huangyhg

is the csys always the origin
all,
when designing 3-d tubing, we start with a coordinate system at one end and develop the geometry to the opposite end. we place a table on the drawing with the xyz coordinates and bend radius to each point. the drawing didn't state the tolerances are non-accumulative.
the problem: the gage maker started in the center of the part and worked to each end of the tube. he believes has the accumulative tolerance from point to point.
question: under what circumstances would the coordinate system (from which all dimensions originate) not be the origin of reference?
adrian
eng-tips forums is member supported.
what dimensioning standard is being applied to the definition?
i rarely seen a tube dimensioned from the center. but, it also depends on the design. i have seen a tube on an airplane engine dim from the center because it was the mounting point with fittings on each end. most of the time it is dim from one end, point to point. the tolerances are whatever works as long as the end point is where it needs to be. for aircraft engines, the mfr usually gives us start/end & mounting points.
chris
solidworks/pdmworks 08 3.1
autocad 06/08
ringman:
ansi y14.5m-1994 drafting standard applied to this drawing
ctopher:
the tube is detailed/dimensioned from the csys end but the gage maker started his design from the center of the part.
i don't understand the gage maker's actions, unless he has some further customer information that you don't. he could be working from an "as used" state rather than an "as manufactured" state.
i used to work with automotive exhaust and rigid ac lines, we always started from one end and worked towards the other. our tubes were made on a manual tube bender, though i'm not sure why a cnc tube bender would be any different. tolerances were per the title block, usually +/-.19 for exhaust and +/-.010 for ac lines.
"art without engineering is dreaming; engineering without art is calculating."
madmango:
i agree with you. engineerings position is the gage maker made the gage improperly or he didn't know how to read the print. my goal in posting this delima was to make sure i am not missing something.
thanks for the feedback!
i have had my share of dealing with tool designers not knowing how to design tools or read drawings.
i once had a tube with several bends that had to fit at the end +/-.05 mm. the tool designer didn't know how to convert and made it +/-.5 in. very expensive to remake the tool.
i suggest your gage maker fix the tool to match the drawing or you will have problems later.
chris
solidworks/pdmworks 08 3.1
autocad 06/08

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