool from a thick wire hangar. I made a loop in one end and ground the other to a sharp point. I twist the wire through the loop and pull it through.
