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
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
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
Im calling out an ANSI Metric 6g class thread.
Craig
RE: Screw thread FIM callout
RE: Screw thread FIM callout
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
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
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.
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
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
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
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
RE: Screw thread FIM callout
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
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.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
"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
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
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
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
RE: Screw thread FIM callout
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
RE: Screw thread FIM callout
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
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
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
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
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
RE: Screw thread FIM callout
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
The standard referenced is in the callout, no note needed.
RE: Screw thread FIM callout
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
RE: Screw thread FIM callout
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
Only kidding... as usual, it is good to know what the standards say. Now if they could only do away with that word "recommended".
RE: Screw thread FIM callout
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
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
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
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
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 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
RE: Screw thread FIM callout
Absolutly. I got lucky.