Plate Threaded

Posted in February 28, 2010 ¬ 4:27 pmh.adminNo Comments »

Plate Threaded
How can I accurately gauge measure a flexible plastic feature?

Its got to be low cost & easy to make. An ABS plastic plate is mounted by its centre to a metal fixing plate, spaced away from it. Points on the perimeter of the plastic plate need to be measured accuratley from the metal plate. Obviously this is a simplified model of the task but the principle is there. I’ve considered a spring loaded pin but the plastic part to measure could flex away so distorting the measurement. I’ve considered a fine threaded pin with a friction break, like some torque screwdrivers work . But I can’t figure out a low cost & accurate interpretation. Any other ideas?

secure the pce in the center, apply a given amount of pressure to distort the plastic.

Use a height gauge with a double dial indicator. Center the dial on the center of the plastic using the attached dial indicator to deflect to X points (2nd dial setting is irrelevent, it’s only used to ensure considtent pressure of the needle on the part.

Zero the digital read out on the height gage.
Move the 2nd dial indicator to the deflected section of the part at a consistent and predetermined location. Adjust the height indicator until the 2nd dial indicator reads the same pressure as it did when you measured the center.

The new reading is the amount of deflection at your specified length.

When using the 2nd dial indicator, use a very low set point so as to no apply excess weight to the deflected plastic. The weight of the indicator may add to the deflection, but if you do it right, the effect will be minimal. Ideally, you want less than 10% ‘gage error’ in your entire measuring system.

Ask a QE to do a gage R&R of the set up to determine the amount of measurement error.

HHO Construction tip #2: The Plate Stack