Wednesday, December 2, 2009

DIY Saw Blade Efficiency Boost

I spent a good part of the late summer preparing our stash of firewood for the wood stove that had yet to arrive. As a consequence of not knowing the maximum log length I would be able to stuff into the stove, we wound up with a good pile of stick and such that were just too long. Many of them were too thick to break (I have some slightly messed up ankles from foolishly trying to break a piece of hickory by jumping on it). So, I employ a pruning saw to cut them down to size.Well, I noticed right off that when the blade was about half way through a log or thick branch, the blade would begin to bind up and would stick. It made it very hard to cut straight through a log. I had been having the same problem with my chain saw cutting particularly hard wood or wood with a twisted grain, like Black Locust.

My father-in-law recently had his chain saw blade sharpened and the craftsman that did the work also added an alternating camber to the teeth of the blade, which creates a cut that is wider than the chain bar. This virtually guarantees enough room to wiggle a bit while you cut and the bar doesn't bind in the process, meaning you cut more easily and efficiently.

I thought about that while I was taking the pruning saw to task again the other night. Why not add an offset camber to the teeth on its blade? Just a millimeter aside on every other tooth would make the cut 3 mm instead of the 1 mm the steel ribbon blade is on its own.

So, using a Vice-grip style pliers and a needle-nose pliers, I systematically bent each tooth in the opposite direction, leaving the double point teeth straight to make sure I had sufficient blade clearing the cut.

It took me about 10 minutes and was pretty easily accomplished. And, as I surmised, the blade now cuts much more easily and rips straight through thick branches with ease. The cut is only a bit wider, but plenty wide enough to keep the blade from binding up. I love it when a plan comes together.

Update 11/28/2012:  Christopher Johnson, whom I met via Google +, shared the following additional information which greatly enhances the above tip.

This is called "setting" a saw.  A good saw always has its teeth set correctly.

For example a crosscut saw has two types of teeth, cutters and rakers.  The cutters are set side to side and are filed on the "inside" to make sharp cutting points.  Their job is to cut the fibers of the wood, scoring it, on both sides of the actual blade.  The rakers are filed like a chisel and are set in line with the blade.  As the rakers move across the wood they shave the wood from between the score marks made by the cutters.

If the set of the blade is wrong it just does not work well.  It can take upto an hour per foot of cross cut saw to sharpen and set the teeth.

I will have to double check my bare blades to see if they are set correctly.

But binding isn't the problem I'm working on with a hand made bow for a bow saw.  You have to control the blade from twisting.  And having thought about it I think I need to add a steel peg (nail) to my saw blade kit.  Then I can take the bow, cut a slot for the blade, use the nail to hold the blade at that end.  A couple of wraps of the inner thread of paracord to form a whipping will keep the bow from splitting.  The other end is just for tension so it can be a simple line to the other end of the bow.

Time to go test all of this out.

P.s. the old timers using crosscut (and bow saws) used kerosene as a lubricating agent which will greatly reduce binding and pitch build up.  The National Forest service uses an Orange product that does mostly the same thing but costs more.  But it does protect the environment from the few drops of petroleum  product that might escape. 

2 comments:

Mark said...

Don't forget your sterling engine driven Fan for the top of your Wood Stove - the distribution of heat will be much better.

Is it multi fuel - will it take coal? To be honest burning wood is nice initially - but the novelty wears off because I always have to keep throwing wood on it. Where as a scoop of coal burns for hours.

J E Carter II said...

Hello Mark! How's winter on your side of the world?

No, sadly, not multi fuel. The next one may be though. I have to check the heat rating on this ridiculously expensive flu vent I have.

I have the plans for the sterling engine fan, haven't made it yet. I refuse to buy that which I can make and have fun doing. :-)

Yes - putting a log on every hour or so is a bit more work than I remember as a kid, but that was a bigger stove my Dad had - would take 2-3 times as much wood as this little high efficiency unit... emphasis on "efficiency" I think. But, it was intended to be a temporary emergency heat source anyway and if it lasts 5 years I'll call it good. Gives me time to save for something a bit larger.