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Screw thread FIM callout

Screw thread FIM callout

Screw thread FIM callout

(OP)
Hello All,

I recently designed a custom screw with a 3mm X .5 thread. This thread is formed by cold rolling and is 1/4hard SS. Thread mates with a nickel plated brass insert that is ultrasonically welded into plastic.

Keep in mind I am new to this screw design stuff...

Turns out when I get the parts that the thread was rolled on at an angle (warbles when you screw it in). This causes some serious problems with force distribution on the threads of the insert and basically cases the inserts to strip out after only a few insertions.

My question is this. Wouldnt one think that if you call out a particular thread on a shaft that the angle at which you can cut that thread (or form it in my case) on the shaft would be limited to some range...inherently?

Anyhow, the vendor comes back to me saying that I never incuded a "FIM" number on the drawing (full indicator measurment) and that although the threads on the screw are at an angle we have no recourse to return them. The FIM measurement on the screws I recieved was 0.070...thats huge if you ask me!

Can anyone tell me how they deal with this issue on a drawing? Is FIM a standard thing to call out? Is what I am experiencing here normal or am I getting "screwed"?

Thanks!
Craig J

RE: Screw thread FIM callout

Craig,

What country are you in/standards are you calling up?  I only have access to the US specs which for metrics are slightly different to the rest of the world in the way you designate threads.

That said the difference may not be relevant given that this is a special.

If you are doing it to the US specs let me know and I'll look it up.

Ken

RE: Screw thread FIM callout

(OP)
Hi Ken,

Im calling out an ANSI Metric 6g class thread.

Craig

RE: Screw thread FIM callout

Can't find the spec right now.  I'll check with my checker in the morning as he had it last I saw.

RE: Screw thread FIM callout

As far as I know, your callout is good. I have used it for years without problems. I have never used the FIM callout. I'm in the USA.
We did business with a company in Denmark and they never had a problem with it either.

Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)

RE: Screw thread FIM callout

This area is covered by ISO 4759-1 Tolerances for fasteners — Part 1: Bolts, screws, studs and nuts — Product
grades A, B and C
.

Regards,

Cory

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

RE: Screw thread FIM callout

OK, found the spec, it was sat on his desk out in the open, if only I’d opened my eyes.

The spec is now ASME not ANSI, shouldn’t make a difference in practice but if this comes down to a legal type thing I guess it might.

Looking at ASME B1.13M-2001, Metric Screw Threads: M profile,  I see FIM mentioned at 5.7.

Quote:

Circular runout is the full indicator movement (FIM) (see ASME Y14.5).  Runout of the crest (minor diameter of internal thread or major diameter of external thread) relative to the pitch cylinder shall not be so great that the basic profile is transgressed.

Sounds like your screws may break this rule.

However, In section 7 ‘Designation of Screw Threads’ I don’t see anything about FIM numbers.

I think your callout should be:-

M3 x 0.5 6g

You’d also obviously need a general note saying something like “Metric screw threads are to ASME B1.13M-2001”

But you probably already new that much.  

It would probably be best if you get a copy of the spec and look yourself as I don’t have time to look in detail.

What thread spec did you call up on the drawing and did your callout meet its requirements?  If you didn’t explicitly call up the correct spec and designate the thread as it requires they may have wiggle room.  

I would be very wary of relying on the ISO as you and presumably your manufacturer are in the US.  The ASME spec designates ISO threads differently from the rest of the world, for starters you always have to put the pitch and tolerance class.  We had that problem here, we used the international convention but called up the ASME and wondered why machine shops kept asking for the pitch, hence we now have a copy of the standard.

I've certainly never called up FIM though, either in the UK or here.

RE: Screw thread FIM callout

(OP)
Cory,

I dont have this spec. Online I can get it for $130, but first can you tell me what it talks about in regards to this topic. Meaning does it talk about inherent tolerances in to threading a screw on a shaft.

Am I in trouble here because I didnt put an FIM number on the drawing or is just calling out the thread enough to expect a good result (to some tol)?

These screws are so far out that Im thinking this FIM number thing is just an excuse...but I cant be sure.

Thanks for the info,
Craig

RE: Screw thread FIM callout

Craig,

I guess you were writing while I was.  Like I said, be very wary of using the ISO if you and supplier are in the US.  Look at the ASME spec.

RE: Screw thread FIM callout

(OP)
Thank Kenat.

So many specs, so little time.

I wonder what they mean about "...basic profile is transgressed." Can you put a number to the "transgressed"? Seems like a subjective thing.

Craig

RE: Screw thread FIM callout

I'll try and have a look at lunch but I think it would be covered by the 6g and whatever values that relates to.

RE: Screw thread FIM callout

Transgressing the basic profile means the part dimensions are outside the envelope allowed by the specification, so it is not subjective.

You don't have to worry about ANSI vs. ASME - they are the same.  ANSI doesn't create any standards, they just approve ones from other organizations.

I wasn't paying close attention - if you are referencing ASME B1.13M, then you can use ASME B1.3M and B1.16M as your other references for tolerances, gaging, etc.

Regards,

Cory

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

RE: Screw thread FIM callout

Cory,

From a practical point of view I agree on ASME v ANSI but if it comes down to a legal, 'you didn't make your parts right' 'well you didn't put the right specs' then it's worth making sure.

RE: Screw thread FIM callout

http://www.boltscience.com/index.htm?

http://www.newmantools.com/tech/threadm.htm

Should help you.

It would be a lot of typing.  

As Cory said it isn't subjective.  The thread form and tolerances are specified in the spec.  I didn't see the FIM number explicitly stated.

Talked to my Checker and we both think you've just got bad screws and maybe the manufacturer is trying to find some way out.

RE: Screw thread FIM callout

ASME B1.13M fully defines the thread form and tolerances.  It also defines how to properly call-out a thread using the standard.

"FIM" is not mentioned in the discussion of call-outs.

Even if it were, it is an inspection method, not a manufacturing control.  

Your vendor is full of crap.

RE: Screw thread FIM callout

Very Succinctly put MintJulep.

Out of interest Craig what standard did you reference on the original drawing?

And yes I know I was wrong in my first post, M3x.5 isn't a special.

RE: Screw thread FIM callout

(OP)
Thanks much for all the good info.

Ok...Gulp. All I put on the drawing in regards to the thread callout was "3 x 0.5 6g". Meaning I didnt specifically call out the standard.

For the record I design plastic parts for a living and this was my first machine screw :)

I have a copy of the ASME standard on the way!

ty!
Craig

RE: Screw thread FIM callout

Don't feel so bad, I've seen lots of drawings calling up not just threads but other things without specifying what standard they are to.

The bad news is that it probably means you don't have a leg to stand on legally but I could be wrong.

I would encourage you to always state the relevant standards on the drawing somewhere, usually in some standard notes.  You don't necessarily have to actually have a copy of the standard, although it's a good idea.

RE: Screw thread FIM callout

Hmm.  How did your vendor interpret the "6G" callout without referring to the standard?  (Maybe they rolled them in a centrifuge at 6 G's?  That might explain how they got them so f%^d up.)  If you do much business with this vendor, or planned to do much business, I would have a brief conversation with the manager/owner/president, stating "make this right or forget any more of my business, and I will go out of my way to tell any and all colleagues of mine how I was treated".  

RE: Screw thread FIM callout

(OP)
Thats a really good question! If 6g was on the drawing then how else are they suppose to interpert the tolerance on the thread?

This vendor has always been a pain to work with. Our procurment/materials deptartment must find some redeaming qualities about them...Of course given enough pain that could change.
Get ready for ssome pain. :)

Craig

RE: Screw thread FIM callout

I would think that secifying 6g would cover you, the same as specifying UNC-2A (for example) on an english thread.  They HAVE to go somewhere to determine what is required.

RE: Screw thread FIM callout

I'd love to be wrong but certainly in any government type work both for UK & US I had to specify the thread standard either as part of the thread callout or in a standard note, same goes for things like welding etc.

Yes they do have to go 'somewhere' but whats from stopping that 'somewhere' being wrong.  If you specify the standard then there's a lot less wriggle room.

RE: Screw thread FIM callout

Unfortunately, your thread callout was not complete, so the vendor may indeed have a leg to stand on.  If the callout had been complete, I'd have to agree that it would be him in the wrong on this.
As far as specifying the thread standard (ASME B1.13M) on the drawing, in almost 30 years of creating mechanical drawings, I have NEVER seen that done.  What is typical though is having a note somewhere on the drawing stating interpretation per ASME Y14.5, which includes references to standards for screw thread representation and gaging.

RE: Screw thread FIM callout

Since when does an ambiguous or incomplete call-out mean "Go right ahead and make a piece of crap"?

How about a vendor picking up the phone:  "Hey customer, your drawing is not completely clear, what do you really want?"

RE: Screw thread FIM callout

Mint Julep,

I agree, if a drawing is at all ambiguous they should contact you.  

However it sounds like this vendor doesn't follow this rule.

It definitely sounds like primarily a vendor problem, but you've got to have your ducks in a row as it were.

RE: Screw thread FIM callout

(OP)
I understand now that my drawing was incomplete and I should in the future refrence a standard explicitly on the drawing.

BUT

I also agree with Mint J., that there is no excuse for threading at such an angle as to cause the part to be 0.070" out of round. Thats just bad workmanship in general!

Thank you all for the great discussion.

Craig

RE: Screw thread FIM callout

Ewh is correct, you don't need to reference every standard that may apply to every feature on your drawing. Reference ASME Y14.5M-1994 and that should cover most everything since Y14.5 references the other standards for you. There are exceptions but for threads and basic design geometry Y14.5 should be enough.

RE: Screw thread FIM callout

If you're gonna go for the 'one reference covers everything' line then maybe Y 14.100 might be a better reference.  

I'm just basing this on what our checker says though, I'm not actually basing it on a definitive statement in a standard.  He's got lots of experience tho (40yrs +) much of it working on mil std packs.

That said he makes me call out the thread ref (it's in our standard notes).

RE: Screw thread FIM callout

UNC-2B = UNIFIED COARSE thread, size class 2B
The standard referenced is in the callout, no note needed.

RE: Screw thread FIM callout

Y14.100 does reference y14.5, which then references the screw thead standards...

But y14.100 also references such stuff as: "MIL-STD-882  
 Revision: D      Chg:      Date: 02/10/00  
 SYSTEM SAFETY PROGRAM REQUIREMENTS ".

I think ewh is correct that, for most of us, y14.5 is usually sufficient.  If you are working with stuff for Mil/NASA application, then you are probably forced to use y14.100 anyway, and thus oughta call it out on your drawings.

RE: Screw thread FIM callout

For clairification I didn't mean that the Y14.5 note needed to be tacked onto the thread note, just that it needed to be in the standard drawing notes.

RE: Screw thread FIM callout

At the risk of making myself unpopular (or more unpopular as the case may be) ASME Y14.6-2001 para 3.2 addresses the issue of whether to reference the thread standard.  

Quote:

In the US the name and number of the controlling thread standard is frequently omitted from the drawing.  Reference is made instead to the designation symbols of the standard, such as series symbols and class symbols.  To avoid misunderstanding, it is recommended that the controlling organization and thread standard be specified or otherwise referenced on the drawing.

It then gives examples of the thread spec as part of the callout.

So it’s only appears to be recommended to put the thread.

Also looking at our copy of 14.5M I don’t see the direct reference to ASME B1.1 or 1.10M or 1.13M.  

In section 1.2 it does reference Y14.6 which in turn does reference these though.

I don’t have 14.100 to hand so can’t check.

RE: Screw thread FIM callout

Boo hiss KENAT!
Only kidding... as usual, it is good to know what the standards say.  Now if they could only do away with that word "recommended".
thumbsup2

RE: Screw thread FIM callout

I may be missing something, but it appears that the thing missing and causing the problem is the relationship between the threaded portion and the unthreaded portion of the part being discussed.  

Without any control of the relationship, (FIM), as stated by the supplier, and without knowing the standards on the drawing for interpretation of dimensioning, it would seem that the drawing is lacking sufficient information.

RE: Screw thread FIM callout

Ringman you may be right but that's not how I understood it.  

I assumed the screw was threaded up to the 'head' and that it was a misformed thread causing the inserts to fail.

As such I would have thought having the thread properly designated should be enough.

Found Y14.100 (again it was sitting right on the shelf) and it doesn't directly reference the thread spec, like btrueblood says so I was wrong in suggesting it would be a better indirect ref.

RE: Screw thread FIM callout

Hmm, KENAT:  

1. I didn't actually look up the spec., I surfed to IHS/Global website, and looked them both up, and clicked the link "specs referenced by this spec".  They are pretty good about picking up secondary references as well (they should be, that would allow them to sell us more paper!).

2. Y14.100 references Y14.5, so it is a more encompassing spec., and just as valid a catch-all as Y14.5 for this problem.  Just that it (Y14.100) also pulls in a lot of extra stuff that you may or may not want to comply with, or ask your vendors to comply with.  Y14.100 is the ANSI continuation of the old DOD-STD-100 which I think was before that MIL-STD-100, and typically applied to any Mil/NASA/aero drawings by contract specification.

RE: Screw thread FIM callout

craigmj,

Does your drawing have a note which states in accordance with Y14.5 on it?  If not, what is the standard that you invoke for your dimensioning interpretation?

Thanks
ringman

RE: Screw thread FIM callout

(OP)
I confessed a while back in this thread that I was lacking the specific standard callout...thats my fault and not one I'll make again.

Whats the old saying "bad experience is unfortunately the best way to gain good experience".

I did call out the thread tolerance class, but was not obviously enough. To my defence the parts were 0.050"-0.070" out of round, which on a 3mm x 0.5 screw is a crap load. You could actually watch the head of the screw wobble back and forth as you screwed it in. Ugly.

The vendor DID eventually take the screws back...

RE: Screw thread FIM callout

I don't think any of us doubted it was primarily a vendor problem.

I was just trying to make sure you had your back covered if it got ugly.

Glad to hear it worked out.

Ken

RE: Screw thread FIM callout

No Drawing Standard being specified leads to 'BEEG PROBLEMS'.  You just might have dodged a beeg bullet.

RE: Screw thread FIM callout

(OP)
ringman,

Absolutly. I got lucky.

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