Like many things in life accuracy is something that can vary from individual to individual.
A boxmaker will usually need to work to very tight tolerances to achieve acceptable results. A 1mm gap on a lid may be unnacceptable.
On the other hand, a carpenter hanging a house door has much more leeway and may be able to work to a 2 or 3mm gap.
What this says is that tolerances vary depending on the scale we are working too. Imagine then what a person making miniatures must work too, 0.5mm in this case may be the absolute minimum, or too much.
Here are some accepted work practices:
Work with good lighting. It is amazing how a reading lamp on your bench will help here.
Are your reading glasses good enough? You can also buy magnifying glasses like jewellers use. Seeing is believing!
Use one ruler consistently for a whole job. It is not uncommon to find slight discrepancies between different rulers and tape measures. Using one ruler or tape throughout a job will add to consistency.
Are your machines set up correctly? A mis-aligned fence on a jointer will mean your 90° edge will not be correct. Being 0.5mm out of square will compound, so that three boards coming together will add up to 1.5mm out of square. That’s a lot!
Don’t forget though that wood is always moving subject to moisture content. Machined wood left lying around the workshop for a week with subsequent weather changes may increase or decrease in width or thickness. Try and machine and complete each process on the same day. Also sealing wood with a good polish will help to lock the wood at the size you machined it to.
Having said all the above remember this is woodwork not engineering. Wood is somewhat forgiving and can be adjusted and coaxed much more than metal.
So how to work to fine tolerances. Naturally good measuring devices help. To this end we at Interwood have some new measuring tools. Our iGaging calipers offer a large readout that can be flipped between metric and imperial (inches) and we also have a digital wheel marking gauge.
These quality measuring and marking tools are available now: