huangyhg

rounding or not of tolerance in fcf with dual dimensioning
just a general question
when dual dimensioning a print that has gd&t. when converting the metric tolerance in the fcf, do you round if the 4th number is over 5? example - .4mm = .0157 would you round up? or leave it at .015?
solid edge v20
what do your tolerance stacks permit?
this one is .1mm total tolerance
solid edge v20
here is a good reference
often it's a good idea to add a 'significant figure' to reduce to effect on tolerance range. since inches are an order of magnitude bigger than mm.
kenat,
one rule of thumb i would use is that the tolerance of the secondary unit is to be equal or less than the primary. if the tolearance is rounded to a number that is greater than the primary tolerance, it would be possible to pass a part on the basis of the secondary tolerance that would not pass per the primary tolerance.
peter stockhausen
senior design analyst (checker)
infotech aerospace services
cadman1964,
i think we have had this discussion a couple of times.
do not generate dual dimension fabrication drawings. use one set of units to show requirements. provide the alternate units for reference, only.
on a 3d cad package like solidworks, you can get away with some stupidity, since the computer is working out the dimensions and the conversions. the numbers in your fcf almost certainly are typed, and you are manually calculating each conversion factor. what is the shop allowed to do when the numbers do not agree?
jhg
this is the problem with dual dimensioned prints. i worked at a place that insisted on them despite my objections so i had a note in the title block that said inches were the manufacturing units and the mm were for reference only. i think you will have to settle on one set of units as inspectable and the other as reference. if the mm units become reference, then i believe rounding up is fine. that's what i did. the other thing i would do is change my inches to match mm like instead of applying a flatness of .005 to a surface, i would make it .004 and that would give me 0,1 to put in the fcf.
powerhound, gdtp t-0419
production manager
inventor 2009
mastercam x3
smartcam 11.1
ssg, u.s. army
taji, iraq oif ii
quote:
i think we have had this discussion a couple of times. do not generate dual dimension fabrication drawings. use one set of units to show requirements. provide the alternate units for reference, only.
yes i do know that's the better practice. but, this is customer generated and sometimes, even knowing were not product designers, we have to draw there part up to there standard.

solid edge v20
see page 89 (10.2.2.2)
dual dims where killed in 1982. you'd think this corpse would be buried by now.
matt lorono
cad engineer/ecn analyst
silicon valley, ca

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