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ANSI Inch Clearance Holes Are Not From B18.2.8

Question asked by Jason Wells on Jun 10, 2017
Latest reply on Sep 6, 2018 by Frederick Law

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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

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Jason Wells Jun 16, 2017 3:17 PM
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Does nobody know how the clearance holes in SW came to be? Surely I am not the first person to ever notice this.
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John Pesaturo Jun 16, 2017 3:51 PM
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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.
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Andy Sanders @ Jason Wells on Jun 16, 2017 3:52 PM
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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.
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Matt Peneguy @ Jason Wells on Jun 16, 2017 5:35 PM
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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.
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Jason Wells Jun 16, 2017 6:27 PM
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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
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Greg Berkeley Jun 18, 2017 7:48 AM
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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.
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Bernie Daraz Jun 16, 2017 8:19 PM
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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.
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Greg Berkeley Jun 18, 2017 7:48 AM
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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
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Jason Wells @ Greg Berkeley on Jun 18, 2017 3:14 PM
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I was going to do the same thing, and you need the max/mins to do that. I recently switched from Catia and I do like the SW hole wizard. I just need to be sure that I am correct when I apply tolerances. I can't do that with the current data in SW.

To butchering an old saying, "We don't want to re-invent the hole."
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Robert Conklin Jun 19, 2017 7:03 AM
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Also,
Counterbores for metric socket head cap screws…
Our shop has the tooling for these sizes, as shown here in the McMaster catalog:

The sizes shown here, from the MSC catalog , are what Solidworks call out in the holewizard:
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?
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Jason Wells @ Robert Conklin on Jun 19, 2017 11:14 AM
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I am glad that some other people are noticing this. Do official SW people participate here? It sure would be nice to get this documented.
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Jody Stiles Jun 19, 2017 2:37 PM
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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
Attachments
- ASME B18.2.8-1999 r2017 Fit Analysis.xlsx15.9 KB
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Dennis Dohogne @ Jody Stiles on Jun 19, 2017 2:53 PM
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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?
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S. Casale Jun 19, 2017 2:58 PM
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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.
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Jason Wells @ Jody Stiles on Jun 19, 2017 3:12 PM
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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
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Jason Wells @ Jason Wells on Jun 19, 2017 3:23 PM
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I just checked the math. Nominal is not equal to the average of max and min.
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Greg Berkeley @ Jason Wells on Jun 19, 2017 4:39 PM
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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)
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Jody Stiles @ Jason Wells on Jun 19, 2017 9:26 PM
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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.
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Solid Air @ Jody Stiles on Jun 19, 2017 10:12 PM
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Jody,

As you know you do not need Beta (hint: I've read the what's new) to change clearance holes, counterbore & countersink diameters. You can just click configure in the Hole Wizard/Toolbox system setting and change away. That's what we did and have never looked back.
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Anna Wood @ Jody Stiles on Jun 19, 2017 10:22 PM
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Jody, Just add a new standard please, if you must....

Or the folks that it is that important that the holes meet their company standards can create their own. Trust but verify... Never assume...

We are perfectly happy with what SolidWorks has had for these types of holes all these years.

The wonderful thing about standards is that there are so many available to choose from.
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Solid Air @ Anna Wood on Jun 19, 2017 10:47 PM
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Anna,

Why does SW need to create a new standard? You can also create your own can't you?
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Dave Bear @ Dennis Dohogne on Jun 19, 2017 11:09 PM
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Well said Dennis.

Dave.
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Anna Wood @ Solid Air on Jun 20, 2017 6:20 PM
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Solid Air wrote:

Anna,

Why does SW need to create a new standard? You can also create your own can't you?
That would be my first choice.... But I can also see SolidWorks trying to fix things and making more work for the rest of us. I did mention in my post that those that are that annoyed can create their own standards.
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Stefanie Davis @ Jody Stiles on Sep 15, 2017 8:46 AM
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Jody Stiles
I happen to be looking at my Holo-Krome reference card....look what I found! Where the Loose fits come from! (ANSI B18.3)

The image below shows what I am talking about...
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S. Casale @ Stefanie Davis on Sep 15, 2017 11:05 AM
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Digressing - Something funny... I spoke with Holo-Krome about the counterbore sizes for various shcs that are shown on those slide charts. Some of the C'bore sizes can't be purchased unless custom. I also spoke with a few aerospace machine shops and they were baffled as well - they never noticed before because they use the 32 64 rules. The conversations were very amusing.

One thing I will write that is important. Unless it's is desired for such, when using, all of the selected options presented in hole wizard and tool box should be verified with real world application, this includes things like the counterbore's Ø, the angle of countersink of a machine screw from tool box, and etc.
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ANSI Inch Clearance Holes Are Not From B18.2.8

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