Struggling to tap some stainless.

[yadnom1973]

I have an assembly I’m making and one of the parts are these small studs of stainless steel. They have an M8 through the center, three M6 blind holes from the back and an M5 from the side.

It’s 303 I think and I’ve not had too much trouble on the lathe. The mill was tricky but I got it down in the end but tapping it is another story.

Feels to me like its binding or something, after a few turns it tightens up quickly, then makes a loud creaking, then breaks the tap.

The force it takes to twist the M8 tap, to cut a few degrees of thread is just under how much force it takes to break the tap so I got an M8 done with lots of oil gong very very slowly.

The M6’s I’m not having so much luck with, broke three taps already and scraped one part. After a certain point the force it takes to cut the thread is just more than the tap can take no matter how slow I go.

I’ve tried everything I could think of today, someone once advised me to mix some anti-seiz and tapping oil for lubrication with stainless so I’ll try that tomorrow. I have a pot of the nickel stuff knocking about somewhere but I think I’ve already tried machining with that concoction and as I recall I didn't notice much difference.

I could really do with some advice.

 

[stevehuckss396]

Have you tried to over drill for a lower percent thread. The drill charts are calculated at 70-75% thread engagement. That's nice for brass aluminum and plastics. For steel's I go down to as low as 50% by using a tap drill that is one or two sizes larger than the size on the chart. Even at 50% the threads are still strong enough in steel that the head will shear off before the threads strip out. Also try a spiral flute (not spiral point) tap. They direct the shavings out of the hole unlike straight flute that just fill the flutes and bind.

Might need to read up on annealing stainless also. Stainless work hardens and my be in a state where nothing will help.

 

[yadnom1973]

Thanks Steve. That sounds like a good idea. I'm going to buy a bigger drill. The blind holes on the back carry the weight but they have about 8mm of engaged thread so there's a little wiggle room there. Even a .2 or .1 over will I think really help. I've had a steep learning curve machining these parts so I'm already acquainted with the stuff work hardening but with a lot of trial and error the right cutting tools at the right speed with plenty of cooling fluid and it can machine quite well, it's just quite a small window and outside of it it's all smoke and noise and blunt bits.

I've looked up spiral taps too, I didn't realize there were even different types.

 

[cheepo45]

You probably need to get some good quality taps-it sounds like they are getting dull instantly. Drilling the hole a little bigger as the last poster suggested will also help.
Good luck-stainless is tough!

 

[doc1955]

I agree with what Steve says plus I use Moly dee it is a high sulfur lube that works wonders on stainless. It stinks but for tapping stainless you have a hard time beating it.

 

[bazmak]

When I have tapping problems I use a combination of taps alternately.Hand tapping not machine tapping
I cut a couple of threads with a taper tap then 1 thread with a plug tap then repeat.Also use the combination drill/tap and spiral flute
WD 40 works well but I have spent 30mins on one tapped hole

 

[yadnom1973]

That's the Moly Dee tapping oil you're talking about? Someone else mentioned using grease instead of oil.

I've ordered some better taps HSS taps, not the most expensive ones but a decent set and I'll see how they fair.

I looked at the combination drill taps but drilling this stuff is already a bit hit and miss. I squirt lots of coolants and then peck with positive pressure at a mid to slow speeds. It works well on the first hole or guide hole, anything up to about a 5mm bit but drilling a 4mm then bringing to size with a 5mm the stuff grabs the bit straight out of the chuck. I've tried every combination of speed and pressure I can but can not get it to work so between having to remove so much material on a pass and having never even tried a hole in one go I didn't think I could make them work. I use milling cutters whenever I can.

 

[yadnom1973]

Looks like Moly Dee is only available in the US, I'm in the UK.

 

[doc1955]

Looks like Moly Dee is only available in the US, I'm in the UK.

It is available through E-bay I think.

 

[Mark Duquette]

If you are still having trouble I would suggest using an express tap. Express taps do not cut but form the thread. You can power tap an M4 thread with these.

 

[ranger]

Hi,
I had the same problem a few years ago, a friend gave me a tub of his late mothers skin cream, E45 or something. I had tried everything, a larger drill, all types of tapping/cutting compounds, WD40, new taps, nothing worked. After dipping the tap in the cream the thread was cut with literally no effort at all, I was amazed. I have also had good results using Swarfega hand cleaner, the green one not the 'gritty' version. I remember a work colleague of mine trying to tap an m8 thread once in steel and nothing worked, then he discovered he was using a left hand thread tap!

 

[chrsbrbnk]

A lot of tapping problems come from the hole your tapping. stainless is prone to work hardening so if you start with a work hardened hole from drilling your going to have trouble hole size is critical a few thou either way makes a difference so hole finish makes a difference . get decent taps greenfield at least we often ed used taps designed for difficult materiel they tend to have a thicker center , fairly narrow flute width and maybe half to 3/4 total flute length with a relief after the flutes , often they had a coating. we used them in high chrome tool steel like D-2. decent tapping fluid, this is not a place to cheese out. A tapping set up that does not side load the tap by twisting unevenly ! almost impossible when tapping by hand with a tee handle ! if you need the hand sensitivity try one of these tee handles that are guided by the drill press spindle or lathe tail stock

 

[minh-thanh]

A lot of tapping problems come from the hole your tapping. stainless is prone to work hardening so if you start with a work hardened hole from drilling your going to have trouble hole size is critical a few thou either way makes a difference so hole finish makes a difference .

And I often fix it by burning it about 600 degrees, letting it cool itself, then burning it again and letting it cool itself. I'm quite successful with this way
Hopefully useful.
a stainless steel part :

 

[larryg]

One of the better tapping charts I've stumbled across in wandering the internet is http://www.guhring.com/documents/Tech/Charts/CutTapDrill.pdf

It gives percent threads for different sized holes before tapping. There is also quite a bit of other good information on that site if you wander around there a bit.

lg
no neat sig line

 

[Carl Reinhard]

When drilling SS do not peck drill. As long as you are throwing a chip keep the pressure on. Naturaly, do not let the chips pack up. Slow down the rpms and use a heavy feed. Generous lube.
Carlos

 

[deverett]

As you are in the UK, I was going to suggest using Trefolex as a cutting lubricant after you had drilled the hole one size larger than the charts suggest.
I've just looked at the price of Trefolex and I will suggest you find an alternative - but I can't suggest one!

Dave
The Emerald Isle

 

[goldstar31]

Try purified lard oil and if it doesn't suit it can be used for cooking

 

[blanik]

Looks like Moly Dee is only available in the US, I'm in the UK.

Don't bother going to the expense of trying to import Moly Dee into the UK. Just look for a tapping compound at your local supplier, that mentions stainless on the label.

If you're using HSS taps, they should cut 303 Stainless OK, and if you use a suitable lubricant, it should be fairly easy. Even my cheap China made HSS taps cut 303 Stainless OK, with just a bit of generic cutting lubricant (I don't use Moly Dee or any other specialist Stainless cutting lube).

Are you using a high speed steel (HSS) tap, or are the taps that you are using high carbon steel (i.e. cheaper tool steel taps) ?

Be sure to start with either an intermediate tap, or a taper tap, and then finish with a plug tap if it is a blind hole.

And lastly - the last 2 times that I broke taps, it was because I'd misread teh Machinerys Handbook and used a too small wrong sized tapping drill.

Hope that info helps,

RoyG

 

[John Antliff]

Being in a similar situation of failing to tap S/S small threads I was advised by my local tooling specialist to use "RELTON 04Z-NRT Rapid Tap Cutting and Drilling Fluid" and drill out 0.1 mm larger holes. I was amazed by the effectiveness of this fluid - I haven't broken any taps since in S/S. I now only use this for tapping and parting off.

 

[Emers]

Hi
Not familar with the mentioned tapping fluids I use tapmagic for stainless it is fantisic. Drilling the hole .1 larger will help only use HSS taps you should not have problems with 303. I screwcut all external threads using tapmagic it is great