Just to clarify something for me since even my customer is not sure. I have a dimension of 1.5 +.3/+.1 which I read as 1.6 minimum and 1.8 maximum. Is this a correct interpretation on my part?

Hi qcman,

We had a similar callout on an older print a few years back (minus-minus in our case) for NIST. When we called them regarding this dimension, their response was the same as your interpretation.

Hopes this helps, Brad

Just to clarify something for me since even my customer is not sure. I have a dimension of 1.5 +.3/+.1 which I read as 1.6 minimum and 1.8 maximum. Is this a correct interpretation on my part?

Hi qcman,

We had a similar callout on an older print a few years back (minus-minus in our case) for NIST. When we called them regarding this dimension, their response was the same as your interpretation.

Hopes this helps, Brad

Brad, are you sure?? I don't know, is the reason I ask. Most every tolerance I have ever seen is a value surrounding a nominal.

Basically as it is stated (which as you stated could very well be accurate), there is no minimum; but just a maximum. 1.5 means nothing. It is 1.6 to 1.8.

If as you say it's accurate, personally I see no value in it. I would think ANSI or a more appropriate reference should be established for writing tolerances, given the # of questions we have had here at the Cove on interpreting tolerances.

This could be correct, but you know you can always check with the customer to make sure that all requirements are adequately defined. :2cents:

If as you say it's accurate, personally I see no value in it. I would think ANSI or a more appropriate reference should be established for writing tolerances, given the # of questions we have had here at the Cove on interpreting tolerances.

I can think of at least one situation where such a tolerance might be used. Suppose you have a 1" pin to go into a 1" hole. The tolerances might well be 1.000 +0.002/+0.005 for the hole and 1.000 -0.002/-0.005 for the pin.



Tim

Hi Brad,

I cannot say that the customer was correct but that was their response to us. At the time we had thought it was typo error on the print, and had made the part at what we thought was nominal. Their response was that the part was oversized due to the minus minus dimension. If I recall correctly he said that theses tolerance were not used too often in the USA, and it was a really old print. He did give me a reference to look it up at that time but we did not have the ref book to do this, so we just remade their parts to their interpretation.

So to answer your question Brad, no I am not sure, and in my 12 years of inspection I have only seen that call out twice with that same company. As mention the customer was the National Institute for Standards and Technology (NIST), yes I do believe that any company can be wrong, but they were adamant that the minus minus was not a typo. Although if anyone has a better understanding of these tolerance’s, I am all ears. Happy days to all.

Brad :D

I can think of at least one situation where such a tolerance might be used. Suppose you have a 1" pin to go into a 1" hole. The tolerances might well be 1.000 +0.002/+0.005 for the hole and 1.000 -0.002/-0.005 for the pin.



Tim

Let me get educated by Tim on this one. When you get a chance, can you explain this above? I don't understand it.

I have in the pass seen these tolerances in this format, they're used to define fits between holes and shafts from a loose running to a force fit.

A good site for engineering issues is – "www.roymech.co.uk",

On the following page:

"www.roymech.co.uk/Useful_Tables/ISO_Tolerances/ISO_LIMITS.htm"

you will find an explanation on:

BS EN 20286-1:1993(ISO 286-1:1988 )...... ISO system of limits and fits. Bases of tolerances, deviations and fits

BS EN 20286-2: 1993(ISO 286-2:1988 ).... ISO system of limits and fits. Tables of standard tolerance grades and limit deviations for holes and shafts

This is one application for these tolerances – not sure if your customer?

Cheers

I have seen it on holes before but this is an open sided channel running the length of the part, auto related. Prints are coming from Japan and I have always interpreted it as I stated before. I have had some say it reads different so I thought I would put my mind at ease and ask you all. Must be a simple reason they do this, anyone know why?

Hi.

I have seen this before on drawings to define a clearance between a bore and a shaft. We produced a bearing bore diameter. The design engineering drawing specifies a bore diameter 17.000mm +0.005/+0.025. Our shop floor drawing would call out 17.015mm +/- 0.010. Our gages and master rings would be using the shop floor drawing and operators would target at the nominal dimension (=0.000 on a reference type gauge) and have a tolerance of 0.010 in each direction.

Kales, that is exactly how we do it also.

I have seen it on holes before but this is an open sided channel running the length of the part, auto related. Prints are coming from Japan and I have always interpreted it as I stated before. I have had some say it reads different so I thought I would put my mind at ease and ask you all. Must be a simple reason they do this, anyone know why?

I used to work for a Japanese automotive company and they frequently called out tolerances like this. Your interpretation is correct.

The reason was usually as Tim described above. The basic feature size was called out, with clearances specified as +/+ or -/-.

Thanks everybody :applause:

Just to clarify something for me since even my customer is not sure. I have a dimension of 1.5 +.3/+.1 which I read as 1.6 minimum and 1.8 maximum. Is this a correct interpretation on my part?Yes, quite correct. :agree1:

I would not look twice at such specifications, as they are run of the mill here. I see them all the time, and just like howste, I am quite certain that this sort of tolerancing is much more common here in Europe and in Asia than it is stateside. Besides, when I worked for Volvo I often noted a bit of commotion when our drawings went to the U.S. and vice versa. There are differences, and this is one of them.

/Claes

Yes, quite correct. :agree1:

I would not look twice at such specifications, as they are run of the mill here. I see them all the time, and just like howste, I am quite certain that this sort of tolerancing is much more common here in Europe and in Asia than it is stateside. Besides, when I worked for Volvo I often noted a bit of commotion when our drawings went to the U.S. and vice versa. There are differences, and this is one of them.

/Claes

Well Claes,I am confused with this kind of specification.Could you please shed some light behind the logic of using +/+ or -/- tolerances?!
I would prefer to call it 1.6+0.2/-0.0,which suffices,then why someone wishes
to write it as 1.5 +.3/+.1?? Just for the heck of it?!No,I don't think so.There must be a jolly good reason for this type of dimensioning.This is a vey good poser,and I am sure some knowledgable person on the cove will be able to enlighten us.
Thank you for telling that this sort of dimensioning is regular,which further strengthens,that there must be a logical reasoning behind it.

Umang :confused:

Well Claes,I am confused with this kind of specification.Could you please shed some light behind the logic of using +/+ or -/- tolerances?!Well... I can try. Like I said, I am so used to it that that I haven't really given it much thought for a long time.... since school, actually. :o

Anyway, there is indeed a jolly good reason for this type of tolerance: It is usually used in order to provide you with the kind of fit or clearance your application requires. As britman noted this practice stems from the ISO System of limits and fits, usually used for shaft and hole combinations and (here it comes) intended to save manufacturing and engineering costs by benefiting from standard round steel bars when they became available in all major industrial countries.

I believe that this system has been in use here in Europe for some sixty years or so (which may explain why I have taken it for granted). Perhaps some fellow Europeans can help me out with further info?

Experimenting a bit with this fit calculator (http://www.tecnologix.net/en/tools/fset_.html) may provide a clearer picture,

/Claes

FWIW, there was a similar discussion a few months ago here (http://elsmar.com/Forums/showthread.php?t=20704).

Just to clarify something for me since even my customer is not sure. I have a dimension of 1.5 +.3/+.1 which I read as 1.6 minimum and 1.8 maximum. Is this a correct interpretation on my part?

Hello qcman,

Yes, your interpretation is correct. In the various national and international systems of limits and fits it is perfectly normal to see a tolerance zone located above, on or below the nominal.

For the applicable ISO Standards: http://www.iso.org/iso/en/CatalogueListPage.CatalogueList?ICS1=17&ICS2=40&ICS3=10&scopelist=

Stijloor.

FWIW, there was a similar discussion a few months ago here (http://elsmar.com/Forums/showthread.php?t=20704).Ah, yes... And I completely forgot about it. Thank's Jim.:agree1:

/Claes

Let me get educated by Tim on this one. When you get a chance, can you explain this above? I don't understand it.

Hi Brad,

Today I took a second look at Tim's mail,and wow!the answer to the poser is already there.

Now it is clear,that these kind of tolerances are used when components are male & female,id est:a shaft and a bush,a pin & sleeve etcetra.Tim has given the example of a pin with 1"dia to go into a hole of 1"dia.The tolerance of the hole is automatically restricted on the negative side,leaving room only on the positive side and hence the tolerance +0.002/+0.005.Similarly the tolerance of the pin is restricted on the positive side and hence the tolerance -0.002/-0.005

Now arises the question,why not say only +0.005 and -0.005 respectively?

And pat comes the jolly good reply that,since you can't practically have 1"dia for pin as well as for hole,you have got to provide 'tolerances' here.This tolerance will depend upon the kind of fit viz:force-fit,push-fit,driving-fit,running-fit, or shrink-fit.So the tolerance has to be shown as +0.002/+0.005 or +0.001/+0.005 meaning,both the positives or both the negatives.

Looking forward for any other explanation from covers.

Umang :tg:

Hi Umang

If you only apply the simple equal +/- tolerance range you could have an incorrect functional use – both hole and pin could come in at nominal, affecting the design function intended.

Tolerances are place to ensure the required clearances - "for intended use", for example a bearing and shaft would have clearances stated for lubrication, of varying viscosity.

Standardization has allowed multi-sourcing by users with the assurance that the end products function.