Cheap square angle tolerance

[MattChow]

Well I decided to have a rummage though my selection of cheap squares that I have acquired over the years to check for accuracy and it would appear that most of them are coming out at around 89.7° or 1mm off for every 200mm of travel which is a nice 3mm over the width of a worktop.

One was a 6" Toolstation special speed square, another was a cheap engineers square and the final on a very old inherited woodworkers square.

What sort of tolerance is usually expected from a "good" square?

 

[AndyT]

I've no idea, but I did take the time to do a similar investigation on my selection of squares, mostly old, in various sizes. By careful filing to get them square and parallel I now know I can pick up any of them and get decent results.

Thinking about it, I'm pretty sure I remember copying a picture of a try square into my woodworking notebook at school, nearly 50 years ago, and recording then that a square could be trued by filing.

I suggest that you don't wait quite as long.

 

[Cheshirechappie]

If most of them are showing about the same error, it might be the checking instrument that's not quite right ....

Maybe it could pay to double-check by using the old trick of finding a board or piece of thick card with a nice, straight edge, placing the squares' stocks against the straight edge, drawing a thin pencil line (nice, sharp pencil) and then reversing the square and drawing another line using the same edge of the blade very close to the original line. Then compare for parallel. If the lines aren't parallel, the difference shows twice the error, which, as Andy says, can be corrected by careful filing.

By the way, it would be a wise move to check that the stocks are in good order, with no burrs or cobs of dirt on the brass throwing the square's register face out of true. Do that before the pencil test!

Edit to add - The acceptable tolerance is the degree of out-of-squareness you can live with for the kind of work you want the square to do. Thus, someone installing garden decking will live with wider tolerances than a fine cabinetmaker would find acceptable - and things can get very fine indeed for engineering toolmakers and quality inspectors!

 

[MattChow]

Thats exactly the method i used with a 0.5mm propelling pencil. The lines overlapped at the root and were 2mm apart at the about 200mm.

I have just finished filing the speed square and the lines overlap over their entire length now. The 45 degrees on the hypotenuse is a mile out but i never use that.

 

[Cheshirechappie]

Thats exactly the method i used with a 0.5mm propelling pencil. The lines overlapped at the root and were 2mm apart at the about 200mm.

I have just finished filing the speed square and the lines overlap over their entire length now. The 45 degrees on the hypotenuse is a mile out but i never use that.

I'd say that was good enough for garden decking but nowhere near good enough for joinery or furniture work - you're doing the right thing wielding the file!

 

[AESamuel]

I true my squares using that same method (it's funny how valuable metalworking tools like files are to a woodworker) but I don't use a pencil to check the square. I use a knife with a very fine point (similar to the stanley one mr sellers uses), and strike a very light line. That way I can register the knife in the line again after I've flipped the square over and have a much more definitive line to check against. For some that is unnecessary precision, but as far as I'm concerned, if I'm taking the time to do it, I may as well do it to the best of my ability.

This whole method (whether pencil or knife) hinges on how straight the edge of the board is you're referencing off. If there's a slight dip in the edge that will lead you to go out of square one way, and a belly is even worse; it could go either! So make sure the edge you're using is dead dead straight.

 

[Sideways]

Just look up about engineers squares. There are EN, BS and DIN standards for these. All essentially the same. Class 2 (workshop use) versions are pretty cheap, widely used in metalwork, and make a nice reference for a woodwork shop as they are better than all but the most costly woodwork squares. It's good to have one for squaring up any machines you have.

 

[Lons]

So make sure the edge you're using is dead dead straight.

I use a knife as well and a bit of 6mm mdf to mark on but have never worried too much about the edge being square, what I do is clamp an accurate metal straight edge to the underside edge of the mdf and register the square against that instead so I know it can't be wrong.

 

[marcros]

are you measuring the inside or the outside of the square? I recall that only the inside needs to meet the requirements of the standard, so if the blade isnt parallel, it isnt a failure (although very annoying)

 

[MikeG.]

Just look up about engineers squares....... they are better than all but the most costly woodwork squares........

No, they're not. Ninety degrees is ninety degrees. It doesn't matter if the square has stamps and certifications all over it, or was bought for 5p at a car boot sale covered in rust and cobwebs. If they're 90 degrees they are equally as good as any other square. The difference isn't in the quality of the square, but in the chances of it being 90 degrees. You may have to search through a few cheap no-name squares before you find one that is accurate, but you can expect the first engineer's square with a kite mark on it to be right. Having an expensive engineers square doesn't mean the right angle you mark or check is any better or more accurate than the one marked by a cheap no-name square that is square.

 

[Ttrees]

Sight unseen, there's more chance a cheap wooden one will be out than a cheap all steel construction though.
Some wild grained stock on some cheapies in the shops causing a gap in the brass wear strip.
That's one reason.
And another is the fact that you have pins in timber which can wiggle about after some time.

I bought a 150mm (no name) engineers square for a tenner from Axi.
This is actually a Soba tool and is just about the best value in the whole shop.
A well finished tool, and I took some snaps for a review on the Axi page.

I reach for it now instead of the carpenters one.
More for checking than line drawing, more reliable for marking out because the trad one
can be wiggled.

Tom

 

[transatlantic]

are you measuring the inside or the outside of the square? I recall that only the inside needs to meet the requirements of the standard, so if the blade isnt parallel, it isnt a failure (although very annoying)

This rule really is daft. It's like saying only one side of a ruler needs to be accurate.

 

[transatlantic]

This whole method (whether pencil or knife) hinges on how straight the edge of the board is you're referencing off. If there's a slight dip in the edge that will lead you to go out of square one way, and a belly is even worse; it could go either! So make sure the edge you're using is dead dead straight.

There's more chance of error due to the user sligtly changing the angle of the blade/pencil to the square as they draw the line back. Or for the knife to fall into the existing track. It's also very easy to add in error simply by not applying equal pressure with the square against the reference.

This is what annoys me with the common 5-cut method you see people use to align their table saw sled. They spend a silly amount of time correcting it to 1 thousands of an inch, completely disregarding the fact that they more than likely have a much larger error in how straight the fence is to begin with. It's silly imo.

 

[AndyT]

The seller's description of the Joseph Marples Trial 1 try squares says:

"The accuracy of the try square is well within that required by the British Standard: BS3322.

These squares have been tested on both the inside and outside faces, with the internal angle being twice as accurate as the British Standard, an accuracy better than 0.01mm/10mm blade length."

(From Toolnut at https://www.toolnut.co.uk/products/jose ... are-9-inch )

So that should give you some idea of what the toolmaking trade regards as sufficient accuracy for woodworkers, with a suggestion that the standard itself might be a bit slack.

If you want to read the whole standard, you'll probably need to wait for your public library to reopen, or buy your own copy for £110.00!

https://shop.bsigroup.com/ProductDetail ... 0000072804

 

[MikeG.]

........ being twice as accurate as the British Standard, an accuracy better than 0.01mm/10mm blade length.".....

That equates to a millimetre over a metre. Adequate, possibly, but I'd have perhaps expected something somewhat smaller than that.

 

[AndyT]

The chart here gives the numbers for DIN 875, a standard for engineering squares, in four grades.

https://toolsmach.com/en/content/29-tab ... tolerances

Looking at the nearest equivalent size, 200mm, and the lowest grade, grade 2, it seems to be allowing a variation of 16 microns per metre, if I have read it properly.

 

[Sideways]

........ being twice as accurate as the British Standard, an accuracy better than 0.01mm/10mm blade length.".....

That equates to a millimetre over a metre. Adequate, possibly, but I'd have perhaps expected something somewhat smaller than that.

I wouldn't buy a spirit level that was worse than 0.5mm / metre and those are commodity products.
Mike made a fair point above, a cheap device can be both square and, potentially, straight. But it's saves time and effort to have at least one tool where someone else has ground it straight and perpendicular, measured it and put their reputation behind their work.
Useful to have a very thin feeler gauge or two as well. These can be bought individually.

 

[sammy.se]

The two biggest headaches woodworking gives me is 1) buying timber 2) getting things square.
Both improve with time and practice, but those are the two.

I bought an engineer's square (from Axi) and a digital angle finder. I use both to try my best to get things (saws, jigs, workpiece) square but it still takes up so much time.

I would gladly pay a little more if there was a guarantee of squareness, so I am please to learn about the engineering squares and their standards that people have mentioned above. I may have to go shopping...

I have filed my cheap aluminium roofing square and am about to file my wickes-bought wood and brass tri-square, which is 0.2mm out over 200mm, so 1mm over a metre.

I'm not touching my metal square from Axi until I know I have a better square

I have also discovered by tracksaw guiderails are not square at the ends, which makes joining them more time consuming. I will have to cut those square on the table saw (or track saw). Ah the 'joys' of working on tools instead of wood!!

 

[MikeG.]

.....I have filed my cheap aluminium roofing square......

It's much quicker the traditional way with a hammer and punch.

 

[MusicMan]

Since 4 x 90 = 360, a full circle, you can make your own high accuracy setting jig for squares. See this thread:

high-accuracy-square-setting-jig-t93871.html?hilit=square%20jig

It's a similar principle to the use of a straight edge, scribing a line then flipping the square the other way to see if the line coincides. The advantages of the jig are that it multiplies the error by 4 rather than 2, and you end up with a very accurate square rectangle on your jig, that you can use for adjusting and setting any of your squares.

I have adjustable squares, and make a habit of checking them before setting out any serious project. Cheap fixed squares can be adjusted by filing, as mentioned above.

I took this method from a manual of metalwork practice written around 1906.