# caliper extender



## Vavet (Apr 1, 2014)

I have a project for work which does not require any machining, but it does require measuring down to 0.001". My boss has cleared me to research and submit a purchase request for a set of large calipers (42" +) for this project. Accuracy is the key to this whole project. I can send him a PO for a set of $4300 Starretts, but I think that would go over like a lead balloon. I also don't want a set of no-name calipers of questionable quality and accuracy for $800. I stumbled across a caliper extender on McMaster. 

http://www.mcmaster.com/#electronic-calipers/=rcngwd

This would work, but I wonder how accurate my measurement will be. Has anyone ever used anything like this? Am I fooling myself thinking I can make this work? 

It might not be machining, but the measurements are every bit as critical. 
Thanks


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## JimDawson (Apr 1, 2014)

Repeatability should be OK, but the problem is the initial calibration.  If you have a known standard you can measure to calibrate the tool then you should be fine.

Edit:

I agree with the posts below, I didn't think about the temperature changes, and it's effect on the measurement.  A fixture with a dial indicator might be the best solution.


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## John Hasler (Apr 1, 2014)

Vavet said:


> I have a project for work which does not require any machining, but it does require measuring down to 0.001". My boss has cleared me to research and submit a purchase request for a set of large calipers (42" +) for this project. Accuracy is the key to this whole project. I can send him a PO for a set of $4300 Starretts, but I think that would go over like a lead balloon. I also don't want a set of no-name calipers of questionable quality and accuracy for $800. I stumbled across a caliper extender on McMaster.
> 
> http://www.mcmaster.com/#electronic-calipers/=rcngwd
> 
> ...



Those are aluminum.  They will expand about .001" per degree C at 42".  IMHO you need Invar and even then you will have to control for temperature.


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## DMS (Apr 1, 2014)

Measurements of that accuracy over those dimensions are going to have to involve temperature compensation as well... just keep that in mind as it will be important regardless of how you measure things. Those extenders seem interesting, but they seem a little awkward. As John says, temperature is going to be a big deal, even the temperature of your hands is going to throw off your measurements a significant amount.

The cheapest way I can think of to do this is based on what Jim said. Get, or have made, a 42" master. Get a steel rod, and attach a dial test indicator to one end. calibrate the dti to read 0 against your master, then you can measure other things relative to the standard. Keep in mind that temperature still come into play. For best results, keep all the tools and equipment in a temperature stable room for several hours so they are at a consistent temp. Use gloves when handling items to reduce heat transfer.

You also have to read the fine print here, even on those $5k Starrets, _resolution_ is 0.0005", accuracy is listed at 0.001" from 0-12, or 0.002" from 12-24". They don't give an accuracy value for dimensions larger than that, but you can figure it's more or less linear (so, say 0.004" over your stated dimensions).

Not a trivial issue to be honest. Out of curiosity, what the heck are you doing that you need +-0.001 over roughly 4 feet?


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## Vavet (Apr 1, 2014)

DMS said:


> Measurements of that accuracy over those dimensions are going to have to involve temperature compensation as well... just keep that in mind as it will be important regardless of how you measure things. Those extenders seem interesting, but they seem a little awkward. As John says, temperature is going to be a big deal, even the temperature of your hands is going to throw off your measurements a significant amount.
> 
> The cheapest way I can think of to do this is based on what Jim said. Get, or have made, a 42" master. Get a steel rod, and attach a dial test indicator to one end. calibrate the dti to read 0 against your master, then you can measure other things relative to the standard. Keep in mind that temperature still come into play. For best results, keep all the tools and equipment in a temperature stable room for several hours so they are at a consistent temp. Use gloves when handling items to reduce heat transfer.
> 
> ...



I work for a bowling equipment manufacturer. We have experienced problems with our lane panels growing or shrinking based on temperature and humidity. They are installed with tight gaps, so a soft spot or bubble develops under the panel if it grows too much and butts into the adjacent panel. I need to do some testing to validate what we've been told by our vendor and try to develop a solution, in the way they are processed, shipped, acclimated, installed, etc. These panels are not wood, but a laminate phenolic. Of course, any significant changes have to be approved by bowling's governing body (USBC) for the sake of uniformity.


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## DMS (Apr 1, 2014)

Pretty cool experiment. Seems like rather than being able to accurately measure distances, what you really need is the ability to accurately measure changes? Would it be enough to stick a tenths indicator (or even a couple?) on one edge of the lane, and reference off the other? If you controlled your measurement components for temperature, you could get some very accurate data with a setup like that, probably more so than trying to get consistent data from a giant set of calipers (I have trouble even with my 6 inch calipers open wide).

There is a guy on Youtube named MuellerNick. He does videos on machining and scraping. One of the devices he shows in some of his scraping videos he refers to as the dovetail-o-matic. Basically a 10ths indicator on an adjustable frame. I'm thinking something like that.


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## Big Rack (Apr 2, 2014)

I would think if you could purchhase vernier calipers that long fairly reasonably but I don't think you could accurately measure to .001 repeatly. I f it's going to be something ongoing I would suggest a standard and use that to calibrate a simple fixture with a indicator at one end Of course everything should be at a even tempature whatever the standard was calibrated at. Does your company perhaps already own a CMM?


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## n3480h (Apr 3, 2014)

Even a CMM will have it's accuracy limitations, and will also be somewhat affected by ambient thermal issues. Can an allowance be designed into the part to compensate for ambient conditions? Could it then be mounted with a full coat flexible adhesive to minimize the bubbling effect?

Tom


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## JimDawson (Apr 3, 2014)

Vavet said:


> I work for a bowling equipment manufacturer. We have experienced problems with our lane panels growing or shrinking based on temperature and humidity. They are installed with tight gaps, so a soft spot or bubble develops under the panel if it grows too much and butts into the adjacent panel. I need to do some testing to validate what we've been told by our vendor and try to develop a solution, in the way they are processed, shipped, acclimated, installed, etc. These panels are not wood, but a laminate phenolic. Of course, any significant changes have to be approved by bowling's governing body (USBC) for the sake of uniformity.




Maybe just measuring and trying to quantify the panels is not the solution.  It could be that a redesign of the panel edges would solve the root problem. I would look at some kind of a tapered lap joint or perhaps a modified tongue and groove joint that would allow some movement but still keep the surface flat and gap free.


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## xalky (Apr 3, 2014)

Do these lane panels interlock, and lay loosely? I'm thinking about a typical laminate floor panel that interlocks. The key to allowing for expansion and contraction is leaving room at the extremities for panel movement. Put them in too tight and your asking for buckling issues in hot and humid weather.

Marcel

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