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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
    Commented Oct 14, 2020 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
    Commented Oct 14, 2020 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
    Commented Oct 14, 2020 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
    Commented Oct 14, 2020 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
    Commented Oct 14, 2020 at 15:47

5 Answers 5

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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
    Commented Oct 16, 2020 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
    Commented Oct 16, 2020 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.
    – user5572
    Commented Oct 20, 2020 at 12:46
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An alternate answer!

While reading "A Little Book of Woodworking Joints" I ran across this figure:

Setting Bevel to Angle for Dovetailing

The chapter on "Simple Dovetailing" has this to say about Fig. 20:

A very good method of setting the bevel is to obtain a piece of board and set up a square line as shown in Fig. 20, and mark off six units — size 1/2 in., say — and then to the left or right along the edge mark off one unit, then drawing the splay line shown, give a line so that setting a bevel to it as shown makes the inclination — or angle — of the blade with the stock 6 to 1, which is probably about the best angle for dovetailing.

To my eye, the sharp angle on the bevel makes it very easy to set the dovetail angle in this manner to a known value by using a shop standard gauge of some sort.

A square end would work, but it wouldn't be as easy to read (in my opinion) and other shapes (a reverse angle, rounded) would make this sort of the bevel-setting impossible.

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    As the picture shows, though, you really don't need any particular end to set the angle... the blade has to cross the horizontal mark just as accurately as the vertical one, and there's no point there.
    – Caleb
    Commented Nov 15, 2021 at 20:51
  • As I said, the point does make it obvious and easy to read. If you want to reduce parallax errors, an acute point is better than a right angle or larger for meeting a mark. It's why pointers are pointers.
    – user5572
    Commented Nov 15, 2021 at 23:20
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It's a reference angle for a few things but mostly its just more accurate at checking depth. Some older slide bevels will actually have the angle stamped onto them. Think of it this way, a point has less surface area to be effected by the surface of material it rests on. So you get more accurate depth measurement. This is important when cutting things like dovetails because you can check the depth of one part to another to match them perfectly, even on angles. Use it by placing the handle flush to the top surface of what you wish to measure the depth of. Slide it down until the point is where you wish to measure to. Lock it in. You then can transfer that depth, including angle to the edge of a board place the handle flat and place a straight edge up to the point. Now you have your depth for the new piece. Draw a line down your straight edge to mark it. If you measured angle as well all you need to do is slide the bevel to known positions along the boards edge, mark, then fip the bevel and mark the mirror cut.

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  • Hi, welcome to StackExchange. Although clearly a sliding bevel can be used in this way (if there's space) nobody seems to, that I've seen. And I don't recall ever seeing it recommended in a text. There are many tools made specifically for this task, as well as others that can (and more efficiently) as one of a range of purposes, perhaps the classic example that comes to mind is the combination square although their use in woodworking shops is comparatively recent. But in addition many vintage examples of user-made depth gauges strongly suggest this use would not have been common in the past.
    – Graphus
    Commented Apr 17, 2023 at 7:25
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I believe that the 45 degree on the blade allows it to slide completely away into the wood to avoid injury in a tool box. The end of blade isn’t square or rounded because the kerf cut into the wood is cut on an 45 degree angle to reduce the chance of the wood splitting.

I suspect that few tradesmen ever slide the blade away. I have quite a few vintage sliding T bevels and some show rust pitting on the angle that they were left for years with the pointed blade exposed.

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