minus minus tolerance
minus minus tolerance
(OP)
Hello,
I need some help and hope someone can help us.
We recieved a drawing that has a diameter called out like with the tolerance set as minus minus.
-0.02
Ø4.2 -0.04
I need some help and hope someone can help us.
We recieved a drawing that has a diameter called out like with the tolerance set as minus minus.
-0.02
Ø4.2 -0.04





RE: minus minus tolerance
RE: minus minus tolerance
Frank
RE: minus minus tolerance
I don't understand what it meen's. would the tolerance range
be 4.18 to 4.16?
Thanks in advance.
RE: minus minus tolerance
Dave D.
www.qmsi.ca
RE: minus minus tolerance
RE: minus minus tolerance
The required dimension is 4.16 to 4.18.
I know that +/+ and -/- tolerancing rattles people, but I like it. People want the CAD file to do CNC programming. It really helps if they know the diameter of the as-modeled feature, in your case Ø4.2.
RE: minus minus tolerance
This place is great!!
RE: minus minus tolerance
drawoh,
This practice was used in the past at my company, but has since been discontinued because of confusion in manufacturing. Bloodydecks is not the first person to question the meaning...
Why would anyone create a feature in a CAD model that is outside the tolerance limits? This can cause issues with CNC, interference detection, etc.
RE: minus minus tolerance
RE: minus minus tolerance
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: minus minus tolerance
Personally I don't care that much, though it does appeal to me to have a round "nominal" as it does seem to confer a little bit of design intent. If you are willing to accept non-symmetric tolerances it's not a big mental leap to +/+ or -/-.
RE: minus minus tolerance
In my example H7/p6 for a 4.2mm diameter would net +0.012/+0.022 on the shaft diameter to ensure interference. (The hole would be 4.2 +0/+0.012)
RE: minus minus tolerance
But who ever said a 2 X 4 was 2" by 4"?
Here is another explanation:
http://gdtseminars.com/blog/2008/01/26/31/
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: minus minus tolerance
bloodydecks,
It has nothing to do with the "global market place".
Chris
SolidWorks 09 SP5.0
ctopher's home
SolidWorks Legion
RE: minus minus tolerance
There is a whole norm (ISO 286) that specifies:
- standard tolerances for certain ranges of nominal dimensions depending on the tolerance class,
- standard fundamental deviations from nominal dimensions which are later used in fit description,
- symbology for limits and fits marking.
Y14.5 standard indeed does not use -/- description for a tolerance, but actually gives an example of limits and fits indication. In 1994 edition fig. 2-3 depicts three methods for this. And in fact cases a & b are similar to the OP's dilemma - nominal dim. is 30 but the tolerance is -/-, only the indication on a drawing could be different.
RE: minus minus tolerance
RE: minus minus tolerance
RE: minus minus tolerance
RE: minus minus tolerance
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net
RE: minus minus tolerance
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: minus minus tolerance
• RC = Running or Sliding Clearance Fit
• LC = Locational Clearance Fit
• LT = Transition Clearance or Interference Fit
• LN = Locational Interference Fit
• FN = Force or Shrink Fit
see also:
ASME B4.1 - 1967 Preferred Limits and Fits for Cylindrical Parts
ASME B4.2 - 1978 Preferred Metric Limits and Fits
the purpose of ISO 286-1/2 and ASME B4.2 is one for using a system of common tools, production methods, and gages. This is the description taken from the ASME B4.2 catalog:
"This standard describes the ISO system of limits and fits for mating parts as it is approved for general engineering usage in the United States of America. It establishes: (1) the designation symbols used to define specific dimensional limits on drawings, material stock, related tools, gages,
etc., (2) the preferred basic sizes (first and second choices), (3) the preferred tolerance zones (first, second and third choices), (4) the preferred limits and fits for sizes (first choice only) up to and including 500 millimeters, and (5) definitions of related terms."
for example, say we want a Ø45mm shaft/bearing assembly that requires a good positional fit but also needs to slide for assembling and for allowing movement during operation. Now from our preferred fit tables (ISO/ASME) we find that an RC3 fit (H7/f6) is a common choice for such function and should also prove economical for our manufacturing.
on the drawing, we can easily show this as:
Hole Ø45 H7
Shaft Ø45 f6
now you are asked by the inexperienced shop, what is H7/f6? so you add the tolerances:
Hole Ø45 H7 (+0.025/+0)
Shaft Ø45 f6 (-0.025/-0.041)
well, there is that nasty +/+, -/- again which nobody seems to like, so we can nominalize it to give:
Hole Ø45.0125 +/-0.0125
Shaft Ø44.967 +/-0.008
I think, it should prove quite easy to find tooling and gages (common) for a Ø45H7/f6 connection, but I would think that one should expect a few blank looks and likely additional costs if they inquired about a drill bit/reaming set and gaging for a Ø45.0125 +/-0.0125 hole and a roller burnishing tool and gaging for a Ø44.967 +/-0.008 shaft.
RE: minus minus tolerance
Quote
"There is a whole norm (ISO 286) that specifies:
- standard tolerances for certain ranges of nominal dimensions depending on the tolerance class"
That's not correct IMHO,
ISO 286 is only used for tolerancing shaft fits, nothing more.
Din-ISO 2768 (part 1) specifies tolerances for certain ranges of nominal dimensions (not ISO 286).
And as others have stated, it is fairly common practice in Europe.
RE: minus minus tolerance
You are right - this was my mistake.
RE: minus minus tolerance
DIN/ISO combines the former DIN specifications completely:
DIN 7150 T1 = ISO tol. and fits for length dim. 1 to 500mm
DIN 7151 = ISO Basic tol. for length dim. 1 to 500mm
DIN 7152 = Creation of tol. fields 1 to 500mm.
DIN 7160 = ISO - deviations for O.D. (shaft) 1 to 500mm.
DIN 7161 = ISO - deviations for I.D. (bore) 1 to 500mm.
DIN/ISO 286 replaces the following DIN specs in part:
DIN 7172 T1, T2, T3 and DIN 7182 T1.