Ways to measure holes center to center?

I was going to wait to pile on my thanks Daryl until my 8" Sorensen got here tomorrow, but I couldn't wait. Having terminal TAS( tool aqusision syndrome) I can't tell you how timely this thread is. Hole layout has always been a tough process for me and I'd never heard of the Sorensen. Makes sense there would be a tool for it but not being a machinist by trade I'd never bumped into it.

But through the other suggestions offered here I used my calipers and my numbered drills as a Gage to accurately figure centers of the 4 hole pattern I've tried over and over to do accurately. The revelation was I'd assumed the pattern would be 1" centers. It was actually .990! So since I just upgraded my mill with a cheap 3axis igaging DRO it was quick and easy to just place the first hole and layout .990" apart 4 holes. And for the first time it came out perfect. For me measuring is just half the battle. I wish I would have gotten a clue and gotten the lo buck DRO before as it has made all the difference. Best $130 I've spent so far
 
[QUOTE="C-Bag, post: 504000, member: 45394
But through the other suggestions offered here I used my calipers and my numbered drills as a Gage to accurately figure centers of the 4 hole pattern I've tried over and over to do accurately. The revelation was I'd assumed the pattern would be 1" centers. It was actually .990! So since I just upgraded my mill with a cheap 3axis igaging DRO it was quick and easy to just place the first hole and layout .990" apart 4 holes. And for the first time it came out perfect. For me measuring is just half the battle. I wish I would have gotten a clue and gotten the lo buck DRO before as it has made all the difference. Best $130 I've spent so far[/QUOTE]
What kind of mill do you have? .990" is very close to 25 mm. If it is an Asian or European mill I would not be guessing 1 inch, very unlikely...
 
I guess the points are getting scrambled. My focus was accurately measuring hole centers, not repairing my mill/drill so I didn't catch Daryl's project just the measuring.

For the record I've got an old RF 30 mill/drill I picked up cheap because it needed a lot of TLC. But it fit my noob capabilities and as time has gone on and my skills and need for greater accuracy have gone up I've upgraded and repaired the old war horse as needed. The project I've been working on is making a machine with 80/20 extrusions. The series of 80/20 I'm using is the 10 series which is supposedly based on 1" and multiples there of. There is also a metric series but your observation Bob makes it seem that while the overall dimension of this material may be 1"s the slot and bolt pattern spacing is metric. Tricky of them.
 
I have always just measured the far side to far side, and inside to inside. Then take the farside to far side, and subtract the near side measurement. Divide that figure by two (That gives you the two center to center distances for just the holes), then add the near side to nearside measurement back in.

A Little simpler written for the math guys:

(far side- nearside)/2 + nearside
 
I have always just measured the far side to far side, and inside to inside. Then take the farside to far side, and subtract the near side measurement. Divide that figure by two (That gives you the two center to center distances for just the holes), then add the near side to nearside measurement back in.

A Little simpler written for the math guys:

(far side- nearside)/2 + nearside
or just (far side + near side)/2
 
The way I do it is select a drill bit shank that tightly fits the hole, draw an x line in CAD, intersect the x with a Y line, create a circle Tangent to X, Y lines and type in the circle diameter (drill shank size). Stick a tight fitting drill bit in the second hole, use digital calipers to measure outside dimensions of the two drill shanks, create a line parallel from the y axis line the distance just measured. Create circle tangent, tangent, and circle diameter (second drill shank size). Now you have a CAD drawing started, CAD has measured distance for you between centers.
 
I received my 8" Sorensen and with some cleanup(it was corroded and stuck) along with training with the provided gage I'm very pleased. It also showed my previous process was off by .010. The bolt holes were exactly 1" apart, not .990 like my caliper/Gage plug method came up with. The Sorensen is far quicker and more accurate and was totally worth the $50+ shipping to me. I guess the good fit this time was due more to the accuracy of the new DRO along with cleaning and adjusting X Y lead screws than super accurate measuring. Wish I would have known of the Sorensen along time ago.
 
Now you have a CAD drawing started, CAD has measured distance for you between centers.

Someday perhaps I'll understand CAD. Thus far I only used a beat up little drafting board and some Trig Tables. I'm pleased to know that CAD is so flexible!!

Daryl
MN
 
The way I do it is select a drill bit shank that tightly fits the hole, draw an x line in CAD, intersect the x with a Y line, create a circle Tangent to X, Y lines and type in the circle diameter (drill shank size). Stick a tight fitting drill bit in the second hole, use digital calipers to measure outside dimensions of the two drill shanks, create a line parallel from the y axis line the distance just measured. Create circle tangent, tangent, and circle diameter (second drill shank size). Now you have a CAD drawing started, CAD has measured distance for you between centers.

I could not get a picture posted to support this post, try this:

upload_2017-8-9_7-16-29.png

Also, YouTube has lessons posted for using CAD programs and they are very helpful.
 
I'm with RJ on this one. If the holes are known to be the same diameter then I measure one with the calipers, zero the caliper, then measure the distance between the outside edges of the holes. Good enough for govt work. :)
 
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