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Ways to measure holes center to center?

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BGHansen

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#31
Here's the 13" Sorenson I picked up off eBay for $50 plus shipping. Pretty happy with the mike, hit the same 11.000" every time on the standard. Daryl, thanks again for the tip!

Bruce

20170623_140900.jpg
 

gr8legs

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#34
After reading about the Sorenson Center Mike I knew I had to have one (It regularly made me crazy to try to accurately find the distance between two holes). All I can say is that the Center Mike is slicker than boiled owl snot. Wow. What it does is measures the near distance and the far distance, mechanically adds them together and divides by two, which is the indication on the Vernier. Takes 10 seconds and indicates to 0.001

They sell on eBay very reasonably and if you ever need to measure hole center-to-center distances this will become your go-to tool.

Stu
 

Uglydog

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#35
gr8legs,
Which length Sorenson did you purchase?
I've wondered if there is any advantage with the little one. They appear to function the same.

Daryl
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BGHansen

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#36
Pretty sure the function is the same regardless of size. The vernier scale is double-sized; 1.000" measured is 2.000" on the Sorenson scale. Pretty simple (but ingenious) device. Start with the LH side at 0.000", measure the distance between the holes on the inside (or outside would work too, just have to do the opposite on the second measurement). Then slide the LH stop from zero to the RH which now starts your next measurement at "where you left off". Do the 2nd measurement and because the scale on the Sorenson is 2X, you are reading the total of the inside and outside dimensions divided by two. Pure genius!

Bruce
 

gr8legs

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#37
I purchased the 8" version and liked it so much (and besides that, I'm a tool junkie) I just eBay'd a 13" one plus the measurement extension bars.

It's a horrible addiction with no 12-step program. Luckily, this site serves as a support group - the only difference being it's a cheering section :)

Stu
 

Uglydog

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#38
If you get a chance, I'm looking forward to hearing about how the extension bars work for you.
My projects tend to be on a larger scale.

Thank you,
Daryl
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gr8legs

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#39
If you get a chance, I'm looking forward to hearing about how the extension bars work for you.
My projects tend to be on a larger scale.
For Daryl and anyone else interested:

The "Booster Bars"arrived yesterday along with a 13" Center-Mike from another eBay seller and I tried them out.

First and most important, these extensions only work with the 13" version of the Center-Mike. They extend the 13" range up to 22 inches center-to-center. Sorensen was clever in providing a full-range of measurements but you had to have both the 8" and 13" basic versions to get the 0.25" to 22" range.

<edit> No, that's not right . . . The 8" will measure 0.25" - 8" and the 13" will measure 0.25" to 13" . . .duh! But the extensions do only work with the 13" </edit>

I'm happy with my purchase - another tool! Woo hoo!

Stu
 
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Uglydog

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#40
That's great information. Huge thanks!

Daryl
MN


Sent from my iPhone using Tapatalk
 

C-Bag

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#41
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
 

Bob Korves

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#42
[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...
 

C-Bag

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#43
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.
 

Superburban

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#44
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
 

RJSakowski

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#45
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
 

Doodle

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#46
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.
 

C-Bag

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#47
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.
 

Uglydog

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#48
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
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Doodle

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#49
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.
 

Splat

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#50
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. :)
 

toolman_ar

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#51
I just read this thread...

Clicked buy it now...

13" + Bars on the way...

Sometimes I feel like it is pear pressure or tool envy.

Very cool tool, surprised I have not seen this before.

toolman_ar
 

RJSakowski

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#52
Some time ago, I came to the realization that every real world part has some deviation from the nominal value. The question is how much.

Engineering drawings all have some implied or specified tolerance for dimensions. The tolerances specified take into account functionality of the part and cost of manufacturing.

Assuming a part is made to specification, which is often not a good assumption (think Asian manufacturing), there still can be a significant deviation from the nominal value,

When a part is reverse engineered, we measure a set of dimensions to construct a new engineering drawing. We have no idea as to what the nominal values were originally and we implicitly set new nominal values and some tolerances around those values. This new set of dimensions and tolerances may actually permit the manufacturing of a part which would be outside of the intended tolerance of the original design. I expect that many of us have run into exactly this problem. Where an aftermarket part advertised as a direct replacement for an OEM part doesn't fit. Automotive parts are a good example.

Another example is R8 tooling. Bridgeport designed and made the original buut never released the engineering drawings for the R8 taper. As a result, all aftermarket R8 tooling as well as the machines utilizing the the R8 taper were derived from reverse engineering. A good many of us have had to rework the keyway on R8 arbors. I have also had to rework the key on a Grizzly mill to keep it from binding.

So how do we utilize reverse engineering when we have no other option. One way is to make an assumption as Bruce did that dimensions were originally intended to be nice whole numbers. I do this myself and when measuring a dimension, check to see if it works in either Imperial or metric formats (I have seen mixed units in parts, mostly in those designed in metric units that throw in a few Imperial dimensions).

Another way is to assume certain symmetries in geometry. If three holes are located on a circle, we will assume the circle is concentric with other geometry and that the holes are equally spaced. When I fitted a backplate to an Asian chuck, I used that technique. I measured hole to hole dimensions of the three mounting holes. There was variation between the three measurements but when I plotted them out in a drawing and fitted a bolt circle to them, I was able to get a better picture as to what the original intent was. A check on the distance of each hole to the registration boss helped to verify the intent.

A third way is to measure a large number of parts, preferrably from the OEM and manufactured over a large period of time, and average the values. If you look at any distribution of values, dimensions include, the spread will typically follow a bell shaped curve. The true value will be somewhere close to the center of the bell. This is not always the case but even so the average value is still a better indicator of the true value
 

Bob La Londe

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#53
I have some small tapered block pairs that have a radius on the back side. A pair of them in a hole allows you to get a fair measurement of the diameter of the hole using an outside mic. If you do not get good engagement it might not be as good as in inside mic, but its pretty good. My inside mic has has a limit, although it will measure smaller holes than my telescoping hole gages. Anyway, how about two pairs of tapered blocks. On pair in each hole. Align the flat side of both sets against a straight edge. Get your hole diameters. Get the outside dimension of the two pairs of blocks. Subtract the radius of both holes. I imagine if the holes aren't total crap that will get you pretty darn close. Probably won't work in thin sheet or in car wheels very well due to the small contact area, but its another tool in your arsenal.

Some time ago, I came to the realization that every real world part has some deviation from the nominal value. The question is how much.
Yeah no kidding. That was one of the hardest things for me to get my head around when I started machining parts. It doesn't have to be perfect. It has to work. If it looks good doing it that's a bonus.
 

EmilioG

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#54
You can also use an edge finder to touch off on 4 points of a hole using a DRO. (courtesy of Tom Griffin Tom's Techniques).
 

BROCKWOOD

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#55
After all this talk about the Sorensen, I went looking & found a deal I could not pass up! $45 + shipping for the 13" version & includes the #12 Booster Bar Accessory. Looking forward to getting this delivered & trying it out. SORENSEN CENTER MIKE 02@.jpg SORENSEN CENTER MIKE 02a.jpg SORENSEN CENTER MIKE 02y.jpg SORENSEN CENTER MIKE 02z.jpg
 

4gsr

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#56
Yeah, I almost bought that one. I passed since I bought the smaller one he had for sale a while back. I'm interested in that "booster bar" and how it works. Let us know.

Nice find!

Ken
 

C-Bag

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#57
I'd be interested in how the booster bars work too, even though I bought a 8" Mike because all my work is within that scale. Seems like you got a heck of a deal Brockwood because that's what I paid for my 8".

I can't believe I'd never heard of this tool before this thread. It has made a huge improvement in my hole patterns, along with the DRO.
 

BROCKWOOD

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#58
Yeah, I almost bought that one. I passed since I bought the smaller one he had for sale a while back. I'm interested in that "booster bar" and how it works. Let us know.

Nice find!

Ken
Will do Ken. I saw where a few here bought the 13" Sorensen + bars, but had no idea what + bars meant. I don't have a clear pic the booster instructions. If they are as clear as the center Mike 3 steps: piece of cake!
 

BROCKWOOD

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#60
Emilio, maybe someone who has theirs can answer your question & mine. Would the Sorensen be capable of directly transferring the distance?
 
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