Reply To: Checking My Combo Sqaure
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Whilst combo squares – good quality ones – are perfectly adequate for most everyday woodworking purposes, they are not precision instruments.
For that you need certified engineers’ squares which are extremely expensive and over-the-top for woodworking, in my opinion.
The narrow-parallel-lines test, done with a sharp marking knife at about 1mm width for the full length of the rule section, will show up any significant inaccuracies to the naked eye, but with combo squares, be sure to do it on a dead straight wooden edge, checking all the combinations that you can load the straight edge in the yoke of the combo.
One useful gadget that is often overlooked, is the digital angle block. This will give you repeatable accuracy to a fraction of a degree, if you need it.
You put the block on one surface, hit the zero button, then replace it on the adjacent angled surface. A right angle will show up as 90.00 degrees. Anything else is not square and requires your judgement as to its acceptability.
Not expensive, and worth investing in for getting into tight spots that you can’t reach with a conventional square.
Good luck