Messages Archive

Subject:
Hardware bonding make FWW

TomD
I was looking through the latest copy of FWW at the market today and noticed that there was an article on making strong joints in a coffee table with threaded rod and epoxy.

Some of you will be aware I have been advocated hardware bonding to this group for about 20 years. The system is probably around 50 years old in boats.

I don't have the issue but from what I could see they had a version of the technique that does not take advantage of two aspects of the technique that are useful. On is the fact you can have hugely loose pins and have far greater strength. The method shown is a lot like doweling, in that many pins are used, and they are tightly fitted. Maybe slightly looser than might be the case if the "dowels" were wood and glued with wood glue. This is fine, but it makes for a weaker joint. HB works so well because it spreads the load over a larger area of wood. So a simple tenon in a round chair part is a lot stronger if the holes are as large as possible, several diameters largert than the pin, but no so large the part is severely excavated to the point where strength is compromised. In the example shown, 4 pins of about 1/4 were used to hold a small leg on a coffee table. The kind of situation where a 3/4" wood tenon would suffice. While on my sailboat, the traveler track is held onto a 3/4" wide piece of Sitka, with about 3 1 /16" machine screws, into probably 1/2" holes, they might be 1/8" screws. That holds the boom down against powerful sails, and the whole rig from falling over to the bow. At any given time the traveler could be over just one screw.

The other feature of the big loose holes is that while positioning the part so it stray tight can be a problem that requires some inginuity if you have big sloppy holes. If you can do it, you have no difficult getting parts perfectly aligned, without hardly any skill being required, other than planing. And none of that if you have plans.

There are lots of other details one could consider, but it was cool to see HB finally get coverage. One reason it may have taken so long is people might feel it was not really woodworking, but what is these days? Might as well use strong hidden kludges, that are easy to do, if that is the way the craft is headed. And in many situation, hardware bonding can be used to get rid of worse hardware options that are even uglier. Like plugged screw holes.

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