Shank Dia. to Threads Major Dia. Equation? 6

[treddie]

Howdie.
I have an application I am building that builds relations for ProE for a whole range of fasteners. These relations are applied to a typical fastener part, that modify it to become a standard fastener at the required specs. I would imagine that most engineers would have little use for this application, but I am applying this application to 3D graphics where visual realism is the whole point. My problem is this; I have built tables for a full range of ANSI fasteners, but only for diecut threads, NOT rolled threads (yet). Because rolled threads for the most part have a shank diameter less than the major diameter, my question is, does anyone know where I can find a table that indicates what diameter of blank to use for a given threads major diameter? Does it depend on material used? Or is there a standard equation to relate the two diameters? Some sources say that the shank diameter is APPROX. equal to the pitch diameter, but I have photographs that clearly show this to be a GROSS approximation. I can't imagine that this whole process would be left to trial and error.
Thank you very much.
treddie

 

[CoryPad]

The shank diameter is equal to the pitch diameter (allowing for usual dimensional variation). The thread rolling process is a constant volume one, so if the blank is at pitch diameter and you indent to the minor diameter, then the same amount of material will flow out to form the major diameter. Anything you have seen that is different is explained by design intent. Examples include reduced body diameter fasteners for improved fatigue resistance and full body diameter fasteners for higher shear resistance. However, both of these types still use a pitch-diameter sized blank to produce rolled threads.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[treddie]

Cory!
Thank you for the response. So that's actually very simple then. I noticed on one fastener manufacturer's page that they used a shank dia. that was in very close agreement with pitch dia (only off by a tiny fraction). It was the photographs that were throwing me. But your explanation for variances makes perfect sense. And I would imagine that each manufacturer would build stock parts according to what works best for them and their manufacturing equipment, and the availability of blank stock sizes. So I am going to build the program to be flexible to accept variances since I am also using the program to reverse engineer parts for 3D viz.
Thanks for clarification.
treddie

 

[rb1957]

unless the threads are machined, like i think most are, in which case thread major diameter is slightly less than shank diameter.

have you looked up the fastener specs (NAS, MS, etc) ?

 

[treddie]

rb1957,
I pretty much followed ANSI and UTS specs from the Machinery's Handbook, but as you probably already know, that book only offers a partial description of the specs, and otherwise, you have to buy the specs which is a huge investment. So I spent literally days cobbling together specs off the web.
For machined threads, the problem was easy, and the application works great with ProE in building really great fasteners (I basically let the blank diameter equal the major diameter exactly). Rolled threads are the new addition to the app.
treddie

 

[rb1957]

i should've read you post more carefully !

 

[treddie]

No problem, there rb1957.

What amazes me is that no one in the CAD/Graphics industry has come up with any "real world" solutions to fasteners and springs. Sure, they have calculators up the yin-ying, but no automated part building capabaility.
As ubiquitous as those things are, they sure seem to be on the list of last things to accomplish. So I guess I just have to do it myself. I certainly got tired really quickly of having to reinvent the wheel everytime I needed a screw or spring.

 

[rb1957]

here we select fasteners based on which ones we've got modelled (well, not really but ...)

designers who has offended people they should've get the job of creating modells of rivets, hi-Loks, screws, P-clips, ... (really)

 

[treddie]

Yes, and for every screw in the known universe with every available thread size and for every conceivable length.

Machined AND rolled.

...and that's just the screws.

 

[RPstress]

Looking carefully at an aerospace fastener (NAS 1004) the end of the shank is turned down so that the rolled portion is smaller diameter than the shank with a short tapered transition region. This makes the external thread diameter almost exactly equal to the shank diameter. This makes sense, in as much as sometimes you want a nice tight fit to the shank (maybe 1 thou inch clearance on diameter). Clearly the thread must not be any bigger than the shank.

 

[treddie]

Thank you, RPstress for the reply. This clearly shows that the world of fasteners has more standards and complications than you can shake a stick at. I wish I could examine all of the standards, but the financial cost would be huge. For now, I will have to stick to "bare-bones" ANSI (with MS9006 cross specs thrown in for cross-recesses). I know that I don't have a complete ANSI B18.6.3-1972, R1977 spec, but even though MS9006 is not ANSI B18.6.3-1972, R1977, for now it looks pretty close.

If I am elected President, the U.S. will have only one standard...ANSI B18.6.3-1972, R1977. Why that one? Because that's the one I started with. No exceptions allowed.

 

[dgapilot]

Have you tried quick assist at

http://assist.daps.dla.mil/quicksearch/

you can get most of the AN and MS specs. While most have been superceded by NASM specs, the content for the most part hasn't changed, just that AIA now controls the document.

David

 

[treddie]

Ah, super! I thought it would be a real pain to gather this info. Especially since ASME wants like $35 per ANSI spec. In what ways does AN/MS differ from ANSI? I can at least check out some of this myself with the limited ANSI specs I have.

 

[tbuelna]

treddie,

For aircraft applications there are also specific bolts for shear loads (NAS1103 thru NAS1120, Hi-Loks, Huck bolts, etc). The shank is held to very close diametral tolerances and is usually slightly larger than the thread major diameter. They also tend to have thin heads and short, closely controlled thread lengths, since they are not intended to carry axial loads.

 

[treddie]

Thanks tbuelna.
Once I get the algorithm written for rolled threads, I'll be ready to populate the program with all of these spec tables. Lot's of work ahead.