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Tapping 6 mm threads in 304 stainless

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smiffy:
   I need to tap 6 mm threads in 12 mm 304 stainless and I have 180 holes to tap .
  So the question is what is the best tap ,straight flute or spiral .I would also like to use a tapping head .
   What speed to run at and best tapping compound to use?
   Thanks Mike

Will_D:
I have been tappping 3,4,6 mm into 303/304 using the Swiss-Tech spiral taps.

I start them in the mill at very low speed, allow them to cut say 4 mm (this is for blind, 8 or 10 mm deep holes) of thread and then finish by hand.

I am sure that a tapping head would be even better.

These taps are designed for machine use. Normal straight flutes are NOT! They produce 3 ribbons of swarf like what a drill does (well they only do 2) that clears the tap and the hole. Straight taps produce chips that need to be backed off and even removed after only a few mm of depth.

sparky961:
I'll assume the holes are tapped through, not blind. There are distinct differences either way.

If you can find a name brand 2-flute spiral point machine tap or three, you shouldn't have to fight with it. Run fairly slow, like 50 to 100 RPM. This is slower than the SFM works out to but will give you better control. Drill slightly oversize if you can, giving you 50 to 60 percent thread. Studies show the loss in strength is negligible. Use a rigid clamped setup with positive alignment of the previously drilled hole to avoid flexing the tap. RapidTap cutting oil works well for me in this locale but any decent cutting oil should give similar results. Run the tap all the way through as far as you dare before reversing to push the chips out the bottom of the hole. Reversing before fully cutting off the chip can bind and break a machine tap, unlike a hand tap that's me and to reverse often.

 Definitely avoid spiral flute taps unless machine tapping blind. They are the weakest of the lot.

Jonny:
Assume drilling and tapping in a mill on centre.

I generally use the coloured ring taps either red for hard materials, yellow or blue for aluminiums, never tried the green. Having used each colour I would say the red works best powered in and out the job on aluminiums or the blue against whats recommended.
http://www.ebay.co.uk/itm/M6-x-1-0-SPIRAL-POINT-RED-RING-M-C-TAP-DIN371-EUROPA-TOOL-TM27160600-NEW-BOXED-/200922962861?hash=item2ec7f11bad:g:ajgAAOSw~CRTrWKV

Green never tried for softer materials than red
http://www.ebay.co.uk/itm/M5-x-0-8-SPIRAL-POINT-GREEN-RINGED-TAP-EUROPA-TOOL-TM31300500-NEW-BOXED-A7-/201284713657

Plenty of cutting oil.

smiffy:
Thanks for the replies I will buy a selection of different taps and see how they perform .
                       Thanks Mike

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