"Orval Fairbairn" wrote in message
news
In article
,
Lou wrote:

I'm building a wood and fabric plane that uses plenty of aluminum
fittings and
hinges. If I have an aluminum block on one side of a spar made of wood
and the aluminum hinge on the other, with a bolt going through, is
there
any reason for washers? It's not that I wouldn't use them, but it
helps when
ordering the correct size bolt. The plans don't mention washers but
the plans
don't call for a few items that seem to me to be necessary.
Lou

Good practice in wood structures calls for a sleeve through the wood
(epoxied into place), slightly shorter than the thickness of the wood,
and large-diameter washers on each side, to distribute the compression
loads from the bolts. It doesn't mater if you have a block or a washer,
as long as there is a means of distributing the loads on the wood.

--
Remove _'s from email address to talk to me.

I understand the original post to say that that the bolt would go through an
aluminum block, then a wood spar, then an aluminum hinge. No need for
washers to prevent wood compression.

You need a washer under the part of the fastener system that you turn during
installation. If a nut goes on the bolt and you rotate the nut to tighten
it, you need a washer under the nut. If you are installing the bolt into a
tapped hole, you need a washer under the bolt head.

If you are putting a steel bolt through these aluminum parts, use a plated
bolt and plated hardware. Otherwise your aluminum parts will corrode in
time. If the fit is close, you may be unable to remove the bolt after the
aluminum corrodes. I know you didn't ask that question, but since you
weren't sure where to put the washer....