5 Replies Latest reply on Jun 30, 2015 10:52 PM by Frank Phelps

    Fit Callout

    Frank Phelps

      I don't know what to do.  I am trying to callout a fit in a drawing but when I place the fit it looks like this.....Fit.JPG

      This is the correct callout "js6" how ever if you look in the machinist hand book....

      Fit1.JPG

      the second column does with the clearance and interference #'s shows that it is not a symmetrical #.  The only way I can get Solidworks manually change them is to take it off the shaft callout and not have anything selected.  Is this correct way for solving this problem?  Thanks in advance.

        • Re: Fit Callout
          Josh Brady

          What are you actually trying to call out?  Based on your description of the issue, it sounds like you are trying to call out a Class LT1 fit, which is a combination of an H7 tolerance hole and a js6 tolerance shaft.  If you are making a drawing of the shaft, you should use the js6 tolerance as you have shown.  If you are making a drawing for the hole that the shaft goes in, you should use the H7 tolerance.  The drawing of the shaft shouldn't say anything about the hole.  The drawing of the hole shouldn't say anything about the shaft.

            • Re: Fit Callout
              Frank Phelps

              Josh -  You are correct.  Sorry I was looking at the completely wrong column.  However should the tolerances not be .00025 instead of .00026?  Thanks for the help.

                • Re: Fit Callout
                  Josh Brady

                  My guess is this has to do with the mm/in conversion.

                   

                  I work in metric all the time.  I'm sure ISO is originally defined in metric.  ISO for js6 is from nominal 18mm to nominal 30mm shaft, the tolerance is ±6.5 µm.  These numbers roughly convert to the values in the inch tables you referenced.  However. 6.5µm is about 0.000255905511811 inches.  If you'll increase the decimal precision of your tolerance in SolidWorks, you will see this.  By normal mathematical rounding, this should round to 0.00026.  However, I am guessing that most inch version tables prefer to round that to 0.00025, which is a miniscule difference but slightly tighter tolerance to guarantee that any part that meets the inch approximation actually falls within the true standard which is defined in mm.

                   

                  So... If you truly want real js6 tolerance, increase your decimal places to show ±0.002559 and you should be good.  :-)

                • Re: Fit Callout
                  Matt Peneguy

                  Josh is absolutely correct.  And good catch Josh, it does appear that he may be calling out a hole fit on what appears to be a shaft...

                   

                  Though, the table in Solidworks appears to be wrong in this case for this size js6 fit (though I don't appear to have the js6 fit in my table in version 2014 SP5).

                  The js6 fit in the Machinery's handbook lists the js6 fit to be +/- 0.00025 and Solidworks, according to Frank's picture, appears to show the js6 fit to be +/-0.00026.

                   

                  I found a similar issue with the f8 fit being off for the 1.97-3.15" diameter size.

                   

                  Frank, the js6 fit is symmetric.  The H7 Hole fit for the above mentioned Class LT1 fit is not a symmetric fit.  And thus the total fit is not symmetric.  I hope this answers your question.

                  You can submit a bug report for this fit via the customer portal.  In the meantime, you may be able to use the fit "as-is".  Depending on your application a couple hundred thousandths of an inch may not matter.