Question on NX 7.5/8.5 Screw Clearance Holes - which standards were used to generate the tables? 1

[MASawtell]

Question for the NX gurus/historians in the forum, what standards were used to generate the tables for the Screw Clearance Holes and Threaded Holes in NX 7.5/8.5? Working with a client that is using AMSE B1.1 (English) and AMSE B18.3 Series (Metric) for the Drill Size for Shank and Counterbore/Countersink, and some of the numbers for Close, Normal, and Loose are not matching. Could the client have had set up NX with the wrong defaults for standards?

 

[JohnRBaker]

I would think not. Those Clearance Hole and Threaded-Hole table tables were established with the release of NX 5.0 and I'm not aware of any changes to those files since then. But if you can provide documentation that the values used in the tables were incorrect, then please contact GTAC and open a IR/PR to the effect. In the mean time, since the hole and thread data files are man-readable (after a sort) and user-modifiable, may I suggest that you edit them (I would use 'Wordpad' as that seems to give you the best formatted text file to edit) to comply with what your copies of the standards indicate and use them instead. If the changes are minor and only effect a few sizes, it's possible that it was a typo that was missed. Like I alluded to earlier, I'm not aware of anyone making this claim prior to now, but it could still be that a few of the specs are incorrect.

BTW, just in case you haven't actually looked for the thread and hole table files, they're located at...

...UGII\modeling_standards



John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[MASawtell]

NX 5.0? Interesting... As for the corrections, that is going to be a project for later, when I get the time to review the table files against the standards - but I do appreciate the location of those tables John.

 

[SDETERS]

How can there be standards for clearance holes? There are some basic values in the machinery handbook for these valuse, but does your tolerance stack determine what hole size to use? This is an area that has confused me with this option in NX.

 

[JohnRBaker]

Actually it was with the release of NX 5.0.2.2 that the current 'Hole Feature' functionality was first introduced and where these tables were first used.

As for where the actual numbers came from, I don't really know as I wasn't involved, at least not directly, with the project when it was being developed although I was consulted when it was originally spec'd since I was the person who collected and formatted the data files used by the legacy 'Thread' feature function (note that this feature never had any need for any sort of 'clearance hole' data so I never spent much time looking for any back when this original project was in development, which was in the late 90's).

That being said, I just dug out an old (from 1970) vendor supplied 'handbook' (this was from 'The Allen Manufacturing Company' supplier of 'Allen Head' fasteners) that I used when I first started working in engineering and I spot checked a few of the sizes included in the 'Drill Size for Shank Hole' table (Imperial sizes only) and while it only included values for 'Close' and 'Normal' clearances, most of the values I checked were consistent with what we're using in NX, to about 3 decimal places or so. I know this is not a definitive source and is certainly NOT what was used when these tables were formulated, and as someone has already noted, I'm not sure if there actually is a generally accepted 'standard'. I know the 'Machinery's Handbook' has no comprehensive set of tables, offering instead a few limited examples for some specific types of bolts or machine screws but nothing that appears to be complete, let alone definitive.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[Toost]

It seems that ISO 273 is an established standard for screw clearances, But you guys discuss "that other standard"

Regards,
Tomas

 

[JohnRBaker]

OK, that covers Metric screw sizes. Anyone aware of the equivalent standard for Imperial size screws?

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[MASawtell]

John, as far as I am aware ASME covered English/Imperial Sizes with B1.1 and Metric Sizes with B18.3 - I cannot vouch for Toost call out of ISO 273.

 

[JohnRBaker]

I did some searches on the internet and it appears that ISO 273 is indeed the appropriate standard for Metric screws and I'll validate this when I get a chance (I'm currently prepping for PLM World next week) and if I see that our current tables are different than this standard, I'll open a PR and offer the document, which I now have a copy of, as support for my PR.

As for a standard for Imperial size screws, I've still NOT found anything definitive. During that same search of the web, which produced a copy of the ISO standard, I found nothing equivalent to it for screws in Inch sizes. Now I have found several documents which provided virtually the same data as I already had with the vendor's 'handbook' that I mentioned in my earlier post above, also from various manufactures of fasteners. I also found references to the limited coverage in the 'Machinery's Handbook', again as I already noted above. In fact, I haven't found anything covering Imperial sizes with more than what is referred to as 'Close' and 'Free' fits. If anyone can point me to something more definitive with respect to Imperial size screws, please forward that information to me and I'll again verify if our tables match that and if not, I'm willing to open a PR requesting that the tables be updated to reflect whatever documentation is shown to be appropriate and applicable.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[MASawtell]

In the process of seeing if the client has a copy of ASME B1.1 and B13.8 on-site. If so, I will let you know John.

 

[Toost]

Sdeters,
When i did the quick search to find the ISO standard, i realized that one of the aspects of the clearance diameter ( Which is fully logical when i think of it...) is when achieving the tightening torque, the area under the head of the screw is important, and if this area isn't indirectly standardized, we cannot standardize a tightening torque for a specific screw diameter.
Now i don't know if the imperial screws has standardized specs like tightening torque, but the Metric screws has.

See for example :

https://www.swtc.edu/ag_power/diesel_engines/lecture/metric torque values.pdf

Regards,
Tomas

 

[MASawtell]

Toost and John, sat down at the client’s Library yesterday afternoon and reviewed ASME Y18.3-2003. In the ‘Nonmandatory Appendix A’ (page 53), there is a Table A-1, which lists Close Fit and Normal Fit, but no Loose Fit. Going to review the numbers from this table with what is listed in NX later, to see how much difference there is with the numbers for Close and Normal. However, I am a bit curious to know where the NX team came up with the ‘Loose’ numbers from.

One other note I need to past on, ASME B1.1 deals with threads (pitch, diameter, etc), but nothing for clearance holes. ASME B18.3-2003 dealt only with English/Imperial Measurements. While I have other documentation (dated back to 1987) that is referencing ASME B18.3.1M and B18.3.5M for Metric sizes, the client’s Library does not have a copy for me to review. If anyone in the forum can confirm if those two standards still exist, please let me know.

Regardless, this has been a very interesting exercise of research.

 

[MASawtell]

Well, the client's Librarian was able to get me a copy of ASME B18.3.1M-1986, R2008, and on page 13, Appendix I - there is a Table for Drill and Counterbore Sizes for Metric Socket Head Cap Screws, Close and Normal Fits, but no Loose.

 

[marklale]

Being a ex-toolmaker, I can tell you that there are standard c,bore tools that come in 1/64 and 1/32 over size. In the day drawings standards were such that a hole call out was drill and c'bore for a certain size hole. We did not know of any engineering standards. This may have come out of the pre 1960 series of hole call outs that just carried thru.

It will be curious to see what you dig up.

 

[MASawtell]

Marklale - had an interesting conversation with GTAC about this query - according to them the numbers used in NX (metric wise) were from Machinery's Handbook (Located in Table 7 on page 1904 of the 26th Edition in my hand, the person I talked to at GTAC had the 19th Edition in his). The labels H12, H13, and H14 from section labelled British Standard Clearnace Holes for Metric Bolts and Screws - which I assume is adhering to the ISO standard that succeeded British Standard 4186:1967. As far as English/Imperial holes, I will have to dig up a copy of ASME B18.2.8-1999 and check out Table 2 for the Labels Normal, Close, and Loose.