Acme thread terminologies

[Sheep]

Working in the aerospace manufacturing fields, I occasionally encounter a drawing that calls out "break feather edge of thread to appx. one half width of thread" on Acme threads. The meaning seems clear to me but I have noticed that it never sems to get done in the places I have worked, with various excuses and/or "reasons" for this. Can anyone explain this term's meaning, exactly? I assume it means to chamfer the entire length of the thread edge, both sides, to on quarter of the thread width. In this case, it is an internal thread as well....how would this edge break be accomplished?

 

[MikeHalloran]

The way I interpret the note, it has nothing to do with the crest of the thread. The referenced "feather edge" occurs at the end of the thread where it intersects a radial plane, e.g. at the axial faces of a nut, or where the shaft is turned down to or below the minor diameter. The intent is to provide a "blunt start" so that attempts at starting the thread will not curl the feather edge over and turn it into a chip or burr that jams the assembly.



Mike Halloran
Pembroke Pines, FL, USA

 

[btrueblood]

Agree with Mike. We usually specify removal of the entire thread for some distance (esp. with multi-lead threads).

 

[Sheep]

Thank you both for the input! Yes, that is ONE of several different interpretations I have gotten over the years and it does makes sense, of course. Btrueblood's answer contains one of the reasons I have questioned this specific callout over time - I have seen that "remove" statement made and sometimes wonder why this one is made in lieu thereof. (this is a double start, btw) I can understand "blunt start" and "remove..." just fine, it's the "break..." part of this callout that always leaves me wondering a bit. Anyway, thank you both - I will take it that way in the future and save my poor old feeble thought processes for the more pressing issues.
Sheep

 

[MikeHalloran]

Agreed, "break" is the wrong word to use in the note; it implies use of a file or deburring tool. The preferred tool is some kind of milling cutter, because there's a substantial amount of material to be removed.




Mike Halloran
Pembroke Pines, FL, USA

 

[roadapple]

The machinist term (in this part of the country) is higbee.

I use ACME threads on the parts we design and the desciptions above are accurate. However, our defination was:

Higbee start of thread - remove the "feather" until a full width (or pitch) had been achieved.

roadapple

 

[KENAT]

Can't remember the exact wording I used last time but it was along the lines of 'remove lead in of thread to full thread form' (that doesn't sound right but it was along those lines).

It was to remove sharp edges and provide a good start point as Mike/Btrue say.

 

[ewh]

I call out a 90 degree (plus a generous tolerance) c'sink to the major diameter.

 

[Cockroach]

I routinely put "remove feather edge from flanks of threading" in the notes of a print. Most threading inserts break the edge as a natural consequence of the machining process.

I've never had a problem.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada