View Full Version : Tapping Stainless Steel

03-23-2007, 05:54 PM
I need drill and tap some holes in stainless steel. I'm planning on using cobalt bits for the drilling, but can't find cobalt taps. Does anyone make a cobalt tap or does anyone have a suggestion on what tap to use?

03-23-2007, 06:12 PM
No suggestions as to which tap, just take it reeeeaaaaallll easy.
Back off and clear swarf with compressed air, every 1/4 turn, if it seems sticky. Any lube will help, of course, but I find Tap-Magic works better than most (and it smells wunnerful when hot :D)

03-23-2007, 06:19 PM
What size holes?
Do you have a large number to do. If so:

Use the largest allowable TDS* drills (HHS with coolant work great) for the tap you are using . 55 % thread is ok
Use only taps that are made for stainless.
The "black coated" ones work well.
Use lots of cutting oil.
Do not let your work get hot....

*check machinery hand book

Tin Falcon
03-23-2007, 09:01 PM
Stainless in not hard to work but you must work with care. It willl work harden. Keep drills sharp. Use a proper speed, too fast will slow things down and cause problems. Use a gun tap spiral flute or spiral point even for hand tapping. use cutting fluid for tough metals. when I worked at the boat yard they bought Anchor lube by the gallon. They did a lot of SS railing fabrication. Anchor lube is non toxic and approved by USDA for food service work. Castrol moly D is also a good tapping fluid for tough metals.

reminds me I worked R&D for a yacth buider one of the woodchucks (The metal shops name for cabinet makers) asked to borrow my drill index. He was drilling stainless he ruined a half a dozen bits before i realized what he was doing he obviously did not know what he was doing. You cant treat stainless like wood or aluminum.

Rich Carlstedt
03-23-2007, 11:28 PM
Anchor Lube is excellent !
Do 50 to 55 % thread percentage for tap drill
Get OSG "Exo Taps

No Problemo's

03-23-2007, 11:46 PM
What kkind of stainless?

03-24-2007, 04:18 PM
Thread Size: 1/4-20
Material: HSS
Chamfer Style: Plug
Ground Thread Limit: H3
Number of Flutes: 3
Overall Length (Inch): 2-1/2
Manufacturer Part Number: C58562

Will that do the job with copious quantities of Tap Magic?
I can't find anything but HSS taps.

Tin Falcon
03-24-2007, 05:33 PM
Anchor Lube is excellent !
Do 50 to 55 % thread percentage for tap drill
Get OSG "Exo Taps

No Problemo's
Rich Has an Excelent suggestion here. Unless this is a one time thing with one or two holes get the right tools for the job ie a tap made for tough stuff with the propper coating and a cutting fluid for tough metals. A good cutting fluid reduces the torque required to turn the tap this in turn gives you better feel and reduces the chance of breaking a tap.

03-24-2007, 05:52 PM
I do that kind of tapping with HSS all the time in 300 series SS. As suggested, the thread percentage is the most critical. Once you're in that 50-60% range it should be pretty easy. A frequent job is a 10-32 in 3/8" 303, for which I use a #19 for 59%, a 3 flute HSS plug tap with Tapmatic Natural, and a tapping head. Never a problem.

03-24-2007, 10:02 PM
Greenfield EM taps are tops IMHO,you need the Rc hardness of the material you are using to select the correct series.They will allow you 65% threads in most 300-400 series SS.

One note,with these you don't break the chip with every turn like a hand tap.These you just power it in,the chip comes out the back like those from a drill.

Rich Carlstedt
03-25-2007, 12:11 AM
Be aware that the two weakest threads for tapping are 8-24 and 1/4-20.
That means that they have the smallest root diameter,divided by the major diameter, so the root of the tap sees a larger than normal load...therefore making these two sizes, the easiest to fail.