Well, I’m just gonna assume it’s destroyed - through excess heat and chip welding.
It was my first time testing a down cut end mill. I did a light surface pass and it did really well. Then I tried some 3mm pockets and it was a major fail.
Tool is a 2 flute 1/8" down cut end mill.
My settings were for a 2 flute 1/8" regular end mill. I tried to throttle back the speed while it was cutting but it was too late. Off to the tool graveyard.
Downcut pockets are the 2 on the far left. Rest are upcut.
Down cut bits are great for shearing the top surface edge of fibrous materials, to leave a clean edge, not so much for solid materials, as it forces the chips down into the material your cutting.
My trick: I only use ZrN coated cutters in Aluminum…they don’t allow the metal to stick to the cutter.
You may be able to salvage the tool by cleaning it in lye (easily sourced as drain clog opener at your grocery store — just check the label).
FWIW, I work in a machine shop were we machine aluminum and stainless steel to tolerances of ±.0002. We NEVER use downcut tools for anything, ever. Also, keep in mind that metals are usually climb cut (not conventional) with some rare exceptions having to do with side surface finish quality. If you want to keep experimenting, try climb milling. For quality finish we also use 3-5 flute finishing tools. Roughing and finishing tools are usually made for those specific functions.
As others pointed down cut is not a good idea for alum. Many people here on the forum recommend single flute O bits.
So for downcut endmills I only want to use them for finishing passes if at all right?
For example:
Upcut will pocket out a depth, use downcut to do a finishing pass to clean up the upper edge?
Yes, if you only use roughing passes with an upcut which have a roughing clearance greater than the defect which they are likely to cause.
I use downcut on wood almost exclusively.
The only uses I make for an upcut in wood is if there is a roughing pass as described above (not very often), or if there are a bunch of tool changes, and if I can set up a final pocketing pass which cuts only the bottom of a pocket which was standing free as an island (usually only a pocket which had a surrounding contour toolpath with a ball-nosed tool to create a rounded edge):
One of the reasons we wouldn’t use down cut tools in metal even for finishing is simply because all edges get a chamfer or edge break, so imperfections left by a slightly worn up cut tool are not an issue. Not doing that leaves sharp edges in metal which will cut skin. Second, of course is lack of chip evacuation, which is what you experienced. Feeds and speed are also important for a good finish and tool life.
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