5 1/4"-6 UNJ internal threamilling

[WWFCAM]

has anyone milled this thread before

 

it's a military spec thread with controlled root crest, is it possible to mill this thread?

 

i need to find the right tools that can do it if possible, or is it only possible by turning?

 

it's also about 8" deep into the part.

 

any ideas

[bogusmill]

I threadmill UNJ threads all the time with a 3 or 4 flute, single point threadmill but nowhere near that large. I've not been able to find any threadmills with the radius already on it. I put that on by hand or farmout to a sharpening specialist.

[WWFCAM]

thanks,

 

i found a thread on another forum,

indicating that the internal thread DOES NOT require cresting, it seem that only the external thread needs cresting,

 

kennametal book has specific inserts for UNJ external thds but use std UN inserts for internal threads, makes me wonder?

 

however I need to get the spec. to confirm the acutal thread requirements for the internal thread form

 

I'll keep diggin'

 

thanks

[Superman]

Threadmilling can be done quickly with the threadform form ground into the OD of a typical endmill

 

or for just to get it done ( like now )

 

Use an internal threading bar from a lathe with the correct threadform tip installed

-use 2D contour-ramp

( ramp = thread pitch )

( perpendicular lead in / out ) ( caution if using arcs )

( RH thread starts from bottom moving CCW, feeding out )

( rotate the bar at the correct cutting speed )

( feedrate controls finish not the pitch and can and will be quite slow )

 

This method can be used on internal and external threads with the same tooling but it will be a lot slower than turning.

 

unless your machine supports turncut function

Turncut example

[DavidB]

UNJ threads mean that the root radius is larger on the male thread ONLY.

All this means for a female is the id of the threads MD is a bit bigger.

No big deal.

 

No need to use UNJ inserts or thread mills when creating a female UNJ thread just use UN.

 

HTH

[WWFCAM]

thanks guys,

we downloaded the spec for UNJ thds, and yes Dave you are 100% correct !

 

we looked at a lathe tool, but time is a factor, single point threadmilling is extremly slow

 

to mill the internal thread, you must check that the tool dia. is small enough to ensure that the thread groove width remains within spec.

 

otherwise the part will be scrap or if possible welded, and remachined