I am building a model railroad and need to drill holes through the plywood top for wires. I've tried straight twist bits, forstener bits, spade bits and brad point bits, but they all leave tear out on the exit side of the plywood. This interferes with wires and plugs being fed through the hole. Anyone know a bit that leaves a clean hole?
I know I could start the hole from the top using a brad point and finish drilling from the bottom up. This is a bit awkward for me to work underneath the layout.
Hi MrRon,
Due to the construction of plywood the back ply being thin will almost always splinter without something to back it were the drill exits. Sometimes putting tape as a backing were the drill will exit will reduce the tear out. When ever I drill plywood I clamp a scrap of wood as backing were the drill will exit.
Hope.This helps.
As a finish carpenter, I find the same problem when doing holes on kitchen and custom cabinets doors and drawers fronts to install handles….If you can't hold a small block of wood at the other side, applying some pressure (most common method), you can try this:
1. Use a sharp, brand new brad point drill bit
2. Use the high speed on your drill….some drill are not fast enough
3. Mark with tape the ply thicknesses on the drill bit
4, Start the hole with moderate pressure, slowly, but when the tape mark is getting closer to the ply face, reduce the pressure and leave the tool do the rest of the hole…
For this type of application I end up either just drill through then go back with a countersink to clean up if the plywood is of good quality and wont continue to chip or use small desk grommets. Both end up making pulling cable smooth and give a clean finish.
You can make grommets quickly from various plastic pieces meant for different applications. I have used the tube supports from McMaster before for example when passing thin wires.
Backer block OR
drill through with a small bit, then drill half way from one side with your finished size bit and finish from the other.
That is only options I know of.
Plus one on the use of a plunge router bit. If your plywood is laying flat, you can use a screw jack to raise up a backer board so it it tight against the underside
another trick that can help is with a brad point bit, drill the hole until the brad point just pops through. then drop some THIN CA glue into the hole.the thin CA will wick into the fibers. let dry a minute,Then either fininsh with drill with barely any pressure or a hand crank drill.
I am not getting why a little blowout on the bottom (where it is hard to get to) is a problem. Drill from the top and use lighter pressure to end the cut and flake of the bits that fray. If a larger hole a hole saw from both sides but that gets back to the hard to get to underside again. As long as the trains run on time I wouldn't worry about the bottom.
I am not getting why a little blowout on the bottom (where it is hard to get to) is a problem. Drill from the top and use lighter pressure to end the cut and flake of the bits that fray. If a larger hole a hole saw from both sides but that gets back to the hard to get to underside again. As long as the trains run on time I wouldn t worry about the bottom.
Fisch are the best Fortnser bits I've ever used and even then there will be splintering on ply. A backer board will solve the problem. Drilling until the tip comes through and then drilling from the other side is also a solution.
I prefer to do the flip once that lead point gets through, and I always back up anything I drill, unless it's something that is buried, and never seen or felt, then I still back it up. Pet peeve about hole blow out.
I am not getting why a little blowout on the bottom (where it is hard to get to) is a problem. Drill from the top and use lighter pressure to end the cut and flake of the bits that fray. If a larger hole a hole saw from both sides but that gets back to the hard to get to underside again. As long as the trains run on time I wouldn t worry about the bottom.
Or, as the holes don't need to be cylindrical, why not use a tapered reamer to finish the holes.
"This is a bit awkward for me to work underneath the layout."
Anyway there is always one end of the wire for which you might need to crawl under the table to pass it through the hole (unless you can use a cable puller inserted from above?).
If you think drilling holes for wires can be frustrating, wait until you mount underside turnout controls!
I use a SHARP 1/16" bit from the top down, close to the inside of the rails, This produces minimal tearout on the bottom. It also will show you exactly where the hole is. I hold a piece of scrap wood over the hole from the bottom and then drill again using a 3/32" bit. That's plenty for a 22 gauge wire feeder.
I use the same method for under-table turnout controls, except the second hole is usually 1/4". Set the turnout and mark the center position of the points on both sides of the throwbar/ties. Remove the turnout, drill, then set the turnout back.
IF tear out would be a problem, I do the "drill a quarter inch hole" by, first, drilling a 1/16th inch hole, then coming from both sides and meeting in the middle.
Like gbarnas said.
In a desperate situation, just holding a piece of wood against the wood where the bit will come out changes the game.
Some are missing the point, the OP doesn't want to "get under the table" so a backer or drilling from both side is out. A good bit with minimal pressure at the blowout point will work. Any blowout wont be seen and will have no adverse effect on the wire. In the event the OP needs to go under there to staple or secure the wire he can use a conical bit to ream the holes if it makes him feel better to soften the edges.
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
LumberJocks Woodworking Forum
2.5M posts
96K members
Since 2006
A forum community dedicated to professional woodworkers and enthusiasts. Come join the discussion about shop safety, wood, carpentry, lumber, finishing, tools, machinery, woodworking related topics, styles, scales, reviews, accessories, classifieds, and more!