Drill diameter for tapping 1/4 inch threads in wood

[Galen Nagen]

I want to tap threads in baltic birch edges for 1/4 inch x 20 screws. I have the tap. Any idea on what size of drill bit I should use?

Thanks

GN

[Bill Huber]

I don't think it will hold, a 1/4x20 is really find for wood. I would put in an insert in the plywood and then you can use the 1/4x20 screw.

Here is a chart for metal tapping.

http://www.boltdepot.com/fastener-information/us-tap-drill-size.aspx

[george wilson]

For METAL thread tapping,a #7 drill is used for 1/4-20 threads. The goal in metal tapping is to get a 75% thread in the hole.

[Jason Roehl]

Anytime I "pre-drill" wood for a screw, I select a drill size that is 1/64" smaller than the minor diameter of the screw so that not only do the threads grip the wood, but the shank of the screw will exert some pressure on the wood, too.

[pat warner]

13/64" (http://patwarner.com/images/pwinsert.jpg), in wood and I use the same diameter in Aluminum alloys.

[Galen Nagen]

Pat, are those type of inserts readily available? Have not seen those kind before.

GN

[Bill Huber]

Pat, are those type of inserts readily available? Have not seen those kind before.

GN

These are the inserts I use and they work very well.

http://www.rockler.com/product.cfm?page=363&filter=inserts

[Galen Nagen]

They look at little different from the ones at the Pat Warner website. The same though?

GN

[Thomas Canfield]

One thing that helps tapping wood is to apply thin CA to the wood prior to and after tapping, and then running the tapping again. That will harden up the wood fiber and make for stronger threads. Another thing is to allow for extra thread dept to increase holding power.

[Nick Amandus]

These are the inserts I use and they work very well.

http://www.rockler.com/product.cfm?page=363&filter=inserts

You can also find these at Lowes and HD

[pat warner]

Indeed, garden variety. Expensive, about a 1$+/ea. But with locking pins, trivial installation.
Difficult to mess up. Have had nuthin' but trouble with the cheaper brass.
You can spin these in x hand, then press in the pins and lock, done in seconds. Good for metal & plastic.
You pay one way or another.
Jam (cross-thread) 1 in brass and you'll know what I mean.

[Bill Huber]

Indeed, garden variety. Expensive, about a 1$+/ea. But with locking pins, trivial installation.
Difficult to mess up. Have had nuthin' but trouble with the cheaper brass.
You can spin these in x hand, then press in the pins and lock, done in seconds. Good for metal & plastic.
You pay one way or another.
Jam (cross-thread) 1 in brass and you'll know what I mean.

What inserts are you using, I could not find them on your site/

[Dick Strauss]

you might have the option of drilling a through hole and using a t-nut on the back side of the plywood...

[pat warner]

I don't sell the other guy's stuff, so you'll find nothing it like there (http://patwarner.com/).
But you will find it here (http://www.mcmaster.com), plug in this part.no (92070A115) for quick find.
A great insert, but you must tap and chamfer.

[Bill Huber]

I don't sell the other guy's stuff, so you'll find nothing it like there (http://patwarner.com/).
But you will find it here (http://www.mcmaster.com), plug in this part.no (92070A115) for quick find.
A great insert, but you must tap and chamfer.

Thanks Pat, those are the ones I was thinking about.

[Tom Esh]

Seems to be only by pure luck that I ever get the screw in type inserts to drive straight and square to the surface. I prefer the tap-in style with a dab of epoxy.