# How are two holes drilled at a center to center distance?



## HMF (Nov 10, 2011)

You need to drill two holes on a drill press or mill at a given center to center distance within say 1/32 of an inch.

How would you lay this out on the workpiece?


Thanks,


Nelson


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## Video_man (Nov 10, 2011)

One way is with "toolmaker's buttons", which are short, hollow cylinders of exactly the same diameter. Easy to make, actually. You locate the first hole, tap it for a holding screw and washer that clamp the first button in place and center the button over the hole (with a dial test indicator or other centering method). Then locate the second hole as accurately as you can in it's location, drill and tap as before. Then clamp the second button in place and by using a micrometer, dial caliper or whatever,  measure the distance between the buttons. Manipulate the second button until it measures the distance you want between centers plus allowing for the diameter of the buttons. Clamp the second button, indicate off it and re-drill your (larger) hole exactly where you wanted it.


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## churchjw (Nov 10, 2011)

A lot of it depends on where the holes are. Are you matching 2 existing holes on another part? Is it a flat surface? For the most part I measure from the edge (first datum point) to the first center then measure to the second hole from the same edge. Bisect these points with a line to give a cross point. Then center punch both holes. You should get a lot more than .030" accuracy. If you have DRO it will give you the center points. :headscratch: Did any of that make since. 

[video=youtube;kqxgzpobygM] http://www.youtube.com/watch?feature=player_embedded&v=kqxgzpobygM#t=164s [/video]

This video is a fair explanation. The square he uses is crap but the technique is sound. Hope this helps.

Jeff


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## Tony Wells (Nov 10, 2011)

Much depends on what instruments you have available, and the configuration of the part or material. At times, it's as simple as a square, a scribe and some Dykem. And good eyesight. In other words, it can be a layout issue. Could be done on a surface plate with a scribe in a height gage. If it's on a mill, you can beat +/- 1/32" easily by using the dials....that's what they are for. Optical center punches work well on accurate layout lines. Easy to hit +/- 0.002 with them.

Got any particulars on the piece. Nelson, or is this a hypothetical situation?


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## DMS (Nov 11, 2011)

Here is a two part series on layout for holes using 3 different methods.

[video=youtube;t6evpRPPlrY] http://youtu.be/t6evpRPPlrY [/video]

The guy has a ton of other videos, all very good.

The cliffs notes are.

1) Coat part with layout fluid
2) measure distance to holes with whatever instrument you have (steel ruler, calipers, height gauge, etc) and mark with a scriber
3a) If you are using a drill press center punch (tip, if your center punch is sharp enough, you can get it to run down the lines you made with the scriber. If you are gentle, you will feel pretty clearly the place where two lines cross, that's where you're holes should be)
4a) pilot drill with small (1/16") drill
5a) drill to size
6a) repeat for next hole

3b) If you are using a mill, center the spindle using a center finder or wiggler
4b) lock the table
5b) center drill/spot drill
6b) drill to size
7b) unlock table
8b) adjust dials to needed offset
9b) repeat steps 4-6 for next hole.


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## EmilioG (Nov 2, 2014)

I need to drill four 10mm holes on a square piece of 1018 steel that is 3/4" square.
Two holes on one side and two on the other side about 2" apart and they shouldn't cross, although it would be OK
if I can get clean through holes.  If they intersected slightly, it would be OK, I just want clean holes with no burrs.
The length of the part is 3" for the holes.  I don't have a height gage, surface gage or indicator. What's the best approach?  Thanks


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## Whyemier (Nov 2, 2014)

A square and a good set of dividers. 1/32"  is fairly "loose" tolerance.  Locate your first hole, lightly punch the center. Set one point of the dividers, previously set to your dimension +- 1/64". scribe your location point. The square would be used for setting a scribe line for your X or Y location. This is what I would have done back in the shipyard if the boss had phrased it as you did.


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