Tapping Stainless steel

[Leakie]

I was going to buy some half round stainless (type 304)to make some molding strips for the running boards on a 1930's Chevy. How hard is it to tap some holes for bolts in stainless? Do I need anything special other than an ordinary tap? Also how hard would it be to round over the ends. Is this something I could do with a disc sander and then be able to polish them up?
Thanks.

 

[Jagmandave]

I use one drill size larger for the hole compared to regular steel, then be sure to use lots of good cutting oil as you tap, and go easy - other than that it's not too big a deal. Cutting oil is the key. If the tap binds, back it out a few turns - blow the chips out with air, reapply the oil and go on.

A new, sharp tap helps too.....

 

[A_Pmech]

The disc sander will work fine for rounding over the ends.

The most important thing to keep in mind when tapping stainless is to use a good quality HSS tap that is SHARP. A dull tap will work harden the material and then you're up a creek. Two or three flute spiral taps usually work best. 50% thread engagement is usually fine in stainless.

Use a tapping fluid such as Tap Magic or dark thread cutting oil from the hardware store to lubricate the tap.

Edit: Jagman beat me to it.

 

[Leakie]

Thanks for the help guys!

 

[gorilla]

Exultant advice above, my back round is from the high vacuum industry where everything is SS'T. The best tapping fluid in my opinion is some stuff called Moly-Dee.

 

[hunter1151]

Some things I might add would be, use a good sharp drill bit, you can work harden the hole before you even start to tap it with a dull bit. The thing about stainless is you always want to pull a chip...........never rub stainless as it will work harden in a nano second. If you are tapping a through hole use a 2 flute gun tap, it forces the chips through the hole as it taps and they will come out the bottom of the hole. I make class 3 threads in stainless all the time and rarely have a problem. We use cobalt drills most of the time for stainless, if you are doing a lot of holes they hold up much better than HSS.