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Screw thread pitch on wood screws

Posted: Thu Nov 17, 2016 8:34 pm
by lakeracer69
I am building a Crackerbox which has 2 plywood laminations on the bottom. I will be using my nice square drive silicon bronze screws for the final fastening.

All the holes are drilled to depth in the sheers, chines and battens with the appropriate taper point bit. the holes are also pilot drilled in the second layer laminations.

I want to use some sacrificial screws to fasten down the first layer while gluing along with plywood blocks that mimic the second layers thickness.

The Silicon bronze screws are too expensive and soft to try to use "twice" for this operation in my experience. For example, do wood screws that are #8 all have the same thread pitch as their silicon bronze boat building screw counterparts? Is there a standard like metal machine screws and bolts?

If you know the answer please let me know. This is all that is holding me back from gluing up the hull.

Thanks in advance.

Re: Screw thread pitch on wood screws

Posted: Fri Nov 18, 2016 7:17 am
by jcallends
Sorry, can't answer your question but will give you something to think about. Many containers, like bottles, have a different thread pitch than the closure that is applied. It's what makes the closure tight. Unless the thread difference is visible, in which case you would strip out the wood threads, your regular wood screws should be OK. A trial on scrap wood would help get your answer.

Re: Screw thread pitch on wood screws

Posted: Fri Nov 18, 2016 5:03 pm
by galamb
Wood screws thread pitch "should" be uniform a given screw size.

So as an example a #8 wood screw has 15 threads per inch, a #10 should have 13 threads per inch etc.

Where you will run into variances is with "specialty" (for lack of a better term) wood screws. You have deck screws, flooring screws, particle board screws etc that are all still (kinda/sorta) "wood screws" but particularly with deck screws they may use less pitch so they will "drive" faster and some flooring screws will have a progressive pitch etc.

But if you stick to a "regular" number 8, it should be 15 tpi whether it's silicon, stainless or whatever...