# Ways to measure holes center to center?



## Uglydog

In a separate thread Brockwood inquired how I intended to measure large holes center to center on a VN overarm support.
Well, I'm finally getting around to answering how I might do it.
But, more importantly while I'm presenting some options.
I suspect that there are many more ways to accurately measure.
I'm very interested in how many different ways we might get the job done.

Please submit  your solution to the problem.

Daryl
MN


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## chips&more

Cordax Measuring Machine


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## Uglydog

This Sorenson Center Mike is my go-to center to center mic. (Yes, they call it a "Mike").
It somehow calculates the actual centers of the holes.
Note the directions.

Daryl
MN


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## Uglydog

chips&more said:


> Cordax Measuring Machine



Great.
Would you please give a brief explanation of Cordax.

Daryl
MN


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## Uglydog

This device uses a dial tail indicator.
It's great for accurately comparing holes.
I've found it awkward for this application as lining up the gage blocks is a clumsy process for me . 
Likely a better way to do this.

Daryl
MN


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## Uglydog

This uses a vernier caliper and some telescoping gages.
Gotta do a little math. Not difficult.
The vernier tips do not have a  not radius therefore I'm not sure that it is as accurate as I'd like.

Daryl
MN


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## Bob Korves

Daryl, I would first measure the overarms, outside to outside dimension, then inside to inside.  Then do the math to determine the center distance.  Then make a gauge the exact length you need and use it as a spacer gage for the stop dogs on the mill table, or just measure the distances between the stop dogs as you set them.  Set up the first hole while against the first stop, then bore away!  Repeat at the other stop.

Edit:  for best results, use your jig borer...


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## Tony Wells

For lack of a Cordax (CMM), If my mill had a DRO I would sweep the holes and get the c-c dimension through a little trig if I didn't want to bother lining up one axis. That's one advantage to a CMM. It will establish an artificial axis independent of alignment with the machine axis and give a direct reading. One assumption is either required, or averaged into the calculations by the CMM, and that is the roundness of the holes. Holes, similar to planes, can be defined by any 3 points in a plane, and for every 3 points, there is only one circle that includes these three points. If the hole is not round, wherever the 3 points are taken is where the center of _that_ circle is derived. Any points beyond the three simply make the infinitely thin theoretical line defining that circle "thicker" so as to include those additional points.  Generally, the more points taken in an out of round hole, the better representation of the actual base circle will be developed and the center of that sort-of-round shape can be determined. Obvious defects such as gouges and intentional sawed expansion slots should be avoided when taking the series of points measurements.


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## BROCKWOOD

Sweet! What width did you come up with?


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## Rustrp

Just a bit of quick input based on my sheetmetal layout experience. The first thing I see is a part with three holes, so my first thought or question is center to center or centers. Do the holes have the same axis? For center to center (if the holes are the same dia. and accurate) I measure outside to inside. If the holes are different diameters then I do the same and add a little math. Of course when the holes do not have the same axis there's just more math because we have center to center and centers to measure. When the part we are measuring is worn the challenge is determining what the hole diameters should be and then their location and if possible we would measure the shaft diameters and centers before the part is removed for repair. As Tony stated the DRO goes a long way in making this easier (not simple) to determine.


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## Bob Korves

My understanding is that you were just looking to bore the two overarm holes.  If there are three, that complicates things a bit, but the approach is the same.


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## Reeltor

Perhaps I don't fully understand the issue.  Problem:  making overarm support needing holes to be correctly located respective to each other.  How to measure the distance between the center of each hole to match the mill in question.

quick and dirty:  the round overarm has a center drilled into it from the factory.  Place cutter head in horizontal position, using a small collet or something similar chuck up a small pointy center in the cutter head.  Slide the over arm to be on the same plane as the end of the pointy thing in the cutter head.  Measure between the center of the overarm and the center of the cutter head.  Will this provide the level of accuracy needed to layout the center of each hole and then drill then bore the large hole on the overarm support for the overarm side?  Mount the overarm support on the overarm and then drill/bore the arbor/cutter head side in place.

I know that I am missing something, please enlighten me 'cause I'm confused, not an unusual situation


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## Uglydog

My intent on this entire thread is who to measure the center of holes. This might be a daunting task for some of us. It wasn't that long ago when I would have been overwhelmed by the problem.
I did not intend this thread to be a conversation about VN overarms. However, if we find a VN which this might fit. Then GREAT!!

The third hole is the broken site glass for the integral overarm oil reservoir.

Tony Wells, That an interesting idea!
I've been refusing to "upgrade" to DRO. I'm also using a cast surface plate. etc... This is my eccentricity. I don't necessarily recommend it... 
I'm guessing I could do the same thing with handwheels. Would have to watch for backlash.

Reeltor,
Perhaps I communicated poorly. As I understand the process you are exactly correct.
This overarm is only valuable as a model on which to base a pattern prior to pouring an aluminum or cast iron copy.
It is my thought that we can bore the support arm and the arbor needs to be marked and bored on the machine for which it will be used.

Again, if we find accidentally find someone who might have an overarm with a center-center distance of  9.150 then a happy dance might result.

Brockwood,
I got 9.150 with the Sorenson. I only took one measurement.
I want to do multiple measurements on both sides of both the A & B and watch for repeatability.
Then it's my intent to build a pattern of these A and B overarms.

Daryl
MN


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## DaveD

I might be inclined to machine plugs out of some scrap material and leave a 1" diameter stub on the plugs. Put plugs in bores, measure outside to outside of the stubs and subtract 1".
Result is your center to center distance.


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## Bob Korves

For making castings, just leave enough room for the overarm and arbor rough holes in your pattern, and the usual over sizing.  Don't forget the draft, on both holes and outside dimensions.  Then machine the casting to fit.  There are plenty of foundries around for doing good iron castings.  If you mistakenly cut the holes oversize or in the wrong places, well, that is why bushings were invented!


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## Technical Ted

Uglydog said:


> This uses a vernier caliper and some telescoping gages.
> Gotta do a little math. Not difficult.
> The vernier tips do not have a  not radius therefore I'm not sure that it is as accurate as I'd like.
> 
> Daryl
> MN
> 
> View attachment 235572



If you don't like the square external measuring edges on the vernier, use the ID side and measure the distance between the far sides of the holes (I believe those sides have a radius on them anyways). Using this technique, is most likely the method I would use to determine the center to center distance.

Ted


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## BGHansen

Uglydog said:


> View attachment 235569
> View attachment 235570
> 
> 
> This Sorenson Center Mike is my go-to center to center mic. (Yes, they call it a "Mike").
> It somehow calculates the actual centers of the holes.
> Note the directions.
> 
> Daryl
> MN


Daryl,

Thanks for the tip.  Just bought a 13" Sorenson off eBay for $50.  Will be much nicer than using those slotted adapters that screw to vernier caliper arms.

Bruce


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## Uglydog

BGHansen said:


> ...Just bought a 13" Sorenson...



BGHansen,
I've been facinated that it does the calculations without electronics!!

Daryl
MN


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## Uglydog

DaveD said:


> I might be inclined to machine plugs out of some scrap material and leave a 1" diameter stub on the plugs. Put plugs in bores, measure outside to outside of the stubs and subtract 1".
> Result is your center to center distance.



Or any size dowel pin or drill rod etc you might have.
However, fitting the plugs might be problematic as it could introduce error (free running, slip fit, press fit). 
Options are great!!

Daryl
MN


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## BGHansen

Uglydog said:


> BGHansen,
> I've been facinated that it does the calculations without electronics!!
> 
> Daryl
> MN


Daryl,

There is a "quaintness" to old school.  Though I did just break out the surface plate and a digital height gauge to scribe some lines on the horizontal center.  Have to admit to finding the center of a 1.375" round mounted in a V-block was easier "going digital"; zero out on the top of the round, then come down 0.6875".  Looking forward to trying out the Sorenson.

Bruce


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## kd4gij

I think I will just get 2 of these.
http://www.machinesales.com/machinery/coordinate-measuring-machines/0000104571


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## Silverbullet

Ball trammels , used with a good steel rule, that's how I learned eons ago. The ball centers the hole on one end the other use inside or outside leg. Once you know hole size , easy peasy. It works easy once you do it.


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## Bob Korves

kd4gij said:


> I think I will just get 2 of these.
> http://www.machinesales.com/machinery/coordinate-measuring-machines/0000104571


I'm thinking wooden yard stick and sharp wood pencil.  Old school organic stuff...


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## Uglydog

Silverbullet said:


> Ball trammels , used with a good steel rule, that's how I learned eons ago. The ball centers the hole on one end the other use inside or outside leg. Once you know hole size , easy peasy. It works easy once you do it.



Like many things, I'd not heard of ball trammels.
http://www.starrett.com/metrology/product-detail/59F
While I've only done a very preliminary search, and may yet find an answer.
Could someone please explain how a ball trammel is used?
Please.
Thank you,
Daryl
MN


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## RJSakowski

How to do it depends greatly on the final intent and required accuracy.  For center to center distances, I usually measure inside to inside distance or outside to outside distance.  For same diameter holes, I will zero out the caliper on the hole diameter and then measure the distance.  Zeroing out will compensate for any errors due to the lack of a sharp edge, important on small holes.  Measuring outside to outside, I use tight fitting pins and again zero the caliper on the pin diameter and then read the center to center distance directly.  The two formulae used to calculate the c/c distance are: inside; c/c = i.d + (d1/2 + d2/2) and outside; c/c = 0.d. - (d1/2 + d2/2).  

In the case of your part and your final intent, I would approach the measurement differently.  Given the repairs and assumed prior use, I would expect egg-shaped holes, in which case, the above procedure gets flushed down the toilet.  Having a microscope on my mill, along with a DRO, I would record coordinates at a number of points around each hole and plot them out in CAD.  Then I would do a best-fit circle for each of the holes and measure the center/center distance in CAD.  Kind of the poor man's version of the CMM in post # 21.  If the mating pins/shafts are available, measuring diameters at an unworn area would be helpful.

Reverse engineering a part is always problematic.  Even on pristine parts, you have no idea as to where in the tolerance band the part lies. A good example of this was fitting a back plate to a Chinese chuck. In theory, the three mounting holes are equally spaced.  However, they in fact were not.  They were probably close enough so the hole clearance would allow assembly and may have been within their tolerance but had I made the new back plate to fit the measurements, I would most likely only be able to install the back plate in one position.  Add to that measurement errors and you can end up with parts the just don't mate.


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## Silverbullet

Uglydog said:


> Like many things, I'd not heard of ball trammels.
> http://www.starrett.com/metrology/product-detail/59F
> While I've only done a very preliminary search, and may yet find an answer.
> Could someone please explain how a ball trammel is used?
> Please.
> Thank you,
> Daryl
> MN


The trammels attach to the rule line the trammel to say the inch line , second trammel will attach close to the second hole . One will have a ball on the attached rod ,set it in hole one the other end will have an inside or outside leg to feel the other hole either side once you have that measurement add or subtract half the diameter of the hole size . That will give the distance between the holes . It can be very precise . Old timer taught me that back in 75


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## BGHansen

Daryl,

Got my 13" Sorenson in the mail yesterday.  Works great though I need a magnifying glass to read the vernier!  Thanks for the tip!

Bruce


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## Billh50

Make a plug that just fits each hole. Then mike the outside of the plugs and subtract 1/2 of each plug. The tighter each plug is the closer the reading.


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## Uglydog

BGHansen said:


> Got my 13" Sorenson in the mail yesterday.  Works great though I need a magnifying glass to read the vernier!  ...



While the vernier doesn't read to .0001 the standard does.
I believe this might be helpful in reading light or heavy on the .001 vernier lines.
Do you find this to be an accurate statement?

Regardless, a fun inspection tool. 

Daryl
MN


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## BGHansen

Uglydog said:


> While the vernier doesn't read to .0001 the standard does.
> I believe this might be helpful in reading light or heavy on the .001 vernier lines.
> Do you find this to be an accurate statement?
> 
> Regardless, a fun inspection tool.
> 
> Daryl
> MN


Hi Daryl,

I do find your statement to be accurate.  In the grand scheme of things, taking an existing part and reverse engineering it to better than 0.001" is creeping into "the emperor's new clothes" area.  I would think the designs on old iron were done in nice and easy 0.250" or 0.500", etc. dimensions.  If my Sorenson told me 6.001" on the spacing of two threaded holes, I'd assume 6.000".  It is a great measuring tool, thanks again for the addition to my layout arsenal!

Bruce


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## BGHansen

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


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## Dresden

Daryl, I suggest you just ask Dennis, your scraping instructor


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## Dr. B

If the holes are the same diameter, may I suggest merely measuring left-edge to left-edge or right-edge to right-edge?


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## gr8legs

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


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## Uglydog

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
MN


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## BGHansen

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


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## gr8legs

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


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## Uglydog

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
MN


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## gr8legs

Uglydog said:


> 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

That's great information. Huge thanks!

Daryl
MN


Sent from my iPhone using Tapatalk


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## C-Bag

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


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## Bob Korves

[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...


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## C-Bag

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.


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## Superburban

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


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## RJSakowski

Superburban said:


> 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


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## Doodle

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.


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## C-Bag

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.


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## Uglydog

Doodle said:


> 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


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## Doodle

Doodle said:


> 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:




Also, YouTube has lessons posted for using CAD programs and they are very helpful.


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## Splat

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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## toolman_ar

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


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## RJSakowski

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


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## Robert LaLonde

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.


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## EmilioG

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).


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## BROCKWOOD

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.


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## 4GSR

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


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## C-Bag

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.


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## BROCKWOOD

4gsr said:


> 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!


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## EmilioG

How accurate is the Center Mike? .001"?


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## BROCKWOOD

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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## C-Bag

Emilio I'm no expert, but the calibration or practice gage that came with the 8" Mike is 4.9967". After some practice I could replicate to well within .001". The Mike is not calibrated for tenths so by looking at where I was between the .001's I could see I was within a couple of tenths. Like reading a micrometer it's all about feel and alignment. For me this is way easier than using a caliper mostly because of the rounded features on the ends of the Mike. 

I'm not sure what you mean Brockwood about directly transferring, but the Mike is made to give you the measurement, not to mark with.


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## BROCKWOOD

C-Bag said:


> Emilio I'm no expert, but the calibration or practice gage that came with the 8" Mike is 4.9967". After some practice I could replicate to well within .001". The Mike is not calibrated for tenths so by looking at where I was between the .001's I could see I was within a couple of tenths. Like reading a micrometer it's all about feel and alignment. For me this is way easier than using a caliper mostly because of the rounded features on the ends of the Mike.
> 
> I'm not sure what you mean Brockwood about directly transferring, but the Mike is made to give you the measurement, not to mark with.


Then you did answer my question, C-Bag! Seems to me that transferring a measured number to any other means of marking & thus replicating a given distance is as we can expect with the as built Sorensen. Now if the Sorensen could somehow directly transfer it's measure: it would be most accurate!


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## C-Bag

BROCKWOOD said:


> Then you did answer my question, C-Bag! Seems to me that transferring a measured number to any other means of marking & thus replicating a given distance is as we can expect with the as built Sorensen. Now if the Sorensen could somehow directly transfer it's measure: it would be most accurate!



It seems to me that the mike's sole purpose is give a quick, direct and accurate way to measure centers without doing math, transferring numbers etc. Because of the way it works, the probes are not at the center distance when the gage gives you the center distance. So it can't be used for transferring the measurements. Which is all right with me. Just like I don't use my mic's as clamps, I wouldn't want to use the Mike as a scribe or punch  

The whole process of determining hole centers has always been like a golf shot for me. A little error at the beginning and you're out in the rough by the end. Armed with the true center measurement and going straight to DRO I've finally been able to make some pieces that fit the first time. Unlike measuring with a caliper, figuring centers, marking, punching, then trying figure in the windage of my worn out mill before DRO.


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## BROCKWOOD

My Center Mike came in. Put a thumbscrew on order & glued a split in 2 accessory mount back together. Yep, 1 of the black stands for the Accessory split in 2 during shipping. Fortunately, this does not affect accuracy at all.  It is the end to end lengths of the 2 rods that matter. The relationship of the 2 rods is also of no consequence. Really, The instructions for the Accessory are all that matters as any known (proven) rod length can be substituted once the math is understood.


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## EmilioG

I noticed that some of the Center Mikes come with a smaller pin attached to the ends of the main pins,? maybe to measure smaller holes?
Or is this a modification?


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## C-Bag

Interesting, I looked at my 8" Mike and it has the holes. I didn't get any pins, but this is good to know. It must be for measuring smaller holes than the regular probes will fit into.


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## EmilioG

So, these Mikes are great for checking existing holes, but with no way to lay out or mark., or for determining the center to center distance of an existing part that you want to copy? It looks like a nice tool but I don't know If I can get much use from it.  I thought about getting one but what would I use it for?  I own a set of Mitutuyo caliper center distance attachments, not the best way to check but may be good enough in some cases.
I also use transfer punches and Heimann trans screws.  How is everyone using these Center Mikes?


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## BROCKWOOD

EmilioG wrote: "....or for determining the center to center distance of an existing part that you want to copy?"

It's sole purpose is to provide center to center distance of existing parts that need copying.

Although I am waiting on a thumbscrew, I tried the Mike on the included standard & came close - the fine tuning doesn't work without all 3 thumbscrews present.  Would have been nice to make my own, but my import lathe isn't good enough to make no3 screws just yet.


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## Robert LaLonde

Well, I bought one of those hole center mics from an Ebay seller.  It arrived a couple days ago, and looked pretty good.  Obviously used, but it "looked" good.  Well, untiI I tried to move the sliders.  They were frozen in place, and no I didn't forget to loosen the knobs.  That's when I looked it over more carefully.  It showed signs of cleaning and polishing, and there were still some small spots of gunk and rust exposed on the outboard end.  

I contacted the seller, but have heard nothing back so far.  I soaked it in penetrating oil over night, and the next morning I gently tapped the first slider with a brass hammer until it started to move.  The space that it had occupied was completely covered with rust and gunk.  100%.  I left it in penetrating oil again overnight, and this morning I was able to move all of the sliders, but judicious use of the brass hammer was still required.  All three sliders were rusted in place.  Its obvious that the entire unit was rusted up, and the seller cleaned off all the visible rust and put it up for sale.  Its a seller with 100% positive feedback.


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## C-Bag

Mine was frozen stuck too, but it wasn't rust. It was some kind of gunk/old oil/galloping crud. Luckily it cleaned up nice, and didn't corrode the markings. I hope you hear back from the seller, sounds like you might need to send it back.


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## EmilioG

It looks like pitting from corrosion, which will affect accuracy. Send it back, and have the seller pay for return shipping.
If you don't hear back from the seller, contact Ebay with photos. They will honor the money back guarantee.  I've never had a problem
even when the seller has a No return policy.  Before an Ebay purchase, I always contact the seller to see if they respond. No response is a bad sign.


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## 4GSR

EmilioG said:


> It looks like pitting from corrosion, which will affect accuracy. Send it back, and have the seller pay for return shipping.
> If you don't hear back from the seller, contact Ebay with photos. They will honor the money back guarantee.  I've never had a problem
> even when the seller has a No return policy.  Before an Ebay purchase, I always contact the seller to see if they respond. No response is a bad sign.


Agree 100%.

Many ebay sellers take this rustied up stuff clean it up thinking they are doing a buyer a good deed by doing so.  Most of them have no clue what a precision measuring instrument is.  Most, it's not their fault for not knowing, they just don't know, but for the many that do, shame on them!


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## EmilioG

Maybe you can make a deal to keep it for less? Ask for a fair partial refund and keep it for parts?
e.g. The smaller tips on the ends are usually missing from these Mikes.  Some sellers will give you a partial refund just to avoid
paying the return shipping cost.  This is only if there are good parts left.  Something to consider.


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## C-Bag

The last 5-6 yrs I've noticed a change in eBay as more what I would call junk dealers have been pushing stuff. I feel like it's harder and harder to get even a fair deal much less the good deals of the past. There is some of that "don't know" but increasingly it's hard to tell if they are just scamming. It is good that there is recourse through eBay and nobody wants a negative but sometimes it time consuming to get this stuff squared away. Good luck.


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## ezduzit

EmilioG said:


> Maybe you can make a deal to keep it for less?...



I wouldn't want it in that rusted condition.


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## EmilioG

ezduzit said:


> I wouldn't want it in that rusted condition.



I wouldn't either.  But if any parts are salvageable, then why not keep what is good for a few dollars.
The tips, sliding parts and knurled screws may be worth keeping? I don't know. I don't have it in front of me.
Just an idea.


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## Robert LaLonde

I entered a return on Fleabay and its going back.  The seller tried to claim he didn't know it was frozen.  Somebody sure put a lot of work into polishing the crud and rust off the exposed surfaces.  I hate it that Ebay has made it so its "ok if the seller owns up when they get caught."


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## EmilioG

Ebay doesn't care about bad deals. as long as they get their cut, but they will be fair, especially to buyers that spend a lot of money. Ebay makes money all from every angle, including postage and the high selling fees make it harder and harder to get a good deal.  I study the listings, do some research and contact the seller first.  Ask questions before buying. It's all on the record.  I also tend to buy from the same sellers.  Your best defense is knowing the current price on an item and contacting the seller. Their response will say a lot. Glad you got it sorted out Bob.  I knew you would.

I made a purchase on Ebay a few weeks ago. The tracking showed it was delivered, but it wasn't in my mail box!  USPS does not deliver here on Sundays, I never received something in two days from 2500 mi. away, so something was wrong. Ebay refunded my money anyway. They took my word.  Ebay said they did it as a courtesy. Awesome.


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## BROCKWOOD

Bad back injury has really put a halt to any activity outside of sitting at a desk, but, I do want to keep this thread alive a little longer. I practiced using my Center Mike on the 10.9996" standard it came with. With several tries, All my measurements came up 11.000". 4/10th error. I measured my Van Norman no24 Arbor Support 'A'. Results with Center Mike are 9.175". I had previously measured the same support with pins, a parallel & dial caliper to read a distance of 9.166". I'll have to shrink down to a size that can also be measured with additional instruments in my small collection to chase down the error. Fun little project!


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## middle.road

And I awoke this morning not even knowing such a thing as a 'Center Mike' existed.
Something else to add to the wish-list, and now I need to go back and read the other pages of this post to learn.


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## BROCKWOOD

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.




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

Sorensen Center Mic time




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




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




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




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




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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## C-Bag

BROCKWOOD said:


> 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 $$.


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## gr8legs

BROCKWOOD said:


> bringing a ruler to a caliper match has bad results.



LOL and good advice 

Stu


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## devils4ever

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?


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## C-Bag

devils4ever said:


> 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.


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## devils4ever

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!


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## Tozguy

What about these





						AMPG,KBC CENTERLINE GAGES,1-850-Z9009,KBC Tools & Machinery
					

AMPG,KBC CENTERLINE GAGES,1-850-Z9009,KBC Tools & Machinery




					www.kbctools.ca


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## Janderso

https://www.ebay.com/itm/Sorensen-Center-Mikes-13-Inch-Excellent-Shape-Mfg-by-Brown-Sharpe/274296316103?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2648
 (scroll down the page a bit)
Yeah, I bought one too.
Hopefully someone will teach me how to use it some day.


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## C-Bag

devils4ever said:


> 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.


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## BGHansen

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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