I’ve been looking to see how to calculate the “depth of cut” for aluminum based on tool size, but have found that there are no formulas for this that can be found on the 'net. (Some online groups have said they simply don’t exist.) As a result, I’m left wondering what a good starting point would be for the actual DOC.
For example, if I use a 1/2" 4 flute square end mill, is 0.200" DOC too small or too large of a cut?
Any help or pointers towards help would be appreciated.
indieFan
can you rephrase please? 
What part has you confused?
indieFan
Your maximun cutting depth is based primarily on the length of the cutting part of the bit. .200 sounds like a safe cutting depth for aluminum in general. What material is the 4 flute bit made out of? Does it have a coating on it? Since your using a relatively large diameter cutting bit and its 4 flute, you could go with more shallow cuts and just run through the metal faster since 4 flute can remove the metal more quickly in smaller chips.
Wait, I may have terminology screwed up. I thought DOC referred to either the depth that the end of a tool sank into a material OR the amount that a tool removed on its side. If not, is the latter referring the the Material Removal Rate (MRR)?
Regardless, I’m looking at how to figure out how much material can be removed using the side of the tool.
indieFan
Indie,
What you are asking about is “feeds and speeds”. You can do a deep cut if the material is fed at a slow speed or if the material is soft. Specially designed tools also have recommended speeds and feeds that need to be used to use the tool at it’s most efficient or what to avoid that might damage the tool. It is an art for machinists to know how to determine all of the setable parameters on the machine. Check here…
http://www.efunda.com/processes/machining/chip_formation_2.cfm
Here is one for drilling,
http://www.efunda.com/processes/machining/chip_formation_2.cfm
This site has a freeware calculator, just click on software downloads.
http://www.virtualmachinist.com/
This is a representative chart that might be a good reference. Rememer that coolant also will play a role in machining speeds and feeds. 0.200" DOC does seem a bit deep off the top of my head, though.
http://www.niagaracutter.com/techinfo/millhandbook/speedfeed/chart1.gif
Hope this helps,
Indiefan
If you are having still having trouble it may be because there are many factors that go into a good part setup. First you said you are using a four flute end mill, this is not the preferred tool for your material, and a two or three flute would work much better in that it would not tend to clog up as quickly.
Coolant is also important when cutting aluminum, along with what type of cutting you are doing such climb milling, conventional milling ,pocketing or channel cutting .The type of machine you use will also affect your results. Are you using a cnc mill? , a standard mill?, or a bench top mill ,each of these machine have different spindle speeds and rigidity .
I am sorry for not answering you question with a number (ie cut .125 deep) but as you can see there is no simple answer. I would be happy to help you with making what ever you are making .I can sent you a cutter and a nice little slide card that make calculating speeds and feeds much easier.
Let me know how it woks out and if you need some help. Your friend on team 107.
Jim Schaddelee
Team 107 mentor 
I agree fully with Jim. There is no simple answer to your question, and as he says, a 2 flute cutter would be better for the job.
A two flute will cut more material per flute than a 4 flute, however since you are cutting aluminum, the more material cut will not matter too much to the cutter. I have rarely broken a cutter on aluminum (once if I recall correctly…). As long as you keep the spindle speed and the feed rate right, as well as use proper cooling, the cutter should be fine on even heavy cuts. Also since there are only 2 flutes, there is more of a relief groove on the cutter, so the chips fly out easier, preventing blockage.
Remember, different materials have totally different cut techniques. For example, I would always cut steel with a 4 flute cutter.
As for the original question, it is hard to say with the info you have given us. If you have a mill that is similar to a Bridgeport Series 1 mill, and in decent condition, you are in good shape to do heavy cuts. If you are running a half inch cutter, 2 flute, HSS, you can probably get away with cutting .250" deep with a 3in/min feedrate. That is, if you keep it constantly cooled. If CNC, you can mostly only judge by the sound of the cutting and the heat produced. If non-CNC, you can usually just go by the seat of your pants and judge the feedrate by the feel you get through the screws.
The main issue with cutting deep is that the part you are cutting has more of a tendancy to be sucked up into the cutter. If you have a part viced down very well, you can cut normally. But if you have a wierd part that isn’t held on too well, be very careful. Take cuts as small as .050" per pass, or lower the feedrate, depending on which direction the part is more prone to slip.
The art of feedrates and cutting depths is hard to perfect, it takes many years to learn, and can’t be easily explained. The more experiance you have on a mill, the better. Hope that helps.
~Veselin Kolev
Start light on the cut and low on the feed rate. If you have a CNC Mill go with the defaults in the CNC program. The nature of what we mill for robotics allows us to go a little slower than a full production shop. So it takes 10 minutes per part longer to go slow, we are only making 2 parts not 10,000. Take your time, enjoy what you are doing and remember the lowest feed rate on a mill still beats a file.
It’s also important to remember that the tool will cut best at different speeds depending upon direction. In other words, drawing the piece towards you along the end mill and then drawing the piece away from you will cut differently even if the depths are the exact same. Good luck!