milling a buncha 303 bars

[kendo]

I got a bunch of parts to make out of 19" long 1x3/4" 303 sst bars
they get milled to .89 x .69" then a channel and some drilling

I'm cutting all sides equally to minimize bowing but its still a problem
not so much when I mill one part at a time, but I tried clamping 5 parts in two vises to mill each side 5 at a time with a 3" face mill, but they bowed too much in the cut

like I said, not a problem when I hold one part at a time and turn it 3 times but thats so slow its taking forever. I cut it with a 2" face mill when I do it this way.

also, I could use some help getting a better finish with the face mill
its a kennametal 3.15" cutter with six 45 degree angled inserts taking .05" per pass at 450sfm and .007ipt
I know I can lower the ipt, but goodness that huge cutter looks like its barely moving
so, would you guys use this tool they way I am?
if so, which way would you tweak those feeds n speeds?

thanks,
Kenny

[PixMan]

The 303 stainless bars are going to have a lot of internal stress from the rolling of them. Your best bet will probably be to take a shallow (skin) cut on all 4 sides, then have them stress-relieved and straightened before final machining. Once you get them back from the heat treater, you're still going to have to shim them carefully to machine to final size, one at a time.

What is the straightness specification of the finished part?

As for finish, it can be hard to get a good finish on 303. Your sfm seems low at 450. What grade of insert are you using?

[kendo]

straightness specification?
no such thing where I work
and no sending 'em out for heat treatment either
they'll have me run 'em 1 at a time for a week straight before they do that

Im using kennametals KC725M insert

thanks for the reply PixMan

[PixMan]

You're not leaving yourself too many options for improving the process. Lower the feed rate to .005 ipt, speed up to 600 sfm. Go to KC715M grade if tool life suffers too much. Take a skim cut on all 4 sides first to relieve the internal stresses. If you have an arbor press and a straightedge, now is the time to straighten them, then finish.

[kendo]

thanks PixMan
thats all I wanted to know - am I at a dead end or what?
theres noone around here for me to ask or learn from, so when I feal like im stuck at a dead end, I come here

[HuFlungDung]

What are your options for getting a wiper insert to put into that facemill? This should make it possible to feed at a high feedrate and get a more even surface.

Also, is your mill trammed fairly well dead square? This may have some effect if you take multiple passes where the edge of the cutter is still in the cut.

As for sideways stacking 5 at a time, that is next to impossible to get a good enough grip on the center 3 pieces so that they stay straight during the cut (they may still spring after release). As soon as you get the sides out of parallel with the first cut, then you're really in deep sh!t.

To really gear up, I'd suggest that you look at some of the Mitee bite clamping stuff, and get some ideas for fixture building using toe grip type clamps, with pull down action. You'd have to build a gang setup as each piece needs to be clamped individually, but you can still get some decently close spacing with the Mitee bite clamping systems.