tapping stainless steel
Is the two flute gun tap better to use in tapping 303 stainless or would a 4 flute cut easier?
Also which tap to use;aper tap,plug tap, or bottom tap?
2 flute 2 flute 2 flute what kind depends on the application.
If you have lots to do, the best taps to use are serial taps. They come in sets of three, but each of the first two taps cuts a progressively deeper acme-like form
If you want to do it in one pass, a lot depends on whether it's a blind or through hole, and how close you need to tap to the end if it's blind
Need more info to answer your question, also: will you be using a tapping head, if not, what machine/ method?
The thread size will be a screw thread like 5/16-18. yes tapping fluid will be used. The hole is a blind hole, that needs threads close as possible to the bottom of the hole. A manual lathe will be used to start the tap, then finished by hand. I had planned on using a plug tap then a bottom tap. I have be tought in the past that the less taper in a tap is very on stainless steel.
Use serial taps if you can get them: they are the best option for difficult, workhardening materials. Failing that use a good quality (US or European or Japanese) HSS ground thread spiral fluted tap, in the lathe, going as close to the end as you dare.
For best results, do it in one powered pass without any stopping or reversing, but if you do stop, you need to reverse sufficiently far to break the chips.
Then take it out of the lathe and use a bottoming tap, using the usual hand-tapping routine.
Thanks for the quick replys.
I'd use a 2 or 3 flute spiral tap with a 3 thread lead. You need to pull the chips out of the hole and not pack them in the bottom like you would with a plug tap. Chase it with a bottoming tap if necessary.
I agree with hess re the spiral flute tap for a blind hole. Also, tapping 303 is about like tapping 1018. You shouldn't have any problem.
a gun tap is designed to push the chips ahead of the tap and would not be used on a blind hole. Taper, plug and bottom refer to the number of partial threads cut before full thread form is reached. I don't know about flutes. I would not try a power 1 pass tap unless I was using a tapping head with a spiral fluted tap (which ejects the chips out the top).
Spiral tap it, although even regular taps work just fine in 303 as long as it's not so deep that chips before a problem(usually less than 2xd). I've done it plenty even with just a drill chuck if no tapping head was available, also depends on quantity. If you have a lot to do then a good spiral tap will save a LOT of time and messing with chips.
Biggest thing is buying good taps that are meant for the material you're working with. I like OSG.
Biggest thing is buying good taps that are meant for the material you're working with. I like OSG.[/QUOTE]
Ditto OSG. Get their catalog. It has a ton of useful info including application guides.
I also recomend OSG taps made for stainless. I used several for tapping 1/2-13 in 316 SS about a year ago. Biggest problem I had was the tap slipped a few times in the collet I was using in the mill.
Good grief - whuts with all the guys freaking out aboot tapping 303?
You can doo 5/16-18 with a three flute spiral flute "modified Bottoming" tap all day with no issues and no special fluids other than you would use for low carbon steel.
I would hafta think that anyone that offers a toy of this nature would be of sufficient quality. I don't even like to use hdwr taps for 12L! (How doo they sell them Vermont/American junk anyway?)
Ox wins the prize.
Spiral flute modified bottoming tap is the ticket.
The spiral flutes pull the chips back and out,and the modified bottom feature gives 3-4 leads of thread (thus dividing up the chip load).
Make sure you use a series designed for tapping stainless, this is very important.
Stainless geometries are ground with more "hook" in the rake face giving it a free cutting action to shear the stainless. They also have more radial relief to prevent friction hardening and binding.
Greenfield EM-SS taps are very popular. Here's some trivia for you: Any high performance tap from Greenfield will have "Japan" etched on the shank. This is because Greenfield buys them from YMW Tap in Japan. YMW is the old Yamawa brand, the same one old timers refer to as "ya-mama".
Here's your tap:
See the price?
Here's what I sell locally for about $7.50
For the money it's hard to beat YG1 taps. Find a local dealer and try some.
Oh yeah, Castrol Moly-D tapping fluid works well in stainless.
Thread forming tap
I don't know how many parts you are making, but I think I would try a OSG thread forming tap [ no chips ] made for stainless and I would try to do it in one pass on the lathe. I would call a OSG dealer and get the right size to drill hole for form tap. MSC has these taps.
Where do you get serial taps ? I have hand ground the crest of taps then followed up with a
regular tap but have never heard of serial taps.
Apologies to all for recommending something which evidently is not easy to source over your way, these days, at any rate (the old timers probly have them tucked away)
Neither McMaster Carr nor MSC appear to list them. They are sometimes referred to as "progressive" taps, but Machinery's Handbook describes them, under "serial" taps.
The best ones I have were made by SKF before they joined up with Dormer, and there was one guy here in NZ who worked for SKF who could access them direct from Sweden (none of his colleagues even knew SKF made taps !)
I bought a lifetime supply from him over twenty years ago, because I do a lot of hand tapping on stainless of unknown provenance which is where they REALLY come into their own (in situ, marine stuff mainly), and good ones last forever, so it's a long time since I tried to source any.
But occasionally I've seen them at specialist tooling supply houses here in NZ.
Google also throws up a lot of hits in India, like dozens ! I guess hand tapping has become a third-world speciality ...
I bet you didn't know NZ was 3rd world, but in some respects we are :-)
Dormer have subsequently been swallowed up by Sandvik, but may still make them (one Google hit suggested that might be the case)
If you know any whizz-kids in that organisation, they might be able to help. I tried to download info from their interwobble site, but my Acrobat installation is acting up and/or their website was written by a sociopath.
Rallying your serve in the "I've never heard of that" game, I've never heard of roll-forming taps which were rated for stainless steel, or even titanium. So thanks for the OSG website recommendation, where I see both material rated as do-able.
HHhhmm, appears that nobody has warned you about stainless steel being a " bit on the grab it " type of material when it's being tapped.
If you want constant and continual success at tapping into stainless steel with a 5/16th x 18 tpi tap, or any other tap that you want to use, then just make sure that you drill the hole ONE METRIC sized drill UP, than what the charts recommend.
For the 5/16th x 18 it calls for a 6.6mm drill, GO FOR the 6.7mm drill, OK you might loose a bit of the thread form, but it more than makes up for NOT having to attempt to try and remove a broken tap.
OK, the drill charts call for certain sized drills, which will give you a 75% thread form, so a drill size UP, might equal a 72% thread form, big deal, still no broken tap, is definitely worth that slight loss of thread form.
By the way, any tap will now work, gun, spiral, bottom, even an old carbon tap will still be OK, if you drill the hole one size up.
Taps do cut better if you drill them over the chart size but if you are making them to aircraft
tolerances you may find they are scrapped in QC.
YEP, I'll agree with that, 'cause we ALL build to NASA specs, now don't we.
Originally Posted by jims