Fixing threads in 17-4, tell me everything you know about roll form taps please!

[Steelphil]

Long story short, I have about 60 threaded holes in some 17-4 PH Stainless. They are M10x1.0, What they need to be is M10X1.5...
Right now our engineers are looking at a few options to salvage these parts, I am going to be running some tests where I will be rerunning a tap down these threads to even see if this will work (It sounds like we will accept an ugly thread as long as it works..)

I have to admit, I have used a form tap once before, and I broke it.
I will be able to buy whatever tools I need to do this job, so I plan to have the best tap I can get my hands on.

My plan is to try roll forming a new M10X1.5 into the old thread and seeing how it looks. Can I get some help on lubrication, speeds and feeds, etc?

I have a New Haas vf3, that rigid taps like a pro, If it would be better I have a floating tap head, would that be better?

I am planning on using generous amounts of Castrol Molly Dee, is there a better suited lube for forms?

My workholding is solid, I am not concerned about that at all, however this is a thread into the end of a shaft with bearing diameters around the outside of the threaded section. I will be measuring the diameters, but with the bearind diameter measuing .750, I have .178 of meat beyond the major diameter. Am I at risk of deforming material that far out?

I have to drive this tap down .800 deep, will this be an excessive load on my spindle/break the tap? It will be only forming over the M10 x1.0 threads, so it probably has less to push through than a straight bore. If I can't run this all the way with the machine, is hand tapping okay with forming taps? I imagine keeping the tap straight is the most important, so I would do that with a tapping jig.

And I guess the last thing I could ask for advise on is speeds and feeds..

Thanks in advance for any insight you guys can provide.

 

[MK Proto]

I would just get 10x1 bolts to fix it.

 

[Steelphil]

I would just get 10x1 bolts to fix it.

As much as I would like to suggest that, that decision is above my head. It's my job to attempt to fix it, If I can't then they're scrap and that's that.. but I would like to give it my best shot.

 

[Jorgo]

Can you do helicoils? Otherwise my limited experience with roll taps says that you won't need to take any special precautions just make sure the hole is the right size. when I'm stressing about broken taps in the mill I just start them in the machine and finish them by hand. It should be a real challenge to break a 10mm form tap though.
Jordy

 

[JRIowa]

I know this much, there's no roll in a form tap.

What's the condition of the 17-4? If it's anything but annealed, probably forget it. Since you're fixing the threads, you need to know what the holes size was before threading to compare it to the size you will need. Have you purchases the form tap yet? Does it have a flute?

17-4 is not as bad at work hardening as other stainless steels. Trying to fix a hole that's already threaded is going to be a challenge. I think that the form tap will want to follow the thread start and start crooked. Then you'll break the form tap. With the 10mm, you might get away with it.
JR

 

[upnorth5axis]

The thread you do have left is going to be cut to hell. Just take a part run the tap in at about 400 RPM and hope it doesn't snap off. You may have to open up the ID some for the tap to even start. If you open up the ID all the way to what it should be for a form tap you won't have material to form around. I'm assuming you are thinking the form tap will move the material left in the hole around to make a better thread. I would go as stated above HeliCoil. The way you are asking about is just making a bad thing worse.

 

[Steelphil]

I know this much, there's no roll in a form tap.

What's the condition of the 17-4? If it's anything but annealed, probably forget it. Since you're fixing the threads, you need to know what the holes size was before threading to compare it to the size you will need. Have you purchases the form tap yet? Does it have a flute?

17-4 is not as bad at work hardening as other stainless steels. Trying to fix a hole that's already threaded is going to be a challenge. I think that the form tap will want to follow the thread start and start crooked. Then you'll break the form tap. With the 10mm, you might get away with it.
JR

I haven't purchased the tap yet. I am looking for advise on what the best tool for the job is first. Would flutes be advantageous over no flutes?

 

[Steelphil]

It looks like the material is hardened to 38-45 HRC..

 

[Jorgo]

I know this much, there's no roll in a form tap.

What's the condition of the 17-4? If it's anything but annealed, probably forget it. Since you're fixing the threads, you need to know what the holes size was before threading to compare it to the size you will need. Have you purchases the form tap yet? Does it have a flute?

17-4 is not as bad at work hardening as other stainless steels. Trying to fix a hole that's already threaded is going to be a challenge. I think that the form tap will want to follow the thread start and start crooked. Then you'll break the form tap. With the 10mm, you might get away with it.
JR

You're right, it's a bad habit of mine to use the terms roll and form interchangeably.
Jordy

 

[Dupa3872]

Just push to go with Helicoil inserts. Drill them out and re tap for the inserts it will be nice and clean. Going back in with a tap on top of the other threads is going to be a mess. Push for using inserts.

 

[Finegrain]

My plan is to try roll forming a new M10X1.5 into the old thread and seeing how it looks.

Doing them that way, it's going to look like crap for sure, if it doesn't break the tap.

Drill them out and put in some sort of insert, either Helicoil or some shop-made thingy if you have room.

Regards.

Mike

 

[stormmin]

How about running an internal burnisher, or multiple if required first to redistribute your material then form tapping?

 

[AARONT]

+1 on the helicoils. It'll be quick, easy, and look good.

 

[Steelphil]

So, I realized something, helicoils would be great.. however I am going to cut a feature into these parts that a standard old helicoil would bust through.. so my two remaining options are to: make a my own helicoils, with a extra fine thread on the OD, and the 1.5 on the ID.. or to try tapping the hole like I was originally talking. I have a bad feeling about this job.

 

[jlevie]

You didn't describe the subsequent machining operation, but a Timesert (or similar) might work better than a Helicoil.

 

[Lumberjack]

To much material is gone for doning what you hope for.

Helicoils comes in various lenghts, try find shortest one. I assume the lenght was your problem?

You almost had it with make your own helicoil, (not knowing the geometry but in short) make it M12x1 and install bushing threaded M10x1.5 internally and voila! Will be as strong as new. Install them with strong Loctite.

 

[Akzle]

10x1 x 20mm hole= 20 teeth. (25.4tpi)
10x1.5 x 20mm =13 teeth.(38.1tpi)

12mm helicoils arent going to leave a lot of material, presumably theyre clamping a bearing retainer or pulley?
But may still be your best option.
Otherwise get your best welder to fill the holes (pretty difficult tiging down 20mm), re temper and re drill.

 

[JRIowa]

It looks like the material is hardened to 38-45 HRC..

Usually, anything above 40 Rc is not cold formed. If it can be done, you should contact Emuge and get an "Innoform" tap to try. They are fluteless, so don't fill the hole with oil.
JR

 

[WizardOfBoz]

You can anneal the parts, but you get dimensional shifts.

Form-threading 45HC sounds impractical. And when you are done, will you have any idea of how strong the threads are? Is this an issue? 17-4PH is often cold formed in "A" state before HT, to increase strength. Not sure that cold forming after getting to H900 or H1025 where you are at will not weaken the threads.

 

[MK Proto]

17-4 is pretty stable if you aneal it try to form tap it and reheat treat. They may all be scraped even if you manage to tap it then cross thread the bolt in it. I dont know how complex the part is or what it does but I would eat it and make new parts. Sucks but would be much better than a failing thread once assembled.