Is there an easy way to cut smooth slots in stainless steel such as 303? By smooth, I mean an even machined finish or better. The slots are 3/16" plus a few hundredths wide, by 3/8" to 1/2" deep, and about three to five inches long. There are always chatter marks on the sides. I've found I can do this with a fly cutter (horizontal, homemade) in brass (for practice) with a cobalt lathe bit that I grind a hook into. The same bit in stainless dulls too quickly. HSS slitting saws also dull quickly. Even dressing the sides of the slot after cutting it leaves chatter marks, though not as pronounced as those of the initial cut. I've been using a two flute carbide end mill on the stainless. Thanks.
A finsh pass with a 4 flute will give a better finish. If you use the endmill route it needs to be cut in three passes minimum - center, then the sides. You will not get a good finish with a single cut unless a side cutting slitting saw is used. I would cut this slot with a side cutting slitting saw on a horizontal mill (hey, they are good for something still!).
[This message has been edited by Thrud (edited 06-20-2002).]
Is HSS the wrong type of cutter for stainless? The one I used dulled quickly.
You got to run hss slow (30 or so sfpm) with plenty of coolant in stainless to hold up.
Best bet is probably rough out with the slotting saw, and finish with an endmill.
You are doing one of two things or both.
1. Your running to fast turn down the revs.
2. You are cutting twice as deep as your dia this makes things more difficult.
1. Turn down the revs. Try something around 400 and use the power feed if you have it. Three passes as Thrud said and very light radial depth on finish passes .005-.010.
2. Ditch the end mill and use a woodruff key cutter or slitting saw. Msc has some larger dia woodruff key cutters with narrow faces.
HSS is great for stainless when it is razor sharp and you use the correct speeds and feeds. The fly cutter you made had to be making some serious surface footage and this is why it dulled quickly. If you pull colored chips off of stainless using HSS you are running it to fast.
Hey, try a 3-flute endmill if you can find one...odd number of flutes will cut much better...
Trebor (is that a reverse Robert?),
Thrud was right when he said 3 pass it. Also you might want to try 'climbing' on the side finish cuts. I had exactly the same problem as you in same material, and I was using 3 flut TC slot drill. Went down a size on the EM and 3 passed it - better but not great, climbed the second piece by accident and it was as clean as a pigs whistle.
3 flute endmills were designed for 10K+ rpm machining of Aluminum - they give a better surface finish than the standard 2 flute.
Watched an Advant thread mill do a 2"-12 tpi by 1.5" deep hole in two passes yesterday took the Hass VM-5 about 1 minute and they never even pushed it. It did the top 3/4" band and then the bottom each one pass - full depth. Sounds very well balanced unlike the normal thread mills. The high pressure through spindle coolant sure threw the chips out with that big drill! Got my hair washed for free...
"Trebor (is that a reverse Robert?"
Darn, and I thought I was a master of disguise. I used my name on another forum and thought it lacked creativity.
Thanks to all for your help. Multiple, and climb passes are what I've been doing, so I'll keep on, and revisit slitting cutters as well. I just don't relish the sharpening part on the latter. A machinist on another forum said he will set up an undersize rough drill first and then follow up with undersize and then final size passes, when he wants precision slots. I'll probably give that a try too.
3 passes - undersize end mill- cut center out first, leave .005 to .010 ea side, climb cut each side to size. Thrud had it right.
HSS should work good on Stainless, use oil, coolant, or a tapping fluid made for stainless.
303 sfpm is 70 - 100 by my books, but might run even slower such as noted above.