GENERAL TOLERANCES 2

[memoi567]

I am curious to your opinions on General tolerances on title blocks. I know of two ways to do it basically give a range or by deciding the amount of decimals. ISO vs ASME

For example:

0 to 1 +/- 0.01
0 to 6 +/- 0.03
6 to 24 +/- 0.06

or

x.x +/- 0.1
x.xx +/-0.01
x.xx +/-0.005

there is also a third way which is a combination of the two which would look like this:



_________x.x___________x.xx
0 to 1__+/- 0.01________+/- 0.004
0 to 6__+/- 0.03________+/- 0.01
6 to 24_+/- 0.06________+/- 0.03

As far as I can tell the ISO tolerance table is easier for the designer, but the table repeats a lot of the same tolerances just in different ranges and for different position. Thus, the decimal way ensures that the designer is more deliberate on the tolerances and dictating each dimension with the correct tolerance (by determining the amount of decimals displayed).

If any tolerance is outside the general tolerance range you have to dictate the tolerance on the dimension itself this is true for both standards, and really is not a factor.

These are the only advantages and disadvantages I can determine. I want to be able to go to my boss and say this standard is better because of this; and really I don't have a strong argument for either style. If my only argument is this is ISO standard or this is ASME standard then its not a good argument in my opinion.

 

[hydtools]

Consider which way is best for your design and manufacturing purposes.

Ted

 

[hendersdc]

As hydtools says, your tolerance format and values will change depending on your design and manufacturing process. Here are examples of what we use for different processes. Values change based on the scale and needs of the part as well.

For machined parts we use your second example where the number of decimal places in the dimension indicate the tolerance x.x +/- 0.1", x.xx +/- 0.01", etc.

For sheet metal parts we use something like the below notes:

SHEET METAL TOLERANCES UNLESS OTHERWISE NOTED:
a. HOLE DIAMETER: +/- 0.005 IN E. FOLD TO EDGE: +/- 0.015 IN
b. HOLE TO HOLE: +/- 0.010 IN F. FOLD TO HOLE: +/- 0.015 IN
c. EDGE TO EDGE: +/- 0.010 IN G. FOLD TO FOLD: +/- 0.015 IN
d. EDGE TO HOLE: +/- 0.010 IN H. ANGLES: +/- 1 DEGREE

For injection molded parts, we will reference a standard such as DIN ISO 2768 (attached) and a certain class within that standard.

 

[pylfrm]

memoi567,

What overall drawing interpretation standard do you use? What units do you use?

Have you considered indicating each tolerance individually instead of using general tolerances in the title block? This is usually my first choice.

Have you considered using a single default tolerance that does not depend on the number of decimal places or the value of the dimension? This is usually my second choice.

0 to 1 +/- 0.01
0 to 6 +/- 0.03
6 to 24 +/- 0.06

This type of scheme is usually my third choice, but only if it clearly assigns exactly one tolerance value to any non-negative nominal value. Your example fails to do that in a few different ways.

x.x +/- 0.1
x.xx +/-0.01
x.xx +/-0.005

This type of scheme is usually my fourth choice. It can make problematic rounding more likely, especially when the resolution of the nominal value is a significant fraction (perhaps more than 10%) of the corresponding tolerance.


pylfrm

 

[CWB1]

IME the applicable print standards are usually defined by industry norms/practice. Given the rarity of title block tolerances today, I'd recommend finding other reasons to pick one over the other if your competitors haven't standardized on one.