Wood can be the material of choice for many kinds of projects, but it often falls out of the running in favor of metal or plastic if it needs to take a threaded fastener. But with a little ingenuity you can make your own wood taps and cut threads that will perform great.

Making wood do things that wood isn’t supposed to do is [Matthias Wandel]’s thing. Hackers the world over know and use his wood gears designer to lay out gears for all kinds of projects from musical marble machines to a wooden Antikythera mechanism. Woodworkers have been threading wood for centuries , so making wood take a decent thread isn’t exactly something new. But doing it on the cheap and making the threads clean and solid has always been tricky. The video after the break shows [Matthias]’ method of cutting a tap out of an ordinary threaded rod or even off-the-shelf lag screws. He uses a simple jig to hold the blank so that flutes can be cut with an angle grinder. The taps work well in the materials he tested, and a little informal stress testing at the end of the video shows promise for long service life of the threads.

Wood threads aren’t suitable for every project, but knowing that you can do it might just open the path to a quick, easy build. This is a great tip to keep in mind.

Interesting. After cutting the flutes I would be tempted to take the bolt to my belt sander and knock off a little bit of the radius so a fresh bolt would fit tightly into the wooden hole. Interesting idea at any rate.

If you watch the video, you can see he does just that with the angle grinder. He also puts a bit of a taper on the bolt.

The same video where he says he can turn the bolts in easily by hand?

This is great idea. I can imagine adding a tiny bit of watered down pva glue when you install screws would really strengthen the threads up and add a lot of life. I’d probably wax the screws first if I thought they might ever want to be removed

I once tried making my own helicoil inserts out of round wire. It worked but more for making the threads more durable than increasing the pull-out force by much, like I had been hoping. In retrospect I saw why of course the coil won’t expand under tensions from the bolt.

Proper anchors are expensive though, so it might still be worth pursuing.

Diy taps made out of bolt/screw, are popular amongst people making their own leadscrew nuts(nylon, delrin etc.). Leftover/cutoff of a trapezoidal screw is much cheaper than a proper tap ;)

Here’s a leadnut tap for delrin I made from 1/2″ acme threaded rod. I got a bunch of the rod for free; took one look at acme tap pricing and went this route. I knew very little about proper cutting geometry, and tapping took some force. But the leadnut works great!

http://reboots.g-cipher.net/rabbot/image/acmetap4_finished.jpg

Next time use Delrin AF (anti-friction). Greatly reduced or no slip-stick due to the difference between static and dynamic friction.

To minimize backlash, put another Delrin AF leadnut on the other side of the block to tension against the threads. Each Delrin AF leadnut then tensions against opposite sides/load-direction of the threads.

I’ve made impromptu single use taps from screws and bolts as needed for 40+ years. It seems to me a pretty obvious mechanic’s dodge once you’ve seen self tapping screws.. But I don’t recall ever doing it to put a thread in wood, just plastic and metal. Preferred tool is a triangular file, but a hacksaw will work in a pinch.

If you *really* want a good thread in wood, make an insert. Chuck a piece of all thread in a drill press. Feed it on to the proper size drill bit for the thread you want to use. Then thread the hole. The reason for doing it this way is to ensure that the hole is centered. A rotating workpiece and a stationary drill bit forces the hole to follow the axis of rotation. You *can* buy threaded inserts from the usual woodworking suppliers, but this *is* HackaDay.

My best example was the result of breaking a plastic nipple off an emission controls device while removing it. A replacement was of the order of $80. Instead, I took a suitable size (~1/4″) machine screw or bolt, cut off the head, chucked it in the drill press, fed it onto a 1/8″ drill bit held in a stationary chuck and then used a flat file to make a taper for the hose to push onto that matched the original plastic nipple.. I made the cut to make it self tapping using a triangular file and screwed it into the part. Once the hole was tapped, I backed it out, applied a dab of epoxy to make sure it was an airtight seal and put it back in. Worked perfectly for many years. I had a tap and die set, but it did not have bottoming taps, so I couldn’t use them because of the geometry of the part. Hence the hack which took less time than driving to get a new part.

What is wrong with wood screws? Then there are those giant wooden threaded studs holding the legs of a square grand on. That was over a century ago. Now wood screws or machine with large “T-nuts” in the case are used. Metal inserts make more sense.

Nothing wrong with wood screws. But I’ve been tapping wood for ages (~two decades?) and it’s amazing. The bolt is significantly stronger than the screw. In hardwood, dramatically stronger. I’ve done A vs. B tests where the wood screws are ripped rather easily out of the wood with a crow bar and the bolts simply stay in. And the drill and tap never splits the wood. And it’s easy to take apart and put back together without stressing the wood parts. I use standard metal taps; and test on a scrap for the best pre-drill size. I start at one drill bit size smaller than the tapping chart says to use for steel. Sometimes requires two sizes smaller. Using the ‘correct’ pre-drill size works, but there’s some bolt wiggle and the result is not as strong: that may be due to drilling with a hand drill and the error means I’m getting a randomly larger hole. I’ve used this with both brass bolts and steel bolts. Careful for snapping the taps for small diameters, as this is tapped dry, no lube.

For larger diameters where I don’t have a tap that size, I too have taken a steel bolt and ground a groove, or two, or three, down it’s length, to make a crude tap. I’ve used those in both wood and plastic (pvc). I did this for the thread size that mounts my Dremel (forget what that is; remember it was a real pain to find).

For most projects, screws in wood is still my standard go-to, or for more structural needs the newer ‘structural screw’. But for those special projects, or when needing maximum strength, I pull out the taps.

Screwed screws. They go in twice as fast, that’s why they use them. They also come loose twice as easy and then I have to replace them. Junk!

I would have thought you could have just forced the screw into the hole, effectively “thread forming” the threads.

Tried that. (Well, bolt into a hole.) Compresses and breaks some wood fibre. Threads don’t have good integrity. Isn’t as strong. Lateral force can split wood.

But I have used that with some CA glue soaked into the formed broken-fibre threads. Mixed results in getting the bolt back in once the CA is dry (but you can tap it to clear a path…). Better if in and out with the bolt a number of times before applying the CA. And mixed results getting a good fit.

Tapped wood (with optimal pre-drill size) method is stronger. Likely due to the wood being cut/sheared so the wood threads have integrity, along with a correct firm fit of threads.

Now I want to see him make the dies for the wooden screw threads to fit in his tapped holes :-)

Two overlapping holes one contains bolt ground down to halfway through he cross section then rotated around until the cutting edge enters the other hole?

Useless, they only work with ambihelical bolts.

Makes more sense to me to use this for plastic rather than wood. Same method applies though.

Next trick is to find a way to do it in glass?

I’ve made taps for steel out of grade 8 bolts. Just make a slight taper and cut a back slanting, short flute so that the chips go forward. Unless you are tapping blind holes this is nice because you don’t need long flutes so you can get the extra torque you need for the subpar cutting edge

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