Determining cause of cutter failure

[nickswimsfast]

I "broke" a 1/2" center cutting niagara end mill (4 flute) on some 1018 rusty steel after surfacing 3 sides of a block. From what I can tell the corners of the flutes appeared to have sheared off. During the "break" it looked like the table jumped away from the part due. Admittedly, I didn't lock the axis on that operation. The shop guy says it failed because we were trying to machine poor quality metal from the scrap yard that has varied hardness. Although, I successfully surfaced 3 faces of the scrap block using cutter speeds and feeds in defined in ME consultant.

2330 rpm
4 ipm
.02-.03 depth of cut
used only the side of the cutter - (about 1/3 of the tool's diameter)

Which circumstance do you think caused the tool to break? Also, is it necessary to lock axis for every milling operation (such as the y and z?)

I was under the impression that locking is good practice - not required. I'm used to running on decent quality bridgeports, not the 1930's Gorton mill that this tool break occurred on.

----------
Also a second question about purchasing end-mills. I was reading http://www.cnczone.com/forums/showthread.php?t=9207

I couldn't make up my mind from the varied opinions. Given that I am a budget limited college student, I was trying to choose according to my funding. I can see myself breaking more end-mills in the future as I learn from mistakes in selecting cutting parameters. Do you believe I can get by with these imports, or should i grit my teeth and continue to get 25$ end-mill's?

Thanks!

[iamstink2k]

it looks like you are climb cutting, it will suck the table in towards the cutter and make it break. you need to make conventional cuts.

also the rpms seem pretty high.

[nickswimsfast]

I'm afraid it was definitely conventional milling. I would reset to the correct side each time.

It was cutting beautifully, and sounded "right", it was making a very smooth surface finish. Z was locked, y was not during the break, and x was on autofeed. I suppose that is a bit high of a speed.

[ctate2000]

Varied hardness is hogwash IMHO. Niagara cutters are very good tools but 2300 rpm for HSS is too fast. Try 500 rpm, kill the power feed and crank it by hand so that you can feel the tool. Having your hand on the control is very important and can tell you when something is wrong. I have seen power feed units jump when they were in need of repair.

[nickswimsfast]

Originally Posted by ctate2000 Varied hardness is hogwash IMHO. Niagara cutters are very good tools but 2300 rpm for HSS is too fast. Try 500 rpm, kill the power feed and crank it by hand so that you can feel the tool. Having your hand on the control is very important and can tell you when something is wrong. I have seen power feed units jump when they were in need of repair.

Thanks for the tips, I tend to agree with you about the hardness thing. In the future i'll try lower rpm's (400-500), the power feed was a bit "buggy" and would easily change direction if the direction handle was barely bumped.

I take it locking the ways is not necessary for average milling then? Thanks again.

[70cyclone]

your RPM was too high...no coolant I assume...did you have the tool tight enough(no slipping)
you should always lock the axis
the problem with used materials is you don't always know what you really have:
has it been hardened
has it been welded
what grade is it really
what kind of stress was it under in its previous aplication
Gorton machines are easily as good as or better than bridgeports