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Posted by Brian Lawson on June 22, 2008, 6:09 pm
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On Sun, 22 Jun 2008 16:05:54 -0500, F. George McDuffee
SNIP
>===========
>Some good observations from most posters, including our resident
>grenches.
>
>Two cautions if you are thinking about going "art to part" from
>customer supplied cartoons.
>
>#1 -- While things are improving, many of the customer supplied
>cartoons are still drawn using the LAR [looks about right]
>drafting standards, and the actual specifications are in the
>notes & dimension text, which the cam programs ignore, as they
>generate the program from the cartoon. In many cases this is a
>result of quick and cheap engineering changes where only the
>dimension text was updated. You will however still generate
>scrap using a program generated from the [old, not updated]
>cartoon.
>
>#2 -- The tolerances specified are not equal/bilaterial from
>nominal, for example 1.7500 +0, -0.010, while the customer
>cartoon is drawn with the feature at 1.7500, not 1.7450 +/-
>0.005, so when the program is generated you are machining to max
>which will also tend to generate scrap with any tool wear
>(assuming outside machining).
>
>Another factor is the rampant excessive cost cutting which has
>eliminated many essential engineering steps such as product
>design review and drawing checking, so the customer cartoon with
>notes and dimensions may not be producible, such as specifying a
>1/2X20 [instead of a 1/4X20] tapped hole in the end of [or
>through] a 1/2 ø shaft. Effectively, the contract machine shop
>is now not only expected to produce the part, but to also check
>the drawing and conduct the design review. It is therefore
>essential that your standard order acceptance form include a
>disclaimer that the part will be produced to the customer's
>cartoon, if that is what you intend to do.
>
>Good luck with your career in CNC machining. and always remember
>that the technical stuff is the easy part.
>
>
>Unka' George [George McDuffee]
Hey Unca George,
Very nice well considered and written answer. I hope the OP
undertands what you have given him, and the thought and time it takes
to write even those 20 odd lines of text.
Good show!!!
Take care.
Brian Lawson,
Bothwell, Ontario.
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>Some good observations from most posters, including our resident
>grenches.
>
>Two cautions if you are thinking about going "art to part" from
>customer supplied cartoons.
>
>#1 -- While things are improving, many of the customer supplied
>cartoons are still drawn using the LAR [looks about right]
>drafting standards, and the actual specifications are in the
>notes & dimension text, which the cam programs ignore, as they
>generate the program from the cartoon. In many cases this is a
>result of quick and cheap engineering changes where only the
>dimension text was updated. You will however still generate
>scrap using a program generated from the [old, not updated]
>cartoon.
>
>#2 -- The tolerances specified are not equal/bilaterial from
>nominal, for example 1.7500 +0, -0.010, while the customer
>cartoon is drawn with the feature at 1.7500, not 1.7450 +/-
>0.005, so when the program is generated you are machining to max
>which will also tend to generate scrap with any tool wear
>(assuming outside machining).
>
>Another factor is the rampant excessive cost cutting which has
>eliminated many essential engineering steps such as product
>design review and drawing checking, so the customer cartoon with
>notes and dimensions may not be producible, such as specifying a
>1/2X20 [instead of a 1/4X20] tapped hole in the end of [or
>through] a 1/2 ø shaft. Effectively, the contract machine shop
>is now not only expected to produce the part, but to also check
>the drawing and conduct the design review. It is therefore
>essential that your standard order acceptance form include a
>disclaimer that the part will be produced to the customer's
>cartoon, if that is what you intend to do.
>
>Good luck with your career in CNC machining. and always remember
>that the technical stuff is the easy part.
>
>
>Unka' George [George McDuffee]