Tolerance on Boeing Drawings

[MrHiLok]

Gouge damage was blended from a web. The deepest blend is 0.020 inch. The blend was accomplished at 20:1 taper ratio. Nominal thickness measured of the web is 0.103 inch.
The material type and stock size is stated on Boeing Part List. The stock thickness as stated on Part List is 0.1 inch.
On the applicable Boeing drawing for the web, no where is the web thickness shown. The drawing gives a generic tolerance on page 1 of the drawing as +/- 0.03 inches. Can this drawing tolerance be used to justify the 0.02 inch blend as being within the drawing tolerance?

Thanks

 

[rb1957]

no ... that drawing tolerance applies to the in-plane dimensions. the thickness really Should be somewhere on the drawing ... often it's in the BoM (as 0.1" Al sheet, 7075T73511), maybe the web is made from sheet stock, maybe it's made from another Boeing part.

 

[bf109g]

What does the SRM say? Are you on primary or secondary structure? 20% blend on a primary structure web sounds a bit deep to me.

I've used the dwg tolerance for machined/chem milled parts but not for sheet metal. I'd think that if you wanted to use a tolerance there, the appropriate tolerance would be that of the sheet thickness in the material spec.

 

[KENAT]

I'd lean toward using the thickness tol on the material spec too if I understand correctly.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[rb1957]

how significant is the blended area ? ... is it large compared to the part ?? is it near an edge, or load transfer fasteners ?? like the other posters, does this part look like primary structure ?? does it look like it'd react pressure loads ??

"no" to all these questions should give you some assurance that the blend is minor.

removing 20% of the material is reasonably significant. i'd recommend a thickness check after blending to verify what's left.

20 thou is going to be outside the sheet thickness tolerance, i'd guess that it's less than 10 thou.

 

[MrHiLok]

Thankyou every one for your valuable input. The blend was minor. I wanted to know if the 30 thou tolerance stated on the drawing could be used. But after careful review, i decided not to used it as justification and did some number crunching instead.
I checked the material spec also, but it did not specify tolerance.

 

[KENAT]

Depends what the material spec was, but at least in BS/ISO specs the material spec itself didn't give the thickness tol, there was a separate spec(s) for tolerances on standard sheet & bar sizes etc.

I had a hell of a time tracking this info down the last time I needed it though and found several conflicting values.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484