Please help small science shop measure 90" plus parts

I'm owner of a small biz; we make and sell science instruments worldwide but run on a shoestring.

Little River Research & Design

We need to accurately measure a part that's ~96 long; to around 0.1" We know how to measure small parts -- can ya'll help with this one?

Right now we tape down a tape measure on the one inch mark, on scribed lines, and use that.

I suspect there is a better way; I'm trained as a surveyor, I can measure miles accurately, but can't figure this out, thanks.

Steve

For 0.1" precision. I think you are doing fine with the tape measure.

What type of measurements are you taking? Just overall lengths or 3D point positions? Contours, hole locations, etc...?

Based on the tolerances you stated a CMM would be over kill. However maybe some nice chap near you would do the measurement for a lunch or something. I know I would if had one and were near you; ya can never have too much good karma!

Draw wire encoder (aka string encoder) connected to the DRO of your choice.

With what appears to be a somewhat small product line on your site; any reason you couldn't just make up cutting jigs for each product part?

The measurements you are performing are using the very same method many (MANY) shops would use for this size part. You can maybe upgrade a little bit if you have a nicely-graduated straight ruler, which you can then couple with a combination square as a "slider" for perhaps some added accuracy (assuming you can set everything up on a reasonably flat table for ease of use). For tolerance as you state, assumed to be +/- .050", I would be doing what you are doing now.


Here's a couple of options:

Steel Rules | MSCDirect.com

ASE-96 96" Straight Edge Aluminum Rule

http://www.swissprec.com/cgi/ISSRIT2?pmaka=12-421-4&pmctlg=01�

I resisted the temptation to list the Starrett 96" heavy spring-tempered steel rule in satin chrome with 4R grads, although it CAN be yours for $2641 MSRP. The caliper extender might be what you feel you need, but it's not clear to me whether it allows you to measure 96"+ at full extension of 6" caliper.

Since you already build science instruments and you are familiar
with surveying perhaps think about building a rather old measuring
device. I think the Romans first used but it may be even older.
Not sure of the correct name but it is just a wheel and axle of a
know diameter and having some graduations. Figure out circumference
roll it along the part counting the revolutions and tally up the
results. I'll think it would be a cool project and give you a pretty
accurate measurement.
spseth

You can buy a cheap laser ranger for $50 bucks or so that's good for +/- 0.0625, which is a little out of your tolerance. However in favorable conditions, i.e. indoor fabrication, they're closer to +/- 0.03125.

With that kind of tolerance, I don't see why a tape isn't enough.

For longer measurements, we have a couple of different length fixtures to use with calipers.

A rectangular piece of sheetmetal with a square cutout at one end, and a pem standoff pressed in the other end. Several sizes like 6", 12", 24", 36", 48", make it fairly easy to measure longer parts with reasonably open tolerances. Most our sheetmetal stuff is ±1mm. lol

Hook the hardware standoff on one end of the part, use the caliper to measure the other end to the square.

I'd say it's probably good enough for ±.005", but wouldn't 100% trust it, nor is it "officially calibrated." Just for reference.

You can get up to 24", even 36" long scales from Starrett that can be butted together using a specially made clamp. The scale goes to up 1/100th's. Just get a magnifier LOL anyway they are good scales and butt together well. You would probably have to make a fixing tool or do a two man measure. A little imagination and you could make a "snap" scale set. Good luck

I assume you have normal metalworking tools and smaller measuring instruments. My suggestion is to make a set of shorter standard bars, from, say, 1" diameter round steel or aluminum rod at the longest length you can measure with precision (12" MIC or caliper?). Tap each end with something convenient (1/4"-20?). Use setscrews perhaps 1-2" long to screw the cylinders together end to end. This will make a standard rod in 12" increments. Put 8 together to get 96". Now make a fixture with a hole in it that fits snugly (.001" clearance) around the end of the nominal 1" diameter standard rod. This fixture holds a 1 or 2" travel indicator, offset from the rod axis by a convenient distance. Make a flat calibrating bar that when bolted to the end of the last standard rod will fit under the end of the indicator. Move the fixture with the indicator to adjust the reading of the indicator to 1/2 of the scale of the indicator and tighten the clamp holding the fixture to the standard rod. Now the part to be tested is measured with the long set of standard rods, using the indicator to read the difference between the end of the standard rod (very close to 96.000") and the part being tested.

The standard rod will be a little floppy, being 1" inch in diameter. For better handling, it could be supported to a more rigid structure, such as an inexpensive 8 foot level, or piece of 1x3" aluminum box tube. There are many ways to implement this concept, depending on your tools and willingness to make parts. My guess, is that with a reasonable lathe, a 12" caliper, and an inexpensive indicator and some scraps of aluminum for making a fixture for the indicator, you could make a system capable of giving results to perhaps =/- 0.01" in two hours or less. Making a mounting fixture (wood?, a level, box tubing, etc) could give you a permanent standard for long lengths.

Best wishes,
Michael

Since the ends are a mirror image, a single accurate rule 48" long should be able to get you within about .01" either side of a center mark. That rule will be far easier to read accurately than a tape measure -- no curl, less tendency to move, graduations to .01", traceable accuracy to begin.

Whatever dimension is most critical (the larger hole?), you could use as a locating point for all the other measurements on that end. Get that point within .01" and measure the other features from there. Over the smaller range (a bit over 12") where all your holes, cuts, etc. are you probably already know how to easily measure things to a few thousandths.

Depending on how you're making these and the quantities, you could use the DRO on a milling machine to locate, drill, and check holes on either end. If you're making lots of these and don't have a DRO equipped mill, you could also make a simple checking fixture about 18" long to rapidly check the various holes, locations, angle etc. Maybe another one without pins to lay it out.

Your .1" tolerance should be easy to hit, even if you're using scribed layout lines and a drill press for the work. Basic idea -- get the distance between two locating points on either end right. Then deal with the 12"+ area on either side with a DRO, pattern, template, normal measuring instruments, or whatever is at hand.

The item TeflonDave is talking about is a Starrett 299 Scale clamp: 299


Lufkin, general and other brands make similar items. They can be regularly found on eBay.

Rich C.