There was a recent discussion over at WoodCentral on the Hand Tool Message Board about the cranked bow saw blade used for making dovetails, well at least the pins. I first saw the blade in Salaman’s Dictionary of Woodworking Tools and put an illustration of the blade in Shepherds’ Compleat Early Nineteenth Century Woodworker in 1981.
I have made several of these blades and as a matter of fact I made two this morning and took some pictures. These are 11 ppi band saw blades, not the greatest blades in terms of set but the number is good and the steel is good.
This is the setup in the vise, this is a shorter vise than I have used before by 1/2″, this one is two inch. I heat the blade to cherry red to remove the hardness, allow it to cool slowly and it is annealed. I then heat the blade between the marks, use chalk or soapstone to mark the blade in the center, and place it in the vise as above.
This is the first bend, which I do with a small square face hammer, then heat the blade again and pound it over until it is about 45 degrees.
I heat the blade up again in the vise, be careful as the vise does get warm. I then beat the blade flat over on the top of the vise making the 90 degree bend. I use a brad punch to drop the teeth at the heel down to the vise top. I then work over the teeth with a brad punch (nail set) to get some set back to the teeth I have just hammered.
I then sharpened up the teeth as needed and it is ready to go. It is not that hard, you can use a forge or a gas torch to heat the blade, a vise and a square face hammer and nail set. You will also need a triangular file to touch up the teeth.
Here are the two blades I made this morning, it took less than an hour to make them. I had intended to make only one, but the first one is cranked the wrong way. Make sure you are bending the blade in the right direction. I had one in my bow saw in front of me and still got it wrong. The odd angles of the blades is normal, when put under tension in the bow saw it straightens out.
I don’t harden the blade again after I am finished, because I don’t think it was that hard to start with. Now while most of the work I do is in pine, it works well on poplar, so I am not too concerned about hardening the teeth again. The first part of the blade is rip, when I do touch up the teeth at the bend I do put a bit of an angle to them, I also whet the entire blade, both sets of teeth to insure a smooth cut.
The hardest part of making the blade is getting the crank in the right direction. Give it a go, it is easy.
I had problems putting up this post, I got dumped a half a dozen times and thought it might be an omen, but I don’t believe in omens.
Stephen
Omens — on the Day of the Dead? Nah!
I like to see when someone else turns something the wrong direction. I have learned to say that I’m making it for left-handers, but now that I live with one, that excuse doesn’t work as often.
Ken
Comment by Ken Pollard — November 1, 2008 @ 6:29 pm
Wow, Is there a picture of how this blade works in action? Or video?
(By the way, I like how your pictures are always annotated with that black/white ruler…I’m guessing it’s 1″, right? Gives a good sense of proportion/scale.)
Comment by my name is adam — November 1, 2008 @ 7:30 pm
Ken,
So your partner is a lefty, well there is nothing wrong with that. Being dyslexic, I have an excuse, I can get the geometry right but then my brain flips things around.
Adam,
Yes the Gnomon is 6 inches long with one inch contrasting blocks, yes I will post something on how it works.
Stephen
Comment by Stephen Shepherd — November 1, 2008 @ 7:41 pm
Here is the link to the video:
http://popularwoodworking.com/article/klausz
I had heard about the video before, but I had never seen it. For that matter, I had never seen a bow saw used. I now have a new tool on my wish list. At the top.
Comment by Luke Townsley — November 1, 2008 @ 7:47 pm
Luke,
Thanks for the link. I have two bow saws, I needed a second with a straight blade as I use the bow saw on a regular basis and I use the cranked blade for dovetails and just to show people how it works.
Stephen
Comment by Stephen Shepherd — November 2, 2008 @ 5:38 am
Wow indeed impressive action with that twisted blade, must try that..
Bob, who althought not dyslexic has managed to cut things the wrong way, more than once. I know makes lots of markings on my pieces…just in case
Comment by Robert Demers — November 2, 2008 @ 7:48 am
Hi Stephen,
So how sharp is the corner at the bottom of the dovetail? Hard to tell from the two videos — which were both great fun, by the way. In the first video, though, he uses a ‘bigger hammer’ to get the two pieces together.
I’m guessing that you have to clean up the corner with a chisel.
Ken
Comment by KenPollard — November 4, 2008 @ 8:59 am
I have seen Roy Underhill, of Woodwright’s shop fame, use one of these saws. His had a very fine blade and very short transition length -from regular position to rolled over- of less than 1 inch. However, his blades tended to break easily, since the heating takes out the temper of the metal in the transition area and makes it weak. Also a tight bend tends to cause a stress rise in the metal.
Comment by John Williams — November 4, 2008 @ 2:00 pm
Bob,
I am dyslexic, so this happens often.
Ken,
The inside of the cut is quite sharp, the teeth cut on both planes and with a little set makes a sharp inside corner. I do trim up with a chisel if necessary. I have done boxes that required little chisel work. I use to use a chisel a lot, but either I am getting better, lazier or more daring because I now cut much closer to the line than in the past.
John,
Welcome, I have seen Roy use his blade and heard of his problems. My blade is quarter inch and while I have seen cracks on one of the blades, breakage isn’t much of a problem. I think the cracks on the outside only are just on the surface, but they are there. Other blades don’t crack. I continue to use the cracked blade to see when if fails, but I have been waiting a long time.
Stephen
Stephen
Comment by Stephen Shepherd — November 4, 2008 @ 4:27 pm