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Question on seeing a + + tolerance
- Thread starter Mikergris
- Start date
- Replies 13
- Views 2,456
If I wanted to be sure, I would contact the customer to make sure it is "+" and "+", and not +/-. That said, it sounds like a pretty high-precision part with a 30 micron tolerance gate. If it is +.25 +.28, then yes, min size is 8.25mm, max is 8.28mm. Good luck --
I saw this type of tolerance a long time ago . If I remember correctly it's not .03 tolerance it goes some thing like this first plus is target size second plus is tolerance . I could be wrong cause of memory but that is what I think it is. I aggree with barbter2 you should check with your customer . While it seems .03 tolerance is excessive you can't be sure until you ask .
Mike1974
Diamond
- Joined
- Nov 5, 2014
- Location
- Tampa area
In the metric world it is an ISO class of fit that drives plus/plus or minus/minus.
Theoretical Machinist
https://kiralytool.com/wp-content/uploads/2017/05/hole-shaft-tolerance-chart.pdf
Theoretical Machinist
https://kiralytool.com/wp-content/uploads/2017/05/hole-shaft-tolerance-chart.pdf
juergenwt
Stainless
- Joined
- Feb 2, 2008
- Location
- Wheaton, IL.
Most likely somebody thinking inches and trying metric. 0.325/0.326" . 0.325 should go, 0.326 should not go.
0.8 mm tol. was most likely +/- 1/32".
Happens all the time in good old USA.
Some people think that in order to design in metric all they need to do is use inches times 25.4 .
There is a lot more to it.
That is exactly why we end up with crapp like this.
0.8 mm tol. was most likely +/- 1/32".
Happens all the time in good old USA.
Some people think that in order to design in metric all they need to do is use inches times 25.4 .
There is a lot more to it.
That is exactly why we end up with crapp like this.
Milland
Diamond
- Joined
- Jul 6, 2006
- Location
- Hillsboro, New Hampshire
Likely clearance for a M8 bolt. And 0.030mm tolerance on slot width/length? Sounds like a dope-slap is in order...
Mike1974
Diamond
- Joined
- Nov 5, 2014
- Location
- Tampa area
Not likely. It is for the reason I stated. Not trying to be a smart ass, but it is a standard. Just like GD&T, even if you rarely see it, or have never seen it, it exists and some designers use it all the time... I made prototypes all the time in the drone world, almost all the bearing fits (and this is important too, normall seen on tighter tolerance, but that's not a 'rule') were dimensioned something like 30mm -.008 -.011 (or whatever). Yes I agree it makes more sense to our machinist brains to dimension it to nominal with an equal +/- , but it is what it is...
Eric M
Cast Iron
- Joined
- Nov 21, 2007
- Location
- Orlando, FL
CarbideBob
Diamond
- Joined
- Jan 14, 2007
- Location
- Flushing/Flint, Michigan
I'd have to agree that this is what is called "lazy engineering".
Allowed but simply asking for problems down the road.
One runs into it but then you have to question of why or if a mistake. A waste of everyone's time.
If one of my designers or even someone above me did this there would be a real dressing down......DFM.
Yet as 74 says sometimes you will see it and have to deal accordingly.
With a larger company I skip the designer and go right to the engineering manager or VP of engineering with my questions and why not KISS. They do not want these trivial problems.
Bob
Allowed but simply asking for problems down the road.
One runs into it but then you have to question of why or if a mistake. A waste of everyone's time.
If one of my designers or even someone above me did this there would be a real dressing down......DFM.
Yet as 74 says sometimes you will see it and have to deal accordingly.
With a larger company I skip the designer and go right to the engineering manager or VP of engineering with my questions and why not KISS. They do not want these trivial problems.
Bob
juergenwt
Stainless
- Joined
- Feb 2, 2008
- Location
- Wheaton, IL.
I can understand how someone who retired 20 years ago could be in the dark when it comes to understanding the "ISO System of Fits and Tolerances" (ISO 286). However - if you are a designer, enginer, craftsman etc. working in today's metal
manufacturing and have no or just very limited knowledge of ISO 286 I would strongly advise to get some training to get up to speed. The whole world uses ISO 286. Designations like "easy sliding fit, tight press fit or running fit" to name just a few will no longer work in today's manufacturing environment.
(A "press fit" means something different to a Russian than it does to someone in Italy or someone in Ohio.
manufacturing and have no or just very limited knowledge of ISO 286 I would strongly advise to get some training to get up to speed. The whole world uses ISO 286. Designations like "easy sliding fit, tight press fit or running fit" to name just a few will no longer work in today's manufacturing environment.
(A "press fit" means something different to a Russian than it does to someone in Italy or someone in Ohio.
Mike1974
Diamond
- Joined
- Nov 5, 2014
- Location
- Tampa area
Let's agree to disagree. Of course I would like to see even +/- tolerances. But in the end, it is all just numbers*. Someone could detail a print 1" -.01-.02" I don't really care, I'll shoot for .985" and be done with it. Of course you have to factor in if it's a manual job or a cnc job. I get it when a cnc part has multiple "conflicting" (one feature +/- equal, and another +0.0- .xxx) features, it becomes a pain in the ass.
*and this is what we as chinists or toolmakers or cad/cam guys are supposed to be a core area of our work.
*and this is what we as chinists or toolmakers or cad/cam guys are supposed to be a core area of our work.
