Thursday, June 12, 2008

Bucksaw Rebuild

Yet another tool rehab (or rebuild in this case) entry. It's almost as if I spend most of my time working ON the shop rather than IN the shop. Hmm. We might be on to something here...

Anyway, a while back I wanted a bucksaw. Why? Well, the wooden bucksaw would be for bucking wood on a sawbuck. You just gotta love English! The only problem was that the vintage ones I could locate all had similar problems that made their further use unlikely - but as I was told on at least three different occasions "That would look great handing on the living room wall!" (Blasphemy! Tools are for using, not decorating!) But really, bucksaws are very cool. They are wonderful contraptions of wood and metal, and loose mortice and tenon joints, that balance the physics of leverage, compression and tension.

I finally realized that I was going to have to make my own - but in order to keep things simple, I decided to salvage the blade and hardware from an existing saw and just rebuild the wooden frame, using the original parts as models - a direct, and therefore simple, fast process. Yeah right. Like I could ever do that.

Here's the donor buck saw:


As I disassembled the saw, I took a good look at the problem areas. First, the grain on the short arm did not run parallel to the length of the arm. So, as the turnbuckle was tightened to tension the blade, the stress of the load ran across the arm at an angle rather than down the arm. This weakness developed into a crack that threatened to completely sheer off the arm along the grain run-out. In the photo, the blade is only slightly tensioned:


Second, the two part stretcher was held together in the center by a pin. The hole for this pin created another area of weakness and it too cracked:


So, as was inevitable, I decided to "improve" on the design. The first problem was easy to fix. I just selected my stock (local birch) to allow for layout with the grain running the full length of the arms. The second problem I solved by replacing the two-part stretcher with a solid one piece design. No hole; no weak point. As a bonus, I only had to chop two mortices instead of four.

Here's what my version of the saw looks like on the bench:

And with some of its buddies:

Side note: The small spray bottle is full of bleach water - as the chopping block (aka: birch stump) sat on the concrete floor it would mold on the bottom. A quick spray from time to time took care of things until the stump finished drying out.

3 comments:

  1. Here I was, wanting to build a bucksaw for my mountainman camp. I googled for ideas and who do I find but Dan. I've been thinking about you guys. I sure do miss you. Great Website. You've been busy. Give Celena a big hug for me and kiss that beautiful boy of yours. All our love from Bend Oregon.

    Chris

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  2. Chris! What a nice suprise! I just love this internet thing! How is the mountainman stuff coming along? Fired up the forge lately? I still haven't made mine yet - how about coming up and helping me?

    You should write a blog on your knives!

    Big hugs back to you and Jennie!

    - Dan

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  3. You correctly identified two points of weakness. But your solution to the second weakness is flawed. The original stretchers were straight pieces bent using steam. The forces generated by the turnbuckle were applied to the ends. That's very strong which is why they could use such narrow stretchers.

    Your solution isn't a bent stretcher but a straight one that's been cut to resemble the general concave shape of the ones it replaced. Because it's a single straight piece it doesn't put the force on the ends. Rather it puts torque on the middle. That's made even worse by making it narrower in the middle where the torque is greatest.

    Your stretcher would have been much stronger if it was straight on the bottom and convex on top. Your stretcher still looks like a substantial piece of wood. So I doubt it will be a problem. But if it ever is then you should change it to look like this Amish one.

    https://www.lehmans.com/images/product/large/572.jpg

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