23 Replies Latest reply on Jun 20, 2017 6:20 PM by Anna Wood

    ANSI Inch Clearance Holes Are Not From B18.2.8

    Jason Wells

      The ANSI inch clearance holes in SW are not from ASME B18.2.8.

       

      e.g 1/4 clearance hole:

                                 Close    Normal Loose

      SW                     .257      .266      .281

      ASME B18         .266      .281      .297

      (apologies if my table format is wonky)

       

      Solidworks' clearance holes are one "size" tighter than ASME B18.2.8.

       

      So where do these clearance holes come from? (i've googled for an hour but came up empty) The best I could find is a reference to ISO 286 and 273. Both of those have a statement "Inch dimensions deleted."

       

      BTW. It sure would be nice of these clearance holes had max/min tolerances per ASME B18.2.8.

       

      Regards,

      Jason C. Wells

        • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
          Jason Wells

          Does nobody know how the clearance holes in SW came to be? Surely I am not the first person to ever notice this.

            • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
              Andy Sanders

              I have noticed.  But in the end, they're clearance holes.  Chances are our shop is making them according to whatever tools they have for c'bores, etc so I get what I get and it may or may not match.  It's makes no difference to me for 90% of my c'bores.

               

              If there's any precision I need, I'll force a specific drill size in the part.

              • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                Matt Peneguy

                Jason Wells,

                If I go to my tools and pick up a 1/4" drill bit, it's going to be the correctly sized drill bit and will drill a 1/4" hole.  That drill bit costs about $3.  How about my $7000 CAD package?  You are telling me that it can't do that hole correctly?  Others here don't seem to be concerned, but I agree this sounds like a bug to me.

                I haven't stumbled across this because we use fitted tolerance holes if we need a shear connection (H9) with custom call outs via a modified calloutformat.txt file.

              • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                John Pesaturo

                I can say I've never noticed that, though I'll also admit I never checked. I never questioned where the (Close) Ø.257 came from as we do that from time to time for a lead into a Ø1/4 dowel hole. Especially when press fitting rather long length dowels into 2" thick plate.

                 

                The (Normal/Loose) Ø.266/Ø.281 are pretty much all standard leads on counter bore sets that I'm aware of. We rarely call the 64th over (Ø.266) out for tight fitting projects and pretty much everything we do uses the 32nd over (Ø.281) as a standard. I don't know that I've ever seen a 3/64's (Ø.297) oversize on a counter bore set.

                • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                  Jason Wells

                  I am not asking about the holes, drills, or tooling. I am asking about the engineering standards that SW used when they wrote the tables. Let me reword the question.

                   

                  What engineering standard does Solidworks use to define bolt clearance holes?

                   

                  Thanks,

                  Jason

                  • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                    Greg Berkeley

                    I just discovered this today as well. I was making a chart with position tolerances based on fixed fastener and floating fastener formula which is dependent on the size of the clearance hole. I started entering values from ASME B18.2.8 and went to SolidWorks just to check that it uses the same values (which I fully assumed they were) and found their hole sizes are considerably tighter. I can just make my chart reflect what SolidWorks uses but I have the same question: what is SolidWorks using to justify the ANSI Inch clearance sizes if it is not the published ASME standard? In most cases the SolidWorks loose fit is tighter than the ASME standard close fit.

                    • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                      Bernie Daraz

                      I don't have that full spec here. It appears that SW normal and loose matches the standard (ASME B18.2.8) of close and normal. 'One' off if you will. Don't believe that answers your question but just offering that.

                      • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                        Greg Berkeley

                        Jason Wells wrote:

                        BTW. It sure would be nice of these clearance holes had max/min tolerances per ASME B18.2.8.

                        I second this

                        • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                          Robert Conklin

                          Also,

                          Counterbores for metric socket head cap screws…

                          Our shop has the tooling for these sizes, as shown here in the McMaster catalog:

                          Metric C'Bores  -  McMaster Carr.JPG

                           

                          The sizes shown here, from the MSC catalog , are what Solidworks call out in the holewizard:

                          Metric C'Bores  -  MSC 01.JPG

                          We prefer the McMaster sizes and we are constantly changing the callout when placing holes with the holewizard,
                          I know I could change the MDB file to reflect the preferred sizes

                          BUT Why can not Sloidworks  have an alternate choice built in?

                          Why does SW use the sizes they have in the holewizard?

                          What is the rest of the world (Non USA) really using?

                          • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                            Jody Stiles

                            Hello everyone,

                             

                            I've been looking into this and it seems that the values for the #0 - 1/2" Close and Normal fits were taken from Machinery's Handbook (I'm using #27, p. 1934, Table 4).  Normal and Close fits outside of this size range and Loose fits in general seem to have been calculated somehow but I'm not sure how.  As noted, none of the fits match ASME B18.2.8-1999 r2017, Table 2 and many of the sizes are not called out in the standard at all.  We are looking into this and how to best fix it in a future release.

                            In the mean time, the data from Hole Wizard and from B18.2.8 is in the attached spreadsheet.  Unfortunately, there's no easy way to get the values into Hole Wizard at this time so you'll have to copy/paste or manually enter them.

                            Jody

                              • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                                Dennis Dohogne

                                Jody Stiles,

                                Thank you for:

                                1. Providing a reply from an official SWX person!!!  Yay!

                                2. Admitting there is an issue.

                                3. Promising to look into it.

                                4. Telling us what the limitations are in the meantime.

                                 

                                Why can't we get more responses from you and your SWX compatriots like this?

                                • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                                  Jason Wells

                                  Thank you, Mr. Stiles.  SW should proceed carefully on this. I am sure there are many offices/shops (my company included) that think the SW provided holes are "standard". I observed this a couple years ago but got busy and let it ride. Here is the thing.  There are websites that call out clearance holes just like the ones that SW has.  Those websites don't provide the provenance of their holes. So those numbers came from somewhere. I don't think SW can just drop one table and add the B18.2.8 table.

                                   

                                  Mr. Stiles spreadsheet has an "average" hole size.  The standard does provide for nominal, max and min.  You have to look at the text in the standard to get the nominal values of hole size from the nominal screw size and the nominal clearance. I did not check, but I would be concerned that nominal is NOT equal to average.

                                   

                                  Two people in this discussion professed a desired to have max and min values. This is important to determining correct GD&T positional tolerances per standard (I forget at the moment which one). The fixed and floating hole positional tolerance equations are in an appendix to that document.

                                   

                                  And if SW is feeling really ambitious, those of us in aerospace wouldn't mind NAS618 spec'ed holes.

                                   

                                  Thanks all for lending your voice to this. I second Mr. Dohogne's comments.

                                   

                                  Regards,

                                  Jason C. Wells

                                    • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                                      Jason Wells

                                      I just checked the math. Nominal is not equal to the average of max and min.

                                      • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                                        Greg Berkeley

                                        From what I remember, and I will check later this evening, ASME 18.2.8 states the tolerances were adopted from ISO 286 which uses an H12 tolerance for close fit, H13 tolerance for normal fit, and H14 tolerance for loose fit. Of course you will have to convert between inches and mm to do this. Since it is an 'H' tolerance for a hole then nominal and minimum are equivalent and maximum is some deviation increased from nominal. In this case, the nominal size of the drill to create the clearance hole is the minimum.

                                         

                                        Here is an example if anyone needs clarity. According to ASME 18.2.8 the drill size for a 1/4" screw clearance hole is 9/32" or 0.28125" diameter, which is ~7.14mm. An H13 fit for this is +0/+.22mm, so min 7.14mm and max 7.36mm, or min 0.281" and max .290" (at least to 3 decimal places). These values are what the standard reports.

                                         

                                        I haven't found a chart that encompasses everything but you can use the link below to calculate tolerances based on H12, H13, and H14.

                                         

                                        Limits, Fits and Tolerances Calculator (ISO system)

                                        • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                                          Jody Stiles

                                          Hi Jason,

                                          Jason Wells wrote:

                                           

                                          <snip> SW should proceed carefully on this. I am sure there are many offices/shops (my company included) that think the SW provided holes are "standard". <snip>

                                          This is my main concern.  We won't/can't simply replace the table due to years of usage of the existing hole data.  The data is not accurate but it's in use and has been working fine for many/most users. 

                                           

                                          We've tossed around ideas like:

                                          1. Provide a new hole table that contains just the ASME hole data (#0 - 1/2").  It would be up to the user/admin to choose which hole to use as presumably one would be preferential to the other.  This may cause confusion as to why there are two "similar" hole tables
                                          2. Provide the tabulated data for the user/admin to manually update in whatever way possible (Hint: Check out Beta 2018).  This puts the burden on the user/admin which is not always appreciated.
                                          3. Provide new functionality in the Installation Manager to allow the user/admin to see the updated data and provide controls to apply it or not.  This may be a non-starter for several reasons.

                                           

                                          We have other holes that have small data errors in them that have yet to be fixed for similar concerns.

                                      • Re: ANSI Inch Clearance Holes Are Not From B18.2.8
                                        Scott Casale

                                        This post amuses me. I've been saying for years that SW does not have their standards up to date or are not accurate. Why we always need to control and verify.