Making a key

[Smokedaddy]

Well if it matters to anyone, the set screw I ordered from McMaster-Carr worked perfectly (M3x0.5mmx16mm long ). So the hex is 1.5mm. Keep in mind that I also went to ACE Hardware local to me but they didn't have it, that's why I ordered it. I made my purchase at McMaster simply because the drawing confirmed the hex was 1.5mm (as the image I posted before confirms). I've also seen them on Amazon in a small quantity. You can easily grip the set screw with your fingers so you don't need to make a handle for it (which would be very easy to make).

[Paul Alciatore]

Getting an accurate measure? I doubt that the fuzzy photos in some of the posts above will cut it. You need a sharp image to get a good measure using photography.

I would make a mold with clay or better yet, one of the commercial molding compounds: A flexible molding compound will help in getting an accurate impression as it can be stretched while pulling it off but it will return to the actual size after that. Add a small piece of wood/plastic/metal to the back of that molding compound before it sets to help keep the dimensions constant. Then make a replica with either plaster or a pour-able plastic. Trim the surrounding material from around the hex and then just measure it. Don't forget to take the shrink/expansion factor of both the molding compound and the plaster or plastic into account.

https://www.alumilite.com/products/silicones/

https://www.alumilite.com/products/resins/

[Smokedaddy]

I've learned to try not and say anything with certainty but I think the hex shaft is not 2mm nor 1.27mm (0.050"). I purchased another 1.27mm cap screw today (meaning the hex is 1.27") turned it down to fit the bore but it doesn't work. So, for my last shot for now, I ordered a set screw M3x0.5mm 16mm from Mc-Master today. It has a 3mm diameter too so it should fit in the bore without machining. It take a 1.5 allen head wrench. I figured since the 2mm seems to spin and the 1.27mm seems to small, the 1.5mm is the best shot. We'll find out soon.

[Noitoen]

To measure you could attach with some tape 2 small pieces of piano wire or something similar to the calipers and reach inside the recess. You could even flatten the wire a little with a hammer.

[Joel]

If it is a tiny bit too large, tap it with a hammer or squeeze it gently with a vice (parallel to the hex flats) and you should be able to get contact on 2 sides.
Or take a piece of round just smaller than the recess and carefully file a slot until it fits the flats. That should at least get you something to measure. If your smallest needle file is still a bit too thick, grind one side to thin it.
Is it sufficiently tight that a pair of tweezers (with the ends ground to suit and held tight/shut with perhaps small vice grips) won't turn the screw out? I have some tiny hemostats, but even if I ground the tips, I doubt they would work.

[Smokedaddy]

Looks like the 0.050" didn't work. On another note. Anyone know of a accurate way of measuring the key? None of my calipers are able to reach the key in the turret. I tried using a gum eraser to get a impression but I'm not sure how accurate that method is. I used ImageJ to take a few measurements.

[Noitoen]

As already mentioned, a 2.5mm grub screw (setscrew) has that elusive 1.27mm, (0.050") hexagon socket in it.

Not all, some are near enough but are 1.3mm. It seems strange for metric but you can get 1.6mm and 1.4mm screws. I suppose that small size they go in 0.1mm increments

[old mart]

As already mentioned, a 2.5mm grub screw (setscrew) has that elusive 1.27mm, (0.050") hexagon socket in it.

[Noitoen]

This one has a .05 hex (3-48 set screw) The direct link does't work https://www.mcmaster.com/screws/thre...type~headless/

[Joel]

There is a link to a 1" SS 4-40 with .050 hex in post #5.
It seems likely that one can be obtained locally at a good hardware store.

[DDF47]

Oops! 4-40 set screw has a .050” hex socket. My bad.

[SHADOW]

Most hardware store have metric fasteners. Try a 2.5mm set screw.

[Smokedaddy]

#2-56 set screw has a .050 hex.

I'm not totally bolt/screw savvy. Have a link?

[DDF47]

#2-56 set screw has a .050 hex.

[Smokedaddy]

Well I gave this a shot this morning. The smallest allen head cap screw I had required a 2mm allen wrench. I had to turn down the head of the cap screw to 3.22mm so it would fit into the bore of the microscope turret. Unfortunately the allen key inside the turrent isn't 2mm, so I'll assume that my original somewhat accurate measurement was correct at 1.27mm (0.050"), guessing of course. Anyone know where I can buy a #0 maybe 1/2" long cap screw as shown in that chart I posted above? I wonder if they are somewhat common and I can pick one up at ACE Hardware?