Percentage Tolerance System

[ghpatil1234]

Hello Everyone,

Recently I have come across tolerance in percentage on some drawings, Can you please help me how to convert this percent into exact value?

Is it legal to use percentage?, I didn't find anything on ASME Y14.5 standard.

I have attached picture for your reference.

Thanks in advance.

 

[CheckerHater]

No, you cannot convert percentage into exact value, because it is used illegally in Perpendicularity callout.

The problem is, Perpendicularity has very little to do with angles. It means that the surface of the part must lie within tolerance zone perpendicular to the stated datum. The surface can be inclined, or have some random shape. Perpendicularity has no control over it.

I personally have no problem with using percentage to specify angle though. ASME suggests using ratio to specify taper or slope, and percentage is one of the ways to show ratio.

So, if somebody was trying to say, that surface in question can be inclined no more than 0.6%, he did it wrong way.

 

[ctopher]

Weird. All my years I have never seen a % tolerance used.

Chris, CSWA
SolidWorks 14
SolidWorks Legion

 

[KENAT]

Any chance it's a missing font in CAD translation or something because without the % clearly referencing to some other dimension/number I don't have the foggiest what it would mean.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[ghpatil1234]

No, its not translation error.
It is 0.6% only.

What I understand usage of % is for optmium tolerance irrespective of the size of the component.
For example:
I'm using 0.05mm tolerance for 10mm length & if I'm using same tolerance for 50mm length it will add-up cost.
Instead of that if I go for 0.5% tolerance I'll have tolerance based on length i.e 0.05mm for 10mm & 0.25mm for 50mm.

One more example added as attachment

 

[CheckerHater]

W-friggin-au!

Couple questions:

1. Percentage of what?

2. Is percentage only applied to Perpendicularity or other geometric controls as well?

3. Do you follow any kind of company standard book?

Your new example is even more illegal than the old one (if it is possible) so I am really curious.

 

[ghpatil1234]

1. Percentage of what? ... Percentage of length of that feature

2. Is percentage only applied to Perpendicularity or other geometric controls as well? ... Other geometric controls also but I mainly came across perpendicularity & parallelsim.

3. Do you follow any kind of company standard book? .. There is no standard, actually I'm searching for standard but my company is using it from long time

 

[CheckerHater]

I have a bad news for you:

Your system is not standard, at least not compliant with widely accepted standards by ISO and/or ASME.

If your company chooses to ignore what the rest of the world is doing and go it's own way, it has to document the way it has to be done and publish it, so everyone involved will get a copy.

Most likely you will not get much advise on this forum, because people here prefer to play by the rules. If you mix the rules of Chess and Checkers in the same game, you will not get advise from either chess or checkers people - you are on your own.

 

[JNieman]

If I were contracted to make parts with that value in the GD&T FCF, I would be sending out a RFI to clarify that block because it's not something I've come across in the ASME spec (from which the GD&T is derived [or ISO if applicable]) and because I see nothing that TELLS me that the perpendicularity is referenced to the length of the object. I don't even see the length in that view, so at the least, the length should be in the same 'eyeful' if it is to be referenced by a FCF.

And which length? The length of the point of the face alone, or the perpendicular distance from the extent of the face to the intersection with the referenced Datum A?

This is why standards exist, to be blunt.

If this print is 100% in-house use, you'll have to train everyone 'domestically' on /what/ your standard is, as well as how to apply it, and document that standard so new people can be trained. Of course, if you use the widely adopted ASME/ISO standard callout methods, which still offer great latitude to do things "your way" in their language, you have a chance of hiring people who DON'T need training on using/reading GD&T (or minimal training) and you will already have a very robust book on usage, definitions, etc. Additionally, you'll be able to access existing knowledge-bases on the internet such as this place. However, if you "roll your own" standard you will be without assistance as no one outside your room will know what you're supposed to be doing.

_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5

 

[ctopher]

Can you please help me how to convert this percent into exact value?

If you have to ask, so with the machinist. Price will go up, or no quote.

Chris, CSWA
SolidWorks 14
SolidWorks Legion

 

[KENAT]

ghpatil1234, .5% tolerance on a 50 mm length at least is understandable.

However, in your example it's a % on perpendicularity with no number to base that % on. Are you saying you think it should be .6% of the length of that face? Without a referenced note or standard I don't see how you can leap to that conclusion.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[drawoh]

ghpatil1234,

The whole point of standards is that we all need to speak the same language. My fabricator must know how to interpret the numbers and symbols I apply to my drawings. The percent symbol is not defined in the ASME standard. Is it percent of length? Is it percent grade? Is it a flakey CAD font?

Your purchase order is a contract. Your purchase order calls up your drawing, making it part of your contract. Your vendor must fabricate your part to a perpendicularity of 0.35%, whatever that means.

--
JHG

 

[ewh]

Specifying perpendicuarity of two (apparently) perpendicular surfaces to the same datum?


“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[CheckerHater]

ewh,
Imagine a cube with two sides of it being perpendicular to each other and both being perpendicular to the third side.

 

[ewh]

got it

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[ghpatil1234]

Yes same principle ewh, Thanks CheckerHater