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  1. #31
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    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..

    Cheers,
    IW

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  3. #32
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    Feb 2019
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    Quote Originally Posted by IanW View Post
    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.
    I totally agree. The way I imagine the tensioning in a saw plate working is similar/analogous to the tension created in corrugated iron. With this in mind is sort of makes sense to me to tension the blade in more parallel positions along the width of the blade. I didn't know that about band saw blades - very interesting. I might try and find somemore information about this as I plan to purchase a band saw in the comming months.

    Quote Originally Posted by IanW View Post
    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......
    When the time comes I plan to do a test and compare between blades - I will report on my findings.


    Quote Originally Posted by IanW View Post
    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..

    I really like the idea of crimping the back onto a piece of plate thinner than what the back is intended for. I was thinking I could try this using a set of feeler gauges, this way I should be able to get a really consistent gap.


    If you were to guess, how much smaller would you make the slot than the blade to fit into the slot?

    Cheers

  4. #33
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    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.

    Regards
    Paul
    Bushmiller;

    "Power tends to corrupt. Absolute power corrupts, absolutely!"

  5. #34
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    Quote Originally Posted by CBaulds View Post
    ....If you were to guess, how much smaller would you make the slot than the blade to fit into the slot? ...
    You have me there, cobber. If I were wanting to try using a 'buffer', I'd try a piece of plate or shim stock about 5 thou thinner than the intended saw blade, but that's purely a guess, it may be too much or not enough. I think you'd find using a feeler gauge a rather awkward exercise, the holder will get in the way & the feelers will be even shorter than your vice jaws (& btw, use aluminium or wood inserts to prevent seriously marking the brass, if that hasn't already been mentioned!). You may cause yourself more bother than you save.

    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...

    Cheers,
    IW

  6. #35
    Join Date
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    Default Brass Back Slitting

    Quote Originally Posted by IanW View Post
    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...
    Ian has hit the saw back right on the spot lol.
    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.

    An FUN.

    Cheers Matt.
    Last edited by IanW; 20th Apr 2019 at 07:20 PM. Reason: fix quote

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