End mill bits and aluminum. Questions.

[SCCoupe]

I am messing with a mill that im currently converting to CNC. I had a few questions about cutting speed and the type of bits to use on aluminum. I have read that faster speeds are needed to cut aluminum, but what speed? My mill only goes up to 3000rpm, is that what to use? Also I have broken a couple of router bits, maybe by trying to cut too fast?(I don’t have any real end mills yet or the R-8 collets for them) I have been testing with the drill head installed with router bits from home depot. I know this isn’t right, but like I said I was just messing around. These are straight cut(not spiral) 2 flute bits. Am I better off with a 4 flute spiral design? Also, is any cooling or lubrication needed for aluminum? I dunno, this is all new to me and I have a lot to learn.

Thanks all.

[RyGuy1788]

You will want to use 2 flute HSS spiral bits and a coolant ( I use wd-40, just spray it on while cutting) for aluminum and if your cutter is 1/4" or less I would run at your full 3000 RPM. the formula is: cutting speed (200-300 for aluminum) * 4 / diameter of bit (say 1/4") = 3200.

[Geof]

Milling cutters for aluminum have a large helix angle. This helps pull the chip up out of the cut.

Unless you are using a cutter larger than 5/8" dia. you will always be using your maximum speed with a carbide cutter; with High Speed Steel it would be 1/2" dia. However, I expect you will not use cutters this size.

I suggest always using 2 flute cutters because this provides more clearance for chips but when you are taking a light finishing cut a four flute is okay and it allows for faster feed.

A cutting fluid is needed for aluminum otherwise the chips tend to adhere to the cutting edge or pack into the flute. Many people use misters which will tend to create a fine aerosol that can be inhaled so prolonged use is not really advisable. A water mixable coolant in a handheld spray bottle works fine and is easier to clean up than straight oil coolants.

[SCCoupe]

Ok, so it basically sounds like I was trying to cut too fast for the rpm i was using(1250rpm). I was keeping the chips clear with air and didnt use a lubricant. So is using a zero helix angle 2 flute off the wall or just doesnt work as well as what SHOULD be used? I dont plan on using these home depot things past testing, but I dont want to blow money on good bits if im going to break them by doing something else wrong.

Thanks again!

[MOOG B-22]

TOO MANY VARIABLES TO ANSWER SPECIFICLY. WHAT KIND OF ALUMINUM? DEPTH OF CUT? FEED RATE? TYPE OF MACHINE? ROUTER BITS ARE A NO-NO, USE HIGH SPEED STEEL, COBALT OR CARBIDE, 2 FLUTE. USE COOLANT FOR LUBRICITY AND HEAT REDUCTION. USE GOOD ALUMINUM. SOME AL's ARE LIKE CHEWING GUM AND WILL BREAK ANY ENDMILL. ALL ENDMILLS HAVE A SWEET SPOT. I.E. SPEED, DEPTH OF CUT,RIGIDITY,ETC. WHICH ALL HAVE A PART TO PLAY IN CUTTING OF ANY METAL. A SWEET SPOT IS WHERE THE CUTTER MAKES NO NOISE, LEAVES A SMOOTH CUT, IN AN ACCEPTABLE AMOUNT OF TIME. WHAT GOOD IS A SMOOTH CUT IF IT TAKES 2 DAYS TO FINISH THE PART? RIGIDITY IS THE MOST IMPORTANT. KEEP EVERYTHING AS SHORT AS POSSIBLE. MOVE TABLE AS CLOSE TO THE QUILL (KNEE MILL) AS YOU CAN. DONT RUN THE QUILL DOWN 6 INCHES IF YOU DON'T HAVE TO. SHORTER ENDMILLS. (LARGER DIA. ENDMILLS ARE ALSO MORE RIGID.) CARBIDE IS 3 TO 6 TIMES STIFFER THAN HSS. GET A COPY OF THE (MACHINIST HANDBOOK) NOT TO CHEAP, BUT A WEALTH OF INFO. WWW.MMSONLINE.COM ALSO HAS GOOD ARTICLES ON MACHINING. ALTHOUGH THEY ARE MORE FOR INDUSTRY, YOU CAN STILL GET SOME GOOD IDEAS. GOOD LUCK

[Geof]

Originally Posted by SCCoupe Ok, so it basically sounds like I was trying to cut too fast for the rpm i was using(1250rpm). I was keeping the chips clear with air and didnt use a lubricant. So is using a zero helix angle 2 flute off the wall or just doesnt work as well as what SHOULD be used? I dont plan on using these home depot things past testing, but I dont want to blow money on good bits if im going to break them by doing something else wrong. Thanks again!

Yes, rpm too slow, feed probably too fast and it is likely the chips packed up in the flute. A straight two flute is close to useless on aluminum unless you are running down an outside edge.

What you should do is grit your teeth and accept the expense of breaking the correct cutters during your learning curve. Using an unsuitable cutter means that your learning is wasted because you learn the wrong thing.