machine screws in tapped holes vs. wood screws

[Barry O'Mahony]

Hello,

Lee Valley sells tap and drill bit "kits" for making threaded holes in hardwood for machine screws:

http://www.leevalley.com/hardware/pa...306,41330&ap=1

The claim that in their tests, the machine screws in threaded holes form a stronger connection than wood screws.

Has anyone tried this? I'm sure I'm not the only one that's had problems putting brass wood screws in certain woods, like White Oak. Even using steel wood screws to "tap" the threads can be problematic; I've snapped the heads off a #4 now and then. I think I might rather try it with a hardened steel tap instead. Heck, I've developed enough of a "touch" that I can avoid breaking a small tap even in something like stainless steel (usually!); I should be able to avoid breakage in wood. But it would only be worht it if the resulting connection was strong.

So would one still use tapping fluid?

[Bruce Page]

Barry, that’s interesting. I’ve been drilling & tapping metal for years but I never thought to give it a try in wood. I think I’ll do some experimenting with it, there's times when it would be real handy!
Thanks for the info!

[Rob Will]

It sounds like a good place for an extra-coarse thread (if there is such a thing). Also I would imagine that the start hole could be slightly smaller than would be required in steel. A threaded insert sounds better to me, perhaps with a touch of epoxy as it goes in. (?)

.02 Rob

[Jim Dunn]

Barry, Bruce and Rob, I've drilled and tapped holes in oak, and hard maple. Just did it like steel but I used fine threads instead of course. I thought about it and decided that fine threads would just be stronger. Also the machine screws were 8-32 and 10-32 as I recall. Not what you would call large taped holes at all. But it did the job and really tapped nicely.

Jim

[Don Frambach]

Here is an example of a commercial use of tapped machine screws into wood:

My SawStop fence faces are secured by machine screws tapped into the plywood. The faces seem very secure and are very flat. I presume that these guys know what they are doing. It occured to me that tapped machine screws would not lead to as much dimpling of the face as would regular wood screws.

added 12/30/05 1:20 AM PST - OOPS!! Just looked again more closely. The machine screws attach to metal inserts. Sorry for the misinformation.

[Ian Barley]

I have tapped 6mm holes in Iroko (like Teak) and Oak. Works fine and while I have no tests I have never had a failure. I would think that the connection is at least as strong as a wood screw, depending on application.

[Bill Antonacchio]

Hi All,

Pat Warner, the router guru, wrote this article for Taunton and he has some more on his web site that I can't quite find again. But evidently he is a proponent of machine screws in hardwoods.

http://www.taunton.com/FWN/SkillsAnd...F.aspx?id=2489

If Pat thinks it is OKwith the meticulous approach he takes to everything he does I would think it is a winner.

Regards,
Bill Antonacchio

[Doug Shepard]

I bought the LV taps, but so far only tested it out on some scraps, but was VERY impressed. I mangled the screw head pretty good trying to pull it out with a pair of channel lock pliers. Just wanted to see how good it held. IIRC I think Jamie Buxton has some threads here with some detailed writeup of tapping wood for machine screws. You might want to try an advanced search.

[Mark Singer]

I think it works fine ....it is just another step that takes time over just using wood screws. In the right application...like inside a fine cabinet to add something or for a jig or fixture that gets repeated use it seems great!

[Lars Thomas]

I've used this method in the past and have been very impressed with the strength. Lars

[Randy Meijer]

Posted this last night; but it apparently got lost during the update??

If you are having problems, seems like the simple thing to do is use a slightly larger pilot hole?? Do you lubricate your screws?? Bee's wax, candle wax or even a touch of bar soap really helps. According to some posts that I've seen, the brass screws you get at the local home centers are pretty soft. You might look for a better quality of screw if you are not using top grade hardware.

Other difficulty I see is the extra time invloved. If you are only driving 6 screws, it's no big deal; but on a larger project with 50 or 100 screws, you will be adding a lot of time to the job??

[Don Baer]

I have been taping wood and using machine screws for some time now. To speed things up I use a 2 fluted tap and instead of a tap wrench I use one of my corless drills. This is a trick I learned years ago when I worked in an electrical panel shop and had to thread hundred of holes a day.

[George Summers]

Other than a couple of jigs, I have not used machine screws for wood fastening. When I did use them for jigs, they worked really well. But, I have made hundreds (well maybe not hundreds, but tens) of ZCI of wood and plywood. In every one I have ever made I use set screws for leveling screws. I tap the four holes and screw in the set screws. I've never experenced any of them vibrating out of adjustment.

George

[Jim DeLaney]

Lee Valley ...claim that in their tests, the machine screws in threaded holes form a stronger connection than wood screws.
Has anyone tried this?... )

Yes, I've used 10-24 and 10-32 metal screws (bolts) in wood on several occasions, with good results. I use a regular metal tap and the appropriate drill (#21 for 10-32), then put a drop of CA glue into the tapped hole. When the glue is hard, I run the tap in again to clean up the threads. I've never had one come loose/strip out yet.

BTW, about fifteen years ago, Fine Woodworking had an article about tapping wood. I hadn't tried it until then. I find it useful for jigs, etc., but haven't used it on any projects that would have a lot of long-term stress on them. I really don't see why it wouldn't work just as well for that, though. I just haven't tried it...

[Frank Chaffee]

Jim,
Thanks for the tip about CA glue.

Frank