Problem- Suggestions for Tapping in 303 Stainless

[All4fun]

I am building a 22LR target rifle action in 303 Stainless. I am going to be tapping 4 holes in M4x0.7 and 5 holes in M6x1. All but one of the holes will be blind and about 5mm deep. I've done a lot of tapping in 6061 and brass but I am a complete novice in stainless. Any tips, tricks, suggestions? What's the best lube to use?
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[cutsall]

OUCH. I see a possible tap snapping nightmare in the making. I would use a thread froming tap like a Balax instead of tring to cut those threads. It gives more tap strength
by eliminating the deep flute clearance of a conventional tap and provides a stronger thread by extruding and forming the thread much like rolling a thread as opposed to cutting. The drill size is critical with this process though and there are a mutitude of tapping fluids and lubricants available. I can't think of any specific brand to recommend but get one specific to your application which is stainless steel. Ok that is my two cents worth. I wish you the best of luck.

[All4fun]

Originally Posted by cutsall OUCH. I see a possible tap snapping nightmare in the making. I would use a thread froming tap like a Balax instead of tring to cut those threads. It gives more tap strength by eliminating the deep flute clearance of a conventional tap and provides a stronger thread by extruding and forming the thread much like rolling a thread as opposed to cutting. The drill size is critical with this process though and there are a mutitude of tapping fluids and lubricants available. I can't think of any specific brand to recommend but get one specific to your application which is stainless steel. Ok that is my two cents worth. I wish you the best of luck.

Thanks for the response. Yah, I'm trying to avoid the tap snapping nightmare if I can. I thought 303 stainless has sulfur added to improve its machinability. So I'd expect a regular fluted tap to work. I had not considered a thread forming tap, assuming 303 would cut OK with a fluted tap. Maybe a bad assumption?
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[djr76]

Run at 20-30 fpm

fpm*3.82/tap diameter(inches) = rpm

Use a tap designed specifically for stainless

[neilw20]

As advised by my tap supplier http://www.goliath.com.au/
I use an intermediate Blue Point gun tap, with tap magic fluid. Works a treat.
Caveat: Chip comes out the front of the tap (and does not cause jamming in the flutes) but in a blind hole you need to retract early, and remove the spiral cut chip which is usually all in one piece.
TiN coated taps failed miserably. Blue point gun tap is important. Whatever the hardening process is, is what makes it work. A standard gun tap was NBG.

I use a resharpened tap for bottoming with the same grind.
If there is room for a much deeper hole than the thread length then it is much easier.

I tapped 100 M4 blind holes in stainless and tap is still going strong.

Look in Goliath list for the Blue point. That seems to be the most important thing.

2 flute taps are much stronger, and being gun taps, with the chip coming out the front, the can have very shallow flutes.

I use my X3 to line up with the hole, and then hand tap with an alignment jig. Until I totally redo the Syil drive sh1t system, hand tapping is my only option unless a purchase an auto reversing tapping attachment.

[djr76]

If its just a one off, I would just use sulfurized cutting oil for a lube, tap each hole 3-4 good threads deep with a cutting tap and hand tap the rest of the way with a tap wrench.

[mactec54]

Hi All4fun

You are right 303 is free machining & won't have any problem with tapping it good taps & a little cutting oil you will get it done Drilling the right size holes for the tapped thread will help a lot as well

[extanker59]

I think the others have covered it but I'd like to throw my 2 cents in. If you are tapping on a machine, I'd use the forming taps. If by hand, use the cut taps.

[All4fun]

Man, you guys are great. I appreciate the advice and insight. The job is definitely a one-off job. I am thinking about making the pilot hole slightly oversize to ease my pain and reduce the chance of breaking a tap. Is that a good idea? I've got many hours in the workpiece already, so don't need a set-back. I also got a PM suggesting Moly-Dee tapping fluid. Any experience with it on stainless?
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[extanker59]

One thing I've learned about small taps: if you feel it break or hear a chirp like it broke, and when you remove the tap it appears unbroken. Don't believe it! Throw it out and get a new tap.

[djr76]

Originally Posted by All4fun Man, you guys are great. I appreciate the advice and insight. The job is definitely a one-off job. I am thinking about making the pilot hole slightly oversize to ease my pain and reduce the chance of breaking a tap. Is that a good idea? I've got many hours in the workpiece already, so don't need a set-back. I also got a PM suggesting Moly-Dee tapping fluid. Any experience with it on stainless? ...

Moly-Dee is some excellent stuff...a lil chamfer is adequate for a pilot, its up to you to have it the way you want it to look.

[mc-motorsports]

if your hand tapping, start with a spiral point as far as you can get, then use another tap with the tip ground down to get to the bottom threads.

And use good taps, this will make all the difference in the world. One of my local suppliers specializes in hard material tooling. I just walk in, tell him what material I'm tapping and he has diffrent grade OSG taps. Said he has taps for up to 60 Rc.

Not too long ago, I had some 304 plate and needed 3/8-16 threads all the way thru. Just for fun, I tried one of my normal HSS taps that I use for MS and AL, it ripped the teeth right off the tap and barely touched the SS. Went to my supplier and bought the OSG tap, told the salesman I was cutting 304, went through like it was cutting butter, total night and day difference. I later asked the salesman what the taps were made from to make them cut hard material vs. a HSS tap, he said Vanadium.

A while back I bought some endmill holders and wasn't impressed with the 3/16" set screw in the side. So, I used a carbide endmill to open up the minor, bought a OSG tap for hardened tool steel, no problems at all. Again, HSS wouldn't touch it.

Spend a couple of bucks on the right tools and you won't have a problem. 303 isn't that tough, but that is a small thread too.

MC