Stonger endmills? (Im breaking these easily)

[cnczoner]

Hi all,

Using 1/8" Enco 2-flute, 3/8" LOC, 3/8" shank, uncoated HSS endmills on 6061-T6. Slotting at 1500rpm, 0.05" doc, 5ipm, the endmills are breaking. I'm also lubing with ATF. So I slowed down the feedrate to 1.5 ipm and that worked, but a simple part took 1.5 hrs!

I hear of people machining much faster than this, so is this related to my 1500rpm spindle? Should I use less DOC and faster feed? Is there perhaps a different type of endmill I should be using? Most other endmills talk about harder cutting edges, but I'm not sure if Carbide or other materials are actually stronger so that I can cut faster...???

Cheers,
-Neil.

[Belding]

For effecient machining with a 1/8" end mill in aluminum you want to be above 5000 rpm. Ideally in the 10,000 rpm range. Thats what my speed an feed calculator tells me.

zac

[cnczoner]

So a higher spindle speed will allow me to use a higher feedrate without breaking the bit? I could easily make a mount for a dremel rotary tool on my spindle head, but I may run out of hp... I need to lookup how my hp a dremel tool has.

Does your calculator give you hp required? If so, how much hp is required to run 1 1/8" endmill at say 10,000 rpm and 20ipm, with a 0.05" doc? Or perhaps I should ask how fast can I feed with a dremel at 10,000 rpm and 0.05" doc?

Thanks,
-Neil.

[Belding]

What kind of machine do you have? You may want to consider a spindle speed increaser. I don't think dremels have a very stable spindle..... You could also try to find a high speed spindle. Like this one http://www.homeshopcnc.com/page7.html

zac

[cnczoner]

This is my mill. The motor does 1800rpm (1.5hp), but after gearing it will do 1500rpm max. Last year I was planning to swap the motor to a 3600 rpm version, but the motor is some not-so-common frame size, and getting a higher-rpm version would only be from a few sources with a high price tag (IIRC ~$400-$600). I could make an adapter plate and adapter bushing to use a more common motor (like Nema 56), but I also want to keep it 110V (as I'm running this in a detached garage), and I wanted to get a motor which would let me use a VFD, but that would probably mean getting a 110V-in, 220V-out VFD, then using a 220V motor. A simple motor swap became a bit involved, so I put it on hold for now.

If I found the correct-sized motor right now, which allowed me to use it on 110V and 220V, I'd jump on it, but for now I've got to work with what I have. BTW, I'm not doing anything production, but I still think 1.5ipm is ridiculously slow.

Cheers,
-Neil.

[mrainey]

Maybe you could try an end mill with a shorter length of cut (stub end mill).

Also consider a four-flute. With only .050 depth of cut, you might get away with the chips not packing in the flutes - air blast or coolant will help.

[cnczoner]

Currently using a 3/8" LOC, which is quite short already, and I'm cutting to a total depth of just over 0.25". Also, squirting on ATF and vacuuming periodically. Interesting thought on the 4-flute -- I have a set of 4-flutes here, but need to check if it goes down to 1/8".

But still wondering if different types of endmills might allow me to get higher feedrates?

Cheers,
-Neil.

[mrainey]

But still wondering if different types of endmills might allow me to get higher feedrates?

That's the benefit of a stub end mill. I didn't realize that you were going .250 total depth. The stubbie would work with one or two .050 passes, but not five.

[mrainey]

Maybe you could get all but the last pass with the stronger stub end mill - LOC on these is 3/16


http://www.richardsmicrotool.com/page29.htm

[mactec54]

Hi cnczoner
Is this cnc or are you turning the handles, by the link it is a manual machine ATF is not that good for cutting fluid WD 40 would be much better in your case & cheaper how are
you holding the endmill if you are using a drill chuck that is not very good as it does not hold the end mill rigid enough you need a soild or collet holder to hold the cutter.

[cnczoner]

The mill is CNC'ed. I recently switched from WD-40 to ATF after some recommendations. So far I think I get a cleaner cut with ATF, but I haven't run comparisons to see which way is making the endmills hotter. I really need to get a cooling system, but I'm still evaluating compressor-less systems (since I'm doing this in a garage in an apartment complex and need to be as quiet as possible), plus I need to figure out some type of enclosure.

The endmill is held in R8 collets now.

Cheers,
-Neil.

[cnczoner]

I found this interesting writeup, and it seems that I should get more feed-rate from solid-carbide, smaller LOC, and a few more flutes. I have an Enco order going out shortly, so I'll add in some endmills that fit these parameters.

Cheers,
-Neil.