Thread forming tube without deformation of OD

[Jhar]

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,

 

[crossthread82]

It would be questionable, the OD might swell with that thin of a wall. You say it can't deform, but how much could it realistically be? .001-.002"?

You're currently thread milling them in a lathe? Why? Surely a tap would be faster. But why not single point them?

You could make a clamp collar similar to a shaft collar to squeeze the OD around the end where the thread will be at.

 

[Jhar]

It would be questionable, the OD might swell with that thin of a wall. You say it can't deform, but how much could it realistically be? .001-.002"?

You're currently thread milling them in a lathe? Why? Surely a tap would be faster. But why not single point them?

You could make a clamp collar similar to a shaft collar to squeeze the OD around the end where the thread will be at.

probably couldn't swell any more than 0.002" before it would cause issues. We have plastic components that press onto each end.
Thread milling is extremely reliable for us and helps account for any tube run out as it just mills away any discrepancies on the ID.
The swarf issue is the real killer, for multiple reasons I'd like to eliminate as much swarf as possible, whether it's fine thread milling swarf or stringy lengths from cut tapping or single point screw cutting.
It needs to be an automated process within the CNC, so manually putting a collar on wouldn't be an option. However if I could have a collar somehow mounted on the turret position that has the form tap, and use it almost like a follower steady, that could work...

 

[Houdini]

Dont know how your holding it now, but can you use pie jaws and keep the threaded area in the jaws while you forming so the tube cant bulg?

 

[Garwood]

Are you sure form tapped threads in aluminum are what you want?

I ask because I kinda went down this road awhile ago and found that form tapped threads suck in 6061. 6061 doesn't really form so form tapping it pretty much makes a shit weak thread even if it looks pretty.

 

[Houdini]

Are you sure form tapped threads in aluminum are what you want?

I ask because I kinda went down this road awhile ago and found that form tapped threads suck in 6061. 6061 doesn't really form so form tapping it pretty much makes a shit weak thread even if it looks pretty.

never had an issue, from what Ive read the threads are stronger. Same in copper also.

Cut Taps vs. Forming Taps​

Taps are the most common method to produce threads in a part. Taps are easy to use and they produce good results, quickly and with little training. Taps can be applied in a multitude of different ways that include hand tapping, pneumatic tapping arms, and canned tapping cycles in CNC machines. There are two different types of taps to choose from when machining aluminum – ’cut taps’ and ’thread forming taps’, which are also known as ’form rolling taps ‘.

BENEFITS OF CUT TAPS	BENEFITS OF FORMING TAPS
Most common type of taps and thread making.	No chips to deal with!
Simple method including hand and power tools.	Works well on smaller threads g. 4-40 threads or M2.5 X 0.45
Different types for different applications: taper, plug, or bottoming.	Excellent thread quality, threads are tighter and stronger.
More versatile and can be used in certain materials that do not produce threads	Advanced substrates and coatings are more common in form taps such as carbide substrates or DLC coatings that work tremendously well on aluminum.
Market is mature, so a wide variety and selection to choose from at competitive prices.	Form taps with advanced substrates and coatings offer increased tool life, allow increased speeds and decrease the propensity for scrapped parts & tap breakage.

 

[SeymourDumore]

Hi folks,
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.

Well, your other likely problem is going to be that IF the tube expands while the tap is in it, it will also shrink back down once it is out of it.
IOW you possibly will be needing a custom roll tap, and even then you will be at the mercy of the consistency of the tube supplied.

But it now begs the question why is a collet chuck ( or any other method of a full grip on the OD ) is not an option?

 

[Rob F.]

Isnt the ID of the tubing going to need to change if you go from cutting to forming the threads?
Is the correct wall thickness tube even available to go right in with the form tap?

 

[Garwood]

never had an issue, from what Ive read the threads are stronger. Same in copper also.

Cut Taps vs. Forming Taps​

Taps are the most common method to produce threads in a part. Taps are easy to use and they produce good results, quickly and with little training. Taps can be applied in a multitude of different ways that include hand tapping, pneumatic tapping arms, and canned tapping cycles in CNC machines. There are two different types of taps to choose from when machining aluminum – ’cut taps’ and ’thread forming taps’, which are also known as ’form rolling taps ‘.

BENEFITS OF CUT TAPS	BENEFITS OF FORMING TAPS
Most common type of taps and thread making.	No chips to deal with!
Simple method including hand and power tools.	Works well on smaller threads g. 4-40 threads or M2.5 X 0.45
Different types for different applications: taper, plug, or bottoming.	Excellent thread quality, threads are tighter and stronger.
More versatile and can be used in certain materials that do not produce threads	Advanced substrates and coatings are more common in form taps such as carbide substrates or DLC coatings that work tremendously well on aluminum.
Market is mature, so a wide variety and selection to choose from at competitive prices.	Form taps with advanced substrates and coatings offer increased tool life, allow increased speeds and decrease the propensity for scrapped parts & tap breakage.

Have you anodized form tapped parts?

 

[???]

Have you anodized form tapped parts?

All the time in 6061. All my products are made using 6061 and form tapped with Houghton 795 MPB. M2.5 up to M8. Never had an issue. Hole size needs to be right and taps are all Hahnreiter. Are you sure your material isn't giving you problems. I use Kaiser, Norsk Hydro and Hulletts exclusively. Not picking on you just asking.

 

[SeymourDumore]

Isnt the ID of the tubing going to need to change if you go from cutting to forming the threads?
Is the correct wall thickness tube even available to go right in with the form tap?

Neither of those were questioned by the OP.

Tube is what it is, pre-thread form is achieved by other means.

 

[Houdini]

Have you anodized form tapped parts?

I personally would recommend not anodizing smallish Aluminum threads, I don't want brittle ceramic threads, but yeah our main customer anodizes all their threads and all their parts are 6061.

 

[Rob F.]

Neither of those were questioned by the OP.

Tube is what it is, pre-thread form is achieved by other means.

This is what he said earlier which leads me to believe the tube is used straight away with no pre thread sizing. Maybe OP will come and say for sure...

Thread milling is extremely reliable for us and helps account for any tube run out as it just mills away any discrepancies on the ID.

 

[Garwood]

All the time in 6061. All my products are made using 6061 and form tapped with Houghton 795 MPB. M2.5 up to M8. Never had an issue. Hole size needs to be right and taps are all Hahnreiter. Are you sure your material isn't giving you problems. I use Kaiser, Norsk Hydro and Hulletts exclusively. Not picking on you just asking.

I use lots of type 3. Form tapped 6061 that looks great, everything gauges right explodes in ano. The crests of the threads aren't homogeneous so they don't rinse well then later on the threads turn to white powder on the shelf.

That's my experience.

 

[Mtndew]

Is there a way to avoid the OD of a tube this size deforming?

Can you make the thread minor a little bigger before tapping? Would that help?

 

[Ox]

OK, so BSPP has now been changed to BSPF, so's not to "sound" like BSPT?
Good grief....


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I am Ox and I approve this post!

 

[SeymourDumore]

This is what he said earlier which leads me to believe the tube is used straight away with no pre thread sizing. Maybe OP will come and say for sure...

Yupp, I missed that !
Threadmill and chips it will stay then...

 

[Ox]

OK, so BSPP has now been changed to BSPF, so's not to "sound" like BSPT?
Good grief....


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I am Ox and I approve this post!

Does this mean that I need to git new gauges that are properly labeled?


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I am Ox and I approve this post!

 

[Vancbiker]

I use lots of type 3. Form tapped 6061 that looks great, everything gauges right explodes in ano. The crests of the threads aren't homogeneous so they don't rinse well then later on the threads turn to white powder on the shelf.

That's my experience.

Place I retired from had in house anodizing. Unless directly specified not to on a drawing, blind holes were plugged to avoid trapping caustic or acid and being difficult to rinse.

Through holes were not plugged unless the drawing specified no ano in threads.

AFAIK, there was no distinction made between rolled or cut threads.

 

[???]

Place I retired from had in house anodizing. Unless directly specified not to on a drawing, blind holes were plugged to avoid trapping caustic or acid and being difficult to rinse.

Through holes were not plugged unless the drawing specified no ano in threads.

AFAIK, there was no distinction made between rolled or cut threads.

My anodiser cleans all the holes out with a tube down the hole. But I can see where this can go south. I have found that on anodising that is sealed with nickle acetate the threads will lock up when you tighten them so I use anti sieze lube on one particular thread that needs loosening for adjustment.