# measuring holes



## marcros (24 May 2013)

This may be a daft question, but how do you accurately measure centre to centre of 2 existing holes? do you measure to the edge and add half of the diameter of each hole? Or can you get some form of conical centre finder ? It seems such a smple measurement, but if you are talking accuracy of half a mm you cant really guess at it.


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## bugbear (24 May 2013)

marcros":1chokugh said:


> This may be a daft question, but how do you accurately measure centre to centre of 2 existing holes? do you measure to the edge and add half of the diameter of each hole? Or can you get some form of conical centre finder ? It seems such a smple measurement, but if you are talking accuracy of half a mm you cant really guess at it.



You can either measure inner-surface to inner-surface (with a normal caliper) then outer-most surface to outer most (with an inside caliper), and average the two measurements, or you (indeed) get conical tips for calipers, beam compasses etc.

BugBear


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## Spindle (24 May 2013)

Hi

I do exactly as you described using a digital calliper.

Regards Mick


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## spinks (24 May 2013)

If the holes are the same size why dont you measure from the right hand edge of hole A to the right hand edge of hole B? That will tell you exactly what the hole centres are


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## jasonB (24 May 2013)

If they are withing the range of digital callipers you will get close enough by doing as you say inside edge to inside edge plus half of each hole dia.

Better is to fit shafts into the holes and measuer overall then subtract half the dia of each hole.

You can then go to plug gauges and slip gauges or centre pitch callipers

J


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## wizard (24 May 2013)

spinks":3ai6cu2x said:


> If the holes are the same size why dont you measure from the right hand edge of hole A to the right hand edge of hole B? That will tell you exactly what the hole centres are


do as spinks says simples


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## Phil Pascoe (24 May 2013)

Yes, but if you do as BB says, you don't need to be certain that the holes are the same size.


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## Spindle (24 May 2013)

spinks wrote:

If the holes are the same size why dont you measure from the right hand edge of hole A to the right hand edge of hole B? That will tell you exactly what the hole centres are

That only works if you are using a ruler - marcros's method works with callipers and will allow greater accuracy.

Regards Mick


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## spinks (24 May 2013)

with a decent rule you should be able to get within 1/4 mm....the OP asks for 1/2 mm accuracy so the method i mentioned should suffice!


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## ChrisR (25 May 2013)

I was taught as an apprentice, which was many, many years ago, to use the method that Spinks, described, assuming both holes are the same size, always served me well, and I am now five years retired. :wink: 

Take care.

Chris R.


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## Johnboy (23 Jun 2013)

If the holes are the same size then measure one with digital calipers and then zero the calipers at this dimension. Then measure outside of one hole to the outside of the other this will give the centre distance directly.

John


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## nanscombe (23 Jun 2013)

marcros":1f1s88tj said:


> This may be a daft question, but how do you accurately measure centre to centre of 2 existing holes? do you measure to the edge and add half of the diameter of each hole? Or can you get *some form of conical centre finder* ? It seems such a smple measurement, but if you are talking accuracy of half a mm you cant really guess at it.



Couldn't you use an appropriately sized brad point bit?

You could hold a piece of wood on the other side. Press the drill through each hole. Measure the distance between the two pin-pricks which represent the centre positions of the holes.


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## Baldhead (23 Jun 2013)

spinks":3sgevsm3 said:


> If the holes are the same size why dont you measure from the right hand edge of hole A to the right hand edge of hole B? That will tell you exactly what the hole centres are


+1
I used this method when fitting roof trusses , a friend who helped was marking the centre of each truss until we pointed out our way, the look on his face was one of amazement.

BH


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## Phil Pascoe (23 Jun 2013)

Yes, that's fine - as long as you are certain the holes are the same size. It wouldn't work if for some reason your trusses were different thicknesses. If you go back to Bugbear's post and do it that way, it works for different sized holes as well. If you've drilled the holes, and you KNOW they're the same size, fine.


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## marcros (23 Jun 2013)

my main application, when asking the question is when copying something that has already been made, or for drilling a router plate etc.


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## Eric The Viking (26 Jun 2013)

Edge A to edge A, every time, and with digital callipers, to boot.

Aren't those callipers wonderful things?

E. (probably needing new glasses again).


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## Myfordman (27 Jun 2013)

Near edge A to far edge B plus far edge A to near edge B all divided by 2

Will give the centre to centre distance even if the holes are different diameters

Easily done with digital very nears. Measure one dimension, zero and measure the other, mentally divided by 2 and ignore any sign


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## Eric The Viking (27 Jun 2013)

You win! You halve the error (assuming its consistent).


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## doctor Bob (27 Jun 2013)

I guess by eye but it's only accurate to 2 dp :lol:


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