Creative suggestions on probing sheet metal

Use your sheetmetal features like sample hits and auto features. Wait until Matt sees this post, he'll tell you. One of PC-DMIS's strengths is sheetmetal.

I saw it, BUT, it sounds to me like it IS one of the situations where Pcdmis falls short.

Sounds like it is a ROUND (cylinder) of sheet metal with holes pierced in it. If this is the case, then sample hits do no good what-so-ever since you have a hole with "unlimited" depths required. The "top" and "bottom" hits can be at the same depth, but the two "side" hits need to be at a different depth to hit the part. AND, since they are all around this cylinder, using 4 (or more) edge points, then constructing a circle won't work since you would need a "workplane" for each hole and so on. Been thinking on it, can't think of an answer that will get it done.

I'm thinking the part is as you describe. It is a very difficult problem. I think there is a solution, but it will be very difficult to do and even more difficult to explain. It will no doubt take some tinkering/experimenting preferably with a "known" part so you'd know when your getting good results.

I'm thinking it may even require iterative measurement involving lots of alignments.

For an example:

Measure and align to the cylinder. We'll call it Z+ for this example.
Measure the hole knowingly shanking the probe (only want rough location).
Align to the cylinder and use the shanked hole to fix rotation about the cylinder. Rotate to X+
Change workplane to X+.

There are two possible avenues of exploration from there.

1) autocircle with 1 sample hit above or below the hole along the cylinder's vector. Edit the x value of each hit individually to get it to hit the edge. This will work if you think you can get it to hit the edge (thicker "sheet metal" like maybe .1 inch thick or more). X values could probably be calculated knowing the hole's diameter and the cylinder's diameter, but I think it would be a lot of work.

2) Edge points (with sample hit(s)) all around the hole, then construct a circle from them. This might work better for thinner "sheet metal", but the sample hits might prove problematic as they won't be "normal" since the surface surrounding the hole isn't "normal"

Now, you might need to go through the alignment and measurement step again to get the best results.

Following that, lather, rinse, repeat for all the holes. Unless you can figure out a way to copy/paste with pattern or loop it (I'm not so sure that works when alignments are involved).

I have no idea if either approach would work. I'd really need a part to play with to get an idea of that.

About the ONLY thing I could think of would be to set the SAMPLE HITS to 4 (if you can, can you?) and set it to take 4 hits in the hole. BUT, set the ANGLE to "45,45" so that all 4 hits would be at the same distance from the center line of the cylinder, if ya follow me. I mean, if you have 2 up/down and 2 to the sides, then the up/down are at the same depth. If you rotate the angle 45 degrees from there, then all 4 hits SHOULD be at the same depth, KWIM? BUT, you would either need 1 or 4 sample hits, 3 would screw it up.

It would seem to let you input 4 sample hits even though 3 is the largest number shown in the drop down.

Here's one more issue that may complicate matters. Are the holes drilled/punched after the sheet is formed into a cylinder or before? One way you would have a nice round hole whose sides are all "pointed the same way". The other way, you might have more of an oval and the sides of the hole will be twisty.

This is a bit complicated. Do you have autofeatures available in your version of PC-DMIS?

I have autofeatures

How thick is the sheet metal?

The sheet metal is only .027 inch

How big are the holes?

Holes are about .5 inch


What is the diameter of the cylinder?

Part is about 120 inch in diameter. There is some curve to the holes and due to the size the depth of the surface can and does vary from part to part.


Those last three are because I'm wondering if you can measure a circle at one level and have all of the hits land on the edge of the sheet metal. Sounds like maybe not.