Optical Center Punch

Check out Rustinox. He posted a video on making one.
 
mikey said:
Go for it but let us know if I was off base. Tried to be honest, not discouraging.
Click to expand...

Oh yea, I get it, man. I'm not trying to brush off your advice either. I know there's limitations to any device that relies on optics and the human eye. The most accurate way to locate holes would be for sure, like you said, to use a milling machine or at least an X,Y table on a drill press. I lack both of those options and even with an X,Y table I'm not sure my drill press is rigid enough to really use it effectively.

I know what your saying about feeling the intersection of scribed lines. I've been doing that lately but sometimes I miss the mark a bit. I even ground two center punches, one at about 60 degrees and another at around 130. The idea was that the 60* punch would more easily find the scribed intersection. I use it to make a very light mark. Then I hit that mark with the 130* punch to make it bigger for the drill to find. The fact that the 130* punch is slightly more obtuse than the 120* spotting drills I use means that the drill should first contact the center of the mark, not the outer periphery, resulting is the highest degree of accuracy.

I also picked up some good spotting drills. Again at a more obtuse 120* so the following 118* drills find center more easily.

I used an optical center punch once or twice in welding school many years ago and was impressed with the accuracy it could give. Even with the tiny bit of clearance between the body and the punch and some parallax, I think it'll be more accurate to use it than to not use it.
 
Way back when I used one that had a small spring-loaded hammer. You'd look through the eyepiece to position it, then pull the trigger to mark the spot. I got the feeling that it was pretty old when I used it (1970s). As I recall it was always offset maybe 0.010" in the same direction, but was good enough for most stuff.
 
Last edited:
You say " I'm not sure my drill press is rigid enough to really use it effectively" If this is true just how accurate do your punch marks have to be? Try using a prick punch, lightly struck, to mark the location of the hole. If dimple location is correct follow with a center punch. If dimple location is off, angle the prick punch and lightly drift the mark until it is on location then center punch.
 
Here's an article describing a build of an optical center punch. It looks to be easily constructed.
 

Attachments

  • Optical Center Finder.pdf
    2.2 MB · Views: 9
mikey said:
I have the one from Lee Valley and I don't use it much but I do have an opinion on it.
Click to expand...
I bought the Lee Valley model several years ago and it works as advertised. I also have an opinion.

This tool is not of the same quality as a lot of other things I have bought from Lee Valley.
  1. The case fell apart at the hinges
  2. The plastic lens chipped
  3. The punch dulled after a few uses
For $62.50, I would recommend looking elsewhere if you're in the market for one of these tools.
 
I love mine. Use it all the time. Punch marks are typically within a few thou which is way better than freehand!
Robert
 
To deal with parallax, wouldn't it make sense to make an aperture sight (a ring mounted to a rod in a parallel plane above the jig) so that your angle of incidence and focal distance are always the same? For you old guys, you could even put a magnifying diopter in the aperture. Seems easy enough. Also, would a groove and a quality o-ring reduce bore play to a tolerable level (pun definitely intended)? I've never used an optical punch, but it seems like the shortcomings can be overcome or reduced with a little bit of mechanic-ing.
 
The sight would be in the way of striking the punch. In practice, I have not found parallax to be a significant problem. That may depend on the brand and the way the lens is made? I do not seem to have much trouble aligning my eye to the center.
Robert
 
You must log in or register to reply here.
Back
Top