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Optical punch
Tinkering_Guy:
Since the first one I made was pretty much ad hoc, and I like the radial design andyf has, and I intend to make another one at some point that's a bit more professional, I drew up plans for my next version. A pic of the plans is attached, but I've also saved them online:
* In Solid Edge 2D format;
* Exported to AutoCAD DWG format; and
* As a PDF document.
Now, if I were to make up construction steps, they'd look something like the following. (I reserve the right to amend these later, when I actually make the thing, and have photos of the process.)
[*]Turn down the base to the appropriate diameter, face it off, centre-drill, and drill/ream the centre hole. If you have an 'over' reamer for 3/8" (i.e., a 0.376" reamer), use that.
[*]Part the base off, leaving a few thousandths for the next steps on the mill.
[*]Mount the base on parallels in your mill, faced side down. Flycut or mill it down to the correct thickness.
[*]Position the base to bore the first keeper hole. Since these are blind holes, you don't need to leave space underneath for drill-through. (Unless you're a klutz like me.)
[*]Centre-drill and work up to the 1/8" drill for the dimple at the bottom of the keeper hole. Drill that one down to a depth of 0.940 or so.
[*]Bore and ream the keeper hole to a depth of 0.875.
[*]Lather, rinse, and repeat for the other two keepers. Put the 1/8" dimple in the bottom of each so it doesn't matter in which one you put the punch.
[*]Glue some thin rubber or fine sandpaper to the bottom of the base and set it aside. Don't worry about the through hole at this point.
[/list]
Now the punch.
[*]Mount up some 3/8" drill rod (or some slightly larger and turn it down), and face it off.
[*]Turn the point onto the punch, and make a clean shoulder. Don't break the edge; you want it sharp for now.
[*]Part it off at about 2".
[*]Put the base with its now-dry glue, friction side down, on a flat slightly-yielding surface, like a scrap of Formica or hardwood.
[*]Insert the punch into the centre hole, punch end down. Hold the base firmly against the surface, and give the punch a rap with a hammer and it should nicely cut out the hole in the rubber or sandpaper. You can now break or file the edge of the punch end if you like. Put the base aside.
[*]Mount the punch back in the lathe, parted (rough) end out. Add knurling if you like (I recommend it), face it off, and break the edge.
[*]Hone the punch tip and heat-treat the punch. Set it aside.
[/list]
Now the optics. Use whatever transparent material you can get; Lucite®, acrylic, whatever. Just be sure to read up on how to machine it, because these thermoplastics can be tricky. Go very slowly and carefully. (Actually, I suspect you're probably better off not using Lucite® because of its curious internal reflection properties. I suspect acrylic is better at light-gathering in this situation.)
* Mount up a few inches of your plastic rod, face it off, and turn it down to 0.550" for about 2". I recommend a shear tool that cuts at the tangent point.
* Turn it down to 0.375" for 1" from the faced end. Unfortunately, the shear tool doesn't let you cut to a shoulder, and you really need a sharp shoulder here.
* Stop the lathe and make the reticle markings.
[*]For a crosshair, put a sharp-pointed bit or scribe in the toolholder, precisely at the height of the spindle axis. Lock the spindle and scribe across the width of the face. Unlock the spindle, turn it 90°, and repeat the lock and scribe.
[*]For a circle, use a tool with a very small nose radius, and etch the tiny circle in the face
In both cases, you want the etched lines to be very narrow.[/li]
[li]Polish up the face and the body of the optic. Very light touches up to about 1000-grit sandpaper (2000-grit if you can get it), followed with Meguiar's plastic polish. Very light touches, very low revs.[/li]
[li]Remove the work and clean it up; wash all the polish off. Turn it around and insert it in the chuck/collet up to the shoulder (protect it with some shim brass or paper or the like.)[/li]
[li]Make a tiny mark at 0.525" from the shoulder, and another ar 0.550". Face down almost to the latter.[/li]
[li]If you have a radius cutter, mount it and set it to a radius of 0.155". If you have to make your own cutter, that's the radius you want.[/li]
[li] Radius-face to the 0.525" mark. You should now have a dome about 0.025" high on the end of the rod.[/li]
[li]Repeat the polishing steps.[/li]
[li]Remove the optic, rub across the reticle face with a Sharpie or other permanent marker, and rub off the excess. This should leave ink in the reticle etch.
[/list]
And that should do it. Your optics and punch should fit snugly in the keeper holes, and freely -- but not loosely -- in the centre hole. The punch is longer than the optics, so you should be able to insert it and tap it without hitting the optics if they're in their keepers.
Bernd:
WOW :bugeye:
Nice write up and plans. Thanks very much.
Just added another project to that never ending list of shop projects. :lol:
Bernd
DeereGuy:
Nice job on the drawings and great write up..thanks!
Rob.Wilson:
Cracking Job Tink :clap: :clap: :clap: :clap: :clap:
Great thread :thumbup:
Rob
Artie:
Holy crap! ANOTHER one of those things that I HAVE to have...... thanks guys, this thing is so simple yet looks to be so effective.... Im doing it today.... Howdy Wilso....
Thanks for starting the thread... very very interesting.
Rob T
As an aside, this thing looks to be particularly useful for those of us who's eyes arent what they were last year.... :( :lol:
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