I tried using TolAnalyst to calculate RSS stackup involving a pin and hole, where the nominal diameter of the pin is smaller than the nominal diameter of the hole.

It seems TolAnalyst lumps the diameter tolerance for the pin, diameter tolerance for the hole and the play betweeen the pin & hole into one single value which it then squares during the RSS calculation (with the 'float fasteners & pin' option checked).

My understanding is that the tolerance for the pin and the tolerance for the hole should be squared separately, then added together before doing a square root. Also, the 'play' value, which is the difference between the nominal diameters, should not be included in the square and square root process.

The TolAnalyst way of RSS calculation results in a bigger RSS value compared to manual calculations. Is there a fix for this issue?

Does TolAnalyst actually do RSS tolerancing? I thought from reading the What's New for 2008, 2009 and 2010 that it only did worst case.

I'm particularly interested in the answer to that question because I have been looking into buying a tolerance analysis package for use with SolidWorks and have ignored TolAnalyst because WC is not usable for many of our designs. I've been using 1.5*RSS for many years by hand or in Excel spreadsheets.

Does anyone have experience with Sigmund or CETOL? Or any other package?

Thanks. Looks like TolAnalyst won't work very well for us. I really want the ability to modify the RSS values.

Jerry Steiger

I'm just started to learn the TolAnalyst tool. I saw that you said there was a float pin and fastener option. Where is that option found? Or is it even an available feature of the tool in 2008?

Joseph

In the 2009 version, the option is available in the last 'page' (Results) of the TolAnalyst wizard, under the 'Analysis Parameters' tab. I don't have the 2008 version, so I can't tell if its available there

Hi Guys,

Im trying to work with TolAnalyst and RSS and from what i gather it is calculating the Square Root of the Sum of Squares of the Nominal Tolernace. This means that calculated results will give you a Spread that represents a process capability index of 1 Sigma or 68.27% yield. I would like the RSS to be calculated at +/- 3Sigma or Cpk of >1.67 which we expect our suppliers to be manufacturing to. Is there any posibility of changing the RSS factor to show this? i.e the calculation would be

Sqrt ((Tol 1 / 3)sqr + (Tol 2 / 3)sqr + (Tol 3 / 3)sqr) etc.

I agree with Daryl the std RSS formula is Sqrt ((Tol 1 / 3)sqr + (Tol 2 / 3)sqr + (Tol 3 / 3)sqr) etc.

However Solidworks Tol Analyst uses Sqrt ((Tol 1 / 2)sqr + (Tol 2 / 2)sqr + (Tol 3 / 2)sqr) etc. I'm not sure if this assumes that an unknown supplier can only achieve 2 Sigma or this is some sort of allowence for nominal shifting? As yet I can't find any way of user defining this value.

OK a little more understanding now.

The std RSS formula is Sqrt ((Tol 1 )sqr + (Tol 2 /)sqr + (Tol 3 )sqr) etc.

Solidworks Tol Analyst divides by two to give a one sided Tol value ie Sqrt ((Tol 1 / 2)sqr + (Tol 2 / 2)sqr + (Tol 3 / 2)sqr) etc.

Sqrt ((Tol 1 / 3)sqr + (Tol 2 / 3)sqr + (Tol 3 / 3)sqr) will give you the std deviation from which you can calculate the defects PPM asuming supplier is 3 Sigma. Hope this helps someone.