Speeds and feeds question

[Martin W]

I have to mill a 1~1/4” flat spot .390” deep in a stainless .139”T moulding to bend around 90 degree corners. I have 492 pieces to mill out. I have been plunging with a 5/8” Center cutting end mill twice for each spot on my Wells Index and have 230 done.
Tonight I clamped one in the K&T and tried a 3/8” 4 flute Center cutting end mill. Plunged down and turned feed on until the correct length. I was running 860 rpm at 1-3/4” per minute feed. Seemed to work much better, but took longer.
My question is what would be the maximum feed rate? I was hoping to go up to 2-1/4” per minute? I thought 860 would be too fast? It seems to cut very well. I was using cutting oil but it cuts well with no oil also.

I can’t use a 1-1/4” end mill because the edges of the T moulding is 3/4” and it would touch the sides. Also the smaller end mill seems to cut better.
Thanks
Martin

 

[Martin W]

They are for washroom partition doors. I make the cut out wider than it needs so we have wiggle room if the T moulding isn’t started exactly centre of the bottom of the door
Martin

 

[spumco]

That stainless is probably 409 or similar - not 304 or 316 so it shouldn't work harden.

Have you considered cutting two slots with a band saw and then snapping the center section out? A light score with a cut-off wheel along the long axis and a pair of wide pliers should pop it right out. I'm assuming it'll be hidden behind the bend so you don't need a precision milled surface.

If that's not possible, the let me - everyone - know what cutter you're using (HSS, carbide, size, flutes, coating) and we can whip up a F&S starting point that won't take forever.

 

[Martin W]

Thanks, I tried band sawing but it is too hard to break the section out after I score it. And it takes longer than just plunging twice. It is a cheaper stainless because it does not work harden and cuts like butter. Its not a precision cut so length and surface finish is not a issue.
I'm using a HSS end mill. I have been playing with the feeds and speeds. 860 rpm at 1-3/4" feed rate works great. Just trying to pick up the pace as I have a deadline.
They never supplied any extra pieces so I have been taking it slow and steady so far. They are not easy to clamp with out damaging and I had one pull out of the vise because I was pushing it too hard.
Cheers
Martin

 

[spumco]

HSM Advisor suggests a 5/8" HSS should be turning 1800RPM at 6-ish IPM in 304 stainless. That's aggressive in 304, but should be reasonable in your stuff. I put in a .390" DOC and .140" WOC, HSS, 4FL 5/8" no coating.

1468RPM is 240SFM. You're doing about 170SFM at 850RPM, with a 0.0004" chip load at 1.74IPM. You can probably notch it up a bit - plunge in to one end slow-ish, and then plow through to the other end of the slot.

 

[Martin W]

Thanks
We will give it a try in an off cut. I never would have thought that fast!
Cheers
Martin