2D Drawing Tools

[Jenn23]

We have had a finding stating that we are not using hand tools correct in measuring 2D drawings. Mind you we have been in business for 75 years and I have been measuring parts for over 25. However, our inspector says we are not correct. Question: Is there a guide or requirements that are listed to use for 2D inspection? And what tools can be used for what style of dimension?

 

[mfgenggear]

what type of parts, tolerance, more details please. what type of equipment

 

[GregLocock]

I suspect that the issue is that drawings should be read, not measured.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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

 

[ewh]

What type of drawings?
The only drawings that I know of that may have direct measurements taken from them are those of a stable material such as ink/mylar that define lofted and other irregular surfaces that cannot be easily defined otherwise.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[dik]

Greg... as an aside, I've often done drawings for measurement... faster than hand calculation in some instances.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[moon161]

Greg... as an aside, I've often done drawings for measurement... faster than hand calculation in some instances.

That's drafting and a legit use of it. At least in manufacturing, drawing take-offs are a no-no. If a dimension is missing from a released drawing, it should be sent to engineering for a clarification and/or revision. IDK about construction.

 

[dik]

It's a tool to help me with my work... the end result is not to prepare a drawing... so, not really drafting...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[rb1957]

sometimes drawings are full size lofts. These are not dimensioned as the drawing is the data/master. As noted above, they are on "stable" media; and also very olde school ... these days we'd use digital masters.

What does your inspector say you should be doing ? is the drawing a full size loft ?

another day in paradise, or is paradise one day closer ?

 

[Jenn23]

Thank you everyone!

This is a 2d paper drawing supplier by our customer. We are making rubber gaskets. The finding was a 96" parts measured by a 48" scale. The operator measured, marked and measured the second portion. the tolerance was +/ .03.

 

[rb1957]

So we're talking about measuring the part (not the drawing). I'd tend to agree with your Inspection ... measuring a 96" length with a 48" rule is probably not best practice.

Claiming a 0.03" tolerance for such seems "optimistic" ...

another day in paradise, or is paradise one day closer ?

 

[MintJulep]

If that's the inspector's only gripe then go buy a 12 foot tape at the local hardware store.

Gasket. 96 +/- 0.03. Design expectations seem "optimistic".

 

[IRstuff]

You have a tolerance of 0.03", so if your required test accuracy ratio was, say, 4:1, it would require a measurement method that has an uncertainty of 0.0075"

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Jenn23]

Thank you again

Our inspector will not allow us to us tape measures. Calibrated or not. Does anyone know of a document with guidelines for measuring with hand tools?

 

[GregLocock]

Check out Gage R&R studies. Trying to measure to 8 thou (h/t IRstuff) in 96 inches is putting you into the realms of a metrology lab, that is surface tables and temperature control. 30 thou tolerance seems a bit mean for a gasket.

We'd use CMM, but even then that level of accuracy over that distance would need special care, in practice 40 thou would be a good result in a workshop setting where moving the CMM base is needed.




Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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

 

[rb1957]

Your inspector sounds like a jerk ! what's wrong with a calibrated tape measure ?

You say it a vendor item ... did it come with a CofC ? or do you guys do receiving inspection as well ??

Could you use a CMM ?

another day in paradise, or is paradise one day closer ?

 

[WKTaylor]

I have used reproduced/paper 'undimensioned 1:1 drawings' for quick and dirty work before... but they all have well established, and clear, 'grid-lines'... either 5.000 X 5.000 or 10.000 X 10.000.

I always measure the spacing between gridlines, vertically and horizontally, in the area where I need dimensions... before measuring straight from the paper with my decimal-inch scale. This establishes <X> [Y] correction factors for the 'scaled dimensions' that I will be deriving [x.xx accuracy, only].

However for QA/QC measurements of un-dimensioned production parts... the original climate controlled Mylar [plastic film]… that has been dimensionally validated between/across major gridlines... should be the actual 'QA/QC standard'.

ASME Y14.31 Undimensioned Drawings - Engineering Drawing and Related Documentation Practices

IF the accurate 2D undimensioned [film] drawing is available, then parts curved in 2D ONLY, can usually be laid on the drawing for 1:1 line-match checks. Make sure Your parts are deburred and are clean of grime/grit oil, etc before using this method to avoid contamination/abrasion of the expensive drawing media.

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[rb1957]

I hope a rubber gasket doesn't need deburring ... (smile)

another day in paradise, or is paradise one day closer ?

 

[WKTaylor]

Rb… unless the Gaskets are made with an Exacto-knife around/thru a metal template.

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[mfgenggear]

Jen23
It's one of the cases where it is easier to manufacture than it is to measure, a calibrated steel rule would be an option. a .030 tolerance is tight for a gasket since it's function is to create a seal.
however depending on the type of part material if flexible like cork, or paper makes it tough. gaskets have been made for generations with no issues.
which method is used should be coordinated with the customer, Important: how are they receiving inspecting this particular part.
also is there an issue, have these been manufacture before? have there been any rejections in past history?
as gasket generally have a very liberal amount of tolerance. this may be excessively tight tolerance.
I would suggest a manufacture simple jig, to simulated the actual fit, go and no go acceptance that has been measured and calibrated. or as Will suggested above recommended with a Mylar.
the cost of inspection method will depend on the quantity of the order, one or two or thousands?
is inspected in the restrained condition or free state will also make a difference.
is there a datum for example the inside periphery is restrained by the assembly of a mating surface. is is loose fit or slight press fit. these functions will make a difference.