Rigid tapping speeds
I have a part to run out of 303 SST with a 10-32 thread through it. I was wondering if you guys use a formula to figure rpms? I am rigid tapping now at 850 rpms but I have no idea if there is a better speed to run at. I'm using a hss tap and water soluble. Any suggestions? Thanks.
Sounds pretty fast... you're tapping @ ~42 sfm. I looked up what Balax recommends - they recommend 20 sfm in 300 series SS - although they do not specify any difference between 303 and 316, I think I'd dorp it down to about half of where you're at. If it's a blind hole, you will want to drop another 25-50% in sfm. Make sure your coolant concentration is high, like 10-12%, or maybe some Moly Dee is in order.
If you are not using a thread forming tap, try one...they work great and the cold formed threads are really nice - just finished a job with about seventy 10-24 threads in T316, used a Balax "Thredfloer" tap and first and last hole were perfect (dribbled Moly Dee in every blind hole just to make sure).
If your doing a through hole, and don't want to stand there dribbling tapping fluid, you can program a move into a small cup full of fluid off to the side of the table to pick up fluid, and then go thread...with a thread forming tap instead of a cutting tap, you don't have to worry about chips either.
All I do is use the same speed as I would with a HSS drill the same size. Works for me and is easy to remember.
My old bosses used to piss and moan that you're sapposed to run at surface footage for the hss tool. All of the guys I worked with (15+ years over me) ran almost all taps under 3/8 at around 400 rpm depending on the machine. If they had to figure ipm on the machine they'd get an rpm that would make the feedrate a whole number.
I just got in from tapping 900 thru holes(.120 wall thickness) in 304 stainlesss 1/4-20 with a $10 cleaveland (J&L sale item) tap at 400 rpm. The tap had a silver hint of color to it, but all cutting edges were beautiful. I could have ran it faster, but I remember my old coworkers bitchen about braking taps.
I do want to try form taps soon, I have heard many good things about their reliablity.
Just my .02
Thanks for the information guys. I'll try form tapping too, just out of curiosity. I don't use them much. We'll see if it works for me.
I use the following SFM's:
(I normally buy Vega brand taps btw)
Plastics about the same as 6061 if I am using coolant, and about 300rpm if not.
Best of luck,
I'll second the forming taps. I've used 10-24 in blind holes in 316L stainless and haven't had a problem with them at all. One guy I know said he used them for tapping 4-40 holes in 400 series stainless and had good luck with them. As far as speed goes, doug's chart above pretty much nails it.