Tapping Threads in Wood?

[Mike Goetzke]

I'm in the design phase for a knock down frame. In the past I would use metal threaded inserts but I have seen a few videos of woodworkers using thread taps right into the hardwood wood itself. This looks cleaner and easier to do but is it as strong/durable as inserts?

Thanks

 

[jeffinsgf]

Boy, that is a giant can of worms.

What size? The larger the diameter, the more successful you'll be.

Are you thinking metal bolt in wood threads, or threaded dowel in threaded hole? Both work, but always back to big holes and coarse threads work best.

Wood species is big, too. You can make some serious threads in tight-grained hardwoods...cocobolo, padauk, beech, hard maple, etc.

Years ago I sold the Beall Wood Threading Kit. It is a fun tool to use and demonstrate.

 

[waho6o9]

I've seen folks use crazy glue to strengthen the tapped threads. 

Best

 

[Mike Goetzke]

Boy, that is a giant can of worms.

What size? The larger the diameter, the more successful you'll be.

Are you thinking metal bolt in wood threads, or threaded dowel in threaded hole? Both work, but always back to big holes and coarse threads work best.

Wood species is big, too. You can make some serious threads in tight-grained hardwoods...cocobolo, padauk, beech, hard maple, etc.

Years ago I sold the Beall Wood Threading Kit. It is a fun tool to use and demonstrate.

Probably 1/4-20 into oak, maple, and ash.

Hey, I use a Beall spindle tap for making custom jigs for my lathe!

 

[Mike Goetzke]

I've seen folks use crazy glue to strengthen the tapped threads. 

Best

Good idea - I do this for my wood lathe spindle tapped holes.

 

[Vtshopdog]

I do it occasionally, can be surprisingly robust.

Usually make a few test tries and drill undersized pilot holes before tapping. Go ahead and over tighten bolts in your test hole to see where the thread stripping happens. 

I like to apply a dab of titebond before threading in the bolt and sometimes put bolt in with the glue, let it sit a few minutes then remove bolt and repeat with more glue, thought being that the bolt forces glue into wood fibers making female threads a bit harder.  Sometimes use epoxy too.

Attached shots are M4 bolts threaded into Lacewood end grain on an audio amp build.  Has held up really well.

 

[Cheese]

Nice stuff [member=68668]Vtshopdog[/member]  [smile]...I've cut machine threads into hard maple using standard metal working taps. Works well, a number of years ago I even cut tapped holes in some fir/pine fixtures that held threaded removable drill bushings.

Infinity sells taps made specifically for tapping wood, the nice thing about them is they have hex drive ends so they are easily driven in with a drill. Standard machine taps need special tap sockets to be inserted with a drill.

[attachimg=1]
https://infinitytools.com/products/wood-taps

 

[Svar]

The key question is how many times your frames will be assembled/disassemble over their lifetime?
Threads in tight grain hardwood will be good for dozens, perhaps hundreds of times.
I found standard metal taps create too loose of a thread in wood. I believe there are special wood taps that are undersized. For smaller machine screws drilling undersized hole and simply driving the screw in works fine.
As mentioned before, stabilize wood threads with glue or epoxy. Insert the screw to spread it and squeeze into the fibers, then remove before it fully cures).

 

[Michael Kellough]

At 1/4-20 size you don’t need a tap, just the appropriate pilot hole. You might want to enlarge the top of the pilot hole a little to aid getting started. When driving the screw use a lot of downward pressure. Since you are not cutting the wood but compressing, put a clamp on the wood so it can’t split.

A cold forming tap (may be the same thing they sell for wood) does not cut the wood. Does the same thing but less aggressively than simply using a screw. At this size the shank can be held by a drill chuck so you don’t need to use a tap handle.

[attachimg=1]

[attachimg=2]

 

[rmhinden]

Infinity sells taps made specifically for tapping wood, the nice thing about them is they have hex drive ends so they are easily driven in with a drill. Standard machine taps need special tap sockets to be inserted with a drill.
https://infinitytools.com/products/wood-taps

I have used the Infinity wood taps on a few projects.  The work very well.

Bob

 

[hdv]

MLCS used to have threading taps for wood too, but I don't know if they still do sell them.

[Edit] I thought I remembered a very old post by Marc Spagnuolu on his blog about this specific topic, so I did some searching. Here's the URL if you are interested in his opinion:
https://thewoodwhisperer.com/videos/tapping-threads/

 

[Packard]

Ikea uses a bunch of different fasteners, but I don’t recall them using machined threads.

They do use Confirmats (or the equivalent).  Confirmats cubit thread that can be re-used several times. 

You cannot take all your cues from Ikea, because some of the decisions are made to satisfy their productivity while maintaining satisfactory strength.  So productivity might trump aspects of assembly that a small shop might find important.

They do use those 1/4 turn fasteners, but not for structure.  They use them in conjunction with dowels.  The dowels (or right angle panels) provide the structure, the 1/4 turn fasteners simply draw the boards together.

I’ve installed helicoil-type threaded inserts.  They cut their own thread into the wood and hold very well.  They are made from steel (helicoils) or from diecastings (insert threads).  But if you can use the insert threads, you probably can used Confirmats.  Confirmats offer the structure of a dowels with the reusability of threaded inserts.

 

[rvieceli]

Mike as Svar says the biggest concern might be how many times you need to assemble/disassemble your piece.

I have used threaded inserts in almost every thing I have made in the last 6 or 7 years. Most of those were 1/4-20. I use the knife edge brass inserts made by EZ-Lok as I have had good luck with them. I am doing the insert into a piece of edge (long) grain hardwood and the screw attaches a piece of steel to it. I have super glued the inserts when inserting., but don't any more because I didn't notice any appreciable increase in performance. I have never had an insert pull out. In fact it is sometimes difficult to get them out if you need to.

I have never however had much luck with using an insert into end grain. I find them difficult to inset and they do not seem to hold as well.

If I needed to attach a piece of edge grain to the end of a board (end grain) I would use something like a cross dowel or a bolt to a captured nut. Drill a hole through the end grain for the bolt and then another hole through the piece face grain for the cross dowel or nut.

A lot of wooden bed frames use a similar arrangement using two dowels or dominoes for alignment with a bolt hole in the middle to a cross dowel or a nut to tighten and hold the frame together.

Ron

 

[Cheese]

I forgot to mention, that if you use metal working taps, the tapped length in the wood is restricted to the threaded length of the tap. With the Infinity taps, the area behind the last thread on the tap is relieved so that you can drive the tap in further and gain more thread length if needed.

[attachimg=1]

 

[Crazyraceguy]

As has been stated, the main thing is how many times it will be disassembled. I have always used threaded inserts in any place where removal/reinsertion is going to be a thing, with really only one exception.
The big screws I use for access panels have a coarse wood screw thread. I pre-drill at 3/16" and drive them in. This is into the face of 3/4" plywood and they hold well.

I can't remember who it was, but I recall someone doing a test of threads in wood and their recommendation was not to use super-glue. They said that it made the threads brittle and they tore out.
The thread forming tap sounds like a good idea, pushing/compacting the fibers, rather than cutting them.

 

[Cheese]

1. I have always used threaded inserts in any place where removal/reinsertion is going to be a thing, with really only one exception.
The big screws I use for access panels have a coarse wood screw thread. I pre-drill at 3/16" and drive them in. This is into the face of 3/4" plywood and they hold well.

2. I can't remember who it was, but I recall someone doing a test of threads in wood and their recommendation was not to use super-glue. They said that it made the threads brittle and they tore out.

3. The thread forming tap sounds like a good idea, pushing/compacting the fibers, rather than cutting them.

1. I've also always used brass threaded inserts in wood (and still do) because I am intimately familiar with how superior Helicoil stainless inserts are in aluminum castings. However, in some situations brass inserts can be overkill in wood.

I'm very interested CRG in how you configure access panels because I'll be needing to install 4 of them in the garage because I'm installing some in-wall water lines.  [smile]

2. That makes a lot of sense to me...maybe a fast setting epoxy would be the better solution?

3. Oh boy...thread forming taps in aluminum & steel are common and now introducing thread forming taps in wood. Hey, hey, hey, I knew we could turn this wood-centric website into a metal-centric alternative.  [poke]

 

[twistsol1]

I have a 3/4 wood tapping kit and have used it many times with no issues.

Below is a 100+ year old clamp that worked great until the 1990's and then some of the threads broke off. It no longer holds. I can't imagine a 3/4 inch threaded steel rod failing in the same way, so the answer to the question "is it as durable and as strong as inserts" is as solid no. Would it work. Probably, but it depends on how many times you assemble and disassemble the frame.

View attachment 1

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[Mike Goetzke]

I know I'm taking my post a little off topic but I have some Domino connectors. I used a few to tie my break-down 3-slab MFT style 4'x8' table. Would these be strong enough to hold a stand up frame together?

 

[Packard]

As has been stated, the main thing is how many times it will be disassembled. I have always used threaded inserts in any place where removal/reinsertion is going to be a thing, with really only one exception.
The big screws I use for access panels have a coarse wood screw thread. I pre-drill at 3/16" and drive them in. This is into the face of 3/4" plywood and they hold well.

I can't remember who it was, but I recall someone doing a test of threads in wood and their recommendation was not to use super-glue. They said that it made the threads brittle and they tore out.
The thread forming tap sounds like a good idea, pushing/compacting the fibers, rather than cutting them.

In metals, it is widely understood that rolled threads are stronger than cut threads.

In rolled threads the grain in the steel (yes, metals have “grain”) is not cut or damaged, it simply flows into the new shape.  Cut steel threads have the grain cut into small segments that can more easily be broken.

You can easily distinguish rolled vs cut threads.  The major diameter on rolled threads is larger than the rod it was rolled from.

The major diameter in cut threads is the same size (or slightly smaller) than the rod from which it was made.

 

[rvieceli]

Mike I feel that in order to give you better advice, a quick run down on what you are actually considering constructing. A quick sketch on a piece of paper will be helpful. Perhaps an estimate on how often this thing would be assembled/disassembled as well

Ron