Blunt start thread/Higbee cut

[guimba]

Hello, I have read the post on here a few years back regarding how to remove the feather edge on the end of a thread, but am having trouble describing the process to the machine shop that makes our parts. Does anyone have a diagram or video that would do a good job of showing how it's done? Thanks!

 

[DrMetal]

- We have our machine vendors do this type of thread end cuts routinely on large ACME threaded parts to remove the knife edge.

- No diagram, but we describe it as ... "Mill or cut back thread ends to the FIRST FULL CROSS SECTION of thread (i.e. Higbee Cut). The removed portion of the thread MUST be milled down FLUSH or slightly below flush to the thread root, or surrounding base metal." If the root is not completely removed flush or below, the mating parts may bind up.

- For the very heavy mating parts that we use this on, it works great!
1st) It takes away the safety issue of the knife edge.
2nd) It makes the thread ends very damage resistant, and
3rd) It makes the test threading of mating parts together a snap ... just back the threads off until you feel or hear the "clunk" of the thread ends dropping together, and then reverse the direction, and start threading.

- We've been doing this for years on parts that weight as much as 1000 lbs, and if machined properly, it really works great. I am sure you would get similar results with other types of threads. Hope this helps.

 

[guimba]

Thanks for the reply DrMetal. The part in question is way much smaller than what you deal with - 3/8-24 - but the effect is the same. It is a plug that is only .130 long, and when one goes to start it into the main piece it can cut you if not properly handled. I had called out 'terminate thread with blunt start' on the drawing, but as is the case of a lot of shops around here, it was ignored. Live and learn. Perhaps if I make it a nice, big note as you recommend they might pay more attention to it.

 

[MikeHalloran]

Slides 7 and 15 have halfway decent photos:

http://www.fs.fed.us/r8/academy/.../Hose_Appliances_Fittings.PPT

Mike Halloran
Pembroke Pines, FL, USA

 

[guimba]

Whoops, I get the dreaded 'page not found' on that one. Can you check the link, Mike? Thanks!

 

[MikeHalloran]

Rats; did it for me, too.
Found it with Google. You can, too.
Not that many ppts in the results.


I was meaning to bring up the point that verbal instructions to vendors produce inconsistent results. In the case of ISO vendors, no change whatsoever.

You need to figure out exactly what the result looks like on your geometry, and put it on your drawings.



Mike Halloran
Pembroke Pines, FL, USA

 

[guimba]

Thanks Mike, that's what I think I'll have to do. Safer that way to get my point across.