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Newb to machining looking for some advice on milling aluminum

Mar 15, 2023
Hello all,
I'm a bit of a newb when it comes to machining. I've done it a little bit, with wood, but most only a couple of times have done some very minor machining in aluminum to slot out some holes or something. I'm really struggling with my current project and looking for some advice.

First off, my machine. This is a machine that I built myself. Building stuff is one of the things I enjoy doing so I built this one after using a chinese 6040 for some small projects. It's got a 1.5 Kw spindle (water cooled, 24k rpm max) on it, and it has descent rigidity for a hobbyist machine. It's kind of based on the OpenBuilds Ox design, with some personal modifications to increase rigidity. I have a coolant sprayer that I have an air compressor hooked to so that it sprays coolant directly at the bit / cut and blows chips away at the same time.

I'm trying to mill some plates out of some 6061 aluminum. All the bits I'm using are 1/8th inch square end mill bits.

At first I was using some 4 flute AlTiBN coated carbide bits. I read that this was bad for aluminum after I completely gunked up and broke 2 of those. So, I ordered some 3 flute carbide uncoated aluminum specific bits. I've already broken two of these as well, but they don't appear to be gunking up like the first set of bits. The last break it just kind of looked like it wasn't cutting fast enough and got bogged down and snapped.

On the most recent run, I was doing 10k RPM at 1000 mm/min feed rate. I was doing .5mm depth of cut on this last one, and the break happened on the first pass. One mistake I made on the feeds and speeds calculator I was using this time is I didn't realize it had a max rpm set to 10k. When I changed it to 24k, it says to run at 24k rpm. But should I really be running that fast? A lot of other things I read seem to suggest much slower RPMs. It also says at 24k RPM to be cutting at 2700 mm/min. That seems really fast considering I'm having a problem snapping bits at 1000 mm/min lol.

I think I'm getting enough coolant, cause the (piece of) bit, and the aluminum itself is cool to the touch even immediately after it breaks.

So, does anyone have any advice, maybe teach this newbie something about what I might be doing wrong here? I'm trying to explore settings and learn, but 4 bits in 2 days, figured I'd ask for some advice before burning some more money haha. Thanks
You should check out other forums that are geared to the home-shop machinist. This forum's really geared toward professionals who generally work on much bigger machines, and the advise we have is oriented that way too.

Good luck, I'm sure you can find someone with relevant information to help.
Aluminum loves coolant; run flood coolant with a nice, high pressure and high flow rate to get the chips out and lubricate the cut. You can cut aluminum with "MQL" (minimum quantity lubrication) or simply spraying some WD-40 on it, but at much reduced parameters. If you can't run coolant, you want aluminum specific cutters with an aluminum specific coating, like Zirconium Nitride, and again, reduced parameters.
I realize this is an old post, but hopefully replies help you out. You don’t know what chatter is yet - I suggest looking up “high speed camera milling chatter” or something like that. The guy on the Breaking Taps account on YouTube has some good video that will teach you more in 10 minutes than all the charts you’ve looked at so far.
What type of torque are you pushing? While RPM's are nice if the torque is too low to begin with the higher the RPM's means even less torque. Try to lower your feeds and speeds , plenty of coolant and if it breaks again look at where it breaks.