Sunday, March 19, 2006

Cutting Large Brace Arches

I went over to a friend's shop last week to cut the arches in the big hammer beam braces. While I was still thinking about how to use a string to make a big compass and scribe the arcs, he walked over to his table saw and ripped a 1/8" strip of poplar, held it to the brace and bent it just so. Voila - a nice little arc to trace with very little effort (upper left picture). I doubt it was a "perfect" circular arc, but it was a pretty darn good approximation - maybe even a little nicer than a circular arc. It then took three of us to wrestle the 8" x 12" braces through the band saw. (10 were Oak and 2 were Poplar - I wish I'd made them all Poplar!)

I had read somewhere that for big timbers it might be easier to keep the timber stationary and roll the band saw. The floor of my friend's shop was not exactly level, and the rollers under his band saw were not cooperative enough to make this possible. So, in the bottom left picture, you can see how we shoved the brace through the band saw... using a rolling roller stand fashioned from a discarded office chair.

It was tough going. To try and keep the blade from binding, we sometimes drove wedges into the kerf right behid the blade - forcing the cutoff material away from the brace and giving the blade more room (upper right picture).

We tried 3 different band saw blades in an effort to make the job easier, but never found just the right blade. We tried a 1" blade with about 4 tpi (shown in picture). This gave a nice smooth cut and was easy to steer predictably along the arch, but it was hard cutting all the way through. (possibly a dull blade to start with, and sap tended to build up on the sides of the blade). We actually cut most of the braces with a sharp 1/2" blade, but this blade definitely wanted to wander and was therefore hard to make a smooth arch with. (Not to fear, 80 grit and a porter cable sander can fix almost any aestheticly abhorrent anomally!) We tried a lot of tension on the blade and that didn't help. The wandering was probably partly due to the crappy, non-bearing, blade guides (also seen in the picture) that my friend had on his machine. We got started at 1:00, beer-thirty was quickly approaching, and we kept blowing the circuit breaker on my friend's bandsaw due to the dull blades. I had enough braces (9) to procede with my house raising for a couple more weeks, so with only three arches left to cut we called it a day. My friend has ordered us some new blades. I speculate a _sharp_ 3/4" blade with about 6 tpi might work best.

In the lower right picture, the black speck on the timber is a powder post beetle that flew in the shop to observe the cutting... and possibly scout out his next meal. We snapped a few pictures of him (see blog entry "Powder Post Beetles II"). In spite of this powder post beetle's precarious proximity to the blade, no insects were harmed while photographing this pesky bug.


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