Fitting the Back to the Blade, Cont'd.
While it stayed on the blade, I could easily pull it off with just my hand - not good enough for my purposes. I started the same process as above, where I was hammering the bend of the brass (but this time with the blade installed) to tighten its grip on the blade - again, in 1" increments, on both sides of the blade until it held it firmly: Occasionally, as the back bent, it was necessary to tap the blade in a bit so it remained fully seated.
This part is very hard to explain, as it's more about the feel of the hammer as it comes down on the blade. You reach a certain 'happy point' where it all seems to come together. I did twelve backs, total (screwed one up, so only eleven saws were made) and I was happy that I had plenty to practice on. By the last one I was really starting to "get it", and the work was coming out much quicker with much less work to remove the hammer marks. You have to work patiently and not forcefully, but not necessarily timidly either.
I can't stress the importance of the anvil, either. The one I screwed up was one that I was working using the "anvil" on the back of my machinist's vise. I was having a heck of a time getting it straight, and eventually produced stress cracks in the brass from working it too much. Eventually, I learned that it really didn't take nearly as much working as I had originally thought it would and that in fact - the less I worked the brass, the better.
Here you can see an end view after I've flattened for it's entire width over the blade:
There it is - the back is installed. However - no matter how careful you are, there is bound to be some damage done by the hammer or bending or what not that you've done to it by this point:
You can kind of see some of the scratches that were made by the brake in the bending process, but what you can't see is there is just a bit of waviness that's been introduced into the brass during the hammering process. The best way I found to clean up the blade is using a belt sander, clamped upside down onto my bench. For really rough work, a 36 grit belt removed material quickly, but leaves too coarse of a finish. It's best to work that up to at least 120 grit belt (toward the end, that's all that was necessary) to get it to a fairly nice "brushed" finish:
You can see some of that waviness I'm referring if you look closely in the reflection of the light, at the top and just to the right of center of the back in the saw above.
While you're sanding the back, the brass can get pretty hot - it's a good idea to keep a bucket of water handy to cool the blade off with, so it doesn't get too hot and begin to lose it's temper. Keep a towel or something handy to dry the blade off with when you're done, because you don't want the blade to start rusting again! For underneath the back, it's not as important to keep the the steel from rusting a little bit. It might even be a good thing - a little bit of rust might help hold the blade in place.
Once I get the marks worked out, I sand the back to about 220 grit. That brushed finish that's left is not the final finish, however, but it's good enough for this stage, as there is still lots of work to do to the blade, with many chances to mar that finish. Therefore, once the hammer marks are worked out of the brass, it's best to leave that final finish until later.
There's one last step to shaping the blade, and that's cutting it to length. The final length at the back needs to be about 5/8" (* see below for comment *) longer than the back, to allow you to attach it to the handle with enough blade to hold the screws. I also cut off a slight angle right behind the brass to fit the handle better, angled down slightly to the approximate location the blade will protrude from the bottom of the handle:
- Added 10/6: Again, I've had the opportunity for others to use these, and have had the comment that the blade should be closer to the handle. The way to accomplish this is to make the final length at the back needs to be about 1" longer than the back rather than 5/8" as stated above, then cut the blade at a steeper angle (closer to 45 degrees) where it fits into the handle. You'll need to account for this steeper angle when sawing the slot in the handle that accepts the blade.
It's a good idea to file off any burrs that are left over from cutting off the blade, and the other end of the blade. I'll give it some finishing touches later.
The blades are now ready to be installed into handles and sharpened...