View Full Version : I knew better but did it anyway.

04-22-2018, 10:59 PM
Milling some 5/16 slots in aluminum and grabbed the first 5/16 end mill in the pile, four flute.
Set it up and dialed in the power feed. turned my back for a few until I heard the wrong sound coming from the mill.
Smoking aluminum, gummed up mill, Looked like the Titanic shoving ice bergs around. The slot resembles Yosemite Valley after a glacier passed.
New work piece and a two flute mill and I am back in business.

Making slotted brackets to mount a dro.

To my amazement every end mill that I have tried, so far, survived the fire and cuts just fine.
I do have to polish the fire scale from the shafts in order to fit into the collets.

04-22-2018, 11:20 PM
Guilty! I've done that more than once. Drop the EM in lye... it will cut fine when the aluminum is dissolved. Happens even on 2 flute if you push them and don't lube enough.

J Tiers
04-23-2018, 01:04 AM
The end mills are HSS. That retains hardness at red heat. It's actually hard to anneal HSS, there is a special way, but just heating it and letting it cool does not anneal it. So not unexpected, I guess.

Still, even knowing that, I don't know that I would expect them to be OK, even so.

BTW, it may take a fair bit of lye to dissolve off the aluminum... I tried to do it once, and had to keep adding more.

old mart
04-23-2018, 08:15 AM
For the rest of the world, lye is sodium hydroxide, NaOH.

04-23-2018, 08:30 AM
I found running them over some steel stock will clear the flutes too. Not sure if it works every time.

Its how I would clear burr bits when porting aluminum.