cutter breakage

[how'sitwork?]

I recall reading somewhere recently that too slow a speed leads to cutter breakage. Having just boobed and broken ( snapped) a 3/4 by 3 in long end mill ( I engaged the auto up feed by accident when milling some aluminium- took a BIG BITE THEN SNAPPED before I realized what I had done ).
Can someone Shed any light on this? Tom ???

I can follow why too slow a feed might lead to heat and blunting of cutter but too slow a speed leading to snapping?

Moral of story- don't rush especially when engaging auto feed. My mill can autofeed the table up as well as cross feed.

[Baron]

Ouch ! Expensive mistake.

[DaveH]

Well that is a sad thing to happen.

The spinning cutter(s) have to be able to clear (cut) the material away.

If the cutter is not spinning (ie stationary) with a depth of cut and the work piece is fed into the cutter something is going to break. Which is why your cutter broke the spindle speed wasn't fast enough for the the feed.

So spindle speed is important with respect to the feed.

If it is a HSS cutter going too fast will cause heat and blunt the cutter.

Still sorry your cutter broke.
 
DaveH

[Highpower]

(02-15-2015, 04:37 PM)how Wrote: I can follow why too slow a feed might lead to  heat and blunting of cutter but too slow a speed leading to snapping?

Moral of story- don't rush especially when engaging auto feed. My mill can autofeed the table up as well as cross feed.

(02-15-2015, 05:28 PM)DaveH Wrote: If the cutter is not spinning (ie stationary) with a depth of cut and the work piece is fed into the cutter something is going to break. Which is why your cutter broke the spindle speed wasn't fast enough for the the feed.

So spindle speed is important with respect to the feed.


 
DaveH

As is the spindle direction. 

Don't rush indeed, and don't ask me how I know.... 

[PixMan]

Chip load per tooth.

Too high = excess load and the cutter "hogs in" and breaks
Too low = rub the sharp edge dull

[Sunset Machine]

That's it in a nutshell - chip load. My mill has the table feed driven by the spindle; going at too slow of an RPM does no harm at all, other than waste time.

[how'sitwork?]

OK guys, thanks for the explanation. Didn't expect Aluminium to break HSS but it did try to take a big bite!

Live and learn.

Willie - I feel your pain!

[Highpower]

(02-16-2015, 01:55 PM)how Wrote: Willie -  I feel your pain!

And I feel yours. But we'll both remember in the future eh?

[Vinny]

I did that once with what I thought was my last 1/8" endmill. I was lining something up and forgot that I had the table up for the next cut. The mill wasn't even on. When I heard that "snap" many 3, 4, 5 and 7 letter words immediately followed. So I ordered up 4 more and the nite before they were delivered I thought to look in this box of misc endmills. Yep, six more in there. Grrr. I broke the second one with too fast a feed for the spindle speed just like How did. I was only milling plastic!

[TomG]

Too high a chip load per tooth is what breaks end mills, but ensuring that the end mill is running at the proper rpm GREATLY reduces the chance of that happening. A 3/4" end mill cutting aluminum should be running at over 2000 rpm. Anything less is asking for trouble. You'll still need to make sure the chips clear out, so coolant may be appropriate as well.

Tom