Limits and Fits table is WRONG

[karthur1]

I just got back a submittal package from a customer. Many markups because of incorrect dimension callout for a certian fit.  When I dimensioned the drawing, I used the limit/fit calculator that is with Inventor.  Now I just compared this calculator with the ANSI B4.1-1976 standard that it is supposed to follow.  What I found was that the values in Inventor are wrong.

I just checked a few sizes and they do not match the ANSI standard. Not sure it there are other fits that have errors in them, but I will bet there are. Does anyone at Autodesk realize that if this information is put out, we have to take it as gospel.  I dont have the time to check every-little-stinking dimension. If the dims in the table is wrong, I might as well type them in myself and forget about using the table.  Am I the only one that uses this stuff? 

Here is a screen shot of some of the errrors that I found.  I also checked this size range for RC3, RC4 and RC5.  They all have errors in them too. I am sure there are more, just dont have the time to check.  We are not talking about "Freeware" here... This needs to be fixed ASAP.

[BMiller63]

I didn't verify this, but assuming it's true, this is shameful. Someone from Autodesk needs to verify this and take steps to fix this if it is found to be true.

[karthur1]

Since I found errors in the Limits and Fits calculator.  I thought I would check what shows up when I edit a dimension in the IDW.Found more errors there.  What shows up there is not even the same as the Limits and Fits Calculator!!

Both are wrong, but you would think that they would jive with each other... well they dont.

Here is three that I checked.  looks like I can forget using any of this and manually enter the dimensions by hand.

Here is a clip from the ANSI Standard:

[conklinjm]

Some of what you are observing is the difference between the Imperial & Metric standards for Fits & Limits ... for the ISO 286-2:1988 edition a 16.0000in e8 fit _will_ have a -0.0053in / -0.0091in tolerance.

16.0000in => 406.4mm => 400+ to 500 mm Size Range => -135 to -232 micrometers Tolerance => -0.00531in to -0.00913in

[karthur1]

In the Limits and Fits Calculator, I have the ANSI B4.1-1976 standard selected.  This is behind the "More options" button in the bottom right.  The help says that "Each standard has it own profile and the units of the nominal diameter and deviations are millimeters for ISO and inches for ANSI."  It doesnt look like they are using the ISO and converting it to inches.

For the edit dimension dialog...I see what you are saying. I dont see where I can select a standard. It does looks like they are just using the ISO standard and then converting to inches, which is obviously an error.

99.9% of my jobs use the ANSI standard.

[dave.anderson]

It seems that the xml data that populates the fits Calc is off.

I looked up the limits and fits in my Machinery’s Handbook (25^th Edition) and here’s what it’s stating:

RC₆ Sizes9.85-12.41      Hole – H₉ (+5.0 / -0.0)   Shaft- e₈ (-5.0 / -8.0)

Hole 10.005/10.000        Shaft 9.995/ 9.992

Based on this, it seems that the Inventor Calculator is off 5 tenths and the Calculator has the Shaft as -.0045 / -.0075 which is the difference for this size. The others have a simmilar issue.

I've logged this with our developers as a change request.

[SKinzel]

I ran across this some time ago.  Drove me crazy for about a day trying to figure out what was going on and if maybe the standard had been revised without me know it.

http://forums.autodesk.com/t5/Autodesk-Inventor/Limits-and-Fits/m-p/3010044#M401309

At least it is being looked at by Autodesk now.

[2grumpy]

Dave, I can not believe, you just admitted to gross breach of care. Autodesk is using data from Machinery Handbook as source of calculation data for your software. No wonder that is riddle with mistakes.

Should not you use data from standards acquired right from sources? - whatever national/country standards?

That explain why few years back when calculating springs in Inventor and checking the results on Mechanical desktop I did have different results so I did have to get it check on specialized for spring design software with manufacturer and have still different outcome. Non of the Autodesk spring was correct.

[SBix26]

Please re-read Dave's post-- he did not say that Machinery's Handbook is the source for Autodesk's data, nor that he is responsible for that data, simply that he looked there to check the numbers being discussed in this thread.

[2grumpy]

It only proved from where the data has been acquired - exact mistakes. 

[BryanKelley]

Hello All,

  Well, it seems we are getting closer to the problem.  At some point in the past, it seems that we used data from APPENDIX I: LIMITS FOR SHAFTS c to x  In it, there is a mismatch in Standard ANSI B4.1, table 5.  We assumed that they would be identical.  Looking at the data in the attached image, we can see that there is a discrepancy. 

In the first image we see the data from TABLE 5 RUNNING AND SLIDING FITS: (Please note that RC5 is clipped to the left.)

In the next image from APPENDIX I: LIMITS FOR SHAFTS c to x, you can see the difference.

This is where the problem seems to be.

[karthur1]

Bryan,

Thanks for the explanation. Interesting that these tables conflict with each other and they are both in the same standard.  My standard has the same tables in the appendix, but I never use these tables.  I just used to reading the main ones.  Not ever sure why they have appendix 1 in there.  Makes me wonder which one is correct!!

The copy of the standard I have was "reaffirmed" in 1999.  Looks like it needs to be reaffirmed again...lol

In my original post, I used the RC6 fit just as an example.  There are errors in the limits and fits calculator for other sizes as well.  Most of the error are in the 9.85 to 19.49 size ranges.  The entire thing needs to be checked.

That answers why we are getting the wrong values for the limits and fits calculator, but what about the "Edit Dimension" dialog in the idw?  Do you know what is generating these errors?

Kirk

[BryanKelley]

Hi Kirk,

  Yes, the difference from the same document we purchased has really raised some concerns.  It's very odd to say the least.

  The second disparity is still being tracked down.

[karthur1]

Here is another error that I came across.  It has to do with .6875 (nominal).  The fit should be LC6(H9/f8).  The design assistant has it right, but the tolerance dialog in the model is wrong.

[a.savard]

Was this resolved? We are still having issues with that.

And tolerances are not the same with the limits and fits mechanical calculator and the drawing dimensions.

Is this supposed to be normal? considering this post is 8 years old now....

Thank you!

[johnsonshiue]

Hi! There is indeed a lot of room for improvement in the way the tolerance is captured and reused and propagated. What Inventor release are you on? Here is the behavior I am seeing.

1) Click on Tolerance command in the right-click context menu.

2) Select Limit-Fit-Stacked or other types allowing you to select H9.

3) Then select Limit-Stacked.

On my machine, I am seeing "0.689193 in" as Upper value.

Many thanks!

[a.savard]

We are currently using inventor 2019.4.

I'm not quite sure what you are telling me here...

It seems that the limits and fits mechanical calculator is not wrong anymore but the ones in drawing dimensions do not match them.

We are having issues with the limits/fits in drawing dimensions in general, some are wrong but not all of them...

What I mean is that if you are going to include the option to use this kind of tolerances I think it's not too much to ask to have correct values in it and that the two different ways of verifying them should at least have the same values.

We are not having problems with this specific case but to give you a few examples of ones that do not work or match:

With an RC6 tolerance (H9/e8) and a Ø9.8750" nominal, the values of the shaft should be max: 9.8700" and min: 9.8670". in the limits and fits mechanical calculator, the values are right but in a drawing if I input these I get max:9.8707 and min: 9.8675 both of wich are wrong.

The same kind of mismatch happens with all e8 tolerance on shafts with diameters between 9.85 and 19.69 inches.

I did not verify on diameters over that but I think you (by that I obviously mean Autodesk not specificaly you) should seriously check the whole thing or make the two things match or at least refer to the same xml or whatever file you are using because all the cases I verified with the limits and fits mechanical calculator were correct.

For now we won't be using the limits/fits dimension type in drawing because it could cost a lot of money to our company.

That being said thank you very much and have a nice day!

[johnsonshiue]

Hi! Certainly, these values should be up-to-date. We do have some standard compliant issues. We are tracking them closely but we have not resolved all of them. Your points are well taken. I will work with the project team to understand the issue better and see what we can do.

Many thanks!

[jan_priban1]

Hello,

thank you for reporting this discordance between DACC Limits and Fits & Drawing. I will let development department know.

Regards

Jan Priban