Default Tolerances in Title Block 1

[phlyx]

We have a debate going on internally here as we attempt to re-design our title block for CAD. The debate centers around the default tolerance call-outs on inch unit mechanical drawings. Basically these are the defaults that are being debated :

- FRACTIONAL +/-
- 1 PLACE DECEIMAL X.X +/-
- 2 PLACE DECEIMAL X.XX +/-
- 3 PLACE DECEIMAL X.XXX +/-
- 4 PLACE DECEIMAL X.XXXX +/-
- ANGLES +/-

What numbers does anyone have for these values and is there any standard that covers this?

Thanks in advance!

~ Phlyx ~

 

[ewh]

yates,
You are being picky. I would have little problem with that situation if the feature being dimensioned was not critical to the part. It would signify that the feature may or may not exist, depending on how accurate it's fabrication was. Granted, if it isn't needed, it should not be on the part to begin with.
Mistakes do happen. The detailer may have meant to use a 4 place dimension or neglected to use a unilateral tolerance on that dimension. This only stresses how important it is that drawings are checked before parts are made. A drawing mistake such as this in no way negates the use of tolerance blocks.

 

[Rentapen]

Think of the shop people. Any fraction must be read from a yo-yo (tape measure), I believe 1/16 is the smallest with better one's marked out at 1/32.
Just wandering.
rentapen

 

[phlyx]

The problem we are running in to is we are converting old AutoCAD and manual drawings to Inventor and when some users run across 1.06 or 1.063 (for 1-1/16) in their haste they model the part at 1.06 or 1.063 rather then 1.0625 and then when you try to apply contraints with the mating part, it doesn't work. The problem is that not everyone would know if .78 meant 25/32 or 20mm. And yes, there is enough difference there to throw constraints off.

::sigh::

~ Phlyx ~

 

[vriyg]

It all depends on what your individual companies are producing. A tolerance block doesn't have to be international "valuewise", it serves your purpose, your drawings, your products. Maybe I am mistaken but the only purpose of a general tolerance block is to avoid repeatitive notes or tolerances elsewhere on the face of the drawing. It does not "dictates" the tolerance value you should apply to any let's say 3 digit dimensions! If you have a .005 dimension somewhere, it would be dumb to leave it without a specific tolerance when the tolerance block states a +/-.005... Same applies to a 15.255 dimension for example. A wrist watch components manufacturer is gonna choose a different tolerance block and values than a bridge builder will.

What I do is actually put a tolerance on each and every dimension (this way I am actually thinking about what is logically required for production) then I come back and remove the tolerances covered by default by the tolerance block.

Maybe I am picky too but I don't see the meaning of having a +/-.015 tolerance on a 2 digits dimension. 2 versus 3 digits... Doesn't ASME Y14.5 specifies that the same number of digits should be read between the dimension and its tolerance?!?

 

[phlyx]

We have a handful of mechanical engineers doing the work of a couple dozen. We barely have enough time to print out our drawings and even less time to place tolerances on everything and check and double-check that the buildup doesn't kill us. We build packaging machinery and it's not laser tolerance work but time is our biggest enemy. Each of us usually has two or three active projects we are designing on and a couple needing support on the floor all at the same time. I would love to look at each dimension individually but we normally have to look at the part, assume what machine it will be produced on and dimension accordingly. For example, doing a 2-decimal place dimension beside a 3-decimal place number on a part that will be 100% CNC is crazy. Time is money and we put on the absolute bare minimum to get the part made. That keeps the cost down and the place in business.

Also, our B-size drawings would grow to be 2 sheets of E-size if we had tolerance call-outs on with every dimension. And they would be impossible to read. Each of us easily turns out dozens upon dozens of deatiled parts and full assembly drawings with BOM's every day. And we haven't had a "checking department" since the 80's.

::sigh:: again

~ Phlyx ~