Reply by Seeharlez

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Posted on Precision: How close is close enough?

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83 posts in 2992 days

#1 posted 01-31-2011 10:49 PM

It’s all relative! At my job I design parts that are steel fabrications, machined parts, welded assemblies and so forth. There can’t be one standard tolerance for everything. Within a single joint you may need very tight tolernaces in the range of thousandths of an inch, but that’s why you usually need to trim to fit. Where as you wouldn’t expect the overall dimension of a cabinet or table to be that tight. In that case you may be dealing with 32nds or even 16ths or 8ths.

What’s really important is where you dimension from. Dimensions should be relative to the surfaces that matter to that particular feature. In engineering this is part of what is called geometric dimensioning and tolerancing (a.k.a. GD&T). it can be quite complicated but the basic principals are very relavent to woodworking, be it for the professional or for the amateur hobbyist. The myth is that GD&T makes things more dificult to make but the reality is the it often reveals that some dimensions can be toleranced much looser and it hightlights the dimensions that really do need to be made precisely. Anyways, thers is lots of info available online on the subject. Wkipedia for example.

-- Greg - Vancouver, BC

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