Why Do You Own A Try Square?

[Jim Koepke]

[edited]

The 9" was made by the
L S S co. Athol Mass. had no idea who that was and wondering if the 5$ I paid was too much.

LOL!

L S S stands for Laroy Sunderland Starrett. If you are worried that you paid too much there are likely many people like me who would be willing to pay you $5 and shipping if it would make you feel better.

jtk

[Rick Malakoff]

Sorry Jim, but thats a keeper the 5$ was for both!
Rick

[Patrick Chase]

For any question like that, there are a vast range of justifications but often just one true answer: "Because I have a Tool Acquisition problem".

Seriously, I have quality combo squares, double squares, and try and machinist squares. The combo squares can do basically anything the others can, but the ergonomics aren't as good. There's something to be said for having a tool that's just the right size for what you're measuring and no bigger. That's why people splash out big money for tools that are both slim/compact and accurate like the Vesper double square (I use mine all the time).

Avoid the Groz machinist "squares" though. The problem is that they aren't very square.

[Patrick Chase]

And here is an excerpt of a test that you should try for yourself:

{When I was a civil engineering student, the professors teaching surveying told me that errors tend to cancel each other out. After graduation, Professor Murphy taught me the truth: errors always accumulate. Test this for yourself. Dimension a board 10 inches wide and 10 inches long with the six sides/ends square/parallel. Using a square and a sharp marking knife (pencil/pen/scribe are too fat), spin a line across the grain and around the sides, and another line with the grain and around the ends. Begin each line on a fresh surface, indexing your knife blade in the previous line where it ended, and reference the square off a different surface when cutting each line. Does the last line meet the first line perfectly, or is there an offset? If there is an offset, the error may be the board. If so, ask yourself why the board is not square/parallel, and if that amount of unexplained error might tend to make a joint or a drawer square and ship-shape or twisted like a politician. If, on the other hand, the error might just be in the square, how do you check to make sure the square is good or bad?}

There were plenty at the time that thought this advice was nonsense, but not a single person that objected mentioned actually performing this test for themselves. Try it.

OK, I'll bite. Having done a LOT of worst-casing and error analysis, it all depends on the nature of the errors and specifically how correlated they are.

They seldom "cancel out" in the real world, except in some very clever designs/processes that are explicitly designed to achieve that. The best you can hope for is statistical independence, in which case the square root of the sum of the squares is a reasonable estimate. Strictly speaking it's only statistically valid if they have normal distributions or if there are a lot of errors of similar magnitude, but it's usually a good ballpark estimate for truly independent errors.

The problem is of course that errors are seldom independent. The case you give is a classic example of a single underlying issue that causes a whole bunch of errors to move in tandem. In that case they do indeed accumulate.

Here's a thought problem to consider to understand the difference: What do you think would happen in the example you gave if you randomly picked a different square from a different manufacturer to scribe each individual line?

The squareness of the wood is likely to be independent of any bias in the square btw, unless the square was also somehow involved in the trueing process.

[Patrick Chase]

The amount of out-of-square that a GOOD combination square can be (and I mean the HARDENED HEAD Starrett combo squares) Is so little that woodworkers needn't worry about it.

George brought this up a couple times, and I think it's worth clarifying: Most combo squares have a hard steel blade and cast iron head. The accuracy of the square is mostly determined by the machining of lands in the head's groove, and in an iron head those will inevitably wear a bit with heavy use. It's pretty easy to bring them back into true by filing, but if you want a combo square that will retain its as-manufactured accuracy then you should go with the forged-and-hardened steel Starretts. I have one and it's both the most accurate and most durable combo square I own. Of course that set cost enough that I baby it even though it probably doesn't need it.

The Vesper double square is similarly made btw.

[lowell holmes]

I do try to have one of each.

[george wilson]

George brought this up a couple times, and I think it's worth clarifying: Most combo squares have a hard steel blade and cast iron head. The accuracy of the square is mostly determined by the machining of lands in the head's groove, and in an iron head those will inevitably wear a bit with heavy use. It's pretty easy to bring them back into true by filing, but if you want a combo square that will retain its as-manufactured accuracy then you should go with the forged-and-hardened steel Starretts. I have one and it's both the most accurate and most durable combo square I own. Of course that set cost enough that I baby it even though it probably doesn't need it.

The Vesper double square is similarly made btw.

As I mentioned,Bridge City tries to ensure the lasting squareness of their combo squares by inserting a little hardened steel pin on either side of the clamp that holds the blade in the head. Not to belittle their efforts, but this system 's lasting accuracy depends upon a few things: 1; How firmly do the bottoms of either pin contact the bottoms of their holes? 2; What are those holes drilled into? Brass or wood? Brass, at least I would hope. 3; The pins are hardened, but are they harder than the blades of the squares? Is it possible for the tops of the pins to scratch the bottom edges of their blades ? 4; Brass is not as hard as normal cast iron. Certainly not in the same league as hardened steel. The hardened steel head will outlast the brass heads many times over. I think the ordinary Starrett cast iron head would also out last the brass head, too. Brass is attractive, and I have made many brass tools. Only where the last mentioned does not apply, though. But I would not use brass on a serious and expensive combination square.

I'm sure a few more of these questions could be asked,but these are all I can think of right now. I think there is no better system than the Starrett combination square with the hardened head. The Starrett system is a LOT more complicated to make than the Bridge city. They have to harden the heads, and have the means to accurately grind the bottoms of those very thin slots that the blades bear against. Bridge City possibly does not have the special grinding machine to accomplish this. And when they are finished, the Starrett hardened heads offer vastly more of a hardened surface for the blades to slide against. This is going to make the straight edges of the Starrett blades STAY straight MANY, MANY times longer than the comparatively tiny hardened pins of the Bridge City.

[steven c newman]

The reason I use the try square? Because the combo is usually set for a certain distance I want to keep checking. No need to square the thing, just set the depth/distance and leave it there. Then I can use the try square to square across, mark a cut line square to a preset mark.
tools1.JPG
Kind of lost in the normal jumble on the bench, but, there is both a small try square and a small combo square sitting there. Was doing 1/2Lap joints at the time. Combo was set to half the thickness of the boards, and left like that. Try square to mark a cut line to saw. Wide chisel to pop the waste off, another to pare it flat. Block plane to help out. Shoulder plane as needed.
DSCF0009.JPG
Seemed to work....

[Michael J Evans]

I own 3 aluminum try squares. They came in a pack that my mom bought me one Christmas. I really thought they were great at first (all I had was a couple smaller steel squares ) but the rules are beveled for some reason, meaning my knife or pencil can mark under the rule blade, which is super irritating. On the two larger sizes I used the pins that hold the rule and body together came loose and the rules can literally be wobbled up and down. I haven't tried any nice try squares but those have definitely left a bad taste in my mouth. Would like to get a nicer one someday for the reason Steven states.

[Derek Cohen]

Michael, I suspect that they are the same design as the one that Stanley and I posted early on in this thread. If so, they are for examining whether something is square, and not for marking. The thin bevelled edge is for that reason.

Regards fro Perth

Derek

[Patrick Chase]

I own 3 aluminum try squares. They came in a pack that my mom bought me one Christmas. I really thought they were great at first (all I had was a couple smaller steel squares ) but the rules are beveled for some reason, meaning my knife or pencil can mark under the rule blade, which is super irritating. On the two larger sizes I used the pins that hold the rule and body together came loose and the rules can literally be wobbled up and down. I haven't tried any nice try squares but those have definitely left a bad taste in my mouth. Would like to get a nicer one someday for the reason Steven states.

Michael, I suspect that they are the same design as the one that Stanley and I posted early on in this thread. If so, they are for examining whether something is square, and not for marking. The thin bevelled edge is for that reason.

Indeed. What Michael describes sounds like a pale imitation of a bevelled-edge master square: The good ones are extremely precise (the Starrett I linked is spec'd square to within 0.0001" per 6"), extremely expensive, and worth every penny if you do any sort of precision work. The bevelled edge allows you to detect very small deviations in squareness. It's possible to visually detect 0.0001" gaps under a beveled-edge square with a strong backlight. With all of that said, a master square is ridiculous overkill for woodworking.

What you want for marking is something like a machinist's square or try square. Note that they can be almost as precise as master squares (the set I linked is spec'd square to 0.0002" per 6", which is still overkill for woodworking), but they're designed for marking.

[Patrick Chase]

On a related note to this thread, I strongly recommend the Vesper double square. TFWW and Highland sell it in the US.

It's basically as compact and handy as a similarly-sized try square, with the advantages of being useful for measurements and accepting small blades to measure things like mortise and dovetail squareness. My sample has better squareness and blade flatness than my Starrett double square despite having a much shorter baseline (the width of the head where it meets the blade). It's easily square to within 0.0005" over 6" when compared to my master square.

IMO it's also a functional and aesthetic winner, with very simple, minimalistic, and usable adjustment and markings. I particularly like the rotationally retained "hook" in the head, which makes blade-swapping very quick.

The only downside is cost.

[Chet R Parks]

Patrick,
Thanks for posting about the Starrett "master square" My Dad was a tool & die maker and I still have his old one with the fitted wooden case. The one I have the blade is 5.50 long and made by Brown and Sharp. I always wondered about it's accuracy. I realize it's not a Starrett but there can't be that much of a difference.
Chet

[Michael J Evans]

Michael, I suspect that they are the same design as the one that Stanley and I posted early on in this thread. If so, they are for examining whether something is square, and not for marking. The thin bevelled edge is for that reason.

Regards fro Perth

Derek

That makes perfect sense. I've tilted my combo square for that exact reason.

I just figured, they were poorly made (which they still are), and that they were going to be a continual P.I.A

[Patrick Chase]

Patrick,
Thanks for posting about the Starrett "master square" My Dad was a tool & die maker and I still have his old one with the fitted wooden case. The one I have the blade is 5.50 long and made by Brown and Sharp. I always wondered about it's accuracy. I realize it's not a Starrett but there can't be that much of a difference.
Chet

I used the Brown and Sharpes as an engineering student (I couldn't afford my own though) and I think they're in the same league. I believe that George said he has B&S master squares, and I doubt he'd tolerate anything less than first-rate accuracy :-).