Simple Autocollimator

If you can see from one end of the planes,lay two straight edges across them and compare for level with each other, even if you can't look in from the end, use a mirror on a 45 deg angle to sight over the two straight edges. If distance between them is what you need to know, make a go /no go guage to fit between the planes and adjust them to where they both touch the guage. Cost two dollars or less if you can come up with some scrap to use.

Thank you hilltopper,

yes, using a straight edge or gauge blocks could work.

This is actually to align the platen and substrate holder in a polishing setup. The platen has rotary and circular motion and its mechanics are rudimentary and tend to wear( we are applying a higher load than specified and the equipment in by no means new). The substrate holder has movement perpendicular to the platen.

I was looking for an optical check of both static and dynamic alignments.

I was thinking of this as a cheap optical setup, then the fun will be to align the laser perpendicular to the first mirror, and stay that way:

If you have got up to 300mm between the faces use a high precision dial indicator on a dial indicator stand & simply set the stand & indicator to run across the underside of the top plate with the indicator stand running across the top face of the lower plate, simple, accurate enough & cheap & if used carefully would show .0005" parallelism error across the width & length of the plates.

Brien.

Mount a mirror on both surfaces. Sight into one using a small dental mirror. If they are not parallel, it will look like a long bent tunnel.