dimensioning squareness
dimensioning squareness
(OP)
Friends,
Question for you... The company I work for purchases a lot of flat Al sheet, of about .050" thick or so. We order these sheets from our supplier per a controlled print indicating their size. Having said that I think our prints probably lack some clarity in terms of sheet squareness. I believe the correct way to handle this is to use some GD&T, with two datums and two perpendicularity feature control frames. However, I'm wondering if that is a bit much? How do you handle this?
-Mike
Question for you... The company I work for purchases a lot of flat Al sheet, of about .050" thick or so. We order these sheets from our supplier per a controlled print indicating their size. Having said that I think our prints probably lack some clarity in terms of sheet squareness. I believe the correct way to handle this is to use some GD&T, with two datums and two perpendicularity feature control frames. However, I'm wondering if that is a bit much? How do you handle this?
-Mike





RE: dimensioning squareness
Perhaps a single profile callout around the perimeter? This could cover size and perpendicularity at once.
RE: dimensioning squareness
RE: dimensioning squareness
Additional thoughts or methods?
-Mike
RE: dimensioning squareness
What drawing standard are you working to?
There is implied 90° for edges drawn at right angle. At least in ASME Y14.5-1994. This will invoke the 'block' angle tolerance. Maybe all you need to do is tighten that tolerance, although generally I'm a user of GD&T.
To do it properly you'll probably want 3 datums, to fully locate if for inspection.
As to the question of making it understandable for those without familiarity with GD&T, I've never found an easy answer for that. You need/want to use GD&T because you believe you can't adequatly describe your requirement using +- dimensions etc. However, the people who'll use the drawing wont understand the GD&T. Catch 22 that has been discussed at length on the GD&T forums before.
In future I'd post questions like this over in forum1103: Drafting Standards, GD&T & Tolerance Analysis.
KENAT, probably the least qualified checker you'll ever meet...
RE: dimensioning squareness
An additional method would be to remove the angle at the corner of the sheet and place a diagonal dimension from corner to corner.
It is harder to get a sheet out of square then if the dimensions are correct.
B.E.
RE: dimensioning squareness
The sheet defining dimension tolerances are plus/minus .030", and we would like the sheet to be square within .050".
Funny you mention the implied 90 degree comment, I've been round and round with our QA guy about this. If he had it his way we would call out every angle between intersecting lines, yeah, not good.
We mention the overall flatness of the sheet, is that the 3rd datum you're mentioning?
-Mike
RE: dimensioning squareness
1. Roughly what size are these sheets (doesn't make much difference, more for me just to better understand the situation)?
2. What is your dimensional tolerance (this will help determine if profile would be the better tolerance)?
For your QA guys benefit, assuming you are working to ASME Y14.5M-1994 then look at Paragraphs 1.4 (i & j) & 2.1.1.2.
Of course for 14.5 to be effect you need to comply with para 1.1.3 and reference 14.5 either directly or indirectly from the drawing.
KENAT, probably the least qualified checker you'll ever meet...
RE: dimensioning squareness
The sheets are roughly 30"x60", and smaller depending on the usage, and the tolerance is plus/minus .030" for each of those.
I'll be forwarding our QA some information about this too.
Thanks,
-Mike
RE: dimensioning squareness
Take a look at 2.7 regarding rule #1, especially 2.7.1.2 Envelope Principle.
This almost gets you what you want. If I understand what you mean by squarness then the +-.030 gets you something like squareness of .060. This is without any drawing change assuming you reference 14.5. You may want to get a second opinion on this but I think I'm correct.
Based on the numbers you give though squareness is slightly more important than overall size which might point away from profile. I've attached a scheme which may work however, no guarantees. Not sure the flatness on B is appropriate given the thickness, maybe straightness would be better.
Really the tolerancing needs to be based on function which I have no idea of.
I'm limited in my GD&T knowledge- just enough to cause trouble
KENAT, probably the least qualified checker you'll ever meet...
RE: dimensioning squareness
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
RE: dimensioning squareness
KENAT, probably the least qualified checker you'll ever meet...