milling a pocket in Al

Get some roughing cutters. They won't load up nearly as bad as finish cutters. Use air to blow out the chips as you go.

You can do that with the endmill ( a center-cutting one). That's why they're sharp on the ends. draw the perimeter of the pocket with a Sharpie or a scriber, set the depth stop to something shallower than the finish depth and go to it. Randy

Perhaps drilling a hole a bit larger than your end mill dia first and then starting the end mill in that hole so you're just side cutting as you go around removing material. Wouldn't want to swiss cheese it as that would give a lot of interrupted cuts and shock loading on your end mill.

They make a high helix 2 or 3 flute center cut endmill just for non-ferrous. Buy one, use it for aluminum ONLY.

I crank up the speed, squirt on a little aluminum cutting juice, and make (lots of) chips.

And what radius in the corners?

Normally, I use an endmill with the diameter of the corners (of the pocket; assuming the radius is not too small). Then I simply mill a rectangle about

That doesn't matter and I don't understand what's complicated there.

Nick

Wayne wrote in news: snipped-for-privacy@wsd1.gateway.2wire.net:

Wayne, Make sure the EM you are using is center cutting. You can tell by looking at the end, depending on the number of flutes, at least 1 will be sharpened across the center of the end mill. A non-center cutting EM will not have a flute across the centerline. You should be able to plunge straight in with the EM if it's center cutting. As someone else noted, use a 3 flute, and keep the chips out of the cut.

On Nov 27, 4:07 pm, Wayne wrote: not easy as your cutting 3 sides at the same time.

Can't imagine why you'd consider drilling. A center cutting endmill cuts very well on its end.

John Martin

I forgot I bought a roughing cutter years back when I thought I'd be doing a rather large pocket. I gave it a try and it worked quite well.

Wayne D.

For this job the radius isn't important. On other jobs as small as possible.

When I did this before with a 3/16 end mill I got a lot of chatter.

So that's how you tell if they center cutting.

Wayne D.

James Harvey (Machine Shop Trade Secrets) cautions against it; he apparently had an endmill try to climb a pocket wall or something like that. FWIW, I do not see any way to follow his resulting advice (which AFAICT is "don't do it"), so I simply proceed with caution.

I find that the up-milling side of any slot takes a little bit of a beating, at least with my machine. I compensate by leaving a little extra material for cleanup.

Bill

Wayne wrote in news: snipped-for-privacy@wsd1.gateway.2wire.net:

Wayne, Wasn't trying for the smart-ass of the month award. I used to teach machining at the local adult vo-tech and you would be suprised at the number of people who had been cutting metal for many years who didn't know the difference between the two types. I plunge mill aluminum extrusions on almost a daily basis, either for anchor fasteners or cbores for bolt heads, etc. You do have to watch your feed though, too much and the em will start walking, as there isn't much flute available at the center to let the chips out.

Feed rate, rpm, depth of cut, spindle, lubrication. Can all be fixed and chatter doesn't matter that much when you are roughening. Simply don't try to mill to size with the very first pass. So your end mill always has to be smaller than the smallest dimension of the pocket. Except you have a rigid mill.

Nick

Anthony, I took it as you intended. The only way I previously knew my end mills were center cutting was that was what I bought. So I learned something.

Wayne D.

Note, BTW, that while center-cutting end mills will plunge, they are not very good at it -- just much better than non center-cutting end mills.

So -- if you have room, the best way down is to ramp down -- feed sideways somewhat faster than you plunge. This clears the chips better. And it is the way that CNC machines normally cut pockets.

Enjoy, DoN.