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Does anyone have a good reference for the reason a typical wood or metal sliding T-bevel comes to a point?

I've always wondered, and recently this tool came up in a semi-famous YouTube video, which rekindled my curiosity. I asked in the YT comments, and someone suggested the point would not be in the way when taking inside measurements, but this seems a reach, as the point angle is fixed.

Some basic searching did not come up with anything concrete, and my venerable Encyclopedia of Woodworking Handtools does not mention the point.

My only poor theory is that the bevel on the point nests nicely inside the stock, so this might be a way to make the bevel a handy straight-edge. (Except mine is is a terrible straight-edge!) Or just so it seats nicely and locks into position for safety of the user and to protect the tool in a toolbox or drawer.

I also saw one reference to the point being handy for marking, which seems like a terrible idea (and another reference specifically called out making sure the edge of the point on a smaller version was dull for safety in a pocket).

Since the bevel along the short edge of the blade itself is some known angle (typically 45 deg.), I suppose there might be marking out techniques (saw, dovetails or similar) where the bottom of the point bevel would be parallel to some reference, useful for squarely marking out the bottom of the waste. Though, given that tails and pins would often be cut at completely different angles from that bevel angle I can't rationalize that, either.

Regardless, all my searches, if they mention the point at all, are inconclusive.

Does anyone know, either from actually using it for a specific reason, or by citing a reliable source?

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  • Interesting.... I hadn't thought of this but you raise a good, er, point. What is it for, and if it is for something (supposedly or in reality, doesn't matter) why isn't this stated and/or widely known? I hope it doesn't amount to convention — so someone made them this way and for whatever reason it just became the way these were done — because then it'll be like the saw nib on old panel saws, where every guy, their aunt and both cousins will have their own (competing) theories. And are only too happy to argue theirs is right and everyone else's is wrong until the cows come home.. [contd] – Graphus Oct 14 '20 at 11:35
  • Now FWIW, some plans for the shop-made variety specifically have a flat end (or maybe two rounded ends) because it simplifies production so much. This doesn't tell us anything however. Although come to think of it, some of these might not be sliding bevels. I'll have to go check some references and get back to you. – Graphus Oct 14 '20 at 11:38
  • I think what I've picked up that this allows the blade to seat into place, while still being easily swung open (although just in one direction) giving minimal gaps which, while desirable, is hardly vital. Small gaps seem to just be something that craftspeople find important on some aesthetic level. If gaps weren't important the end could just as easily be square and the bottom of the 'mortise' ditto, but deeper to clear the corners on the blade when it was swung open (and in either direction). If the blade being able to seat isn't important it strikes me that a more elegant solution [contd] – Graphus Oct 14 '20 at 12:52
  • is matching curves to the blade end and the mortise bottom, the radius of the curve being equal to the distance from the pivot to the end. This way you get aesthetically pleasing tiny gaps and the bevel can swing open in either direction..... which I think is actually desirable, but it's a very minor point to be fair. Somewhat similarly, square blade end and square mortise bottom but the slot is cut longer allows for similar gaps. The blade only needs to be lifted a little (maybe 1/2" at typical bevel sizes?) to swing free, again in either direction. – Graphus Oct 14 '20 at 12:58
  • It's so you can... Wait, no, it's because... Well, maybe... Nope, no idea... Actually, fitting the blade into the case is the only real reason I can come up with. It doesn't need to be 45°, 2 or 3° should do the trick, but 45 is obvious so you don't try to put it in backwards should you remove the pivot screw all the way. – FreeMan Oct 14 '20 at 15:47
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I think the only answer, so far, is that there isn't a specific or vital woodworking reason.

Perhaps, a weak argument can be made that it allows the tang or blade to fit nicely into the stock. This agrees with the few references to this I've been able to find anywhere, including this one from the comments:

"The slot end is rounded whilst the other is cut off at an angle to enable it to open."
Charles Hayward, How to Make Woodwork Tools, 1945

But I am unable to find any other historical reason for this typical design. And, as pointed out in comments, some sliding T-bevels don't have this feature at all!

I did see one suggestion that you can stand the T-bevel up easily on that bevel to make setting up a saw to a common 45 degrees easier. This seems reasonable, except:

  • The sliding T-bevel predates circular saws by many decades (centuries?)
  • Maybe a function of cheap "Mastercraft" tools, but the bevel on mine is vaguely between 43-44 degrees when I check with a protractor; I'm hard pressed to see how you wouldn't just use the T-bevel itself in the manner it was designed, and use a measured 45 degrees instead of relying on some potentially incorrect machined bevel.

I'm going to call it, and say this is a matter of tradition and maybe ease of use. Having the blade tuck into the stock like a folding knife is just reasonable.

I'll leave this one open for a bit in the hopes I'm proven wrong!

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  • FWIW I have had only a few of these pass through my hands (it's not a tool I would typically pick up seconhand to restore for a couple of reasons) and the angle has not been an exact 45° on at least a couple — I didn't check but it was visibly more acute than a 45, and I've seen more obtuse ones too (but there's a chance those were user-modded due to damage to the point). My 'keeper' bevel I remember checking at the time and it is 45°, but not dead-on accurate. – Graphus Oct 16 '20 at 7:48
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    Re. the weak argument about this allowing the blade to seat, I found one reference (and it is Charles Hayward so many would consider this gospel, but he's just speaking informally and, well, he's not 100% reliable...) and it merely says, "The slot end is rounded whilst the other end is cut off an an angle to enable it to open." The angle in the associated image is much shallower than 45°. – Graphus Oct 16 '20 at 7:56
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The cut end provides a point for drawing your angled line up to a corner or an obstruction. Much the same as a drafting square (those triangular drawing tools) allow you to reach the point toward your final drawing destination.

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    A drafting triangle is a triangle, though. and the points are part of the lines you might want to draw. This true for the sliding bevel if you swing the blade over completely, but then the outside edge of the blade will often interfere with getting into a corner. So the utility of this is maybe limited to a small arc. Maybe for drawing or marking out to a corner, but you can do this with any straightedge. Perhaps you can provide a drawing showing what you mean, because for me it does not add up. – jdv Oct 20 '20 at 12:46

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