On Aug 25, 7:59 pm, Fortunat1 wrote:
Fred the Red Shirt wrote roups.com:





On Aug 17, 2:50 am, Charles Vincent wrote:
Fortunat1 wrote:
"Rich S." wrote in
:

"Fortunat1" wrote in message
...
Well, obviously I'd protect it, but I'm not going to rely on
epoxy to bear a load. If I can't get the holes 100% I'll bush
them....

...So I guess I'l just be as careful as I can cutting the holes. Just
looking through Bengelis' book, I see he recommends using a twist
drill to cut the holes, presumably to their final size,...

I would test that theory first. Reamers may or may not give a good
finish on wood. That was one of the reasons I quoted the study I
did. The twist drill gave the best hole finish.

Bits made for wood, high quality brad-point or forstner bits,
may give you a cleaner hole than a twist drill made for metal.
Cheap bits are crap-they'll burn their way through the wood.

Actauly, having tried each on some scrap pieces of spruce, the twist
drill gave the best finished hole and the roundest hole by a long shot.
The 5/16th bolt was a perfect fit after having used a an 8mm twist
drill.

As a rule of thumb, when working wood, use tools made for
woodworking. Duh!

Yes, mostly I do, but in this case, I'll use what works best! I found
the woood bit went a bit eccentric as it went through giving a slightly
tapered bore as it went through.







Wood expands and contracts with changes in humidity and
it does so anisotropically. E.g. a flat-sawn board will
have the highest expansion rate accross it's width, less through
its thickness, and minimal along it's length. Quarter sawn or
vertically grained wood, which is what you usually want for
a spar cap, will have those first two rates reversed.

What this means is that if you drill a perfectly circular hole
in a piece of wood, as soon as the humidity changes it
becomes an oval hole. The same is true of a wooden dowel.

Wood finishes slow the rate at which wood absorbs or
releases moisture to the air so as to prevent moisture
gradients through the interior of the wood, which minimizes
e warpage. But all wood finishes are permeable to some
degree to water vapor.

So don't get too crazy about making the hole perfect. I think
the epoxy approach is a good idea.

'Kay,. but did the bipes of the thirties have the holes filled in any
way? Lots of them are still flying wth their original spars.



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It's interesting to hear of your results on hole quality. I have
also found that a good, sharp HS twist drill works great in metal or
wood. I think the place where the special wood bits like the Forstner
( a fancy hole saw) are used is in drilling large holes. For 1/2" dia
holes or so and smaller, the twist drill is the way to go. If you need
a 2" or 3" hole or so, well a twist drill that size is a huge chunk of
metal, hard to find locally and expensive to boot. Hole saws do OK in
wood ( and even metal if you are carefull) up to 6" dia or so and are
what I use for large holes.

Regards,
Bud