Tolerances in optics are not measured with a micrometer but in wavelengths of light. They're worse than watches. But - if you botch a recementing job with balsam you get all the second chances you need. You could make V-blocks on a milling machine, lapping them to the final finish - and they'd be just as good as the Starrets for recementing. For this purpose the vee need not be precisely 90 degrees, it just needs to be straight, smooth, and at 90 degrees to one end of the block.
Originally Posted by Tom1956