I have a precision Matthews which I recently purchased second hand.  I started with 1/8 end mills and have broken very few.  I have only purchased carbide, which will stay sharper longer if you treat them right.  I have no coolant system, so the key here is to follow the manufactures specs as closely as possible.  ALSO, go SLOW at first and LISTEN to your machine.  If you hear chatter, this is a warning sign or stress on your end mill and your work piece.  You need to slow down and determine what is causing this (poor clamping).  Sometimes chatter is unavoidable, given the limits of your machine, fixtures, etc.  If this is the case, go slow and be patient.

I have found good values on carbide end mills on Amazon and Ebay.  For my limited usage, I am pleased with the value.

Speeds and feeds. RPM is only a part of it.  tool load , machine stiffness/rigidity, feed rate, material, all are a part of not wrecking cutters. 

In steel on my Bridgeport  for an 1/8 HSS cutting (2 flute) I could run 2000-2500 rpm or so, with no oil and brushing chips out constantly, (or and air blast if i ever get it set up) I would do 0.015 or so a pass with a reasonable feed rate.  when center cutting a slot direction of cut doesn't matter, but if i need to open the slot (once its cut through) I would only conventionally mill that is the back of the slot cutting left to right  front of the slot right to left. 

With out seeing what your doing i would hazard a guess that the oil is trapping chips in the cut and that is breaking then or your depth or cut and or feed rate is to high for the rpm. 

MP

Jason Cohenour and  Matthew Parkinson, Thank you! I had videos, but when it started to not work out I deleted them, Maybe I will try some better bits, slow my rate (both depth and speed), not put so much oil in there, and blow out the chips with compressed air?

I'm no machinist by any stretch of the imagination, but let's start with what material you are cutting.

As Matthew pointed out:

Posted by: Matthew Parkinson

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RPM is only a part of it.  tool load , machine stiffness/rigidity, feed rate, material, all are a part of not wrecking cutters.

Then we can talk about depth of cut and feed rate (inverse proportion typically) and RPM on type of cutter.  Personally, I find carbide cutters are brittle and will break more easily under stress than HSS or cobalt cutters. Most of what I know I have learned by trial and error untill I got a better sense of what works and what doesn't.

Generally speaking, when I am slotting a guard for example, I will choose a diameter cutter much smaller than what I want to end up with for width of the slot. Then I will shave the sides of the slot down untill I have the desired width. If I want the slot to finish out at .200", I will cut a slot at .150 or .180 and widen it out untill it's .200

A guy walks into the doctor's office, raises his arm over his head and says, "Doc, it hurts when I do that."

The Doctor says, "Then don't do that."

Whatever you did to break end mills - don't do that any more.

I've had/have three vertical mills. The current large one has been set on the same speed for 10 years. Only rarely do I change a belt to slow it down if I'm drilling something very large. But for square stock, milling handle material blocks, slotting guards material, fabricating shop gadgets, etc., I use the one speed.

I adjust the process of material removal by either slowing down my power feed, or slow down my hand cranking, or taking a smaller bite.

Both of my smaller ones have variable speed and are high torque. I adjust speed according to the material.

We take easy vertical plunges, or we mill by side cutting. We mill man-made handle materials, stabilized woods, softer hardware like machinable stainless and guard shoulders on tools steels. Each of these is going to end up with broken end mills until you have some time behind you standing in front of that machine cussing at yourself.

Back to the opening joke - whatever you just did - don't do that any more.

Karl B Andersen, I had a good chuckle reading that. Yes you are right, usually if something doesn't go well its a good sign that it wont in the future. There is enough new things to learn with the mill, I am doing a lot of trial and error and trying to figure any facts out. 

Joshua C States - I had some videos taken of what I was doing, and then they got corrupted in odd sequence so I couldn't show everything I was doing unfortunately. If I break down the description of the problem, I was trying to cut a cross shape into a hardened hammer head. I am using R8 3/4 collets, and I was using a 3/8" end mill. I was trying to cut down, and started with .002" which I could hardly see, then I decided to crank down the dial up to .005". That seemed to be way more than I bargained for. The mill started to rattle. Now I was in a tight spot where I am not sure that the small gauge on the front of the machine is working at all. It appears as though on the grizzly mill I am supposed to lock my normal quill down with the right side nob, and then use the "micro" nob on the front, but it doesn't seem to work consistently. so I usually end up setting 5 thousands on the main quill and lock the head in place then run horizontally in milling.