Taps for Stainless Steel 316

K

Kroll

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Guys I purchase alittle 316 SS hexagon bar stock to make afew oversize nuts in sizes 1/4-7/16.In the past I have drill and tap some SS but they were not perfect.One of the reasons that I later found out is as example 3/8 ,I had drill out a 5/16 hole for the 3/8 bolt size.I was told by someone that I could have went bigger than 5/16 still have good holding threads.Wish I could find that chart,since my computer went down I have nothing.
Anyway,I have the house brand set of taps and was wondering if there are taps made to handle stainless steel that don't cost arm/leg?
Does anyone have a drill chart that shows the % of threads,I don't remember what its called.Guys thanks again for any help forgive the lack of information ---kroll
 
Hmm. I have heard that, in tougher steels such as stainless, using a 50% thread produces satisfactory results while making it easier on the taps and such - as opposed to 75% thread in aluminum and such. One may be able to find a 50% thread chart.

I would say that that may not work as well for small threads, but larger ones, no issue. At where I work, we (power/CNC) tap 316 and 400-series stainless with small taps, 3mm, 4mm, etc., with the proper size tap drill. Believe the taps are mostly OSG with just a black oxide finish. Use either machine coolant or Oatey threading oil from Lowe's...
 
Agood sharp tap and lots of tapping fluid. And always use never seize on ss bolts and nuts.
 
I used to do a lot of work with 316 stainless, tapped lots of holes in the 1/4" to 1/2" range. I always used a drill bit slightly larger than what was called for. If it called for 5/16", I used 21/64". I also used OSG or Greenfield taps, typically with the spiral point, they seemed to work better.

Since then, I found a wonderful resource for a tap chart, and it is available here: http://www.glacern.com/calc It lists clearance hole sizes, tap drill for 75% thread as well as 50% thread. Plug in the size and TPI you want and it highlights the correct line for you.
 
Kroll said:
Anyway,I have the house brand set of taps and was wondering if there are taps made to handle stainless steel that don't cost arm/leg?
Does anyone have a drill chart that shows the % of threads,I don't remember what its called.Guys thanks again for any help forgive the lack of information ---kroll
Click to expand...

Go to the Little Machine Shop site and print their chart. 50 and 75 percent threads, metric and english, tap and clearance holes.

Or check Mac Hinery's Handbook. But it's a lot harder to use than the LMS charts!
 
X2 what Terrywerm suggested. I just finished a job for my only customer some of which involved tapping stainless standoffs #10-24 #10-32 and 1/4-20. Totally forgot about what material I was dealing with until my tap snapped off on the first pc! Fortunately was able to finesse it out without scrapping the part. Went back and oversized all the holes. Still rough going (my taps may need replacing) but got it done. Phew.
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ImageUploadedByTapatalk1412449105.584094.jpg ImageUploadedByTapatalk1412449125.356068.jpg
 
If you have much to do with stainless, it will pay off in the long run to buy tooling specific for it. Usually that means a premium tool and a premium price to go with it. Absolutely no carbon steel taps. I think that most of us have grown past that stage anyway. But for stainless, even a good, standard quality HSS tap is not the best choice. Factors beyond the base material come into play. Things like cutter geometry and coating(s) make all the difference.

Control over hole size becomes more critical as well, if you want to try staying on the high side of allowable tolerance. This will obviously lessen the stress on the tap, so as long as you have acceptable thread height, you should be fine. Most hobby projects aren't likely to push the limits of thread strength anyway. There is nothing wrong with using a reamer after the drill to size the hole. This is actually advantageous if you are using a form tap. Hole size is very critical in that case.

I have had satisfactory service from Emuge, Vega, and OSG taps, bought with the above factors in mind.
 
Many years ago I worked exclusively with 316 SS and we only used HSS ground thread taps with no coating. Use plenty of Tap Magic or TriClorothane and do not let the chips build up. Turn the tap 1/2 turn and back it up to clear the chip. 316 is not hard, just tough and gummy. Will gall very easy. Tom
 
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