Sunday, November 15, 2009
Making A New Turning Saw - Part V
There wasn't much left to do on the saw, but it still took me awhile. I snuck in one short work session during the week and one longer one today and the saw is done! Wahoo!
To mount the knobs and rods I had to bore holes through both arms near the bottom. First I had to rework the bottom section of the "handle" arm. I had left it wider than the other arm, and while I am sure I had a reason, I couldn't remember why I had done that, and it didn't allow for enough of the rod to clear the arm. While using the spokeshave, I went ahead and reworked the curve in the bottom of the stretcher to more closely match the curves of the arms. After that, I used a brace and bit to bore both holes.
Here's a shot of the saw, at that point:
That was all I accomplished during the week. Today I moved on to mounting the blade in the rods. After filing a flat to stop the bit from sliding off the bolt, I used my small hand drill to make the holes for the pins that would hold the blade. I experimented a little here, and heated the first bolt to red hot and let it cool. I wanted to see if it made a noticeable difference. It didn't. Hmm. That's the opposite of what I experienced with the bolt heads. Maybe I'm mental. I don't suppose bolts have that much carbon in the steel - so no dramatic change makes sense.
Here's a shot of the first bolt in the vise:
Then, using a hacksaw, I cut the slots for the blade. I returned the drill bit to the hole to help me align the slot at right angles to the hole. Here's the result:
Now it was blade time. I assembled the saw and measured the distance between the pins (3p finish nails) in the rods. Then I subtracted 1/16 of an inch and I had my distance for the pin holes in the blade. This would bring the bottoms of the arms together slightly, allowing for the blade to be stretched taught when the tension mechanism pulled the tops of the arms back together, and the bottoms apart. The 1/16th was just a guess. Turned out I should have made it more like 1/8th, but I'm getting ahead of myself.
I cut the blade with an extra 1/4 inch beyond each hole location. Here's my high tech band saw blade cutting apparatus:
It worked great and had no trouble cutting the 1/4 inch blade. The vise allows for more control and the use of body weight to assist with the cut.
To drill the pin holes in the blade, I just clamped the blade to a piece of scrap and had at it. It took some pressure to get started, but once it did, the bit had no problem. I did use my fist under my chin to help apply steady pressure on the handle of the hand drill.
I have heard of other's punching holes in the blade with a hammer, a punch and a block of hardwood (end grain up). I tried this before and didn't have good results. For whatever reason, I've had much better luck with just drilling. Maybe my blades are cheap or something...
Once the blade was mounted in the rods I could make the simple tensioning system. I cut about 12 feet or so of twine and soaked it liberally with mineral oil. It's my pet theory that the oil allows the fibers and strands to slide over one another and "self adjust" so that they all share the load equally. I have no proof that this works, but I dramatically reduced my breakage rate once I started using this approach.
To apply the twine, I wrapped it around one arm several times and then started looping it around both arms. When I ran out of twine, I wrapped the running end around the loops several times and then passed it through between them. I inserted the toggle stick between the loops and started winding. As the twine twisted tight, the extra oil got squeezed out. I just rubbed it into the saw.
To test the blade tension, I plucked it with a fingernail. Here's where I realized that I should have shorted the blade holes by 1/8 rather than 1/16 of an inch. The tenons were fully seated and the blade was not fully tensioned. The real fix would have been to make a new blade, and I probably will - at some point. The temporary fix was to put a washer between each knob an the frame. I kept on applying tension until it started to sound musical; changing from a "thunk" to a "twang!"
Time for some test cuts. Not very pretty, but that was my fault not the saw. I wasn't really watching what I was doing: I kept looking at the saw to see if it was flexing or moving. Nope - ship shape! It worked great.
Here's a final shot of the new turning saw posing in front of its predecessors:
Oh yeah - when I took that last picture, I had forgotten to snip off the nails that are functioning as the pins to final size. Quick work with nippers - should have done it before the picture. Doh!