B grade Engineers square, what are the tolerances?

**simonl** · 2nd August 2012, 05:26 PM

Hi all,

In Stuarts recent cross slide scraping thread, he performed a simple test to assess the error in his B grade engineers square. At the time I thought I should perform a similar test on an engineers square I have, if for no other reason than an interest point of view but also so I have an idea of its error and can compare to subsequent tests later in time.

Well, I finally got around to organising this simple setup. The error I got using the setup in the photo was a fairly consistent 0.05mm over 140mm which halving the result yields 0.025 over 140mm. Both sides of the square are parallel to within 0.005mm which is the limit of my measuring for something that is approx. 36mm wide.

It's all good and well to have this knowledge but how does it stack up to what a B grade engineers square should be? I think it's a B grade square because that's what my dad said it was when he gave it to me before he died.

Also, given that it is easy to measure the error in the squareness, can we improve a B grade so it becomes and A grade?

The square in question is a Moore and Wright 150mm square.Cheers,

Simon

**Machtool** · 2nd August 2012, 08:21 PM

G’day Simon.

You would need to buy the Standard, BS 939. Its several hundred dollars.

I found a site that lists a B- Grade 6” square tolerances.

Fisher Engineer's Squares | Anglo American Tools

+ / - 0.00064” in 6 inches,

I also know, B is the third grade, there’s AA, A then B.

Regards Phil.

(On Edit) I also found the DIN 875 standard.

http://www.limit.se/FineToolsAPI/Dow...24f8f62fb373d1

The third quality grade there, (1) is about 18 microns per 150mm. Fairly similar.

**shedhappens** · 2nd August 2012, 08:46 PM

and there is also the grade B-

which is what mine is now after I dropped it

**Grahame Collins** · 2nd August 2012, 09:21 PM

The question I would ask would be is:

What is your application in using this square.
My square is a 6" Moore and Wright barely 44 years old and it came wrapped up in rust preventitive VP brown paper.I used it for marking out and set up of plates for tacking.

On a good edge scribe a line and flip the square over to the over "hand" and check the blade against the scribe line.

I helped repair squares over the years that had been hammered or arced on.Yes we had richard heads back then.

This involved draw filing and the use of a machine table-machined in two planes that are perpendicular to one another.

Does it help?
Grahame

**simonl** · 2nd August 2012, 10:50 PM

Oh and I forgot to attach the pic:

Hi Phil,

Thanks for the info. I figured if those BS standards are of similar price to the AS then they would want an arm and a leg for them!

Hi Shed,

I always worry that's what I will do to mine. I try to put it back in it's wooden box after every use. I hopeless and putting things back straight away but I have a soft spot for this square so I've go into that habit. At least now if I drop it (ahhhh!) I can repeat the test and check the damage. Hey, If I drop it right can I turn it into an A grade? Or perhaps if I leave it out overnight an A grade fairy will come and touch with her wand and turn it into a real A grade square?

Hi Grahame, I have several squares but this one is my most accurate one. It only comes out when the accuracy is needed. Not very often at this stage but one day I plan on improving my compound and cross slide so it my come into use then.

Simon

Thread: B grade Engineers square, what are the tolerances?

Thread Tools

Search Thread

B grade Engineers square, what are the tolerances?

Similar Threads

Wanted Large Engineers Square

Templet Tolerances

Door Frame tolerances.

Drill Press tolerances

Tags for this Thread

Posting Permissions