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Thread: Tapping threads in white oak

  1. #1
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    Tapping threads in white oak

    I would like to tap a couple 3/8-16 threaded holes in the underside of a dining table I am making in order to bolt on cantilevered arms to support an extension leaf.

    What is your experience with direct tapping threads into oak.

    I know there are other variables here. If it helps:

    Leaf weight ~ 12lbs.
    2 arms bolted in 2 places each (2" from edge + 6" from edge)
    The support arms project through existing table battens (it's a trestle table) , so the bolts will not bear the entire weight of the leaf, but rather are there to draw the support arm flush so that leaf and top are coplanar.

    Blah blah, blah: do threads in white oak hold well?

    I dislike threaded inserts - which I started with. If direct tapping is marginally inferior in this application it's an easier solution for me.

  2. #2
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    My preference would be heavy gauge wood screws. Wood screws have a better thread profile for gripping than bolts.

    Outside of that I would use threaded inserts, I use them routinely. Where are you having trouble there?
    Bumbling forward into the unknown.

  3. #3
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    The issue is driving them in square if threading in the threaded inserts.

    I could epoxy them in but that is messy. how do you do it and what brand are you using?

  4. #4
    I've drilled/tapped for machine screws in hard maple with no issues. My LN tail vise is mounted this way, as is the top of my bench to the trestle.

  5. #5
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    I wouldn’t use epoxy becuase then they are reliant upon the epoxy. I use the E-Z Lok brand.

    For the underside of a table I would use these and use the appropriate driver.

    https://www.mcmaster.com/#90192A154

    The 1/4” size is good becuase the drill bit size is a typical 3/8” drill bit.

    I usually wax them before install.
    Last edited by Brian Holcombe; 03-03-2021 at 12:38 PM.
    Bumbling forward into the unknown.

  6. #6
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    When I drive in threaded inserts I take a scrap piece of anything about 1” thick and drill a through hole sized so the insert just fits in it. Hold or clamp it to the piece you’re putting the insert into. It will hold the insert square as you drive it.
    Steve Jenkins, McKinney, TX. 469 742-9694
    Always use the word "impossible" with extreme caution

  7. #7
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    The tapped threads of my vise criss-cross into white oak are holding very well. But I just finished it yesterday

  8. #8
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    Tapped threads aren’t that great. They aren’t awful by any any stretch but they are not as strong as threaded inserts in my experience.

    Add to that the fact that the insert increases the size dramatically. IE 1/4” bolts are held by 1/2”~ inserts. By comparison 1/4-20 threads are pretty small for wood, they may lose their grip in use and pull out.

    I also ran standard bolts into my bench vise and ripped the threads out a few times until it was finally replaced with wood joinery.
    Bumbling forward into the unknown.

  9. #9
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    This is a fruitful discussion. I'm going to drive the inserts into the table, but will direct thread the leaves. I think the risk is low and I'll get to observe them both over time. The risk of failure is higher on the table side than the leaf side. Even on the table side, the brunt of the weight is borne by the trestle battens. The bolt is only snugging the flex out of the iron leaf support rod near the mating point.

    But I have half a pack of inserts left and will just practice threading them better. Got the insert tool; I think it's a valuable exercise for the future.

    Thanks!

  10. #10
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    If you use my method with a guide block drill the hole with a drill press to insure 90 and use a bit of wax on the insert
    Steve Jenkins, McKinney, TX. 469 742-9694
    Always use the word "impossible" with extreme caution

  11. #11
    Prashun, if the bolts are not going to be screwed in and out, no inserts needed.

    I’ve done it many times both ways and I can’t tell the difference I quit bothering with inserts.

  12. #12
    Never owned insert tool, but made my own. This idea appeared in one of the woodworking rags many years ago. Take a block of wood about 6-8" long, and about two inches high. In one end, drill a thru hole the same size as the bolt that fits into you insert. Then cut out a notch on that end, so you have room for nut and insert to thread on bolt. that passes thru block. Place block on item to have insert installed, and using either a wrench, or socket drive it home. Square every time. Go to Woodsmith.com, tips and techniques, threaded insert jig for illustration.
    Last edited by Bruce Wrenn; 03-03-2021 at 5:40 PM.

  13. #13
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    I use threaded inserts in exotic woods for bottle stoppers. Best installation for me is using the matching bolt with double nuts (locked against each other) and drive with a ratchet wrench. Sometimes i use a guide block for the bolt--but normally just stand a double square behind and eyeball it.
    earl

  14. #14
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    I've tapped threads in a lot of wood. Some wood chips easily and holds poorly, especially with small threads, especially in end grain. I like to drill, apply some thin CA glue to soak into the sides of the hole and let it set up well, then tap the hole.

    I have also used threaded inserts that are glued in rather than screwed in. I've bought these brass inserts from Ruth Niles, 3/8″-16. I see she now offers some in stainless steel now.
    https://nilesbottlestoppers.com/prod...eaded-inserts/
    https://nilesbottlestoppers.com/prod...eaded-inserts/

    These would be good if the screws ever need to be removed.

    JKJ

  15. #15
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    If you tap directly into oak and use steel fasteners, they will corrode. Take a look at T-nuts that have been in oak for a while.

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