ASME Y14.5 Profile of Form

[looslib]

Since I didn't get any response in the ASME forum, I thought I would try the question here.

One of our design groups is using Profile of Form for the shape of the part and then dimensioning the whole part with basic dimensions. I haven't seen this before, how common is it to use this method?

The group I normally work with uses an unspecified tolerance chart and normal diminesioning. With our designs in metric, we don't use trailing zeros so this has caused us some problems with manufacturing. Over the years the designers have gotten used to toleranceing dimensions that need it.

If I took a print of the same part and asked for a quote to build, would I get the same price? I think the drawing with the basic dimensions on it would be a higher price because of perception.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli
CAD/CAM System Analyst
Ingersoll-Rand

 

[drawoh]

looslib,

If your fabricator is scared of geometric tolerances, then they might put up the price. I have had no problems to date with profile tolerances.

If I have a cutout with a lot of radii, and without a requirement for very accurate dimensions, I go to the profile tolerances. I think they are easier for me and for everyone else to understand. Take the case of a specific radius. With linear tolerances, the tolerance zone is controlled by two orthogonal linear dimensions and the radius. Determining whether or not the as-fabricated form complies with this could require a lot of geometry.

With a geometric form tolerance, you accept whatever shape stays within 0.1 of your nominal geometry, assuming you used a form tolerance of 0.2mm. This has got to be easier to inspect.

What sort of tolerances is your design group specifying?

I do not recognize the idea that tolerances are not necessary. Your drawing is part of a contract. You want your fabricator to make you a widget, and you want to reject anything that does not conform to your drawing. If you have no tolerances, everything conforms!

JHG

 

[Cdub]

I agree with Drawho, especially when I have a part (or feature) with a lot of simple geometry. I always utilize a profile control with all basic dimensions. This is a far more simple way to control the part. The "normal" tolerancing your speaking of is a suggestion to the manufacturer about what you want, not a specification.