Sheet Metal Axes question

[MUlissi]

Hello all,

I did a little searching before posting this, but couldn't find anything that answered my question directly.

Part of my job has been updating/correcting old programs from my predecessors, and I find interesting things fairly regularly.

Today's case, I'm trying to make sure there's a program that measures all of the dimensions our inspection report calls for.

I believe I've found one, but I notice it's only measuring one set of points for Gap/Form and Trim points around the perimeter of the part. It is, however, reporting 2 different numbers from the T and S sheet metal axes options in Location Dimension.

Based on context and tolerances, the programmer appears to be using the S value to report the Gap/Form dimension.

I'm familiar with, and regularly use the T dimension, but am unfamiliar with S.

Is this a valid method of reporting a Trim dimension and a Gap/Form dimension from a single point taken on the part, or should I rewrite this and take an individual point for each?

I hope I explained that clearly.

Thanks again!

[Matthew D. Hoedeman]

For anything that uses SAMPLE HITS, the "S" axis is the surface (S) deviation, like the "T" is for the edge.

HOWEVER, there is a problem using surface sample hits for edge points that are on a CURVED SURFACE.

The SURFACE vector and NOMINALS are for the very edge of the part. Unless you can take the sample hit with a ZERO indent, you will get incorrect "S" data. The sharper the curve the more error, the bigger the indent, the bigger the error.

LONG ago I gave up using surface sample hits for edge points. If surface data is required "at the edge", I program a vector points (or a surface point) 2 or 3mm in from the nominal edge. I then use THAT as the relative feature for the edge point to measure relative to. This give correct surface deviation data and correct edge deviation data. I also use GAP ONLY so that the surface deviation isn't part of the edge point results.