This doesn't look right

The failure there will be fatigue, probably chatter had a hand in that. As said, a proper setup is well worth the investment. An ER32 or ER25 collect set - depending on the size of your machine as the cutters you tend to use - will be well worth investing in and give you the most flexibility for what you spend. Easily one of the best investments I made for my milling work. You'll get better life out of your milling cutters with lower runout too
 
Looking at the picture of the fracture, up and to the right, by the shiny glint. Right there, some tiny ding stress raiser began a crack, ending up maybe a couple of mm deep. It was flexing sideways at some high revs, the vibration enough to beat the crack into somewhat smoother surface, and the remaining metal getting cycled into fatigue.

Eventually, the crack propagated deeper, up to the little "shelf". It had no chance to go smooth. The remaining area was now suddenly and catastrophically far beyond it's tensile strength, and the matt surface is of the crystalline structure having been directly torn apart.

At near exactly perpendicular to the crack, to the left, is the deeper line of material that looks as if it tipped out extremely rapidly. Yes, we all have make do at times. There but for.. (It could have been me)! Maybe the defect was there from the beginning, or maybe smaller cuts would have let it survive, I don't know.

I will not try to be wise after the event. 100% hindsight is just not appropriate. I look at it, and all the good advice from the HM folk, and I know how much I may have pushed my luck in the past in much the same way.
 
I put this kind of thing down to "I know better now". We've all been there, the learning is part of the fun :) That chuck must have been a really good fit, they usually just fall off the taper when side loaded and pulled downwards by an end mill (from experience)!
 
Inferno said:
You gentlemen are correct.
Sometimes we work with what we have.

The good news is the chuck is fine. It's the cheap POS adapter that broke.

I guess now it's a good time to shop for an (economical) milling chuck

View attachment 322939
Click to expand...
"It's a poor workman that blames his tools"
 
well this is a new "bad result" of milling with a drill chuck, normally the end mill just decides to go into low earth orbit.

:)

Time to look for a cheep set of morse collets on ebay ;)

ER milling chucks are cheep, collets vary in price, a basic set should be fine for milling.
 
Not to pick on you @Inferno, I understand that we all do the best we can with the tools we have.
I just believe that means we should be even more aware of the details below.
Basically if you have the huge rigid machine, all the best new sharp tools, and years of experience, etc. that is when your speeds and feeds can float around a little with little or no consequences.
When you are pushing the envelope of the machine, the cutter, and your experience that's when you need to pay close attention to the details.

There's a few things I don't understand......

First what does this mean:
Inferno said:
Every time I heard the bit chatter a little, I would run the mill chuck up a smidge. That kept the chatter down to nothing.
Click to expand...

Do you mean that when you had chatter, that you:
a) decreased the depth of cut by pulling the end-mill up out of the cut some, or
b) tighten the chuck onto the end-mill with the chuck key, or
c) tighten the draw-bar holding that MT-3 taper in.

Second, were you indeed using a draw bar?
If not, then perhaps the MT-3 taper came apart due to an aggressive cut and the chatter.
If the tool dropped down that could snap it real quick.

Third, cutting speed. You really do need to have some concept of this to make your end-mills last longer.
Even just calculating a starting point and then stepping the RPM up or down based on the initial cuts.

Assuming a high-speed steel end-mill, for Aluminum, I'd want to be about 110 sfpm.
For a 17mm end-mill (call it 3/4 inch) that would mean around 550 RPM.
I calculate conservatively for my worn, light hobby machines.

This online calculator: https://littlemachineshop.com/mobile/speeds_feeds.php
suggests 200 sfpm and therefore gives 1020 rpm spindle speed.
Perhaps your top-end speed was too high?

Last, what was your depth of cut?
If too deep it can mean large sideways forces on the end-mill, chuck and arbour.

I am very glad you weren't hurt!

-brino

EDIT: one more thing..... for hogging Aluminum getting the chips out of the way is crucial.
A two flute end-mill is preferable to a 4-flute, and often end-mills with a "faster" flute spiral are used to move chips up and out.
 
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The good news is the chuck is fine. It's the cheap POS adapter that broke.
[/QUOTE]

Somehow I think that's doubtful.
 
Some good advice above.

I see a few problems here.
Drill chucks are not end mill holders, they are not designed to take radial load
Morse tapers can not be used for milling without a drawbar
A 17mm end mill is way too big for your machine, about 8mm is the max. You have seen my machine and the largest end mill I normally run is 1/2'' (12mm) for any serious material removal.

There are Morse taper endmill holders available, but can only be used with a drawbar. Any milling operation requires that the tool holder be secured with a drawbar or other securing system designed for milling operations.
 
Well, that was a lot to read with morning eyes.

So, yes, I was using a drawbar morse taper. That much I know better than to even try.
Interesting comment about using a 2 flute vs a 4 flute for hogging. I don't think a 2 flute would have lasted as long but since I didn't try, I don't know for sure.
I was using a HSS end mill. If I could afford a set of better ones, I'd buy a set of better ones. Right now, for a lot of tooling, I buy what I need when I need it. With the exception of drill bits. I got a killer deal on a few hundred new industrial drill bits. Can't pass up 100lbs of drill bits for $50. (going out of business auction).
The cuts I was making were no more than .020".
When I said I'd back off when chattering happened, I was decreasing the depth of cut.
I ordered a set of ER 32 and ER 25 collets and adapters. The right tools will minimize mistakes later.
Good advice on the size of the mill bits. 10mm seems small. But, at 10mm I probably wouldn't have broken tools. Advice noted.
The metallurgical report made my eyes spin but I see what you were saying, I think.
The drill chuck may be fubar. I won't know until I put it back on the machine and that's not going to be for a while. I'd need another adapter and that's not a priority because I have more drill chucks. When I do put it on I will check it the way I was taught in school. Put the smallest bit in it and see if it dances. The smallest bit also can help to see if a jaw is bent. If there's a better way, I'd like to know.
If I were guessing, I'd say the drill speed was about 1200rpm. I might do the math on it later to be sure.


I might have missed something along the way. I'll post a picture of the part I'm making when I'm done with it. I could post a picture of the damaged part now but, well, I can tell that most everyone is a bit like me when it comes to things like this. Even though there's a lot of friendly advice, there's a tiny bit of ridicule included. That's OK, I have a think skin. LOL

I did a small investigation of what happened. Oddly, despite the obvious "wrong tool for the job", that was a contributing factor more than why the catastrophe happened. Well, to be fair, it was probably also the cause but the actual BREAK was something more. When the chatter happened, the depth I was milling at was about 7/8". When the chatter pushed the bit just enough over, 7/8" of mill bit caught the edge of the piece and then it grabbed. It grabbed enough to shift the head of the mill attachment (cheap design swivel head of the mill part) and then the head moved which grabbed more and there was something that was going to give. That .625 diameter section of the morse adapter was the weakest point. It snapped. There was just too much momentum going in the spindle and pulleys for the machine to stall.

There's a mod to be done to make the mill head more secure and I am looking into that very soon.

When I get a bigger work area, I will probably get a true mill. For now, I just need more patience and better tooling.
 
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