In house tolerance standards
I am the Machine Shop Supervisor in the "Engineering Department" at a major paint company. This is a very hands-on position as it is only me and two welders. When I first started there were only the default tolerances on the print that the CAD software put there. There are two Designers. One had no idea what a tolerance is and the other was taught in school that there is no place for fractions on a mechanical print. The department manager did not know what a tolerance is. I was getting prints for the mill and lathe that were dimentioned in fractions and band-saw and weld projects with 3 and 4 digit call-outs. (As a note I would like to say that this shop is strictly a support facility that caters to production, facilities, R&D and distribution.) Many projects are reverse-engineered, and some are semi-architectural, and others are in-house designed, tooling and fixturing. I requested a tolerance block call out as follows:
X/X = +/- 1/8 (to support welding projects)
.XX = +/- .02 (to allow the use of stock edges of material when application allows)
.XXX = +/- .005 (good all around machining tolerance)
.XXXX = +/- .0005 (bearings, dowls and other press fits)
I understand these are very general, but they cover most of the work done, and it is a good starting point. The idea was pretty well recieved except that the designer that went to school would not have any part of fractions on a print. We got a new manager and I gave him a quick lesson on benifit or use of a tolerance and won my case. Since then the designers have attended a GD&T course and the battle resurfaced. One of the issues screwing with my head is during the design process, I have been taught to use standard numbers in the design, these represent common fractions and wire sizes. Basicly, anything you will find on a fraction/decimal conversion chart. .75, .375, .188 etc. If I were to accept .X = +/- (.1/.2/.3 etc.) as a tolerance and a location, the only standard number that I would have to work with would be .5. Anything else would have to be rounded/assumed. A .25 target would be .3? I have several friends that work in heavy GD&T companys and they still retain the use of fractions for in-house fixturing. I have looked all over the internet for examples of what I would like, and I see many prints with a tolerance block simalar to what I want. I cannot find a GD&T example with a tolerance of .X or larger. Can I get some advice? If have to accept all decimal an all decimal format, metric would be a much better option. Thanks in advance ~ Mr Wolfdog
Query regarding Tolerances(Decimal & Fraction)
I received drawing from my customer, In that drawing All liner Dimensions are in Inch and (mm).
My Query is that, Tolerance table incorporated in drawing have two type of tolerances.
[LIST=1][*]Decimals(±0.05) & 2.Fraction(±1/64). [/LIST]
Which tolerance to be used?
Thanks in advance.