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gundog
12-18-2005, 07:01 PM
What is the secret to tapping stainless bar stock. I bought some SS round stock at the hardware store I bored it 5/16" like the 3/8" tap calls for and my tap felt like it would break so increased the hole by about .010". I got the holes tapped but it was really tough. Do they make special taps for SS? I am going to do some more of this same part and I will buy a diffrent tap if they make something for SS. The guy at the hardware store could not tell me the grade of stainless the round bar was made of I am guessing it was 304.
Thanks GD

SGW
12-18-2005, 07:27 PM
I think the secret to tapping stainless steel is to buy a SS alloy that is machinable. 303 is not bad. If memory serves, 304 can be pretty difficult.

Where did you get your tap? If at the hardware store, a truly GOOD tap would probably help. Look in MSC www.mscdirect.com (http://www.mscdirect.com) or other supplier, see what their "top quality" tap brand is, and get one of those to try. It does make a difference. ISG, Sossner, Hansen-Whitney, Brubaker...there are a bunch of good ones. It's hard to imagine how a tap can be worth what a top quality tap costs, until you try one.

Maybe other folks have more specific suggestions.

irontoart
12-18-2005, 07:35 PM
I've sold OSG taps. They have taps specifically for tough to machine products. Greenfield in our main tap line and they also have taps for inconel and monel. These would probably work better.

motorworks
12-18-2005, 07:41 PM
Yes
If you plan to do more, then buy a tap for stainless.
see Travers tools or kennametal for more info
As well check you tap chart or handbook for TDS and go as large as possible.
Coated taps work better then the "shiny" ones.Use the correct oil for tapping stainless.(seal oil works great!)
Try and buy your stainless from someone who knows what grade they are selling!

coles-webb
12-18-2005, 07:44 PM
Stainless Steel tends to work harden as the tap cuts the metal. Use a good cutting oil and do not use a taper tap. use a good quality HSS Plug tap. If you use a taper it cuts a little at a time which will work harden the metal with each cut. The quicker you (deeper) cut that is taken the less metal will be work hardened. Good luck.

Mike

gundog
12-18-2005, 08:47 PM
Thanks for the info guys I will try a new tap for sure and next time. I will go somewhere they know what their selling also.
GD

Carl
12-19-2005, 02:15 AM
<font face="Verdana, Arial" size="2">Use a good cutting oil</font>

I'll second that.

Mcgyver
12-19-2005, 08:02 AM
25 years ago, my high school machine shop was in the process of switching over to metric. I remember the tap set they acquired - there were three taps for each metric size, not plug taper and bottom like we're used to, but each tap cut progressively more of the thread, ie it took all three to cut the full depth of thread.

Now, for cutting a 1/2 20 thread this a waste of time, but for cutting a 4/40 thread in ferrous, especially tought ferrous like ss or chrome moly, what a great idea! yet it seems to have gone the way of the dodo.

In tough stuff with small taps I replicate this a little bit by alternating between a taper and bottoming tap, cut a couple of rev's with one, then switch. Yes, its a pita, but I almost never break a tap cuz i switch up to this technigue when i think i'm gettng close

SGW
12-19-2005, 10:56 AM
What irontoart said -- it's "OSG," not "ISG."

My memory ain't what, um, something...

Allan Waterfall
12-19-2005, 11:51 AM
<font face="Verdana, Arial" size="2">Originally posted by Mcgyver:
25 years ago, my high school machine shop was in the process of switching over to metric. I remember the tap set they acquired - there were three taps for each metric size, not plug taper and bottom like we're used to, but each tap cut progressively more of the thread, ie it took all three to cut the full depth of thread.

</font>

I got some from here,you have to use them like you described.
http://www.arceurotrade.co.uk/

Allan



[This message has been edited by Allan Waterfall (edited 12-19-2005).]

PBMW
12-19-2005, 03:14 PM
I tap 304 all the time on my CNC sa well as manually. 500rpm and moly dee works a treat
Jim