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Tapping Threads

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Blog entry by thewoodwhisperer posted 885 days ago 5168 reads 2 times favorited 13 comments Add to Favorites Watch

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During the construction of my Split-Top Roubo Workbench (which is nearing completion), I was surprised to see Benchcrafted's plans calling for numerous tapped threads. Instead of attaching the various components of the leg vise using screws or bolts with nuts, they actually recommend cutting threads into the wood! I certainly understood the concept of tapping threads, but I never really considered applying it to woodworking. After picking up some taps and cutting a few myself, I am now a convert! I can just imagine the possibilites in the world of jig-building alone!

Before learning to tap threads, I thought it would be helpful to review other types of mechanical fasteners and why they might not be as good as a bolt in a threaded hole.

Nails
Nails are pretty much a brute-force way of holding things together. The nail is driven into the wood, splitting and compressing fibers the whole way. Over time, natural forces cause the wood around the nail to compress even further eventually leading to joint failure.

Screws
A step up from a nail is the screw. When you rotate the screw into the wood, it pulls itself in and threads itself into the fibers. The good thing about screws is they are removable, but over the course of years the cut threads become wider and wider and the screw will eventually loosen up.

Threaded Bolts
This is the star of our show today. Once the threads are cut into the wood, you can pretty much remove and replace the bolt as many times as you want and it really doesn’t do any damage to the wood. This is because the bolts threads are sized perfectly to fit into the threads that are cut into the wood. So this is perfect for applications where you may need to loosen and tighten components on a routine basis.

Tapping Threads
All you need to make a threaded hole is a drill bit and a tap. The drill has to be a very specific size and and you can typically find drills and taps in matched sets such as this one. If you need help matching up your bolt, drill, and tap, refer to the handy charts on this page.

Here’s how the system works. The drill bit is used to create the perfect size hole. The tap is then driven into the hole cutting the threads on its way down. You have to be very careful not to strip the threads during this part of the process but in a dense hardwood like maple, you should have no trouble at all. While you might be tempted to use a traditional T-handled wrench for this, I found it much easier to use a power drill at a very slow speed.

Tee Nuts
One alternative that we can’t forget to mention here is the Tee Nut. These little threaded inserts accomplish the same thing as the threaded bolt technique only instead of actually cutting threads, we simply insert a threaded insert into a hole. They are very easy to use but unfortunately, the way they connect to a workpiece leaves a little to be desired. Over time, the small teeth that go into the wood fibers can break or the wood itself can compress, causing the Tee Nut to lose its grip. So while they can get the job done, I don’t really see them as a good long-term solution.

-- For free video tutorials and other cool woodworking stuff, check out http://www.TheWoodWhisperer.com



13 comments so far

View Bertha's profile

Bertha

12951 posts in 1296 days


#1 posted 885 days ago

I can’t even concentrate on what you’re saying with that bench at the top. I want to lay atop it and flounder naked in its glory. Sorry, carry on:)

-- My dad and I built a 65 chev pick up.I killed trannys in that thing for some reason-Hog

View oluf's profile (online now)

oluf

256 posts in 1641 days


#2 posted 885 days ago

Ihave been using cut threads in hardwoods for years. Make sure you use USS not SAE thread pitch in wood though. The only problem I find is that standard mill taps are somewhat short. I would like more threads in wood sometimes. I have been mounting casters for years with direct threads and bolts through the flanges. I use 1/4-20 or 5/16-18 bolts

-- Nils, So. Central MI. Wood is honest.Take the effort to understand what it has to tell you before you try to change it.

View CalgaryGeoff's profile

CalgaryGeoff

936 posts in 1084 days


#3 posted 885 days ago

Hi Mark,

Hey did you ever get the Ebony Crib? ;-)

You sure looked excited in the video here on tapping threads into wood. I’ve never tried it yet but will certainly do so when able. I thought for sure without a doubt the threads in wood would strip under light torque. The scrap you used in the demo held very well.

What would you think/suggest as the minimum depth for threading? Do you think it would work on 3/4” stock? I’d guess it works better on hard woods like maple better than cedar.

Cheers

-- If you believe you can or can not do a thing, you are correct.

View thewoodwhisperer's profile

thewoodwhisperer

601 posts in 2786 days


#4 posted 885 days ago

Are you talking about a submitted project? If so, welcome to the back log. :)

As for minimum depth, I have no clue. I am very new to this myself and just wanted to share the technique for others to explore. It should work in any thickness stock and you’ll probably have better success with harder woods. Also, end grain probably won’t hold as well as side/face grain.

-- For free video tutorials and other cool woodworking stuff, check out http://www.TheWoodWhisperer.com

View Roger's profile

Roger

14166 posts in 1406 days


#5 posted 885 days ago

very kool. I’d be lost without T-Nuts

-- Roger from KY. Work/Play/Travel Safe. Kentuk55@bellsouth.net

View Trackman's profile

Trackman

53 posts in 1040 days


#6 posted 885 days ago

Very interesting. I never even give this a thought. Now I have to find some project that I can give this method a try on.

-- Trackman, Washington

View Grandpa's profile

Grandpa

3051 posts in 1278 days


#7 posted 884 days ago

Interesting idea. The only time I have tapped threads in wood, I made some blocks for my grandson’s Cub Scout troop. I took 2×3x3/4 inch blocks and drilled a hole in the center of the face. I tapped a 5/16-18 hole and put a bolt in it. It used chalk on the threads. They wanted to make bird chirpers. When you turned the bolt in and out of the block it sounded like a song bird chirping. I got the idea for the chalk from turkey calls that use chalk.
This seems to work nicely. I have been in a manufacturing environment where I watched people using air powered drill motors to drive a taps. They really do a job but when one breaks you need to have safety gear in place.

View Sarit's profile

Sarit

466 posts in 1742 days


#8 posted 884 days ago

That’s a great idea Marc. I have been designing around the use of threaded inserts all this time and never imagined that I could have simply tapped the wood itself. Do you know if there are any practical limits to this approach, like bolts should be at least 1/4” diameter or so?

P.S. You look like you could use some sleep. Hope you and your family are doing well.

View thewoodwhisperer's profile

thewoodwhisperer

601 posts in 2786 days


#9 posted 884 days ago

The technique is very new to me so I really don’t have any guidelines. The Benchcrafted kit included numerous bolts of various sizes and they all seemed to thread in nicely. But I am sure there are limitations.

-- For free video tutorials and other cool woodworking stuff, check out http://www.TheWoodWhisperer.com

View Gpops's profile

Gpops

245 posts in 2047 days


#10 posted 884 days ago

Congrats on the baby. Your life will be forever changed and I don’t mean simpler. Been following you since you started your Woodwhisperer podcasts. Great information mixed with your sense of humor. Good seeing your build over on Charles Neil’s web site. Question, Any kind of lubrication, wax, grease, etc. needed to cut crisp threads? How does humidity affect the threaded holes if left empty? Don

View thewoodwhisperer's profile

thewoodwhisperer

601 posts in 2786 days


#11 posted 884 days ago

Thanks very much Don. The baby has indeed made life a lot more complicated, :).

As for lubrication, I would say some wax would go a long way in helping this process. As for humidity, I’m sure it would have an effect. But being new to the process, I dont have much experience to draw from. I guess we’ll find out over time. :)

-- For free video tutorials and other cool woodworking stuff, check out http://www.TheWoodWhisperer.com

View Greg In Maryland's profile

Greg In Maryland

382 posts in 1600 days


#12 posted 883 days ago

@ Al, I didn’t need that image. Thanks buddy.

I use this method on a much smaller scale—mitre bars for table saw jigs and such. I try to cut the mitre bar as close as I can and then use set screws to fine tune the adjustment. I drill and tap the holes, and then put a little super glue in the threads (with out the set screw, of course), let it dry and then adjust away. So far, it has worked like a charm.

Congratulations on the birth of your little leech. As R.E.M. sang: ‘It’s the end of the world as [you] know it.”

Greg

View nobuckle's profile

nobuckle

1120 posts in 1363 days


#13 posted 883 days ago

Mark, thanks for the post. I’ve been using taps to thread holes in wood for quite some time. I am often able to apply techniques I’ve learned as a toolmaker to wood working. One thing I’ve learned is that it is better to tap hardwoods rather than softwoods. Another tricky issue is making sure that you are tapping the hole staight. This is best accomplished when tapping holes as you did in the video. It may not be that easy in a thinner piece of material where the threaded hole goes all the way through. In cases like these it is best to use a guide of some sort that you know is perfectly square. This way you can check to make sure that your tapping the hole at a perfect 90 degrees.

-- Doug - Make an effort to live by the slogan "We try harder"

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