Measuring tools question

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Doug4d3s
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Measuring tools question

Post by Doug4d3s »

For literally most of my life, I have wanted a "dial yardstick".... a measuring tool that is at least three feet long, but that has an indicator dial that travels along it and reads out in greater accuracy than is possible with a yardstick or measuring tape. Through the years, a tool like this would have been a HUGE advantage in most all of the projects I ever tried to do.

(image below)
Image

.......does anyone make a tool like this?
We are in the age of $30 .001" Chinese dial calipers, this cannot be so difficult.

-----------------

If nobody does, then how does anybody measure stuff 2-3-4 feet long, accurately? I have seen the 24" dial calipers, but the ONLY linear-dial-scales like this I have ever seen are the surface table gauges, that only go up to 12" or 18" or so.
~
easymike29
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Re: Measuring tools question

Post by easymike29 »

These could probably be modified for your use.

http://www.medfordtools.com/metalworkin ... ipers.html

Gene
randyc
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Re: Measuring tools question

Post by randyc »

Doug,

The inexpensive Chinese DROs are nothing more than long digital caplipers. They are available for under $100 and all you need do is mount your shop-made caliper heads to them. They are available with self-contained batteries and read in both metric and inch.

Easier still would be to make a vernier caliper out of a yardstick. The entire contraption could be made from wood except for the measurement jaws. It would have to be calibratable for temperature and humidity but that should be fairly simple to devise for any reasonably handy guy. The accuracy could be within .005 inches over thirty inches.

Although this isn't the same thing, I use a short length of yardstick cut at an angle of 5.7 degrees (a 10 : 1 angle) as a vernier device to level my radial router arms.

Image

Every graduation on the yardstick is magnified by 10. In use the simple tool is placed on shop-made parallels under the two rails of my radial router and slid until the tapered length is tangent to one of the rails. Repeating the exercise on the other rail gives two readings where the rail touched the measurement tool.

Subtracting the two readings and dividing the difference by 10 gives the difference in height between the two rails. A difference of less than .005 can easily be detected and that's close enough for woodworking. I use the same tool to adjust the knives on my planer - can get to less than .005 very quickly and then use an indicator to get within .001.

Simple stuff. A vernier caliper would be a fun Saturday afternoon project.

Cheers,
Randy

Edited to add: "Machinery's Handbook" has a short section on verniers. If a yardstick is calibrated in 1/8 inch increments like the one shown above and if the vernier is calibrated in 32 divisions, then it is possible to read within .004 inches. Larger numbers of graduations on yardstick or vernier will improve resolution. As a woodworker, I would find the combination of 1/8 inches and 16 vernier graduations a handy compromise since this would read in 1/128 of an inch increments or 1/2 of a 64th. More than adequate even for fine furniture making.

Second edit: Just for grins, a "yarstick" vernier with .005 resolution:

Image
Last edited by randyc on Sat Jul 31, 2010 5:50 pm, edited 1 time in total.
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mklotz
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Re: Measuring tools question

Post by mklotz »

You're probably looking for something called a Caliper Extender...

http://www1.mscdirect.com/CGI/N2DRVSH?P ... 0148377117
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mechanicalmagic
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Re: Measuring tools question

Post by mechanicalmagic »

I think I would start with a "Trav-a-dial".
http://www.southwesternindustries.com/s ... ent1.shtml

This is basically a read head, with a dial indicator. It is pressed against a long flat surface, (user supplied), and can move any distance. There is just friction between the drive wheel and the flat surface.

They were the thing to have before DRO's, and were used on lathes and milling machines. e-bay probably has them from time to time.

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dly31
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Re: Measuring tools question

Post by dly31 »

Since many (most?) sources of measurement error are cumulative, it is generally more difficult, more expensive, and less necessary for large items to have accuracies like small items. Things like six-foot micrometers have, however been made. Thermal expansion, surface finish, and measurement pressure (feel) tend to limit such applications.

High resolution measurements are much simpler if overall accuracy is not required, such as for comparing two large items.

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Harold_V
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Re: Measuring tools question

Post by Harold_V »

mechanicalmagic wrote:I think I would start with a "Trav-a-dial".
http://www.southwesternindustries.com/s ... ent1.shtml

This is basically a read head, with a dial indicator. It is pressed against a long flat surface, (user supplied), and can move any distance. There is just friction between the drive wheel and the flat surface.

They were the thing to have before DRO's, and were used on lathes and milling machines. e-bay probably has them from time to time.

Dave J.
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Harold_V
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Re: Measuring tools question

Post by Harold_V »

dly31 wrote:Since many (most?) sources of measurement error are cumulative, it is generally more difficult, more expensive, and less necessary for large items to have accuracies like small items. Things like six-foot micrometers have, however been made. Thermal expansion, surface finish, and measurement pressure (feel) tend to limit such applications.
Indeed! The bulkheads for the Sergeant missile were 36" in diameter, held to ± .005". They were permanent mold magnesium castings, which got machined before assembly. We had a 36" micrometer, which was not easy to use. We also had a pi tape, which proved to be far more reliable.

Harold
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mbrusso39
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Re: Measuring tools question

Post by mbrusso39 »

For $10 I picked up a 24" long vernier caliper from Harbor Freight. It is made from aluminum....but for $10 it has proven itself much better than tape measure for those projects around the house (obviously not to be used in the machine shop for anything critical). it is "good" to the nearest 8th or so...
Doug4d3s
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Re: Measuring tools question

Post by Doug4d3s »

Well, I suppose it would help to point out that I'm not really looking for very precise accuracy--I don't need anything like .001" at all. Just .01" would be great, or even some kind of a metric arrangement that went down to tenths of a millimeter.

I imagine I'll do some kind of vernier arrangement, with the stick-on rulers on a piece of flat stock. And I'd need several lengths, because measuring a ~2-foot piece of something with a ~6-foot vernier caliper isn't going to work real well.
~
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steamin10
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Re: Measuring tools question

Post by steamin10 »

Evans rule is a major maker of carpenters rollup tape measures found in any Home store. It should be noted that they can have a variation due to the printing process. They are accurate to 1/4 inch in 12 ft, IIRC. When we worked with steel sheeting for cuts and slitting on a metal line, we had to use tape rules that were certified and compared to a master tape measure for 2001 cert compliance. All rules were checked against a master daily. Bent hooks and small descrepancies meant we went through a lot of tapes in a year.

When I ground Mill rolls in my youth, I used and fought with a set of Mics that were up to 70 Inch for diameter with up to 5 inch extensions. A 60 inch diameter mill roll was pretty common, and getting a good reading on a warm roll was not. It will teach you the finer points of the art of measurement, if you pay attention.
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AlphaGeek
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Re: Measuring tools question

Post by AlphaGeek »

Doug,

Maybe I missed the post where you answered this, but why wouldn't you just use a 12-inch digital caliper with a reach extender as mklotz suggested? It's pretty easy to make one of these with multiple lengths of extension arm so you can cover whatever range you want.

Heck, if you wanted to simplify even further, you could have a single extension bar made of hardened/ground stock. Drill and ream mounting holes at 6.000 inch intervals and use shoulder bolts for a close fit, and you could measure anything from 12" to 48" using a single ~36" extension bar.

If you want to get really fancy, you could sacrifice a cheap HF caliper to get hardened/ground jaws for your extension bars.

-AG
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