Thread forming tube without deformation of OD

[guythatbrews]

I had never heard of bspf before this post. I found the explanation bspf was changed from bspp because that was too similar sounding to bspt. Here is maybe a more plausible explanation of bspf.

 

[Pete Deal]

Have you anodized form tapped parts?

I have some parts I make. Thousands of holes over the years small ones in my case, anodized parts, 6061. If the hole size is right and some knuckle head anodizer doesn’t over etch them the screw breaks before the threads pull out.

 

[Tom-AMS]

Hi folks,
I am making thousands of internal 1/2" BSPF threads 1" long in aluminium tubes (1" OD 3/4" ID) on some CNC lathes.
Currently I am thread milling these threads but this is causing significant fine swarf issues, and I would like some stronger threads too.
I would be thread forming them, but the OD of the tube needs to not deform from the pressure of the thread forming. Is there a way to avoid the OD of a tube this size deforming? Gripping the OD in a collet chuck is not an option.
Keen to hear any ideas!
Thanks,

years ago we had a similar job, forming ID threads in thin wall AL tube - AND- keep OD within tolerance range. We made a Box Tool with two 180° follow rest bearings that attached to the form tap's holder. I attached a sketch of the tool we made. Ball brgs mounted on adjustable, eccentric, hex-head "axles"; locked in place with set screws.
edit: other OD turning operations prevented us from using a steady rest.

 

[Peter Colman]

Is there a chance of screwcutting most of the thread and then following through with the tap?