Make a Wood Tap From a Bolt

The ability to cut threads in wood can be useful for many projects. Often the needed tap can be expensive and a car ride away. For many applications, a tap can be made from a spare bolt. This simple tap can be made in less than 5 minutes with amazing results.

Step 1: Tools and Materials

Tools:

• Angle Grinder
• Bench Grinder
• Drill

Materials:

• Bolt or screw the size of the desired threads

Step 2: Shape Tap

If using a bolt, cut off the hex head. Create a slight taper on one end of the thread using a bench grinder. You can rotate it by hand or by using a drill to ensure an even taper. This will center your tap when using it.

Step 3: Clamp Tap and Cut Flutes

Clamp your tap on a work bench or in a vice and cut 3 or 4 flutes along the tap. This will give somewhere for the wood chips being cut from your threads to go.

Step 4: Clean Up Threads

Using a nut, run it up and down your tap. This will clean up any burs developed from cutting the flutes.

Chuck the tap in a drill and verify that it runs true. I haven't noticed any damage to my chuck from clamping directly on the threads. If you are concerned about possible damage, grind the threads away with a bench grinder.

Step 5: Tap Hole

Drill a clearance hole just smaller than the minor diameter of the threads. When tapping the hole go slowly and back out after every other revolution or so to clear out the wood chips. These threads will not be as strong as a threaded insert or a t-nut, but they are very useful for some applications.

What other shop tricks do you have up your sleeve? Let me know in the comments.

Comments

[gizmologist]

I'd leave the head on the bolt so that I could tap holes using a wrench. Thread a nut all the way onto the bolt FIRST, before doing any grinding. Then when done grinding, thread the nut off to clean up the threads. This trick also works very well whenever you have to shorten a bolt.

[tomatoskins]

I completely agree when cutting a bolt that you need to put a nut on first. And I thought it would be the same with the tap. However with the slight taper placed on it at the beginning, the threads don't get misaligned as much as cutting the bolt off completely would.

If you try to use a standard wrench on a tap it won't thread completely straight and it will wobble out the hole. That is unless you use two handles like a traditional tap and die set. I also noticed that the small amount of play between the hex head and the wrench or socket being used can cause the threads to not be perfectly straight.

I used a tap made from a bolt to thread the end of a rolling pin (instructable will come after Christmas) and it was just slightly out of square. The tap needed to have the hex head on it so it could freely change depth opposed to being firmly held in place with my tailstock like this tap would be. So the hex head definitely is useful is some situations, however the threads may be slightly out of square.

[Poppy Ann]

Hi, you said

"If you try to use a standard wrench on a tap it won't thread completely straight and it will wobble out the hole."

this all depends on who is doing the tapping I have tapped many holes without a tap wrench and never had one not straight as long as you take the time and keep watching the tap to make sure it is still straight you will not have a problem, having to use a bolt or some threaded rod to cut the thread just needs a little more concentration, also on large diameter holes it would be better to leave on the head of the bolt or to put two nuts on a piece of threaded rod and lock them together makes it much easier to apply the higher torque required to cut the thread.

[tomatoskins]

You are correct. As long as you can apply a 100% moment with no lateral forces you will be fine. However this can be difficut. Which is why standard tap and die sets have two handles on them. When you apply a couple monent there will be no lateral forces to wobble out the hole. Both are possible, one is just more likely.

[KellyCraig]

True. If you, for example, use a ratchet to hold the tap, hold the ratchet at the head, rather than out at the handle.

Too, I've used my cordless drill to tap many holes.

[bpark1000]

Simple way to get thread square is to drill a clearance hole in scrap piece of wood. Slide the tap through that, and while holding the scrap firmly against the item being tapped, start the tapping a few turns. Then remove tap and scrap, and continue tapping.

[CXYyuppie]

Pure genius! I'll try this next time. Thanks.

[Poppy Ann]

A great idea.

[thaddaeus]

Great advise. And poetic, too!

[rejenk3]

I’ve used the technique where I didn’t have a tap the right size (speciality or metric). Works fine in aluminum too. We tap wood in building radio control planes frequently and it works fine. An additional trick is to tap the wood, apply thin CA glue to soak in the threads, retap after glue sets.

[amclaussen]

EXACTLY!, but adding a little candle wax to the Cyanoed thread aids in maintaining the Cyano reinforced thread better! Amclaussen.

[kreidence]

This is a great way to reuse bolts with burred heads. Something which would otherwise end up on landfill.

[jimofoz]

Nice idea that I've used before. A couple of comments:
Yes, standard taps will work fine on wood.
If you want want to toughen up the threads a bit, soak with some CA (superglue).
Lee Valley Tools did some testing awhile ago and found that especially in the smaller sizes (screw sizes 4 & 6) a tapped machine screw held better than a standard wood screw.

[Time_and_Turning]

Great idea, and thanks to other commenters; I wouldn't have thought to use CA glue to stabilize and strengthen the threads.
But if the 'clearance' hole drilled in the wood is smaller than the minor diameter of the screw, it's not a clearance hole at all. You actually don't want a clearance hole; you should aim at a 75% thread; that is only 75% of the internal and external threads are engaged. If the wood is
very soft, go for 80% or 82%; likewise if it is very hard you can go down to 50% or so. Tables for what drill sizes to use for clearance and 50% and 75% thread holes are readily available.
Anything higher than 82% risks the tap or the bolt binding in and/or splitting the wood.

I make bottle stoppers and other objects held on the lathe with a machine screw chuck of one
sort or another. Some kits recommend pre-tapping the blank (and the purveyors of those kits
will happily sell you a tap the works with their chucks), or using threaded inserts (also sold by
kit people. I have never had any trouble by using the screw on the chuck to cut it's own threads
in a properly sized (75%) hole.

As we used to say in the '70s, Your Mileage May Vary.

[francati]

Cut "The Flutes" with what ?????????????????????????

[tomatoskins]

You can use anything you have. I used an angle grinder shown in step 1, but a triangle file or dremmel tool would work just as well.

[Broom]

Instead of clamping the threads in the drill chuck, or grinding the teeth away, go one tiny step further and grind three flats on the gripping area. They don't have to be ultra-precise; IME eyeballing them is good enough. Then the teeth of the chuck will have better surfaces to grab, with less slippage possible even when they are just-tight.

[amclaussen]

Threads cut into wood are too weak. To reinforce them, apply cyanoacrilate glue (aka Krazy glue) to the recently cut threads, allow to dry and rethread them lightly and carefully with your tap. Then apply a very little quantity of candle wax. the glue-hardened wood thread will be much more durable and strong! Amclaussen.

[MichaelS918]

Made a few of these during my 10+ years doing automotive repair to clean out threads of bolt holes or nuts. Until I eventually broke down and bought a nice, complete re-threader set from Mac Tools. lol Never would have thought to use the same application for woodworking, but makes a lot of sense. Nice job.

[tigger_SB]

going to try this.