Y14.3 probably won't apply, as it is directed at MDB. The OP is refering to board drawings which were most likely created long before that standard was written.
There should be some sort of tolerance specified, whether it is in the drawing notes or in a related company spec. An allowable tolerance has to be applied somewhere.
"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]
D**n, caught skimming again! Sorry about that, fcsuper. Thanks for the heads up.
A "loft drawing" in my understanding is a series of sections of profiles, i.e. wings, and were often done in ink on linen or mylar at full scale without any dimensioning other than butt-line, water-line and/or fuselage station locators.
"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]
EWH is correct. It is a complex profile in ink on mylar, usually associated with aircraft parts.
My case is for small run production parts where, frankly, GD&T paper gaging and that sort of thing is way over any reasonable need from the inspection department.
EWH suggested a company standard or a block on the drawing. Those were also in my mind. I have heard 0.030" over the length of the part for one OEM standard but I'm unable to confirm.
I have suggested to perhaps control the tolerance on our printed lofts by controlling the lineweight so that the part passes inspection if the inked line can be positioned on the full contour of the part. Has anyone heard of this sort of control used? It would certainly make the gaging easy for the inspector and allow flexibility in tolerancing.
Your method may work if tolerance = line thickness is acceptable.
If relying on plotted prints, be sure to include dimensioned vertical and horizontal lines to verify plotter accuracy.
"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]
In some cases lofted drawings are made by joining a series of sections, and these sections are fully dimensioned & toleranced.
In these cases you can potentially do inspection at the places where the sections are. Either CMM or 2D profile go & no go gauges.
(It's called 'lofting' because it originated in ship yards where it was done 1:1 on big rolls of paper, in the 'loft' above the construction shed - so I've been told.)
Yes, joining of sections is a given for large parts. It's hard to fit a full size wing section on an 36" wide sheet. ;-)
They were not however always hard dimensioned as that could require a s**tload of dimensioned points to properly define an irregular profile (at least for aircraft lofts).
"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]
Isn't that why you have 'J' and above sheet sizes?
While I never got to play with them 1:1 drawings on large rolls of paper tens of feet long were still in use not that long ago, I know some aircraft still in operation used them.
Anyway, that's why I said in some cases. The parts I'm thinking of were fairly small from 'aircraft accessories' shall we say.
I thought computers had replaced the need for loft drawings. I remember one of my bosses started out doing loft drawings. At that time, there was just no other way to do them except by hand and ideally, full scale. These then became the templates for the guys building the planes. I believe he did the loft drawings for the P38.
Computers may have more or less replaced the need for 'new' loft drawings, but there are plenty of A/C flying that pre-date the widespread introduction of CAD, let alone that pre-date 3D-CAD.
Not every company has CMM capability. If you don't have a computer measuring device, you cannot inspect an undimensioned profile without a plot. I don't believe our inspectors even have email.
