Saw back types, what else have we come up with besides folded and slotted?

Discussion in 'Saw Makers Forum' started by Force10Matt, Jul 15, 2022.

  1. Force10Matt

    Force10Matt Active Member

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    So, I've been playing in the machine shop this week making a batch of slotted backs, whilst doing so I've been dreaming up other designs of backs and means of making them grip the plates. I've had some success with mechanically adjustable hinged design but it's in it's infancy and a bit heavy and clumsy, if i get it to a point where i'm happy with it i'll share it here. Anyway, it got me thinking, The only other type of backs i've seen are the excellent self tensioning ones that Shane Skelton makes, either with a built in spring or a hidden screw. I'm curious to know if any of you folk have experimented with alternative back designs?
     
  2. shoarthing

    shoarthing Most Valued Member

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    "Folded" is quite a broad term, re: saw-backs, esp. before around 1830 . . . but yes; Mr Skelton's new tensioning-designs appear to permit reliable use of thinner grades of modern saw-plate than slotted-and-pressed backs.
     
  3. Dusty Shed Dweller

    Dusty Shed Dweller Most Valued Member

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    Anything that doesn't allow the plate to be held under tension is a waste of time - 200+ years of saw making and material science says so. Tension is essential because it's what keeps saws tracking properly.

    Slotted backs are OK for many users, but anything that locks the blade in place (also a rusted plate in a folded back) has very little compensation factor and eventually you'll mung it. Then, how do you fix it?
     
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  4. Force10Matt

    Force10Matt Active Member

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    I'm with you Dusty, Although I make a few slotted and bonded saws I do vastly prefer folded backs especially on larger saws, I've had good results with slotted backs on the dovetail saws I make but they're quite shallow depth plates and fairly unlikely to warp, I've never had much luck with slotted designs on saws with larger, deeper plates. The one I'm working on at the moment is 17 inches long and 3 and a half inches deep, I couldn't risk using a slotted and bonded back as it's just too likely to get written off. It's the adjustability and repairability that's got me scratching my head, I really like how slotted and bonded backs feel in use and am messing around with designs which replicate that feel without sacrificing the ability to adjust should it be required. I was just curious to see if any of you had also played about with your own designs really.
     
  5. Force10Matt

    Force10Matt Active Member

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    25
    So here's the design i've been working on.

    An adjustable, slotted back.
    The back has a slot cut both sides, the plate sits in one side and the other side is drilled and tapped with a grub screw every 20mm with spacings alternating left and right to give a screw every 10mm, when the screws are tightened they force the top slot apart and the bottom together clamping the plate, The top screw in the handle passes through the back and blade pinning it all together, you can then nip up few screws at the toe, pull the blade tight and rely on them to hold the blade stretched between the toe and heel while you tighten the rest of the screws down. The 42 screws are lubricated, m4 and tightened to 50 N.cm, which if my maths is correct gives me a clamping force over the total contact area within the back of 3.2Nmm2 or 464psi. In human terms, it aint moving unless you want it to. _MG_7312.jpg _MG_7315.jpg _MG_7317.jpg _MG_7319.jpg _MG_7320.jpg

    This one was just a proof of concept, forgive me the sloppy execution, i wanted to avoid pouring days and days into a project that diddnt pass go.

    In use the saw feels different to either a folded or slotted back, it tracks a line effortlessly, has that zingy feel that a good folded saw has but also somehow feels like a slotted saw. it's just a little on the heavy side for my taste but then again it is a little over 17 inches long, i think if i go down this route again i may taper the depth of the back and adjust the torque of the screws along the length of the plate to compensate for the alteration of leverage and clamping force on the blade, it'll allow me to shave off maybe an ounce and a half from the weight at the toe, perhaps even a make Disston no9 style protruding toe? Perhaps i'll just suck it up and remember that bigger saws weigh more.

    I'm keen to hear what you lot think of the design.

    Cheers

    Matt
     
  6. shoarthing

    shoarthing Most Valued Member

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    61
    Hi - great fun, & admirable you've given this slot & counter-slot concept an empirical outing. Interesting to hear your future experiences, as you continue to use & adjust this saw . . .
     
    Last edited: Jul 23, 2022
  7. Force10Matt

    Force10Matt Active Member

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    25
    Cheers shoarthing, I'l keep you updated.
     
  8. Charlie Earnest

    Charlie Earnest Member

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    8
    Matt, the saw looks good but wouldn’t it just be easier to use a friction fit. A friction fit, if done correctly, accomplishes the same thing as a folded back and is allows for removing the spine as well as getting rid of problems in the toothline.

    I’m also curious as to how the screws pull the plate and introduce tension. It seems to me grub screws are providing clamping pressure and that compression is directed perpendicular to the tooth line simply holding the plate rigid. Which of course is what most backs on saws do and what they are meant to do. I recently made a dovetail saw that used no clamping pressure on the plate where it was inserted into the spine. I used three screws I made that simply passed through the plate and spine in order to hold the plate in place. The handle hardware didn’t pass through the plate either. Instead it simply applied pressure to the plate to keep it straight and from wandering laterally. The saw worked just fine and since there was nothing passing through the plate in the handle the plate wasn’t being put into compression when jamming up against the flat screws on the push stroke. My thinking is that this sort of system would allow for a plate to heat and cool, stretch and shrink without interference thereby reducing distortion in the saw plate that normally occurs during hard use.

    The saw is pictured below. It’s a single piece of bubinga shaped to look like a Kenyon dovetail. It utilizes a patent by Woodrough and McParlin that was never produced, although I’ve taken further than their patent and added a few things of my own.
     

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    shoarthing likes this.