Stellafane Foucault-Ronchi Testing Stand

This Foucault-Ronchi testing stand is a variation on the classic design presented by Stellafane here:  https://stellafane.org/tm/atm/test/tester-main.html

The primary issue I had with the design is that digitized plans weren't really available.  Basic images had some dimensions, but no 3D models were made to modify or customize the design.  So, I decided to model my own version of this testing stand, building from the basics of the sliding platform that has been used by so many amateur mirror-makers over the years.

For this variation, I wanted some easy methods to swap between Foucault and Ronchi testing, as well as an option to plug into a small portable power bank to power the green LED.  To achieve this, I designed a filter slide holder where I can slide a Foucault slide into position with a razor blade for the knife edge, or I can swap in a slide with Ronchi screen glued into place.  This makes it very simple to change back and forth between the two.  The only issue is that they don't have the same precise distance to the mirror's surface, but this would be difficult to achieve anyway when nudging the stand while changing slides.  So, I readjust after swapping slides regardless of how close they are to the proper distance.  Mounting holes in the slide holder are meant for #6 pan head screws.

I also added some simple knobs that fit onto carriage bolts with square features beneath the bolt head.  A bolt and split lock nut will keep the knob firmly attached when making adjustments.

The power bank holder will most-likely be useless to anyone else, as it's an older power bank and wireless router combo unit that has been replaced with a newer model, by this point.  A short USB cable has been fabricated to power the green LED with a current-limiting resistor soldered inline.  Hot glue should hold the LED firmly in position.  I would recommend the flat green LED, rather than rounded ones, as they'll project light onto the mirror better without having to flatten the tip by hand.  These are the LEDs that I purchased for this project:
https://www.amazon.com/gp/product/B077XDN49X/

Light reflections in test images are likely when blocking half of the green LED with the razor blade.  It is recommended to paint the blade flat black or coat it with some very thin felt, tape, or flocking material to absorb light.  I had a bit of Protostar flocking material with adhesive backing, which I used for this purpose.  Also, coat or cover the back of the green LED with black tape, liquid tape, paint, or other material to prevent the back of the LED from shining right into the camera.

For the Ronchi slide, I used 100lpi grating trimmed to size and glued into position with CA glue and a thin retainer component.  The razor slide shouldn't require a retainer.  Black electrical tape may work fine, but the blade typically stays in position on its own for me.

The tubing brackets are designed to work with 0.5in OD metal tubing.  I happened to have some left over from an old curtain rod, but you could purchase some tubing to use.  As long as it is quite straight, it should work just fine.  The brackets include some holes for #6 pan head set screws, as well as holes for some small eyelets that screw in place, normally used for hanging picture frames with wire.  The eyelets are used for the return spring that holds the sliding base against the adjustment bolt for accurate adjustment and measurement.

Speaking of measurements…  the dial indicator I used is a Mitutoyo 1-inch depth dial indicator with a 3/8-inch diameter base that just presses into the hole with friction.  Adjust for your own dial indicator, if needed, just make sure it's a snug enough fit that it won't come loose when making adjustments.  The touch block is used to reach close enough to the dial indicator to measure distances.  This may also need to be adjusted based upon the dial indicator used in your own build.  The shallow pocket in the dial indicator is to glue in a thin metal plate or something hard so the tip of the dial indicator has a reliable position to measure from.

Lastly, I'd recommend a thin film of silicone grease on the metal tubing to facilitate easy sliding of the platform and accurate measurements.  Use a strong enough spring, as well, so it keeps the platform pulled against the adjustment bolt and dial indicator.  For the adjustment carriage bolts, I'd recommend going with approximately 4-inch-long bolts.  I used 1/4-20 UNC bolts, nuts, and the wood threaded insert.