How do you drive bronze screws into oak?

Discussion in 'Wooden Boat Building and Restoration' started by sdowney717, Oct 20, 2024.

  1. sdowney717
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    sdowney717 Senior Member

    I need to put in some long screws. I know to predrill. But what size drill and how to tell from the screw?

    And, how about a steel screw to form the threads first? As if I could find one, doubtful.

    Looking at these, what size number are they? They are 3 and 3.5" long.

    upload_2024-10-20_16-25-55.png
     
  2. Dave G 9N
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    Dave G 9N Senior Member

    I copied your photo into Excel twice. I cropped one to the edge of the tape measure (Nice job lining it up, by the way) and rotated the image 90°. That made it easy to measure the screw diameters. {EDIT and totally failed to read the dimensions correctly, mistaking 16th for 32nds, so the only decent advice was to read the tables for yourself. Jehardiman is right of course, the best way is a caliper, but if you don't have one in the shop, and I have worked in a number of shops sadly lacking a caliper, the diameter isn't always easy to read} The larger one is {not} a #10 and the smaller one is {not} a #8. I looked for a convenient size chart, and found
    https://www.mcfeelys.com/screw_size_comparisons {which only covers smaller screws}
    Having looked at the picture and played with it in Excel, I have come to the conclusion that the easiest way to do this {remotely} its to take a good picture, blow it up and use it as described.

    They also have a pilot hole chart.
    https://www.mcfeelys.com/drilling_chart
    Cool, I didn't know where to look. { and still don't apparently}
    #10 counterbore is um, I spent more time looking at the table and less time on the rest. I think is says that the pilot hole for hardwoods should be 9/64 and the counterbore 7/16. You had better read it yourself.

    The thread dimensions look like they follow ASME B18.6.3, Table 29, "Dimensions of Plain (Unslotted) and Slotted Regular and Large Hex Head Screws." That indicates the a steel wood screw can be expected to have very similar dimensions.
     
    Last edited: Oct 21, 2024
  3. jehardiman
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    jehardiman Senior Member

    First, you need to know the screw size, and for this you need a set of calipers and a chart like this.
    https://support.jamestowndistributors.com/hc/en-us/articles/360021736334-Wood-screw-size-chart
    Next, you can look up a pilot hole chart like this and choose hardwood.
    Pilot Hole Drill Bit Size Chart for Wood Screws | Woodworking Guides https://handtoolessentials.com/blog/tools/drill-bit-sizes-wood-screw-pilot-holes/
    For bronze in hardwood, it is recommended to go one drill size larger due to the softer metal and for oak I recommend beeswax or toilet ring wax to lubricate the screw.
    The depth of the pilot is always a matter of debate. If using a taper bit, I go the full depth of the screw. If using a straight bit, I drill a little less so the point sets.

    EDIT: X-post with Dave G
     
  4. sdowney717
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    sdowney717 Senior Member

    Good chart

    The wider shank screw is .29, root is .20 so those are #18

    skinnier longer shank is .21, root is .155, those are #12

    The #18 are pretty big screws, I have a lot of them. They had been used to hold on a toe rail mahogany on the boat.

    The longer #12,s can not remember where they were used.

    upload_2024-10-20_17-47-39.png
     
  5. sdowney717
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    sdowney717 Senior Member

    I was thinking maybe see if a small steel lag bolt might match the wider shanked screws, that way you can drill, twist those steel ones in, then swap in the bronze screws.
     
  6. Tops
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    Tops Senior Member

    Howlandwoodworks and sdowney717 like this.
  7. sdowney717
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    sdowney717 Senior Member

  8. sdowney717
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    sdowney717 Senior Member

    likely have to drill the shank in the oak at one size drill bit, then use smaller drill bit for the root threads

    I really dont want to have any break on me.
     
  9. sdowney717
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    sdowney717 Senior Member

    I am also thinking, use the Teflon rector seal T plus 2 as a thread lubricant. It will have 2 advantages, screws will drive easier, and, the stuff will help keep water away from the bronze screw. perhaps less chance of corrosion. I did use it on the 1/2 " bronze keel bolts. I wrapped 6 or 7 inches of knitting yarn greased up with the stuff on the base and lubed the threads too. I also coated the bronze bolts with JB weld to keep them dry inside the keel.
     
  10. Dave G 9N
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    Dave G 9N Senior Member

    Sounds good, but one note of caution for smokers. Don't smoke after handling PTFE lubricants. Polymer fume fever is not to be recommended.
     
  11. gonzo
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    gonzo Senior Member

    Those are actual wood screws and not the self tapping type. The hole needs to have two different diameters. The small one is the lenght of the thread and the bigger the length of the shank. The shank is tapered so it fits thight into the pilot hole which is a bit smaller than the minimum diameter. Screws hold due to friction, teflon and other exotic lubricant may allow them to loosen. Wax and soap have been used successfully for a couple of centuries. A toilet ring only cost a couple of bucks and will probably last you a lifetime.
     
  12. sdowney717
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    sdowney717 Senior Member

    Will post pics, I am replacing a section of the front skeg keel due to worm damage.
     
  13. seasquirt
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    seasquirt Senior Member

    Sometimes the root diameter of the screw isn't parallel, so check for that. Get a test block of same wood and drive the bronze screws into it, same grain orientation, to be sure after your drill bit size selections, that they don't bind before bottoming, and snap at the head. Safer than trying to extract a broken bronze thread from your work. I've cleaned up screws for re use, in bulk, on wire wheel, warmed them up a little, and dripped or dipped candle wax on, as a wetted coating, which stays on without mess; candles are cheap and many other uses. For the tapered shank size, the shank acts like a dowel and needs some friction, but not too much, and avoid wood splitting from being too tight at the end. Use a collar stopper screwed onto the drill bit for drilling the shanks, if by hand, so it doesn't bite in and drill too deep, removing too much thread wood. Only use a steel thread former screw if the thread pitch exactly matches, exactly, otherwise you are weakening the thread wood by virtually cross threading it. A sharp multi fluted countersinker makes round countersinks, not ragged faceted ones.

    If you have a spare bronze screw you can turn it into a self tapper with a hacksaw cut beginning at the start of the point thread form, angled just off the axis along the screw, aimed slightly to RH side of the head, and hacksaw blade angled/leaned over to the left almost tangent to the root diameter, to give a sharp cutting edge on the screw. Don't use it to cut full depth screw holes, but just to relieve the upper threads, and blow the dust (swarf) out of the holes before final fitment.
    I use the same method on hard bolts of special size, if I have no thread tap that size on hand, with multiple cuts to make a temporary emergency hand tap.
    Last thing, clean out all the driver slots, no paint, glue, or corrosion, and use the best fitting sharp square screw driver you can, not an old worn out one. Happy screwing.
     
  14. sdowney717
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    sdowney717 Senior Member


  15. gonzo
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    gonzo Senior Member

    The zinc plating is really thin. It works OK in dry locations. Home Depot will deliver to your house.
     
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