Thread: Brass Back Slitting
15th Apr 2019, 09:08 AM #31
A comment I meant to make yesterday was that tensioning one edge of the blade only is a bit counter-intuitive in my view. Hand saws are tensioned along both top & bottom edges, which seems more logical, as it forms an even "pull" on both sides which serves to resist bending of the blade either to left or right. I know bandsaw blades are tensioned along one edge only, but that has a specific purpose to do with tracking as the blade heats up. Even the most frenzied sawyer I've seen wouldn't generate the warmth of a bandsaw blade.
So, being both lazy & unconvinced, I'm happy for someone else to put the effort into research and development on the merits of tensioning backsaw blades. If by chance it turns out to be a very good idea and the proof is convincing, well, dammit, I guess I'll just have to learn another skill. Though I may have left it too late for that......
And Matt had the same thought as I did re crimping the back with the plate in place. Because of springback, you need to over-crimp a little, which is a lot harder if you are crimping against a sliver of spring steel. It might work well if you have some thinner plate than the blade the back is intended for. It's not too fraught if you take it easy & test frequently, you'll quickly get the hang of how much of a squeeze it needs to get the desired effect. I concentrate on getting several inches at the front & back of the spine to the right tightness, the middle section isn't as important, imo. When adding the spine at final assembly, start at the handle end and tap the corner on, then tap it down bit by bit. The plate should feed in nicely as you go. If you try to tap it on all at once, it's far too difficult to keep the entire blade & slot aligned with just two hands!
If by chance you over-crimp severely, you could always run it along your slitting saw again, & start over. Been there, done that early-on..
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20th Apr 2019, 06:39 AM #32Intermediate Member
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If you were to guess, how much smaller would you make the slot than the blade to fit into the slot?
20th Apr 2019, 07:36 AM #33
Could it be that the backsaw is tensioned along the tooth edge only because tensioning of the top of the plate is achieved as the spline is tapped on to the blade from the toe? This clearly can only be accomplished if the kerf has been closed up to less than the thickness of the plate and would not work for splines or backs that are glued in. However traditionally the folded back, and in modern times the back that has been slitted and then closed up a little, would achieve this.
"Power tends to corrupt. Absolute power corrupts, absolutely!"
20th Apr 2019, 10:30 AM #34
You may be over-thinking this, it really isn't all that difficult to get a nice closure of the slot if you are careful, just give it a bit of a squeeze, test, squeeze slightly harder if necessary, & so on. You'll quickly get the feel of what is needed for your particular spine/plate combination. And although the squeezed slot might be slightly uneven if you were to check with an electron microscope, it can't be any worse than a folded back. The slots in some of the commercial backs I've seen are far from perfect...
20th Apr 2019, 11:30 AM #35
Brass Back Slitting
Having had a little metal work experience, I often find a lot of apprehension towards metal work.
An I come across a lot of “over thinking”, metal in some ways is better than wood it can be reversible(Car crashes [emoji849][emoji849][emoji849]).
Get some scrap off cuts and start bashing metal it’s actually quite a fluid material.
Last edited by IanW; 20th Apr 2019 at 07:20 PM. Reason: fix quote
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