Sqare squares

[Mr T]

I've spent a while this morning truing up the engineers squares in the tool kits on my student benches. I found that most of them were out of true on the outside edge despite being OK when purchased. This is due to wear from using them with a marking knife. If you've had your square for a while it's worth checking. I fettled mine using a mill file and finishing on a diamond stone to smooth out the file marks. I know this will not give you gnats nagger accuracy but I think it's good enough for general work.

I would be interested to hear from those with mega accurate, and pricey, squares such as Starrett whether they use them for knife marking. Are they harder steel so don't wear, if not how do you restore them to GN accuracy?

Chris

 

[bugbear]

I'll try to find my old post, but I had a Moore & Wright combo square, with hardened rule, and the rule was massively dished on both faces, presumably from use with a scriber or similar.

It was one of the first things I corrected when I got a proper (granite) surface plate.

So, yes, even posh hardened things wear.

BugBear

 

[custard]

I've spent a while this morning truing up the engineers squares in the tool kits on my student benches. I found that most of them were out of true on the outside edge despite being OK when purchased. This is due to wear from using them with a marking knife. If you've had your square for a while it's worth checking. I fettled mine using a mill file and finishing on a diamond stone to smooth out the file marks. I know this will not give you gnats nagger accuracy but I think it's good enough for general work.

I would be interested to hear from those with mega accurate, and pricey, squares such as Starrett whether they use them for knife marking. Are they harder steel so don't wear, if not how do you restore them to GN accuracy?

Chris

Interesting point. I've used the same Starrett combi squares on a daily basis for many years, and I do use them for marking out with a knife. I check them against each other on a flat reference surface fairly regularly and I can't detect any error.

I suspect Starrett do use exceptionally hard steel, but I also suspect most newcomers to woodworking don't handle a marking knife particularly deftly, it's just one of those things you learn over time. I've seen more than once a student running a marking knife along an aluminium or cheap steel ruler, and pare off a thread of metal because they've twisted the knife inwards!

 

[Racers]

I have trimmed off metal from carpenters squares with a kiridashi marking knife but not from a good engineers square.
I have polished the edges of car boot engineers square with a diamond stone, but I haven't found a More and Wright one that a file would touch.

Pete

 

[Tasky]

Possibly just me, but I always wondered how people got Squares square in the first place...

Having seen the rants on Amazon Reviews from those who bought a small try-square or something and found it to be "out by a whole one-eighth of a bloody milimetre... this is TOTALLY unacceptable!!", it makes me wonder what they're using to check this and how they know it's out.

 

[Mr T]

Possibly just me, but I always wondered how people got Squares square in the first place...

Having seen the rants on Amazon Reviews from those who bought a small try-square or something and found it to be "out by a whole one-eighth of a bloody milimetre... this is TOTALLY unacceptable!!", it makes me wonder what they're using to check this and how they know it's out.

The way I checked mine was to offer the square to piece I know has a true edge then clamp another straaight edged piece against the edge of the square, Remove the square and lmap another straight edge piece against the previously clamped piece, remove the previuos piece then offer the square up to the new clamped piece. In this way I have (relatively) accurately checked by reversing the square. I could even check it with a feeler guage to see if it was 1/8th mm out!

Chris

 

[Tasky]

The way I checked mine was to offer the square to piece I know has a true edge

I meant waaaaaaaaay back, in the beginning, when the Earth was void, dinosaurs walked the land and the first ape decided that his tree wasn't sitting quite true enough... :lol:

 

[novocaine]

Greece : a^2+b^2=c^2

Egypt : cross staff and plumb line.

other methods are available.

 

[MusicMan]

Possibly just me, but I always wondered how people got Squares square in the first place...

Having seen the rants on Amazon Reviews from those who bought a small try-square or something and found it to be "out by a whole one-eighth of a bloody milimetre... this is TOTALLY unacceptable!!", it makes me wonder what they're using to check this and how they know it's out.

The way I checked mine was to offer the square to piece I know has a true edge then clamp another straaight edged piece against the edge of the square, Remove the square and lmap another straight edge piece against the previously clamped piece, remove the previuos piece then offer the square up to the new clamped piece. In this way I have (relatively) accurately checked by reversing the square. I could even check it with a feeler guage to see if it was 1/8th mm out!

Chris

Chris, with your courses to maintain you might be interested in my square checking device, adapted from a mechanical engineering tool. It uses the fact that four right angles = 360 degrees, hence needs no calibration, and is four times more accurate than checking against an edge. And once set you can check a square very quickly, in fact I make a habit of doing so before each new project. I estimate that I can check a square to 0.003 degrees.

Keith

high-accuracy-square-setting-jig-t93871.html

 

[MusicMan]

I meant waaaaaaaaay back, in the beginning, when the Earth was void, dinosaurs walked the land and the first ape decided that his tree wasn't sitting quite true enough... :lol:

See my post above. Even back then, four right angles got you back to the beginning!

Always best not to need an external standard. Like the Whitworth tests for straight edges and flat planes. If three such objects fit together perfectly, they all have to be correct.

Keith

 

[sunnybob]

"out by a whole one-eighth of a bloody milimetre"....

What particular tape measure did they use to get that one?

ROFLMFAO.

 

[Beau]

Hi Chris. I would have sworn my Moore and Wrights were still perfectly straight and square but on close inspection there is some visible hollowing on the outside of the blade of my most used small square. Never had any visible shaving come of from marking knives but clearly been worn. Not measurable with my tools but visible when held up to the light. Few more year left in mine before they need to be replace though.

 

[Eric The Viking]

I only have one BS-marked square, but several other engineers' squares. The small ones are really handy for things like setting the drill press and bandsaw, but... the problem is the inside edge of the blade:

I do check them, and a couple are off enough to be a nuisance. But if the error means it's greater than 90, you have to try to take material off right next to the corner. I can't see how to do that easily.

Does anyone have a good technique?

 

[Mr T]

Chris, with your courses to maintain you might be interested in my square checking device, adapted from a mechanical engineering tool. It uses the fact that four right angles = 360 degrees, hence needs no calibration, and is four times more accurate than checking against an edge. And once set you can check a square very quickly, in fact I make a habit of doing so before each new project. I estimate that I can check a square to 0.003 degrees.

Keith

high-accuracy-square-setting-jig-t93871.html

Thanks for the link Keith. As you say it uses the same principle as we use to square up the cross cut fence on a table saw. I might make one for easy checking of my squares.

Chris

 

[Tasky]

What particular tape measure did they use to get that one?

Oh, you'll love this - User photos show a Bahco tape measure... which is what revealed the error, on a Bahco combination square!!

 

[MusicMan]

high-accuracy-square-setting-jig-t93871.html

Thanks for the link Keith. As you say it uses the same principle as we use to square up the cross cut fence on a table saw. I might make one for easy checking of my squares.

Chris

Yes it's the same principle as the 5-cut method for a crosscut fence.

I made mine out of hardwood (seasoned for 160 years!) as I wanted the practice in making edges really straight and square. Doing it again, it would be faster and maybe still more accurate to use metal, probably T-track but checking first that they really are straight by seeing if they all fit together without gaps. Could probably get to 0.001 degree that way.

If you do make one I'd be interested in your experience and whether it saved you significant time.

Keith