The mystery of the shape shifting wedge.

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Sam_Jack

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The tale, as all great mystery’s are, is shrouded in legend. I was given a table top, which was a surprise. 36 square feet of Tasmanian Blackwood. The underside recorded a history of the ‘carpenters’ who had worked on the timber, since 188 –(xxxx). It was; and still remains, a most lovely ‘lump’ of wood. Not easy to work – for ‘Blackwood’ has it’s secrets. No matter – and I digress. Bear with me, there is a point.

My ‘shooting board’ has been handed down for three generations. I decided to make from part of the Blackwood a ‘jewellery chest’ for the reigning monarch of home and hearth. Not a big problem, until I read the curse scribed by ‘Tom’ in 1892 underneath the great slab of gifted Blackwood. Won’t bore you with details, but it advised that whereas the wood would behave immaculately, ‘other‘ timber’ would not be tolerated close by during the work. So much for fancy.

But – my shooting board has done, since 1941 (Grandads) some serious work. Before starting on the Blackwood, I thought to make a new square wedge for the shooting board – a job long put off. So I did; a good journeyman’s fit, Pine and it fitted perfectly, with about a 3” tail.

Next day, the same wedge is a full inch shorter – fit perfect; but, shorter, you understand. Must have muffed it methinks I. Cut another – in Pine – immaculate fit. Later that day, that wedge was at least an inch short and no matter what I did – was always 3mm too long –at the business end.

That Pine was a store bought “DAR” for what that’s worth, the shooting board wedge, now twice accurately cut, shrinks in bizarre way every morning.

Why gentlemen? Why?

I’ve made a new wedge from an offcut of solid, reliable Oak. At 20:00 (o’clock)_ it fitted just fine; at 2100 it was ‘narrow’ and now at 2200 – it is short by 40 mm – again.

Anyone – any answer – please. Genuine request.
 
Never mind the shooting board, do your feet still reach the pedals in the car?
Mike.
 
Well, that’s me told. I just thought to cheer up a dreary – band saw laden Christmas with a ‘mystery’. It’s all ‘so serious’ here; however, as it happens, that wedge did actually ‘shift’ shape ( a fair bit in fact) and the scribed ‘legend’ is genuine.

I love it when you don’t need a Spratt to catch a Mackerel. Really, a Startrite Mercury with a Clark motor? Then which Epoxy resin? It’s not me who needs to get out more; really, it ain’t………..
 
There's nowt like a wee hookery moctookery to muckle up the grublarkins.
 
I'm trying to fathom what thread pitch i need on this nail to hang a piece of plate glass :D
 
Ok, genuine (speculative) answer. A similar thing happened to me when I made a little Japanese style toolbox with the lid secured by a double tapered wedge.

post1188183.html#p1188183

I too used old, well dried wood, from Victorian furniture. I made the box, planed an over-long piece to make the sliding wedge and fitted it carefully. Then I cut the ends off so it was all neat and lined up properly with the fixed wedge. Next time I looked at the box, my wedge was too small so when it was tightened up, the ends were about half an inch away from where they should be.

I think it must just be moisture loss from the wood making the wedge shrink in its thickness. Most of the loss will be from the newly exposed end grain and when I trimmed my dry wedge to fit I exposed a fresh bit of the interior. The wood is like a loaf where you can feel the end surface dry out, unprotected by the crust. And even if all the outside is stale, the middle will be more edible.

So the moisture loss makes a very slight reduction in the thickness of both wedges. This tiny amount is then amplified by the geometry - a tiny bit off the width allows a much greater movement end to end. (This fact is exploited in the design of simple wedge shaped gauges in engineering work, which allow holes or gaps to be measured more easily than if you laid a rule across the gap.)

My solution first of all was to put a strip of tape along one side of the wedge. I followed this up by giving the box away!

I hope this helps. Season's greetings to all. :ho2
 
Thank you Andy,

Very much. We have had some pretty remarkable weather here. Rangining for 18c with 70% humidity to 37c with >83% humidity; not to mention torrential rain and some spectacular thunderstorms providing golf ball to egg sized hailstones. My timer is stored ‘outdoors’, but under good cover. After I had repaired the trashed skylights and when it stopped pouring down – I thought it was time to do a bit of the ‘Christmas box’. As stated – I began by making a new wedge; which, did over the next couple of days, do some remarkable things.

The ‘Pine’ was a cheap, DAR piece which was, probably, fast dried, run through a machine, bundled up and sent out to market. Not having the equipment; or interest to ‘test’ he piece (being a practical working sort) – I simply used a portion for my ‘wedge’. Alas, but no matter, the Oak has returned, in the better more stable weather conditions to a workable state and seems quite happy to perform design function. Even Sellars bangs on about ‘atmosphere’ and how it can affect timber. I can, with some certainty describe the ways in which stock is affected by local conditions. I can even reach the pedals in my car, without medication. Not only that, the joinery, floor, staircase, doors and windows I made (by hand) for my last architect client won an award. Aye, lack of humour, no flexibility of mind or wit and some blinding sense of self worth, does indeed the pedant make. Pearl before swine; don’t ban me - I quit……Farking Band saws – is that it?
 
Sam_Jack":36vohagd said:
I love it when you don’t need a Spratt to catch a Mackerel. Really, a Startrite Mercury with a Clark motor? Then which Epoxy resin? It’s not me who needs to get out more; really, it ain’t………..

Haha :lol:
 
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