Any ideas on how to get a nice hole drilled in foam? I used 2 inch foam for the base of my layout and laid the track right on top using liquid nails. I’m now ready to add some signals. These are slow motion semaphore signals that require drilling a 1/2 inch (13mm actually) hole in the baseboard for mounting. The problem is every time I’ve attempted to drill a hole, the bit just tears the foam up to much. The hole winds up being larger than needed and the signal won’t stay straight up.
I’ve had two thoughts. One is to use some modeling clay around the base of the signal to adjust the position, the other is to “glue” a piece of 1/4 inch plywood to the foam and drill though that.
3 options come to mind. The idea you had of gluing is close to my 1st thought! Using some scrap 1/4" plywood/masonite withthe hole predrilled in it. Center the hole over where you want the new one and just hold firmly in place.
option 2- use a hole saw of the desired size to at least penetrate the top half of the foam and finish with a regular twist drill bit.
option 3- works well for blue/pink foam WITH SUPPORT FROM BELOW! Use a pc of thin wall metal tubing that has a slight chamfer filed on the one end to sharpen it a bit. Locate the business end where you want the hole and using a twisting/rotating motion start to push it down into the foam. Doing this with unsupported foam will create a hole below that is 4-8 times the diameter of the tube.
The hole saw will work. Have you tried using a spade bit intended for wood? That may work better than a twist drill. You will have to be careful to keep the drill located exactly on center or it will want to wander too I imagine.
This method has worked for me. Take a knitting needle or awl and push it down through the foam to the wood base. Drilling can tend to rip up the foam. Then use a 1/4" drill to go through the wood. Insert a regular plastic drinking straw down through the wholes and it makes feeding wires down through easy.
This method does work best!!!
The drinking straw will prevent wires from “catching” in the foam while going through the newly made hole.Also makes removal and replacement of the wires much easier if it is needed.
Works fine for wires, yes. The original post was about a 1/2 inch hole for signal mounting.
My personal choice would be a 1/2 inch hole saw, filed into the end of a piece of 1/2 inch copper tubing. Rotate fairly quickly and feed slowly. Remove and clear every quarter inch or so until the hole is deep enough to accept the signal base. If there’s still some foam left, use the soda straw in the appropriate location to provide a conduit for wires.
If you want to salvage the original holes, modeling clay would be a poor choice of filler - it stays soft and most kinds are difficult to paint over or glue to. You might make a test with drywall mud, laid on in fairly thin layers. The end result can be painted and glued just like any plaster.
I assume that the semaphore has a 1/2-inch piece that has to fit into that hole. How deep does that piece need to go into the base?
I would use a small piece of something a quarter-inch thick. Masonite, plywood or even foamboard would work. Just something stiff that you can put a hole through. Then, you can gouge out the hole in the foam for the rest of the semaphore support shaft.
I had a similar problem. I heated up a piece of pipe on the stove (not red hot) and ran it right through like butter and than drilled thru the plywood with a wood drill.
What about some of that Great Stuff or other expanding foam sealers to fill in around the base in the bad holes. It is an adhesive as well as a foam filler and once hard can be trimmed with a hobby knife easily. I would assume since it is for filling gaps and insulating that is does not eat foam, but it might be smart to test it on scrap first.
I think I have some experience on this by now :). I never figured out how to use the grid thing and plaster and never had materials and advice available (surprise, surprise, no mr hobby shops in my country), so I have used the foam for everything and everywhere.
The methods with piece of plywood, hand-pushing, plaster around the thing, the drill bit by hand and many other methods have been tried and are still used at some places.
For signals, I however use the following method: I first drill a 6-8 mm hole through the foam and the baseboard and then use a hot 35W soldering iron to make the hole as big as I need. This method is clean and produces a hole in the foam with “hardened” walls, which makes the whole thing more stable.
Hope this takes you somewhere.
Happy new year all!
Just turn while pushing down. It takes out a nice core. This photo is of hidden staging so there is no roadbed. The punch works fine through ws roadbed too.
When you drill the plywood substrate, use a wooden “shield” so that the chuck of the drill doesn’t tear into the foam when the bit breaks through.
"What about some of that Great Stuff or other expanding foam sealers to fill in around the base in the bad holes. It is an adhesive as well as a foam filler and once hard can be trimmed with a hobby knife easily. I would assume since it is for filling gaps and insulating that is does not eat foam, but it might be smart to test it on scrap first. "
I suggest using lightweight spackling compound. It is easy to work with, does not shrink, and when cured is exactly the same consistency as the original foam. You could either cast the signal in place in this stuff, or use a greased form of the right diameter that could be withdrawn after the cure to leave a perfect hole.
I was just experimenting with this. My best solution so far for a 1/2" hole is a Forstener bit…for those not familiar with them, they are kind of a middle fround between a spade bit and a hole saw. They make a nice neat 1/2" hole on the surface, but they do require a firm grip on the drill to keep the bit from walking as it goes down through the foam. But for my purpose, feeding through Unitrack mini Tamiya connectors, they work quite well.
Thanks for all the suggestions. The one that worked best was using a forstner bit and turning it hand to drill the hole. A hole saw may also have worked, but I couldn’t find one in 1/2 inch size, only 3/4 inch and larger.
For a 1/2 " hole in the foam I would take a short section of 1/2 electrical conduit (EMT) and use that to punch the hole in the foam. Use a drill bit for the bench work/ underlayment. Just need to poke the foam out after each use
I have used some extra long spade bits bought at Home depot, they were 3 inches long. I have not had problems with ripping the foam and it goes faster. Regards, andy
