I have a supplier in China who wants to change a tolerance from ±0.05 to +0.05/0.20 This is for a pocket depth on a CNC aluminium machined part, and we just can't get our heads around the proposed tolerance. As far as we understand, it's supposed to be a double positive tolerance. :? Can anyone make any sense of this?
I've seen this before on close toleranced stuff where they wanted to indicate the intent of the size to be used. If the size is 1.00 then the range is 1.05-1.20. 1.125 ± .075 is just as equal.
Hi, I can't be sure without knowing more about the feature in question and its intended mating part; but double positive or double negative tolerances are normally associated with limits and fits. If that is the case? There are better and more recognised ways to convey the dimensional intent. Regards Neil
Yes, I can tell some clues. I was in need of a special gear set. I contacted to the Japanese company to ship me a simple 8 cm diameter set they sell, less than a 200 gr materials. I was asking how i can pay by credit card. After contacting more than 10 times, eventually a friend of mine visiting Tokyo slolved the problem. They met, my friend paid cash and got the material brought to me. When I purchase on-line it takes 1 week. This took about 3 months. I can advice; to go through by some locals and tell the problems to him who can understand you.
Not unusual. Double positive (or negative) tolerances are sometimes used when tolerance zone is all on one side of a nominal dimension. For example, your pocket might be a clearance for a nominal 10mm plate which itself has a ±.05 tolerance, so the pocket depth would be dimensioned 10mm +.05 / +.20. You also sometimes see such tolerances (on the minus size) where the nominal is a stock material size, with the minus tolerances giving room to clean or polish the stock to a slightly smaller size.
