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Not a straight edge - a cautionary tale.

A

Andy Kev.

Nordic Pine
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I'm currently working on a book case which will be 5 ft tall. My longest straight edge is 4 ft, so I bought a very long (about 7 ft) spirit level at the local DIY place:

Long Level.jpg

I assumed that being made of aluminium, its accuracy would be good enough over a length of 5 ft. However, I discovered yesterday that at one end the base curves up a bit, making it look like the piece of wood has a downward bow. Once I realised that, there was no problem. Nonetheless, I think it worth pointing out that you can probably only trust a true straight edge to function as such. The longest I could conceivably need would be 6 ft but I might start looking for one.
 
Trusted brand names mean less and less these days but are probably a good place to start when measuring accurately is concerned
I had a headsratching half hour putting slabs down with a cheap " level" that lied ( and laughed at me) before I had the sense to test it
 
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...and I bet that even if you found them in a shop, they'd be in packaging designed to prevent you setting one against another to see if they touched all the way along. 🙁

I can remember being told that a plasterer's darby was a good compromise for someone needing a reasonable straight edge without going for engineering quality and price, but I've never needed to check that.
 
You need to be careful when buying levels, once I needed a two foot level in a hurry as one of my crew damaged theirs. In store checked 8 levels , either they were warped or if straight they didn't level the same when flipped over. Finally found a good one.
 
duke said:
You need to be careful when buying levels, once I needed a two foot level in a hurry as one of my crew damaged theirs. In store checked 8 levels , either they were warped or if straight they didn't level the same when flipped over. Finally found a good one.
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Absolutely. In the old days here in U.K., we had a species of level that was guaranteed to still function properly when dropped several stories off a scaffold (trés expensive). I carried out your test on some of them; rejected the lot. Finally found a straight Rabone Chesterman 4' that has served me to this day (45 years and counting).
 
AndyT said:
...and I bet that even if you found them in a shop, they'd be in packaging designed to prevent you setting one against another to see if they touched all the way along. 🙁
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As I recall, all of the levels, from the inexpensive store brand to the more expensive Stabila, are not packaged. However, it never occurred to me to check the level for flatness using another level.
 
Mike said:
As I recall, all of the levels, from the inexpensive store brand to the more expensive Stabila, are not packaged. However, it never occurred to me to check the level for flatness using another level.
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I withdraw my cynical remark!

The classic engineering approach to making a straight edge is to make three. If any two touch closely along the whole length, they are straight.

You need to check with three, since two could touch if they were wonky but matched.
 
30-odd years ago I found myself building toilets in the sand in Mexico, at an orphanage. Two very large burger-loving American ladies looking after 70-odd little children. I was part of a team aged from just out of school to not quite retirement. I had some skills so I was laying concrete blocks. Freshers who had only recently learned to tie their shoelaces were digging 8ft deep pits (by hand, no machinery). It was hard and very hot work, even in October/November.
I asked if they had a spirit level I could use. They had two, "But I don't know if they are true or not", said the maintenance guy. So I took them, swept a clear path on a nearby concrete base and laid the levels down. They read true. So I turned them around and they still read true.
The bloke was delighted, "You've been around a bit!". I think it was a compliment. (Edit Complement? Wash my mouth out with soap and water - I do apologise). A short while later I saw that he was showing the test to a mate of his.
I should have been nominated for a prize of some sort, really.
S
 
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AndyT said:
Was it one of these? Marples catalogue, 1938:View attachment 55860

View attachment 55861
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That's the brand Andy, though the ones I saw had metal bodies. They were vaunted as the complete canine testicles, so maybe the hardware shop I was in had bought in 'seconds' but flagged them as the real McCoy?
A lot of the builders I knew recommended them.
 
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