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Long Straight Edge options?

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bp122

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Any recommendations for a 2m long straight edge for flattening a workbench top?

The workbench is (or will be) 1.8m long.

Are the long spirit levels that builders use appropriate for this application?
 

TheUnicorn

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I would be going to the woodpile, looking over potential candidates and checking for a straight edge by looking along the length, comparing against a taught line or a known flat surface.

I'm sure that a good quality long spirit level would do the job perfectly, it would also do a good job of removing weight from your wallet
 

Jacob

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Usual to do it by eye - just crouch down and squint. A couple of winding sticks can help (make your own) or just plain up a longer length for a straight edge.
There's a bit of an obsession for "flatness" but it usually doesn't matter much.
 

Woody2Shoes

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I use my 6ft spirit level or my 6ft featheredge (the forge steel one from Screwfix is good and cheaper at £25) if I need a straight edge. Any decent size aluminium extrusion that you can find lying about would probably do.
PS winding sticks might help too
 

bp122

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I understand that winding sticks are useful to see if a surface is flat across its width or twist along the length. How can one use them to determine if the bench top has a bow or a cup along the length?
 

Cabinetman

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Funnily enough I was visiting a guys workshop yesterday (big style commercial set up) and he has one of those, then I looked up and the sanding belts for it were hung up in the ceiling ready, and I had a definite feeling of being in Lilliput – as in, they were enormous and it was like my sense of scale had gone out of the window completely. Ian
 

Phil Pascoe

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An aluminium extrusion is fine for most purposes - I have one from a scrapped shower cubicle, I suspect the more irregularly shaped ones are more likely to be flat.
 

eribaMotters

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I would not worry to much. I built big and heavy with a 3" beech top 30 years ago and when I moved realised the bench had hollowed slightly to the shape of the floor.
When I need a long straight edge I use either a wide ripping of an 8 x 4 sheet of plywood or a length of Trespa offcut.

Colin
 

pe2dave

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I understand that winding sticks are useful to see if a surface is flat across its width or twist along the length. How can one use them to determine if the bench top has a bow or a cup along the length?
Fair comment, but 'by eye' for cupping, turn on edge and by eye along the length. Twist is hardest to spot, hence winding sticks.
Try it on any old piece of wood.
 

Jacob

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The key thing is to get the surface of the actual workpiece flat. This is quite possible even with rough bench.
 

Ttrees

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You can get very accurate with a pair of parallel timbers.
I shim this lab countertop to a good tolerance for doing long work with some adjustable blocks.
Adjustable as in those offcut blocks are not totally squared and can be messed around for that press fit.
Regardless if you're planing or shimming to get the bench flat, using a straight edge,
having a pair of beams means you can double the error of the workbench and arrive to a point where you can trust the bench for laminating.

Make sure the timber beams are as long as the bench, otherwise it's very likely that trusting it for longer stock will result in the ends being wastefully nipped off.
Much less likely to be so wasteful if it were the other way round, as would it be more apparent, because the plane won't cut as readily into a hollow.
Make them parallel so you can pair them to make sure there is no spoon factor happening.

To me, that means that it is the slightest of bit of convexity by an unmeasurable amount
so the work sits on the ends, but the gap in the center of long work is invisible, or at least when grasped by light hand pressure.

BENCH CHECK.JPG


The only problem is that those timbers always seem to get used up.:rolleyes:

Nice to have a lightweight beam of some description none the less.
I have some sort of aluminum beam and it's pretty handy, haven't a clue what it was used for beforehand, sorry.
Plasterers tool perhaps?
SAM_3979.JPG
 

shed9

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A laser line will also aid in checking the surface relative to itself. I don't mean self-levelling lasers just a laser line used across the bench to pick up on irregularities across it's length. It's not a single solution but will help in seeing those areas quickly. Even the cheap ones are good to a couple of mm over 10m.
Personally I wouldn't worry too much about it being perfectly flat, winding sticks and the right planes will do the job on a 1.8m span.
 

bp122

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A laser line will also aid in checking the surface relative to itself. I don't mean self-levelling lasers just a laser line used across the bench to pick up on irregularities across it's length. It's not a single solution but will help in seeing those areas quickly. Even the cheap ones are good to a couple of mm over 10m.
Personally I wouldn't worry too much about it being perfectly flat, winding sticks and the right planes will do the job on a 1.8m span.
I do have one already, so might be an idea.
Cheers.
 

JohnPW

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Perhaps make one, actually 3 then each one will be dead straight, (check all 3 against each other). Would be limited by how bendy they are though.
 

David C

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A one meter straight edge should be sufficient. Examine the center then slide it left and right.

Starrett make one that used to cost about £140, these were the best, many other straight edges are not straight.

Tolerances are important !

Some say that stabila levels are good.

Best wishes,
David Charlesworth
 

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