Measuring Extremely Flexible and Stretchy Parts

I'm trying to measure a piece of laser-cut fabric that is very soft, flexible, and stretchy. The properties of the piece make it almost impossible to fixture on the OMM measurement stage repeatably. The sample is about a foot square, and has tolerances of +/-1mm.

Any ideas on how to constrain this part so that the measurements can be repeatable? I tried sandwiching it between to pieces of glass, which makes it flat, but the x and y dimensions are still not repeatable.

Has anyone else ever tried to measure something similar?

How do you hold it in position while it's being cut?

How do you define tolerance on any dimension for such a flexible part?

- Leigh

How do you hold it in position while it's being cut?

How do you define tolerance on any dimension for such a flexible part?

- Leigh

I would look to the engineer as to what and how to measure the part.

Tom

Perhaps not practical to inspect the cut part directly.

Ask the customer what they need from you regarding inspection report/COC.

Maybe qualify a procedure. Qualify the laser cutter (presumed CNC) by cutting measureable medium.
Qualify the cutting/work holding set-up by concurrence with your customer.

Is the fabric sufficiently uniform it can be weighed to at least verify if it covers the proper area? How uniform is the size? A rectangular part might be inspected by holding the narrow axis at the mean dimension, and measuring the long axis.

AWY said:

I'm trying to measure a piece of laser-cut fabric that is very soft, flexible, and stretchy. The properties of the piece make it almost impossible to fixture on the OMM measurement stage repeatably. The sample is about a foot square, and has tolerances of +/-1mm.

Any ideas on how to constrain this part so that the measurements can be repeatable? I tried sandwiching it between to pieces of glass, which makes it flat, but the x and y dimensions are still not repeatable.

Has anyone else ever tried to measure something similar?

Click to expand...

Try acetate plastic, transparent, one sheet under, no cover, borrow a hair dryer adjustable for low/no heat, blow it to a relaxed state, allow a touch of static build-up.

Shouldn't much move after that so long as measurement is non-contact, optical or such.

BTW.. you think fabric that size is challenging, you should have tried running thin, open-cell low-durometer 'Ensolite' foam through dies on a 1940's vintage punch-press to make shock buffers for 1970's era hearing aid reproducers. Product ell-shaped and not a lot larger than those 'sprinkles' kids put atop an ice-cream cone. RPITA, but we eventually made it work.

Until we discovered the damned stuff hardened from exposure to human sweat about three months into a 12-month warranty, and had to start over with a molded Silicon rubber.. that gave but six months, on average. Cover the warranty, go back to the drawing board...

Probably the easiest method is making a template from something stable and inspecting the parts before removing them from the machine. Eyebrow the edges and chamfer the corners of the template so you can prove you're actually to the lines.

This is a clear-cut case where working with the end-use application is required. If this is for a customer, have the discussion about the material characteristics and end-use functionality, and how the process can be controlled on your end. If this is for your own end-use application, have that discussion with yourself and your internal "customers". Trying to measure a workpiece as you describe it is not going to be reliable or repeatable. The process for making the part needs to be, though.

Thanks, everyone! These are really good ideas! I'll pass them along to the engineer.