I’ve done several projects (my latest) where it was necessary to tap wood or MDF to use a machine screw. There are several ways to accomplish this. I’ll go over the several methods I’ve used, and two more standard methods that I haven’t yet experimented with.
Just Drill and Tap the Wood – Just tap it like you would a piece of metal. Here’s a drill and tap set from Amazon for just over $20* that you can use for this or the next method of attachment. Probably the weakest way here to attach a machine screw to wood, but it might be all you need.
Use Repair Putty as an Insert - This may not be a standard technique, but I use and explain it in this post about making a MDF Geneva Drive. There’s more detail in that post, but the basic idea is: cut a hole, insert putty, let dry, then drill and tap. It seems to work pretty well, especially compared to tapping MDF.
One thing to keep in mind while putty tapping is that the putty doesn’t necessarily fall off of the tap as metal would. If tapping feels “mushy,” remove the tap and clean the grooves. Then reinsert and finish your tapped hole!
Update 3/10/2013: Per Farley’s excellent comment below, I tried tapping the putty by embedding a lubricated screw and pressing putty around it. See the results in the video below:
Tee Nuts – One of the more popular ways to use wood with machine screws, these little devices are hammered or pulled into the wood from the opposite side. I’d trust the strength of these over any of the other methods, as illustrated in this external article about installing tee nuts for use in rock climbing gym holds.
Threaded Insert – Another more conventional way to attach wood together using machine screws is using a threaded insert. Just drill a hole and either thread of pound them into your wood. These inserts can then be used with machine screws. Similar inserts also work well with plastics such as polycarbonate. Since I’ve never used this technique, here’s a little write-up from wood magazine about using these inserts.
Update 3/10/2013: Per Steve’s comment, I tried drilling the hole and putting super glue inside of it. I’ve only tried it once (and had to drill the hole twice), but this seems like an excellent way to tap wood, maybe better than repair putty. See the video below for more details.
So there you have it, how to use machine screws with wood. Thanks for the suggestions, and please let me know in the comments if there are other good ways to tap wood for machine screws!
*I haven’t personally tried this set, but it looks OK for $20.