Threaded fasteners & holes best practices

[ehill]

We are in a transition period at my company right now, where we are bringing several global databases together soon with PLM, as well as trying to roll out standardized components for DFM purposes. There are a few aspects of these efforts (new library parts, globally standardized hole tables) that are causing us to reevaluate how we model threaded holes and fasteners.

Historically we have not closely controlled how our users have modeled threaded solid geometry, cosmetic thread features, or threaded holes. Some discussion on "what we want" makes it seem like there will be some trade-offs between one practice and another. The general wish list is:

1. Threaded fasteners inserted into threaded holes should not generate any interference (to simplify and encouragethe use ofinterference checks)


2. Geometry of critical areas should reflect actual geometry - drill point, maximum thread diameter, etc. (to enable accurate analysis of clearances to adjacent geometry)


3. 3D/drawing notes for threads should be consistent (I expect we can make this happen with standard hole tables)


4. 3D/drawing callouts for threads should be shown instead of manually entered (hole tables again)

We have tossed around ideas such as making the solid feature for male fasteners maximum thread diameter, making hole solid feature size minor diameter or a fraction of major diameter, using pitch diameter, and so on. Before we grind out the details, I thought it might help to poll the user community to see what works for other companies. Any feedback is appreciated!

Best regards,

Eric Hill

ASM America

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[ptc-1932745]

Just my $.02,



I do and suggest modeling all parts in a 'stock safe' condition. Having
said that, condition #1 will never be correct with this method. How
about PTC make threaded fasteners and threaded holes a unique feature
type with respect to interference checking and weight analysis?



# 2,3,4 seem to be doable especially with the newer hole feature (WF4,5
?) and accurate hole tables and notes (you will have to make these
yourself).

I haven't checked in CREO 1 or 2 but are drawing drill/hole tables still
not parametric?



Your biggest problem could be that older parts don't get the advantages
of the newer hole callout info ever unless you recreate the hole
features.





Christopher F. Gosnell



FPD Company

124 Hidden Valley Road

McMurray, PA 15317

[MikeFoster]

Hi Eric,

We model all threaded holes at the tap drill diameter and use a cosmetic thread at the major diameter

Ø This has the advantage of threaded holes that look like threaded holes on the drawing and the part.

We model all off-the-shelf male threaded fasteners at the tap drill diameter with no cosmetic thread

Ø This has the advantage of not interfering with the above holes and x-sections through fasteners on assembly drawings look correct.

We model all custom male threaded fasteners at the major diameter and use a cosmetic thread at the tap drill diameter

Ø This has the advantage that the male threads look correct on the drawing and the part

Ø It also has the only disadvantage of this whole approach in that there will be interference between custom male threaded fasteners and their mating part - We just live with this downside since we don't produce very many custom male threaded parts.

BTW we use the tap drill diameter instead of the minor diameter in the above because it's easier for most people to look up.

Mike Foster
ATK

[davehaigh]

I elected to dispense with the hole tables and the whole hole feature for holes.

I use a family tabled UDF. That allows me to do the drafting call out the way I want it in the UDF saving the time on detailing the part.

I gave a talk on this a few years ago at PTCUser.

[kbrault1]

Hi Eric,



The attached file has the screw modeled with the threads at the tap drill
diameter. The solid features are at max material. The thread OD is a surface
representing the min full thread length. There are two points on the
centerline at 1D and 2D thread engagement at min thread length. The drive
feature is just cosmetic.



Our holes tables (not attached) have customized notes.



When assembled correctly there are no interferences. Too large of a screw,
fine thread screw in course hole, too deep of thread engagement and
misalignment will show up as an interference.



The screws do look like shoulder bolts in a section.



Kevin

[PrashantChandan]

Good to see post on DFM topic! From the points described we are working on most of the areas. The clearance and interference checks are critical aspects of assembly validation. We have resolved the problem of those checks by providing a facility to add a database and provide standard clearance values. Also Check for axial and radial clearance for fasteners. The facility for validation of standard holes and diameters is available. The biggest problem I have observed is people using callouts to explain about features for fastners For most of the manufacturing these call outs are useful but for design / CAE upstream it is difficult to process such manual information. Till the time we have solid Geometry in place automating DFM checks are easy but more the manual inputs it takes long time. You may want to check how we do it in this Creo Parametric video.http://communities.ptc.com/videos/3028

Prashant Chandanapurkar

Design and Manufacturing Group

www.dfmpro.com

[ptc-141274]

HISTORY. We are looking to switch to True Type fonts in Pro-E. There are multiple reasons, but the primary one, that was elevated to management, is that we are getting faint text in the PDF. Depending on printer, it can come out light. According to the Engineering Tool person, PTC is using a 3rd party PDF writer or something to that effect. If we go thru the window print manager it comes out fine.

With that said:

Has anyone had push back as the Font didn't adhere to ASME Y14.2?

We want to stay with a Font that comes with WINDOWS so it is readily available (as well as can be expected) across sites etc..., but there is a nothing that matches ASME Y14.2 exactly. The specification does not state a specific Font, just "Lettering should be single stroke gothic". Note it says, should, not shall.

Then the last sentence on page 8 of the specification says, "Therefore, the basic requirement for lettering on a drawing is to produce fully legible copies."...

I guess I am asking, what Font are people using whose drawings are per ASME Y14.1?

Any tip for dealing with the symbols (centerline, cbore etc...) coming out thinner than the text now?

Creo Elements/Pro 5.0, M100


Doug Pogatetz
Northrop Grumman Corporation
Phone: 224-625-4823
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