Did a fun thing today
On the big big Kalmar Nyckel, trunnels are used for fastenings in many places,
mostly planks on the hull and deck into the framing underneath. A trunnel is a
wooden dowel that has a slot in both ends. You put a wedge in one end and drive
it wedge first into a flat bottomed hole. As it bottoms out, the wedge spreads
the trunnel and locks it in place. You then drive a wedge into the top. So the
trunnel is wedged in place at the top and the bottom and acts as a bolt.
The biggest we use is 1-1/4” and driving them into existing holes that old ones
have been taken out of has always been a hassle. I made a chair devil with a
round recess in the blade that matches the biggest trunnel, and that has worked
well, but I thought that a dowel plate would be faster. The question in my mind
was could you drive something that big made of Jatoba, a very hard wood, without
crushing the wood or wearing yourself out. Also, the local machine shop wanted
$200 and another $175 to heat treat it.
One of the other volunteers is a machinist and he made one to my specs with
1/64” steps either side of 1-1/4”. I turned up a couple of Jatoba blanks just
big of 1-1/4" and we had at (past tense of "have at’). Here is a picture:
https://www.flickr.com/photos/ruby1638/46456769695/in/dateposted-public/
It did a passable job with reasonable effort - actually once it was sized at the
biggest hole, the 1/64” steps were fairly easy. But you could see a ring at the
start of each blow that was a little off of the finish of the travel of that
blow. Then my machinist mate had an idea - we stuck one in the 20 ton press and
shoved it smoothly through and it it made a beautiful thing. Just the hint of a
bow along it’s 7” length, but good enough for shipbuilding. So now we can make
our own accurate trunnels without a drawknife and shave horse, but still be
galootish.
How cool is that
Ed Minch
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