What idiotic thing did I do now?

[turbo2ltr]

I need to cut three 1.17" holes in some sheet metal. I figured I'd run a test on this piece of aluminum.

Besides battling some weirdness with my machine that causes it to do wacky things, I was amazed to see an end mill *melt* through this aluminum.

The feed is set to 30ipm, but I have a knob I can turn to vary it from 10% to 200%. It didnt make a difference. Sipindle was at 4000. .25 2 flute end mill.

Was it just too much spindle without enough feed? I have no idea what alloy the sheet is. Whatever it is, I guess it's pretty soft.

[dertsap]

did you use any coolant or lube ?

[turbo2ltr]

No, been doing everything dry up to this point. Though I just have to add coolant as it's all set up to go.

[Geof]

That looks a bit like a zero temper piece of aluminum alloy. Can you bend it easily without any cracking?

[dertsap]

you'll definitely need some coolant or oil for that

[tobyaxis]

As already mentioned try using coolant or oil even if you have to apply with an acid brush. Just don't get the brush caught in the drill.

My suggestion is to use a small drill around 3/16 dia. Drill every location. Then use a 1/4 dia End Mill to Spiral Interpolate the necessary diameter. Leave .003 on the side for a finish pass and that should do the trick.

Feeds and Speeds

For the Drill 2500-RPM@7.5-IPM
For the End Mill (2 Flute) 3500-RPM@14-IPM

Try to get Tin or ZrN Coated cutting tools.

Good Luck

[turbo2ltr]

Originally Posted by Geof That looks a bit like a zero temper piece of aluminum alloy. Can you bend it easily without any cracking?

Hmm, like this?

[tobyaxis]

Hmmm....That is a bit too soft. You may want to try using a Fixture Plate to clamp the sheet metal down, then the operations described above.

[Geof]

Originally Posted by turbo2ltr Hmm, like this?...

I guess that does qualify as "bend easy without cracking".

You really did not do anything idiotic, actually you were doing the correct thing in trying a test cut on some scrap, it just turns out the scrap was not suitable.

The bend test works quite well for any aluminum alloy. For bar stock just cut a 1/16" piece off with a bandsaw and try bending it in a vise. If it breaks before it gets to 90 degrees it will probably machine okay.

But no matter what alloy and temper you are machining coolant or lubricant is almost essential.

[turbo2ltr]

I have been putting off setting up the coolant because I hear it can go rancid and smell pretty badly pretty easily if you dont use it often. I don't machine very often (a few times a month), and I dont want to have to buy 10 gallons of new coolant every time I want to do something on the mill. So can anyone recommend a coolant that will last for a decent amount of time (months?) that doesn't mind not being used for weeks without stinking up the shop?

[Geof]

I don't think you will find a water mixed coolant that meets what you want. A compromise is to use ATF (Automatic Transmission Fluid), just brush it on where you will be cutting (like tobyaxis suggests above).

[Al_The_Man]

What about Varsol or WD40? I have found that worked for me.
Al.