I'm going to run a little counter to some of the folks here. I think it's how you're using your mill that is producing the issue. There is simply no way that even a light machine should be wearing out end mills like this IF IT IS NOT CHATTERING and provided you're not trying to run too light a cut with a lot of rubbing. Bad chatter will chip away the cutting edges and then heat from the friction does the rest. Trying to remove too much metal at one pass and using a very light cut can produce a case of too much rubbing and again wear and heat does the rest and takes off the edge. The cutter needs to cut to stay in the game. You can actually go with too light a feed and ruin a perfectly good cutter due to wanting to try for too big a bite.
It'll cost you ONE more "cheap" end mill to test all this out.
First off the cheapest of the cheap cutters too often come with poor grinding on the ends. So right off the bat ensure that whatever cutter you have has the proper relief angles and that it's the same side to side. I've had pretty good luck with the Asian endmills sold by KBC for around $7 a pop. Some are TiN coated and some are plain HSS. The TiN cutters seem to be the ones that most often come with bad grinding. So now I tend to buy the plain ones. These have worked nicely on both steel and aluminium projects.
Next is the machine setup.
For a bigger project such as this which is going to push the mill to its limits you need to tighten up the gib strips so there's a bit of drag in the table wheels. it's not enough to just remove the play, you need a little preload on the gibs so that as the machine flexes when cutting it does not open up the dovetail engagement and allow for any movement and thus chatter. And hopefully I don't need to tell you to lock up any axes that you are not using. Locking the travels greatly stiffens the machine. Only the axis being used should be unlocked during any cuts. Same with the head itself. Lock that spindle travel unless doing a plunge cut with it. Sorry if this is overly basic but I don't know where your skill level is other than you said you don't do much in your opening post. So excuse me if I wax poetic on the basics too much here and further on.
Next is the amount of overhang in the cutter holder. It's even more critical in a smaller and lighter machine that the cutter be located as close as possible to the end bearing of the spindle. If you're using a cutter holder that extends out such as this one shown just below then ditch them and go with something that sits in tight to the nose of the spindle as shown in the second or third pictures. You might even switch over to using collets to grip the cutter shanks. A small hobby mill won't need any more holding power than that since you won't be removing all that much metal at one go.
Getting the end mill as close to the nose bearing as practical is probably one of the biggest reducers of chatter to be had on a small machine. The end of the milling cutter is already sticking way out and adding a projecting holder just multiplies the issue. I can't stress this one factor enough. If it ain't stiff and short it is GOING to chatter on a lighter machine. I know this will be somewhat limited by the sort of machine you have and what the spindle taper is. And if you come back and tell us that you're putting your end mills into a drill chuck I'm going to slap you backside of the forehead with a base ball bat ! ! ! ! NEVER DO THAT! ! ! ! There isn't a drill chuck around which, other than by the purest of luck, will be centered enough. And never mind the flex in the arbor. At least there's nothing a home shop guy is going to be willing to pay for.
This one is a serious "no no". In fact with this one being an MT2 holder it's pretty much a waste of metal for milling anything-
These are more like what you want. Hopefully your mill uses an R-8 or MT3 mounting so you can use these short ended holders-
Next up is cutter size. The leverage from a larger diameter cutter is going to seriously flex the machine which opens up the risk of bad chatter. So you're better off using a smaller size for roughing work and live with some patience in wasting out the metal. The stiffness of the machine will only support so much metal removal per minute. And using a cutter which is smaller, within reason, will work with the machine in a more balanced manner. On a small and light table top rig this means that you may only be able to run a 1/2" or if it's a very light machine you might be limited to only a 3/8" size. The goal is to run at a size where you can push hard enough to cut a reasonable chip thickness while getting a resonable material removal.
Feed rate. The cutter needs to be removing a reasonable thickness of chip short of inducing chatter. This loads down the machine which will flex and produce chatter when it springs around. So the idea is that a larger cutter removing a reasonable chip might only be able to cut a slotting operation at a .050 depth of cut. But a smaller diameter cutter might get away with running a .150 depth of slot per pass.
Hopefully it is becoming clear by now that you need to balance the cutter's diameter along with the depth of cut and the need for the cutter to be producing actual chips instead of dust. And you need to select a cutter diameter that allows the machine to cut in this way and remove a usable amount of metal without chattering. A cutter that is trying to remove too much so that it's just rubbing and producing dust is going to wear out. You need to see actual chips coming out of the cut. They'll be SMALL chips on a small machine but they need to be chips. Otherwise you're going to take off the edges and the cutter will soon be ruined.
This has to be all tempered with the nature of the cut. If you're using an extended cutter to reach down deeply then you'll need to limit the depth of cut so you don't get any chatter.
Speed can also be a killer when it comes to chatter. Any machine will chatter if you hit the resonant frequency of the setup. It's not a crime to slow down the cutter. And if slowing it down allows you to slice away a better chip this is going to help both the cutter's lifespan as well as the surface finish. Again you just need more patience. The speeds given in feed rate and cutter speed tables are MAXIMUMS that are aimed at production work where they want to balance tool life against production rate. As hobbyists we not only can but WANT to run at significantly slower speeds than the tables show. The machine also has a say in this since any lack of rigidity that results in chatter is a sign that we're trying to be more greedy than what the machine will support. The "scream" you hear in response is the machine telling you that it's not happy.
I realize that some allowance is needed for small diameter cutters that need higher speeds to reach a proper SFPM and to avoid too strong a cut that can result in snapping them. But that's OK since I've yet to see a hobby machine of any size that can approach the speed in the table for a 3/16 diameter cutter. But for the bigger sizes consider the option of running down at closer to 1/2 or so if what the tables say for diameter to RPM for each material. The cutters will live longer and you'll get less chatter in the light machine you have.
Of course all the previous hints about climb vs conventional milling still apply.
Some sort of fluid on the cutter will prevent any gumming up. Back in the early 90's I bought a gallon of one of the then new miracle fluids that mixes at around 30:1 water to fluid. I use it fairly generously but shy of flooding the machine from a little squirt bottle to keep the work wet and cutter free of gumming on both my lathe and mill. It works like a treat on most metals in the drill press as well. Superb stuff. This one isn't available by name anymore and I'm not seeing a lot of information other than at Enco's web site they seem to have the same stuff sold as "Wesco M-16 Mist Coolant" which lists a 4oz/gallon of water mix ratio. That sounds a lot like the same stuff I've got. The colour in the picture looks similar too. But any coolant which mixes up clear or lightly coloured at around the same mix ratio will likely be the same thing.
That's about it for what I've got. As you can see it's not any one thing. You need to trim up and balance all the factors to where the machine will cut well so you get a decent end mill life.
