[Cl...] Posted February 27, 2019 Share Posted February 27, 2019 So here's my question; the two basics (.2540) actually extract on the model as .252, so then that would mean the .254 is the maximum width? Is my evaluation correct? .002 total tolerance (+.002 / -0.000)? Link to comment Share on other sites More sharing options...
[Ja...] Posted February 27, 2019 Share Posted February 27, 2019 If the nominal was .254 with a profile .002 in the minus material direction then your nominal would shift to .252. If that's what you are getting on the model now then you would have to use bilateral to meat the print requirements. I would discuss it with the customer. I have modified them like that myself to check a unilateral profile on a vision machine that doesn't have a unilateral option. Link to comment Share on other sites More sharing options...
[Cl...] Posted February 27, 2019 Author Share Posted February 27, 2019 So the tolerance is +.000 / -.002? Any one side bigger than .254 would be a bad part? Link to comment Share on other sites More sharing options...
[Me...] Posted February 27, 2019 Share Posted February 27, 2019 Yes. The number after the circled U is how much extra material is allowed. In this case it's 0, which is actually a unilateral tolerance, but I see it a lot. So .254 is the max, .250 the min. (.002 per surface) Link to comment Share on other sites More sharing options...
[Aa...] Posted February 28, 2019 Share Posted February 28, 2019 To stress what Robert said, that's a unilateral .002 PER SIDE. It looks like the model you're working with was created at the center-of-tolerance (at least in this one feature). Link to comment Share on other sites More sharing options...
[Cl...] Posted February 28, 2019 Author Share Posted February 28, 2019 So you are stating that it is .254 +/-.002? Link to comment Share on other sites More sharing options...
[Cl...] Posted February 28, 2019 Author Share Posted February 28, 2019 Please sign in to view this quote. The 4 flats on the model extract @ .126 (x2 = 252) Link to comment Share on other sites More sharing options...
[Ja...] Posted February 28, 2019 Share Posted February 28, 2019 What is the point of unilateral profile anyway if the nominal shifts to the center of the tolerance zone anyway. I have seen parts built to the maximum size and then we couldn't keep it in spec because they went by the nominal on the print and didn't notice there was a one direction tolerance. Link to comment Share on other sites More sharing options...
[Me...] Posted February 28, 2019 Share Posted February 28, 2019 You're preaching to the choir. Any profile tolerance is bilateral as long as you bisect the tolerance zone. There must me some technical reason they do it, like material condition or something, but in practicality it's a huge PITA. Mostly because of exactly what you stated... the machinist makes it to "nominal" and the part ends up being on the borderline of acceptable/rejectable. Then add in some process like anodize and it all goes to hell in a hand basket! 😱 As far as the OP question, since you don't know what material condition they modeled the CAD at, you need to go by the Basic dim, which would make it .252 +/- .002, or .254 -.004, etc. Edited to add: I don't know what Datum -A- is. If it's a plane perpendicular to the features, like the top, then it's as I stated. If it's not and it controls the X/Y location as shown from the top, then you need to treat each surface individually as +0, -.002 and not as a width. I'm treating it as if -A- is the top and the profile is best fit as a width. Link to comment Share on other sites More sharing options...
[Ri...] Posted February 28, 2019 Share Posted February 28, 2019 That is because Profile is not meant for manufacturing, but only for quality control/fit-function. Link to comment Share on other sites More sharing options...
[Me...] Posted February 28, 2019 Share Posted February 28, 2019 Hi Richard, Can you elaborate? I guess I don't get it. If the profile callout is the only thing that controls the feature then it's being used for manufacturing, as well. And as stated earlier, a unilateral/unequal distribution profile is the same as a bilateral that splits the zone. It creates the exact same geometry. I don't understand how a unilateral profile is more useful than a bilateral from a quality & fit perspective. But then, there's a lot I don't understand. 🤣 Link to comment Share on other sites More sharing options...
[Cl...] Posted March 1, 2019 Author Share Posted March 1, 2019 Please sign in to view this quote. -A- is the OD cylinder concentric to and beneath the feature in question (Controls X& Y) Link to comment Share on other sites More sharing options...
[Ri...] Posted March 1, 2019 Share Posted March 1, 2019 Please sign in to view this quote. The reason I say it's not for manufacturing is because it doesn't tell you anything. It's just a number. Go out and tell a machinist to fix his Profile, and see what his reaction is to you. It's not so bad when it is on a print controlling Form/Location of a Plane, but if it's a true free-form/spline shape then there are a lot of basic dimensions that are controlling that. Most of the time Unilateral tolerances are thrown on there because drafters like to draw at MMC for assembly to ensure that the assembly will work. In addition, when you are working on forgings/castings, a Unilateral with all the tolerance on the positive side is needed because negative material means that it most likely won't "clean-up" in post machining. Link to comment Share on other sites More sharing options...
[An...] Posted March 4, 2019 Share Posted March 4, 2019 Please sign in to view this quote. Just playing around. See attached.Contribution_04_03_2019.pdf Link to comment Share on other sites More sharing options...
[Ri...] Posted March 4, 2019 Share Posted March 4, 2019 Ah, but you are only looking at the linear dimension, not the form/location/orientation of the feature. 😜 Link to comment Share on other sites More sharing options...
[An...] Posted March 6, 2019 Share Posted March 6, 2019 See attached.Contribution_05_03_2019a.pdf Link to comment Share on other sites More sharing options...
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