Guys, we were tapping some mild steel pieces today in a JohnFord CNC mill today and I am getting torn and rough threads. We are ridged tapping them and using light colored cutting oil. They are drilled with a 7/16, then run thru them with a pipe reamer, lightly chamfered, and tapped. The tap is a gold(TIN?) coated brand new tap, and they are running them at 180 rpm. Seems like poor steel and the parts have been torched out. They are small parts and a production type job.
Any ideas or suggestions? I have alot of ideas, probably silly ones, so wanted to ask. Thinking of trying a slower rpm and feed...maybe relieving some of the tap threads on the back side so there isnt as much engagement if that makes sense, and thought about a heavier oil, maybe with sulfur in it. Was wonder also if you could tap it not quite to depth, then go back slightly deeper as a finish cut kinda? Since it uses a synchronized tap cycle thought about that...
Thanks for any ideas... Thanks.

It sounds like you are running hot rolled steel or A36 which is sometimes horrible stuff to get a good thread in. A sulfurized tapping fluid might be worth trying but if you are using water based coolant try taking the concentration way up; such as if your normal mix is 5% go to 25%. I have done this for large fine pitch tapping with success. You can always drain some of the rich mix out and dilute again when the job is done. Another thing is take the speed up not down. I have found often faster gives a better thread and have run 1/4"-NPT at 1000 rpm in C1018. Peck tapping if your machine can do it will also help.

Thanks Geof for the info...Hadnt thought of going up in the speed. Will give these a try in the morning! Thanks again.

you could try rocol...comes in liquid or paste form


www.rocol.com/corporate/english/index.php

Thanks man. It was definately in the fluid believe it or not. Coolant didnt work in the machine...light oil didnt either. Used some "Tap Magic" that we had sitting there and it worked great and didnt chipp any more tpas and the thread looked nice, not torn or rough like before. Thanks again!