# How to locate a center punched hole for drilling?



## HMF (Apr 20, 2011)

Guys,

After a hole has been center punched in the material, how do you accurately locate the "dimple" with the lead drill?

I read the following methods:

Re-punch your prick punch mark. Line up close, start drilling with a lead drill. Use an 1/8 " or so. The drill will follow the path of least resistance and start in the punch mark. The finish drill will also follow the path of least resistance (1/8" hole).

Or use a wiggler and magnafier, followed by center drill, drill, boring bar, and reamer works.

If great accuracy is required, a bore scope can pick up layout lines within .001. Or use toolmakers buttons. Buttons can be made from a scrap of .500 drill rod, faced square and drilled .281 or so. Drill and tap @ hole locations. Clamp buttons and adjust with height gage, venier caliper, or standards. Indicate your buttons in. Drill and bore as above.

Are these suggestions correct- or is there a better method you know of?

Thanks,


Nelson


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## pjf134 (Apr 20, 2011)

What I do is face off end of rod till no dimple is there, then punch using mag. glass, then start a hole using small center drill. Proceed from there with drilling or whatever is required for job. I am not making parts for NASA though. Lining up your live center with center of part checks for alignment of tailstock too. This will get you close for most jobs.
 Paul


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## 8ntsane (Apr 20, 2011)

I assume your talking about getting on the punch mark on your mill. If so, the wiggler with the pointy end works as good as anything. On the drill press it can be done with a centre drill , and it will centre itself, but how accurate? thats questionable. The main problem with punch marks, is getting the punch mark exactly where you want and need it 

Paul


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## Tony Wells (Apr 21, 2011)

Paddy reminded me of a method I used on a radial drill. I crammed a dead center into the spindle and, with the column and head unlocked, float the thing around until I could plant the center point in the punch mark. Then lock everything.

On a mill, I use a somewhat odd method if I really need to use the punch marks. It's hard to explain without pictures, but I'll try. Mag mount an indicator on the side of a drill chuck or use an Indicol to hold it. In the drill chuck, mount a short, accurate "pointy rod". Between the "pointy rod" and the punch mark, pinch up a small dead center. Or something with a female center on one end and a sharp point on the other. Point the indicator at the lowest point possible on the body of the dead center. Now rotate the spindle and observe the indicator. Since the indicator is rotating with the spindle, any error in the concentricity of the dead center, and hence the punch mark is indicated. 

This method also works on a lathe to indicate a punch mark on a plate, for instance, in a 4 jaw chuck. Of course, in the lathe, there is the variation of sticking the indicator on the bed or wherever, and pointing the indicator near the large end of the dead center near the work. When the work is rotated, the dead center "wobbles" until the work is running true. Let me know if this isn't clear, and Ill try to draw up something or take a pic.


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