Need Help!- stainless 303 ball bottom hole

[atlantic23]

hello can anyone help me with the feed and sfm appropiated for a .312 ID ball bottom hole, only to get started, the material is stainless 303 and if you can tell me, for carbide and cobalt speeds that will be great, is the first time I am gonna machine
a ball bottom hole on stainless and I dont wana breake anything so should I drill to the same ID size of the ball endmill and leave enough material for the ball botom, it or should i use a round drill?
thank you all for your time and sharing your knowledge.

[JimPAC]

How deep?

How many flutes?

Whats the tolerance?

[JimPAC]

First of all how rigid is your Spindle?

SLOW SLOW SLOW!

If you want a nice smooth finish then pre drill and leave .010 to .020 in the hole and be careful to drill as deep as possible with your drill bit.

Assuming you have a 4 flute ball nose E.M. submerge in cutting oil or lube and turn spindle to around 200 RPM hand feed? if CNC peck .020 until desired depth at .2 feed!

[atlantic23]

is 1" deep, we havent bought the tool yet so part of my question is how many flutes and carbide or cobalt? the tolerance is +- .005 thank you for your help, and i am using a cnc lathe.

[JimPAC]

Wow pretty deep Bud!

Whats your finish req's?

Pretty much the same as my last post 4 flute is good!

Quantity usually decides Carbide is best!

Is this live tooling?

You can make it work fine just keep the flute length as short as you can and flood it while pecking!

Just take it slow and you'll get good results without chatter in the bottom.

You welcome any time.

[PixMan]

You're on a CNC lathe so no worries, and no need to go slow with that tolerance. Worry about chip packing, not speed as long as you're using carbide.

Drill first with a good "N" (.302") drill, put the full-diameter lip edge close to the final depth minus 1/2 the ball diameter. Now get a good center-cutting 3-flute long 5/16" diameter ball mill and plunge to final depth. Use TiCN coated carbide if possible for tool life, or slow it down to 250sfm.

[atlantic23]

hi everybody today unfortunately i broke the ball end mill i had 1800 rpm ,
and 4 flute carbide, but i notice they give me a regular end mill not a center cutting ball mill, and i should have checked what kind of mill will work, plus the spindle dont sound good it has scars of nasty hard crashes so do you guys think i should go with cobalt? should i peck or not, there was defintly chip packing, i used .003" feed for the id and
.0015 for the bottom, the cobalt drill did ok are ball bottom hole dificult or am i doing something terrible wrong . thanks for your help.

[PixMan]

You definitely need to peck if seeing chip packing. That's why I suggested a 3 flute center cutting ball mill; less flute, more clearance.

You might do well to just get HSS for this job. Much stronger transverse rupture strength, but slower speeds.