I have some fins i want to use with my current board. The holes they have are larger then the holes that the board has and i am wondering what i could do to use these fins with my board.
I know the obvious solution is to drill out the holes in the board but i'd rather not go that route (risk of damage/unknown how thick the abs around the holes is.
So my question is, can i fill the holes in the fins and then redrill them to a smaller diameter and if so what would i use? Given that the expoy with not be pressed at all how could i deal with air bubbles etc and would it even bond to the material around it? Should i chop up some glass and mix that in or use micro balloons or something?
I have zero experiance with board building and using expoy.
4 mil is an odd size for a fin hole. I tapped an epoxy micro balloon insert for a board handel and it worked ok. Should work better on a long shaft with latteral forces then on a short shaft with the screw being pulled out. Find the correct drill and tap set and you should be good. Oh and to fill the hole remember to inject the mix with the tip at the bottom leaving the tip in the epoxy as you fill not squirting down onto the top of the pile. You avoid voids and bubbles that way.
You are going into too much trouble! You probably have M6 fins and M5 holes. That means if you drill the hole there should be stil enough ABS or what ever, because you are not making that much bigger hole. On the other hand, if you fill the fin holes, you will have a problem epoxy sticking good, because you won't have much smaller hole. There is another problem, drilling the holes straight and accurate. Than you have to have a tool, to cut thread into the hole. How are you going to do that, if you don't even have the measuring tool, to find out how big is the screw, you are going to use.
I think you can adapt the fins holes to the smaller screws easily. You need some petroleum jelly ("vaseline") and relatively thin laminating epoxy resin.
Coat the screws with a layer of vaseline to act as a mold release. Also coat the BOARD screw holes (not the holes in the fin!!!) and area around them on the board with petroleum jelly. Put masking tape or more jelly on the outside of the fins to prevent any resin drips from sticking. Place a drop or two of resin in the bottom of the hole in the fin. Dip the threads of the screws carefully in resin, so they are lightly coated with it. Position fin under the board. Carefully screw the epoxy-coated screws into the fins. Check to be sure the fin is installed correctly. Wait until the next day. Unscrew the screws, remove the fin. Clean off any drips of epoxy (should be easy since you should have used masking tape or petroleum jelly to protect all surfaces, except the inside of the fin holes.
Now you will have a fin with well formed epoxy threads that fit those silly little screws. The angle of the thread will be correct for the installed fin position, etc, and it should be easy to remove and reinstall the fin when you need to. If you switch boards and want to reuse the fins with bigger (standard size 6mm or 1/4") screws, you can just get a tap and clean out the epoxy threads you have added.
BTW use the laminating epoxy because it is thin enough to flow in and form threads. DON'T use microballoons for this, they would probably weaken it. Straight epoxy will do it. As said above by somebody else, the threads don't have to be perfect, since the screw is not holding too much tension, unless you crash into objects all the time....
But it would still be easier to widen the holes in the board!!!! A typical plastic insert in the board would be 15-30mm wide, so making holes 6mm instead of 4mm is not likely to be a problem....