Threaded inserts for hardwood

[Steven J Corpstein]

What do you use for threaded inserts when you're putting them in hardwood? I've always used the brass ones in the past, but they are a bear to get in straight and sometimes lift the grain. I'm countersinking the hole but they still give me fits.

[David Eisenhauer]

Haven't used any in a while, but now that you mention it, they are a pain. I use the drill press (turned by hand) to get them started by screwing in a bolt with a couple of deadheaded nuts into the insert. I had forgotten about the lifting action and remember using a chisel to clean up the lift. I also remember that the ones I had a supply of seemed to have a very wide slot that was hard to match up with some kind of driver and, combined with the soft brass and tight drill hole in hard wood, resulted in stripped out head. Sucked.

[Kirk (KC) Constable]

I used some steel ones from McFeeley awhile back. They drive with a square driver, or an allen wrench...I can't remember. The recommended hole was too small, but I figured it out.

KC

[Jamie Buxton]

For a driver, use a longish bolt with a couple of nuts threaded on it and jammed together. Drive it with a socket wrench, and lean on it heavily while you start the insert into the wood. Leaning on it keeps the insert driving into the wood instead of letting it try to pull up the wood fibers.

Depending on what you're doing, you might also consider tapping the wood directly. Most hardwoods tap nicely, and hold machine screws securely.

[Hoa Dinh]

I take the average of the larger and the smaller diameter of the threaded insert, then use as the size of the pilot hole. If I don't have a drill bit that size, I choose the next larger bit. Then I use the approach David Eisenhauer outlined above with one exception: I coat the wall of the hole with epoxy glue.

[pat warner]

"What do you use for threaded inserts"

Real threaded inserts, Steve. Click link.
Drill, machine tap, then gently screw insert in x fingers. No drill press driving, plum trivial.
After the insert is where you want it, press in the lock pins and get on with it.

Routers

[Jamie Buxton]

Pat --
What is that? It isn't like anything I've ever seen.
Are you tapping the wood, then screwing in a metal insert into the tapped hole? And the insert has internal threads for the removeable machine screw?

Jamie

[pat warner]

100% correct Jamie.

[David Eisenhauer]

Where do you get that kind from Pat?

[Jamie Buxton]

100% correct Jamie.

So what good is the insert doing? After all, you've already tapped machine threads into the wood, so the pull-out failure force is set by that interface. Why not just run your screw directly into the tapped threads in the wood?

[Jim Becker]

So what good is the insert doing? After all, you've already tapped machine threads into the wood, so the pull-out failure force is set by that interface. Why not just run your screw directly into the tapped threads in the wood?

Jamie, if the screw were going in once, tapping the wood would likely be very equivalent, IMHO, as there will be no wear. (assuming it's a nice hardwood) But the insert gives you the ability to install and remove the screw/fastener frequently if you want. It takes the wood out of the picture "where the wear" will over time begin to cause problems.

[Cliff Rohrabacher]

Jamie, if the screw were going in once, tapping the wood would likely be very equivalent, IMHO, as there will be no wear. (assuming it's a nice hardwood) But the insert gives you the ability to install and remove the screw/fastener frequently if you want. It takes the wood out of the picture "where the wear" will over time begin to cause problems.

And of course add to that the fact of the additional diameter. The insert spreads the stress over a larger surface area effectively making the "base" for the bolt somewhat larger than it would be without the insert.

Granted no machine thread in wood is ever going to be anything comparable to the same thread in Steel but HEY, when you want a machine thread in wood there really are only three ways to get it: (1) a nut of one sort or other; (2) a threaded insert; (3) using a very large diameter & very hard-wood with a heavy buttress or acme thread.

With #3 you'd still have severe strength limitations. Almost all the time, driving a machine tap in the raw wood is not going to yeild more than a decorative means of attachment.

[pat warner]

Source for locking threaded inserts: A garden variety connector in any machine shop supply catalog or house. Reid, McMaster, etc.

[Jamie Buxton]

With #3 you'd still have severe strength limitations. Almost all the time, driving a machine tap in the raw wood is not going to yeild more than a decorative means of attachment.

Cliff --

Try drilling and tapping a machine screw into hardwood -- say a 1/4-20 into maple. Orient the hole so that you're going into face grain -- that is, not end-grain. Make the tapped hole at least four screw diameters deep. Insert a screw. Try your favorite method of pulling out -- claw hammer or whatever. You'll find it doesn't come out.

It isn't really too surprising. The biggest difference between a machine screw and a wood screw is that the latter is tapered so that it cuts it own thread, while the former needs a separate thread-cutter. Yeah, there are differences in thread depth and shape and pitch, but that's the small details. They both have threads to grab the wood, and that's the important part.

Jamie

[Jamie Buxton]

Jamie, if the screw were going in once, tapping the wood would likely be very equivalent, IMHO, as there will be no wear. (assuming it's a nice hardwood) But the insert gives you the ability to install and remove the screw/fastener frequently if you want. It takes the wood out of the picture "where the wear" will over time begin to cause problems.

Jim --
Presuming that you don't cross-thread the screw, what's the mechanism for hole wear? You're sliding a nice metal screw into a recess which fits it.

Jamie