Canted saws

Discussion in 'Help Forum' started by Peter Barnes, Aug 21, 2018.

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  1. Peter Barnes

    Peter Barnes New Member

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    2
    New to posting generally, new member.
    I've read through the articles on canted saws and there is an aspect not covered as far as I can see.
    Done many years as a professional tool restorer with a special interest in saws.
    I found that refitting the back to the blade frequently results in a wobbly edge which I learned to cure by tensioning the cutting edge of the blade, top front of back vertical on bench, striking firmly down on front teeth with nylon mallet.
    This has the effect of pulling on the toothed edge, the back holds most of the blade length and the blade is driven slightly into the front end into the back, instant cure, usually.
    I discovered this myself but it occurs that it may have been common practice in the trade with the end result that blades are repeatedly driven in at the front whenever it looses tension for whatever reason.
    I realise that this doesn't impact on the early canted illustrations but it would explain why 95 % of used blades are canted, mostly all the way in.
     
  2. fred0325

    fred0325 Most Valued Member

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    Hi,

    It is always nice to have someone posting who is working with saws, especially repairing as opposed to manufacturing from scratch. I will hold my hands up and say that I know little about this subject except for a few rather desultory efforts at saw blade bashing in order to take out waves and kinks, and with varied and probably random success.

    I find it fascinating that you use driving the saw blade further into the back at the front in order to re-tension it. I have never heard of that before and it would be interesting to know if anyone else has. Conventional tensioning, and certainly tensioning as I have (very badly) practiced it, I have always believed relies in striking the plate with a flat head or very large radius hammer head around the area to be straightened in order to to put minute concavities into the plate. These (ideally invisible) concavities put the tension back in the plate if positioned correctly. As an example of how it should not be done, I have one saw that looks like someone has taken the wrong side of a ballpein hammer to the plate and has put a neat line of "dings" all the way down the blade just above the tooth-line.

    I can see that the method that you describe would put a cant from back to front on the blade, but this must have a limit to the amount of cant that it can impart. On some blades that I have seen the cant is much greater than could be achieved by this method alone and must either have been done at manufacture for some reason or during usage by purposeful or overly enthusiastic differential sharpening.

    (I haven't read any of the literature and so stand to be enlightened upon what the reasons for canting are thought to be).

    If my memory serves me correctly, there is an article on this site somewhere discussing the shape and positioning under the back of blades of 18th/19th century saws. The blades in question were not straight lines from back to front, but were pared down at the front forming a sort of curve/angle in the blade under the back. Have you come across one of these blades in any of the saws that you have repaired, and if you have, how did it work out?

    Fred
     
  3. Peter Barnes

    Peter Barnes New Member

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    2
    Hi fred,
    I think that saw doctoring as you describe it is confined to handsaws and circular saws, not sure it can work on a backsaw, happy to be corrected.
    It is easy to demonstrate the effect I'm describing, take any old backsaw, put blade in vice with a 3mm gap below back, use a strong screwdriver to lever the back up at the front end by a mm or two, then look at the blade, a significant bow has appeared side to side.
    To correct it, front of back on bench and strike front teeth firmly as above, problem disappears again.
    Ovbiously the blade can be levered out sufficiently to render it uncanted [if there can be such a word], then straightened as described, usually leaves a horrible line where it was but fairly easily cleaned off.
    Peter
     
  4. Dusty Shed Dweller

    Dusty Shed Dweller Most Valued Member

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    93
    My two cents worth. I have some theories on canted saws based upon repairing thousands of them.

    1. Some saws were purpose built from scratch with a cant. These tend to be older (<1850), very light saws with narrow plates (say 2" or so) for dovetailing and fine joinery etc and I think the theory is that it makes it easier to cut to a baseline if the saw is canted.
    2. Most saws (especially those with a plate wider than about 3") acquire the cant because the user adopts the simplest way of getting rid of the wavy toothline issue - by knocking the front end of the back/spine down, which tensions the plate and pulls it straight. This creates a cant.

    When disassembling backsaws I find in the greater number (I reckon 90% or so) of cases the plates actually aren't tensioned - most are what are termed in the trade "slack". They rely on the back to impart enough tension to keep the blade straight. I reckon there is a lot in that. If Dissto nand S& J etc didn't smith the plates then that must mean something. The technique for fitting a spine under tension is simple and goes;

    1. Immobilise the plate in a wide jaw vise.
    2. Insert back/spine from the toe end- slip the slot over the nose from above and work the spine down along the length of the plate with a mallet
    3. Most important- when positioned give the spine a horizontal rap from the handle end to tension the plate into its final position.

    Hammer tensioning in backsaws is adopted to repair lumps and kinks arising from misuse. You'd want to be careful doing it because it does distort the plate (you're kind of distorting the plate in a controlled manner to remove distortion). If you mess it up I have a devil of a time repairing it for you. I hammer smith all mine because I prefer the feel but backsaws are very tricky.
     
  5. Dusty Shed Dweller

    Dusty Shed Dweller Most Valued Member

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    93
    Another characteristic of canted saws.... ever note how canted saws always have a pistol grip handle? You don't find canted gents saws or cants on saws with "stick" handles. I reckon this is due to the physical action of the human arm and wrist when cutting.... with stick handled saws some lateral wrist motion comes into play which a cant would exacerbate. With canted dovetail saws I can see how the reciprocating motion of the arm can use a cant to advantage - it assists cutting to the "view" side of a baseline. If your wrist is locked in position (as it should be) it is difficult to angle the saw to strike the baseline on the view side of the cut first - a cant assists this.

    Personally I can split a line with just about any backsaw made but I cant do it with a straight handled saw. It's because my wrist doesn't reciprocate a single vertical plane.