Stainless 304

[pauls]

I need some suggestions. I've been making exhaust parts for race cars out of mild steel by plasma cutting and cnc milling off the 1/16th extra with a carbide mill. I've tried to use the same technique on 304 stainless and I need some help. First, drilling stud holes with flood coolant with HSS 1/4" bits even at ME consultant ratesjust kills the bit after 8 holes_what type bit would you reccomend? I'd also like to be able to profile the edges in one pass 0.5" deep taking off 1/16th but so far this isn't possible with my cobalt tin or carbide EMs-some suggestions would be helpful.
Thanks
Paul

[Karl_T]

Remeber the machinist' mantra for stainless. 304 she's a whore, 303 she's for me.

If you aren't welding switch to 303. But 303 don't weld. 304 work hardens easily, lower speeds and higher feeds are in order. If you dull a bit, you work harden the heck out of it and now you got a real mess. Keep your tools sharp, change out before dulling. Use coolant. I always try a little cussing and swearing, but it never seems to help much, still I'm sure I'll try cussin' next time I run 304.

Karl

[ChrisJ]

I don't have a real good understanding of cutting SS also.

I have read on this forum to make sure your feed and speed are on the upper end in order to prevent the hardening that occurs if the end mill sits in one place for too long. Also it has been stressed, "tons of coolant". Some seem to like the cobalt coated end mills. It would be great to have someone who mills this material on a frequent basis to chime in and elaborate on the best methods for machining 304 or 316SS.

But I am just absorbing this information at the moment with the intentions of milling 316SS in the near future.

Chris

[DareBee]

I will basically repeat what Karl says.
I know 304/316 is difficult to machine but i usually don't have that much trouble.
I may be wrong but IMO ME is about 4X too fast on their drilling feeds.
If you do this non stop for a living, the tooling guys (such as Sandvik or Iscar) will come right to your shop and do testing with you to get you the right tools and feeds for your specific application. Talk to your local reseller to get something going.

[toneV8]

Can somebody tell me where can I find tools for exhaust tip.

[imwllc]

i have to mill flats on the o.d. of some 316 stainless parts i make, they are .866" thick and i take the whole depth and i need to remove .155" of material, i take it in two heavy passes and one finish pass of .030". i use an indexable endmill that is a 1" diameter made by dapra. you may want to try taking the cut in two faster passes rather than one pass, burr control may be better also when you profile. i had a lot of problems with these until i made a fixture about twice as heavy duty as i thought i needed, the vibration of the first fixture was the main cause of my tooling failing. can you describe the part and your fixturing more?

[imwllc]

also for drilling my stainless i always use 135 degree split point cobalt drills, screw machine length, or as short of flute as possible, and i never peck drill anymore than the drill diameter, i use a standard 120 degree spot drill, i assume you must be peck drilling?

[ViperTX]

I agree with imwllc....vibration and someone mentioned "work hardening"....also you're probably trying to profile with the side of an end mill on some pretty hard material. if you have alot of these to make...I would look at some Laser cutting these with a secondondary dross removal operation.

[take a cut]

I agree with viper on the laser if not try rough grinding the edges off first to remove the worst part of the hardness from the plasma. Check the air for water dampness in the line tends to make the edge harder i find.

[pauls]

Thanks for the input. I'll try your suggestions tomorrow.
Paul

[ViperTX]

toneV8....not sure who sells the mandrels to form exhaust tips...I suspect that they are all custom made

[toneV8]

Which companys build tools for exhaust tips, bending tools, end forming tools.........for cars.