Milling aluminum - newbie pointers - advice - ???

[radioactive]

Hey everyone,

Brand new to milling, it's always looked interesting, but never done it myself (until this past weekend). So I bought a milling machine, converted it to use Mach 3, and now I have a problem. My garage is covered with chips...

I've read a few books on the subject, read alot of info on this forum and a few others, trying to learn as much as I can. I'm looking for general info you can provide that might seem obvious to you, but might be eye opening to a newbie like me.

My machine has a 3 HP spindle and runs a max speed of 4000 rpm. I will be milling aluminum almost exclusively. I've read about how to calculate speeds and feeds but no one seems to mention the depth of cut (DOC)? What should your DOC be with a given end mill size, any rule of thumb to go by? How about the step over amount? How much of the previous pass should the cutter cover on the next pass? Any rule of thumb to go by?

For milling aluminum, most people seem to recommend a 2 flute cutter and then for the finish pass with less material removed, use a 4 flute (or more). So the more flutes, the higher the speed, and the slower the feed, the better the finish will be?

I have a mist setup that I just got running (it was in disrepair), however I don't really want to coat everything in the garage with this stuff, so I'm leaning towards making my own flood setup. Any pointers?

[djr76]

In your machine, a 2 fl solid carbide cutter I would go full rpm and 1.5-2x diameter in depth in a full cut with lots of coolant. If it chatters, either lower the rpm and/or speed up the feedrate.

[thackman]

Which grade of Aluminum are you trying to machine they vary quite a bit. I only have 1.5 hp and a 4" precision grinding vise and my only issues have been the part coming out of the vice, re-cutting chips in deep pockets, and chip evacuation on small endmills.

[radioactive]

Mainly 6061 aluminum. I purchased a Kurt D688 vise, so clamping the parts shouldn't be an issue...

Wow, 1.5 to 2 x the diameter! That sounds like a ton of material removal with each pass...

[Rally]

1" * 2" = 2" = Stupid
Trial and error will be your best Friend simply because of all the variables in all machines.
Feeds and Speeds! There are many Calculators and the basic information can be found in the machinery's handbook. Good Tool manufactures will also supply that info for there tools. RPM's! I would stay at recommended speeds while it may not matter all that much in aluminum the spindle will wear out quicker.

[radioactive]

Originally Posted by Rally 1" * 2" = 2" = Stupid Trial and error will be your best Friend simply because of all the variables in all machines. Feeds and Speeds! There are many Calculators and the basic information can be found in the machinery's handbook. Good Tool manufactures will also supply that info for there tools. RPM's! I would stay at recommended speeds while it may not matter all that much in aluminum the spindle will wear out quicker.

Sorry, I don't follow you on the 1" * 2" = 2" = Stupid comment? Was this refering to the depth of cut of 1.5 to 2.0 times the diameter size of the endmill?

I do understand that it will take some trial and error and have been using some references including the machinery's handbook for speeds and feeds, however I've had a hard time finding info on the depth of cut to be used.

I thought a DOC of 0.125" was alot of material...

[djr76]

Originally Posted by Rally 1" * 2" = 2" = Stupid Trial and error will be your best Friend simply because of all the variables in all machines. Feeds and Speeds! There are many Calculators and the basic information can be found in the machinery's handbook. Good Tool manufactures will also supply that info for there tools. RPM's! I would stay at recommended speeds while it may not matter all that much in aluminum the spindle will wear out quicker.

How is that stupid? please enlighten me o' great one

[pking321]

there are a ton of variables when learning the trade, no book out there knows how your machine will react to different situations, practice=perfect. as far as the doc goes, 1.5-2 is way to much unless you have very small stepovers, imagine a full diameter cut with a .5 endmill .75-1.0 deep, that would snap the toool right in half, so again practice=perfect, the less the stepover the deeper you can cut as, but i never go beyond .75 diameter depth, like with a .5 cutter no deeper that .375, just a rule of thumb i was once taught and its worked well, another one is when reaming the reamer should be twice the feed and half the speed of the drill, good luck. 1" * 2" = 2"=that guys stupid, and its rpm not rpm'S

[Rally]

Originally Posted by djr76 How is that stupid? please enlighten me o' great one

Try taking that kind of cut with the e-mill berried into the material that deep!
I don't think so!
Maybe you use SUPER end mills that allow you to do that but in real live that will not work.

PS: The Stupid was not directed toward you I was talking about a "stupid move" trying to go that deep.

[Geof]

There is a relationship between Depth Of Cut and Width Of Cut, aka Step Over.

If you are cleaning up an edge and the width of cut is something like 10% of the cutter diameter then a depth of 2 * the cutter diameter is quite practical even on a machine with limited horsepower.

If the width of cut is something like 100% of the diameter then the depth will have to be much lower and may be less than 50% of the cutter diameter.

A rule of thumb that can be used is that the width multiplied by the depth should be no greater than half the square of the cutter diameter; in other words a 1/2" cutter full width should not go deeper than 1/4" but a 1/16" face pass could be done at full flute length.

The speed and feed also come into it and the machine simply may not have the torque and things will have to be backed off.

[Rally]

Originally Posted by radioactive Sorry, I don't follow you on the 1" * 2" = 2" = Stupid comment? Was this referring to the depth of cut of 1.5 to 2.0 times the diameter size of the end mill? I do understand that it will take some trial and error and have been using some references including the machinery's handbook for speeds and feeds, however I've had a hard time finding info on the depth of cut to be used. I thought a DOC of 0.125" was alot of material...

Yes I was talking depth!

Here is something to try!! Lets say your using a 3/8"e-mill and you are trying to cut something out. I would try something like 2500 - 3000rpm .150 to .200 peck at 30"min.

However! this will depend on the machine and how much your spindle can pull.
I do assume that you are not going to do production runs!
As noted above by another poster almost every machine acts just a little different and trial and error is a must.
Setup will also come into play when higher precision is required.
I would like to help more but it is hard without running your machine.

[ImanCarrot]

You also need to know about Climb Milling vs Conventional Milling. It does make a difference. I only ever use Climb milling unless the part is very rough even then switch back to Climb when it's cleaned up.

Here (about 3/4 of the way down)

http://en.wikipedia.org/wiki/Milling_cutter

In the end it is all down to trial and error. Bad things that require correction include:
-Smoke comming from the machine.
-Parts flying across the shop.
-End mills snapping in half.
-Aluminium "welding" itself to your tool.
-Screaming noises from the cutter.

What I like to do is feed the table manualy and see how it "feels". I then program the beast to go at that feedrate with that depth of cut. Generaly I use a depth of less than half the diameter of the cutter with a stepover of between 50 and 75 percent. But, that's for pocketing and the like. Edge milling I always go easy- I hate tool deflection.

Oh, and don't clean dem chips up with an air line, tempting as it may be, you'll find them everywhere including in bits of your machine that you don't want them to be along with an expensive repair bill.

[Edit]Just re- read that and it sounded a little tounge in cheek so I thought I'd add Safety: if you machine too hard or fast things have a tendency to go wrong and human flesh is a lot softer than aluminium or your HSS cutter- always think safety! [Edit]