Machining Anodized Aluminium

[rruybal]

Hi Bud,
If you look at the two tools side by side you'll see so much more clearence and space between the flutes on the high helix end mill than on the router bit. This is why we use these cutters to machine aluminium.
There are so many factors to consider when trying to mill a mirror finish, as far as I know you'll get a mirror finish when you use the right tool, speed and feed and cutting fluid. Cutting fluid is very important, it not only cools the part and cutter but is also a lubricant. It keeps gummy materials from binding to the cutter for a better finish. In the machining world finiches are graded by Micron. If you attain a 2 micron finish it is considered a mirror finish because it has the smothness of glass. If you get a 16 finish it's considered an ecceptionally good finish. Usually most machining is in the range of a 32 finish which is considered a standard finish throughout the industry. The High Helix on the endmill is ground so that more of the tool is engaged with the surface of the part ellimating vibration, which greatly deminishes the finish. This undesirable condition is called "CHATTER", and you'll be able to hear it as it increases propotional to the the ridgidity (or lack of) in your setup. A high helix endmill is designed to eliminate the (bounce) of the cutter as one flute disengages and the other digs in along the suface of the part as you machine.
You have more than enough RPM, so you must make sure that you have plenty of coolant. This is why you'll see CNC machining centers' totaly enclosed. If your machining head is ridged and your set up is ridged, you're half way there. Can you control the RPM. If so you may want to experiment with the RPM and feed rate. you may want to keep a
.004 load on on the cutter. A lot of people think that the slower you go the smother the finish. This is true to a point. But not always and not in every situation. Let me know how this goes, and good luck.

rruybal

[zeoncomp]

Thank you for the explanation ... I understand perfectly what you're saying except the ".004 load on on the cutter" .... and yes . I can control the speed

Thank you again
--remy

[rruybal]

Hi Bud,
The .004 load is actually the feed rate. Here is the formula;

Cutting Speed in inches per minute = 3.14159 X Diameter of tool X Spindle RPM
Divided by 12.

So if your RPM is 2000 and your cutter Diameter is .1875 = 2000 x .1875 = 375 X 3.14159 divided by 12 = 98.17 ft. per minute. this is the formula for a feed rate of .012 inches per revolution. This is the standard from the Machinery's Handbook. So if you want to drop it down to .004 per. revolution just divide it by 3 and you have 32.72333 ft. per minute. If you don't have a big machine that is ridged you'll want to cut this feed rate to about
.002 per revolution which is 16.361665 or 16.4 ft. per minute.

I don't want to confuse you with a lot of this stuff, but feeds and speed rates are important. they are the thing that gives you the finish your looking for.

Hope this helps, and good luck
rruybal