How square is your square

[MusicMan]

In my calibration laboratory we have to have the calibration equipment verified/calibrated to national standards by a UKAS laboratory.

Gerry

Yes indeed, for parameters such as length, but you don't need a standard for either straight edges or squares. You know that a straight edge is a straight line and that a square is an exact quarter of a circle. The classic mechanical engineering verification procedures are:

1. The Whitworth test for a straight edge (which could be called the foundation of precision engineering).
Take THREE straight edges and ensure they all fit (rub) together precisely. Then they are all straight.
The theory is that if edges A and B fit together, they are either straight or bowed the same amount. If A and C fit together, ditto, it means that C is a copy of A or a copy of B. But if A is not straight, then B and C are mirrors of each other and will not fit. Sketch it out to be convinced.

2. As mentioned by several, use one of your straight edges to draw a line, reverse the square and see if it agrees (use the same edge of the square). This is usually quite good enough for woodwork using the factory-machined edge of a manufactured board. Still better, check the edge of the board against any TWO of your rulers and check these against each other.

2. The four-angle test for a right angle takes them around a full circle. This is thus four times as accurate as the straight edge method. It has the benefit that the jig ends up with four very accurate right angles and you can instantly check any square against it. I described it here:

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

I found this in a book on precision engineering published in 1906. In that case it was made out of metal and used to very high accuracy for small engineering squares. I made mine out of wood just for fun and a test of planing etc skills, and achieved an accuracy of about 0.003 degrees. It would be easiest to make it out of aluminium extrusion (using the Whitworth test for straightness of course).

No, you can't credibly check a square with a digital angle gauge. These have a resolution of 0.1 degrees, which is not that good in woodworking terms (that's a mm out across a 600 mm board) and besides, the angle transducer used will have an unknown linearity error.

A little brag on length: I did once design and have built an X-ray interferometer for NPL, calibrated, with a resolution of 10 picometres, but that's overkill for woodwork!

Keith

 

[MusicMan]

But who calibrates UKAS's calibration equipment? :shock:

A quick search reveals the existence of a collaborative approach by all the EU national accreditation authorities - https://european-accreditation.org/mutu ... /#benefits

Now, you may be thinking that such collaboration will be threatened by Brexit, and you'd be right. If Britain ceases to be a member of the EU it will no longer be eligible to be a member of the EA. However, this statement - https://european-accreditation.org/ea-a ... of-brexit/ - suggests that if the UK does leave, there will be a two year transition period to work out how to keep the good work going and not mess it all up.

Maybe the Engineers are doing a better job than the Politicians! :wink:

This is one thing that won't be affected by the appalling Brexit, since the collaboration system is international not European (though euro-collaboration is extremely valuable). I used to be in metrology, and worked happily with both PTB (Germany) and NIST (USA). ALL SI units are related directly to six base units, which are themselves related to a fundamental physical property, such as the wavelength of atomic transitions of some sort in a specified material. 2019 is a keynote year in this since the last unit, the kilogram, has just been brought in line. It is no longer based on a lump of platinum in Paris but on the watt-balance, relating it very accurately to the fundamental units.

The function of national metrology labs is to verify any secondary standards (much quicker for practical use) used by ACAS calibration labs, and to verify that they are carrying out the procedures for tracing their measurements accurately to the SI base units.

Keith

 

[powertools]

It was only a matter of time before the EU were mentioned in how square is your square.

 

[Sgian Dubh]

2. As mentioned by several, use one of your straight edges to draw a line, reverse the square and see if it agrees (use the same edge of the square). This is usually quite good enough for woodwork using the factory-machined edge of a manufactured board.
2. The four-angle test for a right angle takes them around a full circle. This is thus four times as accurate as the straight edge method. It has the benefit that the jig ends up with four very accurate right angles and you can instantly check any square against it. I described it here:

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

To be honest, Keith, I've been surprised at the both the number of responses, and some of the heat generated over what is essentially a basic bit of kit, i.e., a square. As you, and others have noted, for probably 99% of woodworking needs, all that's needed to test for good enough is a straight edge of something like a piece of MDF, ply, solid wood, etc to press the square's stock against, a fine pencil line (or knife line if being pernickety) scribed along the edge of the blade on to the wood or board material, flip the stock and check for the blade coinciding with the scribed line.

What struck me was your description at your link for your four-angle test, because it instantly brought to mind the five cut test for checking the squareness of sliding table cross-cut fences. Simply, find a piece of flat board material, the larger the better within reason, say ~800 X ~800 mm, put one edge against the fence, take a small cut. Rotate the just cut edge to the fence, take another small cut. Repeat three more times with the last cut being one where the sawblade starts out just skimming the first cut.

This last skim tells you the squareness of the fence, i.e., does the blade just skim all along which equals square, or does it drift away from the edge or take more of the edge as the sliding table is moved forward.

Lastly, the rotation of the board clockwise or anticlockwise during the five cut test is determined by the position of the cross-cut fence, i.e., if it's set in front of the cut board or if it's aft of the cut board. Slainte.

 

[Bm101]

6 Pages.

 

[Bm101]

Can you imagine the fellas who made this...

Right lads.
Got the drawings.
Anyone got a DIN875/0 square?
No!?!? :shock:
Ahhhhhh. FFS! So Close!

 

[SMALMALEKI]

But who calibrates UKAS's calibration equipment? :shock:

A quick search reveals the existence of a collaborative approach by all the EU national......:wink:

So after Bredit the squares might not be square anymore !!! :shock: 8)

 

[MusicMan]

2. As mentioned by several, use one of your straight edges to draw a line, reverse the square and see if it agrees (use the same edge of the square). This is usually quite good enough for woodwork using the factory-machined edge of a manufactured board.
2. The four-angle test for a right angle takes them around a full circle. This is thus four times as accurate as the straight edge method. It has the benefit that the jig ends up with four very accurate right angles and you can instantly check any square against it. I described it here:

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

To be honest, Keith, I've been surprised at the both the number of responses, and some of the heat generated over what is essentially a basic bit of kit, i.e., a square. As you, and others have noted, for probably 99% of woodworking needs, all that's needed to test for good enough is a straight edge of something like a piece of MDF, ply, solid wood, etc to press the square's stock against, a fine pencil line (or knife line if being pernickety) scribed along the edge of the blade on to the wood or board material, flip the stock and check for the blade coinciding with the scribed line.

What struck me was your description at your link for your four-angle test, because it instantly brought to mind the five cut test for checking the squareness of sliding table cross-cut fences. Simply, find a piece of flat board material, the larger the better within reason, say ~800 X ~800 mm, put one edge against the fence, take a small cut. Rotate the just cut edge to the fence, take another small cut. Repeat three more times with the last cut being one where the sawblade starts out just skimming the first cut.

This last skim tells you the squareness of the fence, i.e., does the blade just skim all along which equals square, or does it drift away from the edge or take more of the edge as the sliding table is moved forward.

Lastly, the rotation of the board clockwise or anticlockwise during the five cut test is determined by the position of the cross-cut fence, i.e., if it's set in front of the cut board or if it's aft of the cut board. Slainte.

Yes, it's exactly the same principle, essentially 4 x 90 = 360! A natural standard.

Keith

 

[SMALMALEKI]

Thank you for all the replies. I have learned a good deal from all of them. I now have bought two Starrett ( made in China) they passed the straight edge test.
I also made it to Axminster and returned the square. I teated few more squares of Axminster precision squares and they were all similar.
They kindly offered a good deal on BridgeCity square and now I have both cheap (£6) and midrange (£66) in my tool box.

 

[Bodgers]

Thank you for all the replies. I have learned a good deal from all of them. I now have bought two Starrett ( made in China) they passed the straight edge test.
I also made it to Axminster and returned the square. I teated few more squares of Axminster precision squares and they were all similar.
They kindly offered a good deal on BridgeCity square and now I have both cheap (£6) and midrange (£66) in my tool box.

Ahhhh, so NOW we see the motivation! If all you really wanted was some justification to make a Bridge City vanity purchase, none was really needed.

First time I have seen Bridge City being referred too as 'Mid Range'...


Sent from my Redmi Note 5 using Tapatalk

 

[transatlantic]

Thank you for all the replies. I have learned a good deal from all of them. I now have bought two Starrett ( made in China) they passed the straight edge test.
I also made it to Axminster and returned the square. I teated few more squares of Axminster precision squares and they were all similar.
They kindly offered a good deal on BridgeCity square and now I have both cheap (£6) and midrange (£66) in my tool box.

I've just bought the same Starrett sqaure. Pretty damn good for £6. I hope it stays square.

 

[Rorschach]

Do you have a link for the Starrett?

 

[SMALMALEKI]

Thank you for all the replies. I have learned a good deal from all of them. I now have bought two Starrett ( made in China) they passed the straight edge test.
I also made it to Axminster and returned the square. I teated few more squares of Axminster precision squares and they were all similar.
They kindly offered a good deal on BridgeCity square and now I have both cheap (£6) and midrange (£66) in my tool box.

Ahhhh, so NOW we see the motivation! If all you really wanted was some justification to make a Bridge City vanity purchase, none was really needed.

First time I have seen Bridge City being referred too as 'Mid Range'...


Sent from my Redmi Note 5 using Tapatalk

I could not resist the offer of exchanging the Axminster square to BridgeCity. The aim was to get a replacement square from Axminster.

 

[SMALMALEKI]

Do you have a link for the Starrett?

I bought mine from Amazon. Free delivery next day.

Starrett K53M-200-S Try Square https://www.amazon.co.uk/dp/B00RD59JIO/ ... OCb6A85CT9
I hope the link works here.

 

[transatlantic]

Here is mine :
https://www.amazon.co.uk/gp/product/B00 ... UTF8&psc=1

 

[Doug B]

Thank you for all the replies. I have learned a good deal from all of them. I now have bought two Starrett ( made in China) they passed the straight edge test.
I also made it to Axminster and returned the square. I teated few more squares of Axminster precision squares and they were all similar.
They kindly offered a good deal on BridgeCity square and now I have both cheap (£6) and midrange (£66) in my tool box.

Not that there’s any thing wrong with it but as you stipulated it with the Starrett, you now have 3 squares made in China

 

[Trevanion]

The Bridge City square is a little overbuilt for my taste, very heavy with a thick blade. Some people might prefer that though. At least they don't have the "real" Bridge City tools price :shock: Harvey tools in China seems to build them quite well with a good QC.

Has anyone got a Vesper Square or Bevel? Always fancied one of those if it wasn't for the price tag.

 

[shed9]

Has anyone got a Vesper Square or Bevel? Always fancied one of those if it wasn't for the price tag.

Just had a look - https://www.vespertools.com.au/vesper-s ... y-squares/

:shock: gorgeous but have to agree the price is just as startling.


Edit: They do offer 10% of for anyone who can evidence they are a student of a recognised woodworking school worldwide. Prices aside, nice to see tool vendors doing this.

 

[Doug B]

Has anyone got a Vesper Square or Bevel? Always fancied one of those if it wasn't for the price tag.

I bought one of his sliding bevels a few years back when Chris was at the European Woodworking show, the locking mechanism is excellent as is the overall build of the bevel as you’d expect from the price I was just a tad disappointed that the blade wasn’t perfectly true on one edge, it wasn’t much out & was easily remedied but still not what I expected.

 

[Trevanion]

Edit: They do offer 10% of for anyone who can evidence they are a student of a recognised woodworking school worldwide. Prices aside, nice to see tool vendors doing this.

I think Workshop Heaven did some form of discounted student bundles at one time, not sure if he still does them or not. Also not sure if you had to prove you were an actual student or not either, but are we all not learning all the time? :lol:

the locking mechanism is excellent

I've never figured out how that mechanism actually works, I've never seen one in person or any of the knock-off mechanisms like on the Bahco bevel. I imagine there is some witchcraft involved.