[squale]

Okay I am looking for a tool like what I have drawn up in my attached photo. Does anybody make a tool like this already or know where I could have one made, etc.?

I need to measure the I.D. of plastic tubes used in say hand creams, toothpaste, etc. before the tubes are sealed closed. As we all know these tubes are very flexible plastic so holding them in round perfectly is not very easy. And for any tube sizes bigger than 1" in I.D. I do NOT have PIN gages that big.. my pin gages only go up to 1" in O.D.

Thanks all!

[christinandavid]

Hi,

Looks like a Bowers Gauge (but they are three-pronged...)

Could you measure with a Bowers Gauge if the tube was supported externally with a ring gauge? Or make your own stepped plug gauges?

DP

[HuFlungDung]

Could you make your own gauge? Something similar to a unibit step drill, but without the gash for a cutting edge. Just get somebody with a cnc lathe to whip up a few. You could specify whatever step you can live with at each diameter. Laser mark the diameter on each step.

[Vern Smith]

How about rolling up some shim stock, plastic or metal, inserting it into your tube, let it expand, mark the position of the inside edge, and do the circumference math backwards.

Vern

[squale]

step gages or plug gages will not work within my budget.. I need to be able to measure tube I.D.s from 1" I.D. up to 3" I.D. in .002" increments and accuracy. We would be talking 1000 different 'steps' on a taper gage or go-no go gages.. that would cost a FORTUNE and mean a LOT of different tools around. So I need something that is adjustable to handle a specific I.D. range.. maybe a tool that could do .5" in one tool... so that would mean I would need 4 total tools.

remember it has to keep the flexible plastic tube in PERFECT round while measuring the I.D. down to an accuracy of .002". The I.D. measurment must take place about 1" INTO the tube from the open end.. so the tool must be able to go INSIDE the tube and expand or contract it's measuring size range.

[Shotout]

I think you are still going to end up with a lot of tools looking at what your drawing was suggesting. If your tool expands .5" it will end up with gaps between the pie wedges that are going to distort the tubes as they expand. Depending on the material you're measuring then before you had enough positive force to cause a ratcheting thumb knob to slip then the material will have distorted enough to cause your circle to have flats between the pie wedges. Relying on feel and a slip fit isn't going to be very accurate or repeatable with material that distorts easily. Either way your not going to be able to hold your .002 resolution on easily distorted material

If destructive testing is allowed then you could rig a fixture to hold a section of the tube then take a spline measurement of the circumference using a CMM to get an accurate measurement. You could hold it out of round and still get an accurate circumference and then you can easily calculate your diameter. For a fixture you could convert a small tool makers vise, two pins on the fixed jaw and one on the movable centered between the others. Slip a ring of material on the pins and open the vise until the material is taught, preferably using a torque wrench set to below the amount of pressure that is required to stretch your material being measured. Then simply take a few points from each pin and return to the first pin to get a spline length. Divide the spline length by 3.1416 to get your ID measurement.

A capability study would tell you how frequently you'd need to repeat your procedure to maintain the tolerance range you have.

step gages or plug gages will not work within my budget.. I need to be able to measure tube I.D.s from 1" I.D. up to 3" I.D. in .002" increments and accuracy. We would be talking 1000 different 'steps' on a taper gage or go-no go gages.. that would cost a FORTUNE and mean a LOT of different tools around. So I need something that is adjustable to handle a specific I.D. range.. maybe a tool that could do .5" in one tool... so that would mean I would need 4 total tools.

remember it has to keep the flexible plastic tube in PERFECT round while measuring the I.D. down to an accuracy of .002". The I.D. measurment must take place about 1" INTO the tube from the open end.. so the tool must be able to go INSIDE the tube and expand or contract it's measuring size range.

[HuFlungDung]

Or instead of stretching it with pins, just squash the tube flat and measure across the maximum length on the OD. Two times this length plus 2PiR - 2R = circumference of the tube OD, where R = the wall thickness of the tube, which is probably easily gauged with a dial guage.

I'd try this on a known sample (measured with a plug gauge) to begin with, to determine how accurate the formula is due to unintentional stretching of the sample.

[christinandavid]

Have used dental wax in the past to take impressions of features for measurement purposes. What about filling the tube with the stuff, let it harden then pull it out and measure the OD?

DP

[Pandinus]

use the flexibility to your advantage. take two semicircles 3/Pi inch in diameter (gives a circumference of 3 inches for convenience, just under 1 inch in diameter) attached to a caliper. Spread the caliper in the flexible tube, add twice the measurement to the 3 inches and have a cheap calculator nearby, divide by Pi. Get a programmable calc and just enter your measure and it gives your diameter. Or if your willing to spend a few bucks, program a pic to read a digital calipers output and display the diameter!!

[sambo67]

if you have a 4 jaw chuck you can mount two pins , one opposite of each other, place your tube over the two pins and open one jaw until your tube will not slide over pins freely then remove tube and measure over your pins.

[wms]

Bowers could make you a special anvil with a dozen fingers or more, (instead of the normal three),to do what you need ..

Or several anvils to cover your range, as I doubt one would have enough range.

Keep in mind that one reader head would probably fit all the anvils..so one head could be used for multiple anvils..Unless you need to have all of the sizes in service at the same time..

Bower is serviced and sold by Folwer in the US..


http://www.bowersmetrology.com/