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liveaboard wrote: ↑Sun Sep 18, 2022 2:06 am
I'm making a bunch of quick change tool holders for my lathe.
The only dimension that has to be accurate is the 82mm distance between two grooves.
With no DRO, I used a micrometer to measure before the final depth cut, adjusting as necessary.
This worked well once I got the hang of it.
Not that I'm glorifying the lack of a DRO; I'm just making do.
Locomotives, aircraft and battleships got built long before there were any DROs.
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liveaboard wrote: ↑Sun Sep 18, 2022 2:06 am
I'm making a bunch of quick change tool holders for my lathe.
The only dimension that has to be accurate is the 82mm distance between two grooves.
With no DRO, I used a micrometer to measure before the final depth cut, adjusting as necessary.
This worked well once I got the hang of it.
Not that I'm glorifying the lack of a DRO; I'm just making do.
Locomotives, aircraft and battleships got built long before there were any DROs.
There was a lot of cut to fit and drill in place in those days
Even today, with CAD / CAM / CNC aircraft manufacturers have what they call 'shim cells' where they make the pieces that have to be created 'to fit' the accumulated tolerances 'as built'
^^^^^^
The Air Force has problems with the boom on the new KC-46 tankers.
The KC-135 while less efficient overall has a time proven boom.
A shop I was with recently, was asked to quote on some Boeing drawings from 1974 through a sub-contractor.
There were specific part designations pointing to data tables on various pages that had to be cross referenced with other data tables to arrive at the required dimensions for the finished parts.
All of this came in a digital file with hundreds of scanned pages, with no real directory. It took most of an afternoon to sift through PDFs with penciled in references, noted by hand decades ago.
This makes me think of the “Shim Cells”.
One or two of the notations got me pointed towards them being tanker boom parts.
It was kind of an unpleasant circus and still left some final dimension info in question.
We decided not to quote when we couldn’t find a constant human reference/contact at the requesting outfit.
With Covid, it seemed that different Engineers were there on different days and no one was dedicated to that quote or
able to answer inquiries in a timely fashion.
1974 was my first Tool Room job with no DRO and a circular slide rule. We did some pretty tricky stuff back then.
Illigitimi non Carborundum
'96 Birmingham mill, Enco 13x40 GH and Craftsman 6x18 lathes, Reid 2C surface grinder. Duro Bandsaw and lots of tooling from 30+ years in the machining trades and 15+ years in refinery units. Now retired
one of my first jobs in the CAM / Solid Modelling world was to help a fellow in Ohio (forget his name or company), who was working on 747 door hinges designs (this in 1989 or so)
Seems that of all the doors / hinges in the 747, there were no 2 alike -> in reality, only the guy with the CNC program knew what was what because none of the paper drawings was correct and ALL had to be 'fudged' depending on which hinge on what door -> seems the original 747 was designed on paper prior to CAD back in the late 1960's
So...this fellow's project was to take all of the CNC programs that built the door hinges (in some cases reading paper tapes) -> back plot them into a solid model by reading the G-CODE (which was a big feat in 1989), so that 'as built' drawings could be made so that Boeing would finally know exactly what hinge fit what location in which door.
Bill Shields wrote: ↑Sun Sep 18, 2022 8:47 pm
Even today, with CAD / CAM / CNC aircraft manufacturers have what they call 'shim cells' where they make the pieces that have to be created 'to fit' the accumulated tolerances 'as built'
that is really interesting Bill !
We made high precision custom dies and our approach was to never use shims due to the complexity of fits and tolerances.
What you describe is what we called " Stack Up" and our approach was to monitor the parts as they were made in the Die Shop
Some of our Dies went to 55,000 pounds in weight.. but anyway say we had 7 two inch thick ( example) pieces at +/- .001" and we needed 14.000" +/- .001" and the first 5 came out at 10.004. That meant we red-lined the tolerances on the prints for the next two ( -.002) .
Some Stack ups were irrelevant and others were critical so the shop guys stayed in close touch with one another during machining
Sometimes it was a battle when different engineers designed the Mating parts and did not want the tolerance changed --then the chief engineer
settled that issue
Rich
Edit..When customers called for spare parts after having our product for awhile , it was Critical that "Red-lined Drawings" be used for fabrication.
