Ways to measure holes center to center?

I have a metric motor with metric mount spacing & thought it would be interesting to grab the Sorensen & see what measurements could be made on the mount bolt hole pattern.

A strait edge yielded 3 15/16 on the left side of the 2 holes & 3 7/8 on the right side.

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That's 3 29/32 center to center with quick measuring & averaging. Holes must not be the same diameter.

Sorensen Center Mic time

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Yep, that's about 2 1/2' of case for a 13" Center Mic.

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Step 1 measured 1.950 (half scale is used in order for the tool to do the math).

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Step 2 is positioning the caliper so it's a slide rule type of generating the answer.

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Step 3 is the final answer. Close up of results.

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3.934" is the answer from the Sorensen. 3 29/32 = 3.9065 from the ruler.

Obviously this is not a situation where precision matters. But it does point out that bringing a ruler to a caliper match has bad results.
 
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I have a metric motor with metric mount spacing & thought it would be interesting to grab the Sorensen & see what measurements could be made on the mount bolt hole pattern.

A strait edge yielded 3 15/16 on the left side of the 2 holes & 3 7/8 on the right side.

View attachment 296453

That's 3 29/32 center to center with quick measuring & averaging. Holes must not be the same diameter.

Sorensen Center Mic time

View attachment 296454

Yep, that's about 2 1/2' of case for a 13" Center Mic.

View attachment 296455

Step 1 measured 1.950 (half scale is used in order for the tool to do the math).

View attachment 296456

Step 2 is poisoning the caliper it's slide rule type of generating the answer.

View attachment 296457

Step 3 is the final answer. Close up of results.

View attachment 296458

3.934" is the answer from the Sorensen. 3 29/32 = 3.9065 from the ruler.

Obviously this is not a situation where precision matters. But it does point out that bringing a ruler to a caliper match has bad results.
I absolutely concur Brockwood. I'd never heard of the Center mic before this thread and since getting it I've not had to wallow out a hole to make a pattern fit since. I don't care if I used a caliper, a ruler or what it would always be just enough off to have to jury rig it. The Center Mic and the cheapo DRO have totally upped my game. And for not a lot of $$.
 
After reading this thread, I want one! I'm not sure how much use I would get from it, but it is so cool! I always have trouble getting accurate measurements from existing holes.

Any advice of what to look for? Rust? Frozen slides? Size?
 
After reading this thread, I want one! I'm not sure how much use I would get from it, but it is so cool! I always have trouble getting accurate measurements from existing holes.

Any advice of what to look for? Rust? Frozen slides? Size?
It is a really useful tool. I don't use it everyday so that works against me as there is a procedure and feel to use it. A case is a necessity because it includes the instructions and another crucial piece is the practice gauge that looks like a piece of stainless flare bar with two holes in it. For me I saw no need for a huge one so I think mine is 10-12". Mine was kinda frozen with some corrosion but cleaned up really nicely. If it's all rusty that's a fail as its stainless and it means it was not taken care of. Check the pics to make sure the probes aren't bent. And know you can't do really small holes without the probe tips. Good luck, for some reason they have gotten crazy expensive last time I looked.
 
Okay, I pulled the trigger. I got this one on eBay for $40 + $15 shipping. It's claimed to be in excellent condition with the small points and reference. Seems to have little to no rust. I'll let you know in a week when I received it!

CenterMike_edit1.jpg
CenterMikeCloseup_edit1.jpg
 
Okay, I pulled the trigger. I got this one on eBay for $40 + $15 shipping. It's claimed to be in excellent condition with the small points and reference. Seems to have little to no rust. I'll let you know in a week when I received it!

View attachment 323310
View attachment 323311
I think that's real close to what I paid for mine. That's cool it came with the little probe tips, mine didn't.
 
They sold an 8" and a 13" model, plus some "booster rod" to extend the travel. There are seller's on eBay who will think they're made of gold, but they usually sell for about $40. You've got a nice one there.

I had the 13" one and got a Buy It Now for $25 shipped for an 8" about 3 weeks ago. It worked out OK, but I didn't look over the photos very well. My 8" is missing the RH slide clamp and fine adjust screw. It still works, maybe a little faster, but not as accurate. I just used mine this past weekend to measure the slot distance on a Harbor Freight 16x30 cart.

Bruce
 
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