Accurately Positioning Holes Drilled in Metal

[Rich Jakowski]

Here’s a very basic question for the great group of experts on this forum. How can one be certain a hole drilled in metal goes where you want it to be? Let me start by saying I’m not a machinist, but have been fooling around with tools for ~50 years. I usually begin this process with a punch mark that I try to locate by eye. I then drill the hole with a drill that's smaller than what I want the hole to be to see if it really is as centered as I intended. If everything looks OK I make a final pass with the appropriate size drill.  But - here are a couple of problems that seem to crop up fairly often:

1. The initial punch mark is slightly off center and I have to “drift” it over to where I want it before starting to drill.

2. After drilling the first, smaller hole I find the hole is still slightly off postion and have to mess around with a needle file trying to center the hole before drilling with the final, appropriate size drill.

On more than one occasion my method has resulted in a complete failure and I have to weld the hole and start over. BTW: the second attempt is always harder since the welded metal has to be annealed and even then it never seems to drill as easy as the initial hole. I’d love to learn any tricks you guys might have to reduce the chance of error when locating and drilling holes in metal, especially the ones need to be accurately positioned when assembling lock part sets.

[George F.]

If you find your punch mark is slightly off it's intended spot, use a center drill to get it where you want it. A center drill is a stubby looking shank that is very rigid, it has a center section that has no cutting flutes , is just a smooth shank. On each end there's a very short cutting edge about 1/4" long. This rigidity allows the bit not to follow the punch mark unless you want it too. it's best to have the work in a drill press vice,  or a    z-y vice.  You only drill down a little so the original punch mark has been removed. After you have the hole moved to where you want it, change the center drill for the drill bit assortments you need.  ...Geo.

[B.Habermehl]

Use a prick punch first in your layout process. This is a more pointy version of the center punch 60 degree included angle point verses 45 degrees on your center punch. You can grind it to a bit sharper than 60 degree point. The advantage to the sharper point is it is easier to place the punch more  accurately. You can actually feel your scribed layout lines with the sharp point. Punch lightly  then deepen the punch mark with a center punch.   BJH

[davec2]

Following George F's advice, I would also invest in a good drill press or mill vice and good quality, sharp drills.  Nothing will put a hole in the wrong place faster than not holding the work piece rigidly or using a dull drill.

[flehto]

As said previously, scribe the 2 centerlines and take a pointed punch  {60 degrees, inc angle}and run it done the first scribed line until you feel it fall into the second scribed cross line and center punch.  I then re-punch using a standard center punch.  Then use a small  drill that's slightly  larger than the  web of the finish drill. ....Fred

[44-henry]

The center drill is your best bet starting out. I have also found some uses for an optical center punch which can really help with some jobs.

[P.W.Berkuta]

It all starts with the holes layout . You punch it in the wrong position and it ends up in the wrong place. No secrete here A center drill will start the drill in the hole where the center punch is started.  A milling machine will move the hole to the position you want when you f$%# up. A hand electric drill will move the hole also . If you are looking for CNC accuracy then use a CNC machine. Hand made IS hand made and the skill that goes along with hand made -- some people are better than others : Enough said -- sorry for being blunt but it does boil down to skill and talent.

[jerrywh]

#1-- never trust your eye to find the center of an object.  Measure or use dividers.  Then do it with the prick punch and center drill as described.  Center drills won't drift.
   

[JBlk]

My son is an antique collector and he told me the easiest way to spot a phony is that the piece is to perfect.I am sure that there were some real craftsmen but when you consider the tools and conditions they worked under, I'll bet they made mistakes to.

[Rich Jakowski]

The center drill is something I forgot about, even though I have a few of these in the tool box. Additionally, the prick punch with a sharper angle also makes a lot of sense. I agree with P.W. Berkuta that the issue of skill can never be left out of this picture, also tempered with a bit of patience to take the time to make sure that punch is exactly where you want it before you give it a whack with the hammer.

I always try to keep the old expression "Never enough time to do it right, but always enough time to do it over." in mind when doing things like this. 

[jerrywh]

JBIK
  Well if any body ever needs an excuse for making a mistake , that is the oldest and best one around.  The only defect in it is , some of the gumakers don't think the [ old masters] ever made mistakes. 

[NSBrown]

One thing I've learned at my bench is:

       The slower I go, the sooner I ge done.

[rick landes]

I have a Starett spring loaded center punch that I use vs a hammer and a center punch.

After marking out (measured...as Jerry noted) I bring my CP point to the crossmark at a flat (say 30 degree) angle to the work surface. Then locate the point to the mark and roll the punch upward to perpendicular relative to the work surface, push the punch down and the spring "snaps" the mark for the center drill.