Glass as an aid to quality control.

[Andy Kev.]

I stumbled on the following idea at the weekend and it worked well, so I thought I'd offer it for consideration here.

I have a piece of glass measuring about 2' x 1' x 1/2" which generally gets used as a surface on which to do glue ups as glue is so easy to wipe from it. I'm currently making a small box of about 1' long in order to store lesser used chisels. I'd planed all four sides and then squared off all the edges and was sure that everything was bang on. As luck would have it, the glass was on the bench and so I stood the pieces on it prior to glue up as part of a last check. It was immediately obvious that one end piece was leaning about 1° - 2° out of vertical. That had not been apparent during previous checks on the bench top (poss due to tiny crumbs of wood being there?) and I'd either not checked that side or had missed the error with my square. As a result of the relevant correction with the block plane followed by a second quality control check on the glass the box fitted together absolutely bang on.

So the bottom line is that in future the final quality control check for components which need it will be done on the piece of glass and with the combination square. I mention this in case anybody might find it to be of use.

 

[Ttrees]

I thought this was going to be a candling trick, as plenty of guitar building folks use a glass box with a light inside for checking joints like the center seam of soundboards.

In my eyes its a huge benefit to have a reliable surface that you can check on.
Flip the work over and immediately see where the low spots are,
A cheap angle poise light combined with this technique is what you would not want to be without.

Having to use winding sticks would seem a real pain to me, and is a much speedier and more reliable than having to use a straight edge.
To my mind every winding stick is at least 3 or 4 times too short for its purpose.

If you want to have a surface that good, you can spend an awful amount of time making a bench that will stay that flat though, might be worth it depending on your view.
You could quickly make a shorter surface plate with a stop, but I'd rather the whole thing to be flat for assembly purposes.

Cue flat composite door rant, hat coat (hammer)

 

[Andy Kev.]

I agree with your idea that most winding sticks seem a bit short for purpose. I use two 60 cm aluminium rulers which are wide enough on one edge to stand up. That said, if a tool is traditional - and the shorter sticks are - they are probably good enough for most purposes or the design would have changed over the years.

I regard my bench as being generally flat i.e. it doesn't look out of true and it certainly is good enough for most purposes. I'm sure I ought to take a jointing plane to the surface but dread doing it. Has anybody got any ideas on dressing the surface of the bench? A generally flat bench does of course have no negative impact on the use of winding sticks.

In general terms the importance of the check on the piece of glass tends to become more important the shorter the piece of wood is but most of a big piece can be checked as well, all of it in fact, so long as the overhang isn't enough to make it tip off the glass.

 

[MikeG.]

....... I'm sure I ought to take a jointing plane to the surface but dread doing it........

Savour that dread. Go with it. Don't fight it..........your bench is fine, and doesn't need flattening.

 

[AndyT]

My bench is flattish but not perfect.
In a similar way to the piece of glass, I have a couple of offcuts of mdf that come out as needed. They touch each other all over when stacked, even if one is flipped over. I reckon that means they are flat.

 

[Just4Fun]

I flattened "my" bench at my woodwork evening class. Having been in a school for decades it was in a poor state. Removing all the gobs of glue and paint made a big difference to the usability of the bench. Planing to remove divots/damage and a small amount of twist made little real difference in my view.

 

[Inspector]

You're starting to get into the metal working arena of measurement and verification. They don't use glass because it flexes and the flatness isn't vary good. That's why they use granite surface plates and in some cases cast iron. If you really want go to the same lengths of flatness there are inexpensive surface plates available from metal tooling suppliers like Chronos if you want to take your work in that direction. With one you can check your straight edges and rules for straightness and with a good reference square check and adjust all your squares too.

Overkill for woodworking but some like to go there.

https://www.chronos.ltd.uk/cgi-bin/sh00 ... a311220071

A table to help you make sense of the straightness and flatness standards. Or make your head spin a little. :roll:

https://toolsmach.com/en/content/29-tab ... tolerances

Pete