GD&T tolerance or band? Using a symbol like parallelism //

[marcusja2002]

Its been a while since I've used my GD&T knowledge

When using a symbol like parallelism // the numbers next to it in the box is that a band or a tolerance. Say its stated as .125 inside the box, is that +/- .125 or is that a band of .125 or a tolerance of +/- .0625?

Thanks in advance,

 

[Eredhel]

Can you upload a pic of what you're looking at?

 

[marcusja2002]

 

[ncwalker]

It's a band. The surface affected by the marking must be parallel to Datum Y defined as two theoretical planes both dead parallel to Y that are 0.12 apart.

 

[Eredhel]

Is that print metric?

 

[marcusja2002]

Sorry for the delays in replying, My emails didnt notify me someone replied.

No its in inches.

 

[Eredhel]

Setting GD&T stuff aside, it seems like a weird callout. Parallel within .120 inches is a ton of tolerance. I'm used to seeing .005 or .010. How long and wide is the part?

 

[marcusja2002]

They are between 3 and 5 feet wide. This is connected to a fab shop, so 5-10 thou isn't feasible. I do agree it is a bit much, I would have liked half that called out, but we were so focused else where on the print it was an over site. Since it already made it to our vendors its not worth raising the flag now, but I can change it moving forward with new prints. Knowing its a band helps a lot though.

 

[Eredhel]

Ah, of course. I had machining tolerances in my head instead of fabrication. Sorry about that.