Choosing End Mill Size/diameter?

[RegisG]

Do you use the largest end mill that can fit your work piece? Or, is there some rule-of-thumb for choosing the diameter of end mill to use? Does it matter (in some way) what diameter you use as long as your are within speed/feed limits?
S L O W L Y .... learning
Appreciate advice.

Regis

 

[Reeltor]

I don't think that there is one right answer to your question. So much will depend upon how ridged you mill is. A Cinci with a vertical head can spin a 1" end mill without even thinking about it. The same end mill will give a table-top mill fits. A lot will depend upon the material being milled, power available to the spindle and how stout is the setup. I usually use the biggest cutter that I have on hand (and is sharp) to get the job done.
Mike

 

[T Bredehoft]

I usually use the biggest cutter that I have on hand (and is sharp)

That about sums it up. I find, however, that my PM25 works best with about a 3/8 or smaller cutter, except for facing. A half inch cutter will work but it seems to bounce, each flute impacting the work makes its own vibration.

 

[RJSakowski]

I am not an expert at selecting end mill size so heed the advice. Some things to consider.

Large end mills require fewer passes to complete the operation and in some cases such as creating a circular pocket on a non CNC machine, it makes it simpler to use the exact size end mill.

However, larger end mills require more torque, often not available on a small machine. The lack of rigidity of a small machine can cause more chatter with a larger end mill. They also cost more than smaller end mills. If you are using a large end mill on a small machine, you are most likely only using a small portion of the cutting surface deue to available power and torque constraints so,unless you have the ability to resharpen the end mill, much of its utility is wasted.

I have a CNC machine and can run pocket routines so my usual choice for an end mill is 1/4" to 1/2" with 1/4" or 3/8" being the most used. I sometimes use a 3/4" for facing larger surfaces to reduce the number of passes.

 

[RegisG]

That about sums it up. I find, however, that my PM25 works best with about a 3/8 or smaller cutter, except for facing. A half inch cutter will work but it seems to bounce, each flute impacting the work makes its own vibration.

Well, I do have a PM25 and that helps.
Thanks all,
Regis

 

[Reeltor]

Just to add a note, use the proper cutting fluid. It can make a real difference. For aluminum, WD-40 or kerosene works well, for steel, Oakley thread cutting oil can be found in the plumbing section of Home Depot or Lowe's


Mike

 

[sanddan]

That a good question, looking forward to the comments.

I seem to use 1/2" most often unless the work requires something smaller. My favorite 1/2" is a 3 flute carbide I bought used off CL. All my other endmills are either 2 flute or 4. Something about that 3 flute just works.

 

[Andre]

Large endmills put radial force further away from the spindle rotational axis, meaning they require more torque and impart more force on the workpiece. For this reason, when milling with less than ideal setups, or delicate parts use the smallest endmill possible.

 

[JimDawson]

I'm with @Andre on this one. I normally use 1/4 or 3/8 solid carbide end mills (and router bits). It takes a little longer to remove material, but they don't load the machine too much. If I need to remove a lot of material, I'll grab a 1/2 or 5/8 cobalt rougher. The cutting forces on the machine are less than a standard end mill. For flatting a large surface, I go for the 2 1/2 inch face mill.

 

[chevydyl]

My knee mill doesn't like the bigger end mills, 1/2 or smaller work the fastest for me (cnc) I'm able to run em harder, because as said it doesn't take as much force, so I can keep the feed rate high, and the spindle rpm optimal. Don't get me wrong, I do use a 1 inch and 3/4 end mills, and smaller but those big guys I need to slow down and keep watch, I busted through the wall slotting with a 3/4 5 flute rougher, slow feed and slow rpm, and it when it through you could see some serious flex, as well as it moved the part, abom79 showed that in a video, same problem, it grabbed instead of cut, and that can be a problem with large end mills when you don't have rigidity in your setup or machine.

When cnc machining my material removal rate will be higher with a half inch than a 1 inch, because I run the smaller one waaaaaaay faster on the inches per minute