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Optical punch

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Tinkering_Guy:
I saw this idea on one of the Yahoo! groups, or someone's site, or something.  Anyway, the idea is


* insert one of the optics in the through-hole,
* peer through the optic and move the thing around until it's right where you want a punch mark,
* hold it firmly in place while you remove the optic and replace it with the punch, and
* give the punch a tap with a hammer.


There are two optics, both 3/8" acrylic.  Each has a flat end and a lens end.  One has a crosshair etched in the flat end, and the other has a small circle.  Both etches are filled in with Sharpie.  The punch is 3/8" water-hardening drill rod, with one end knurled and a small point turned on the other, hardened and tempered.



The aluminum body of the punch has one through hole and three not-quite-through holes drilled and reamed to 3/8", for keeping the pieces.



Gluing a piece of non-stick rubber sheet to the bottom would complete it by making it frictionful when positioning.

Making the optics was arguably the most challenging part.  I had to calculate the appropriate radius for the lens based on the length of the optic and the refractive index of the material, and then make a tool to cut that curve (since I don't have a radius cutter -- yet):



In retrospect, I should have made the cutter from normal square cross-section turning tool stock rather than boring-bar stock, since the latter is a right bugger to get leveled before tightening in the toolholder.

After cutting the lenses, I used #1000 wet/dry sandpaper, followed by #1200 and #2000, and finally Meguiar polish to make both ends nicely transparent.  (I also discovered the hard way that you do not try to polish acrylic at high revs.  ::) )

Stilldrillin:
That looks a handy Tinkering tool.......  :clap:

Ideal for when you`re wearing the wrong pair of specs!  :thumbup:

David D

Bernd:
Very nice little write up on making that optical punch. :thumbup:

Thanks Tinkering_Guy. Could you did a little write up how you made that cutter for making the optical curve. :bow:

Bernd

Brass_Machine:
I agree with Bernd.

Very nice. I would like to try my hand at one, but I think the optics would give me fits.

Eric

andyf:

--- Quote from: Brass_Machine on July 20, 2010, 10:33:55 AM ---I agree with Bernd.

Very nice. I would like to try my hand at one, but I think the optics would give me fits.

Eric

--- End quote ---

The optics aren't that difficult; you don't need perfection, as long as the middle is OK. I made mine by trial and error, putting a very steep "coolie hat" taper on the end of a Perspex (= Lucite) rod, and then filed it over using a slight rocking motion to get a shallow dome, followed by fine grade sanding, metal polish and finally toothpaste.  

The shoulder on my "magnifying rods" is positioned such that, when placed in the central hole in the base, the end of the rod is about 0.5mm above the bottom. The three outer blind holes are for storage. The lower slightly fuzzy pic shows the circles (about 2mm and 1mm) inscribed on one of the rods. They are off-centre in the photo, because I couldn't see them through the viewfinder and thus couldn't get the camera exactly vertical above the lens. What is surprising is how much light gets down via the lens through the base to illuminate the job.



Andy

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