Using a shell mill

[mrk]

What is the general thinking for using a shell mill in aluminum?


http://www.jlindustrial.com/NSM-0999...D/product.html

The tool is Cobalt and 2.75" with six flutes. I cut my hand a bit taking it out of the package so I know it is sharp []

So this weekend I plan to try some cuts. Basically my goal is to make a very smooth finish for the face of a part. The shell mill is big enough that I can finish in one path. I only need to remove .07" from the stock.

This is now the biggest tool in my collection. What type of feed/speed should I use with it? I have been using max RPM for all my tools so far since I only get 3k from my spindle. The biggest tool I used in the past was a 1" roughing EM and it cuts well at 800sfm with .007" fpt with good result at .5" depth and 45% step over. For finish pass I was using a .75" tool at .0025" fpt and was fairly happy with the result. I had some lines to buff out by hand but all and all the result was decent. My hope with the shell mill is that I can cut faster and produce a finish that does not have lines that need hand buffing.

Here are the questions?
1) Feed/speed
Can I push it beyond 800 sfm how about my fpt? Basically I want a smooth finish but I also want to know what the speed limits for the tool is (in 6061).

2) How much material can I remove per pass?
In the past I have used 1/2 of the end mill size as a rule of thumb. Would this still apply? I am assuming that HP will be my limit. I need to do the math but if anyone has a guess that would be helpful. I have 5hp spindle drive.

[big_mak]

I wouldn't run it at max RPM. Stick with 800 SFM. Do you have Flood coolant? Use this as you would a face mill. With 5hp try 1/8" deep cuts, and see how your machine fares. You will be limited by how you hold the part, and the rigidity of your machine. I'm running a 3" carbide tipped face mill @ 4000 RPM and 120IPM @ .12" DOC I could push it more if I wanted, but I am looking for surface finish. If I increase the speed I can see the base metal picking up and dragging. This is with full flood coolant too. Experiment with it and I'm sure you will find this to be a useful tool. You may even like it for simple outside profiles too.

Have fun and show us your results.

[Glacern]

Use it at the same SFM recommended for typical HSS/Cobalt endmills (more importantly, the SFM that works for you on your machine). The cutter material hasn't changed, so neither should the SFM.

Are you using it for facing, side milling, or both?

[Mcgyver]

you'll still get tooling marks, that what files are for 800 seems high for for hss in AL, try 400. if you are after the best finish, consider fly cutting. its a lot cheaper than shell mills. i have the ability to resharpen them and still don't much bother with them if you're only taking off 1/8 or less. And by grinding the tool properly you can get a top notch finish. with a 5hp mill it would nothing to take off .125 with 2.75 flycutter at say 500 rpm....but try the shell mill and see, it will certainly work

[tobyaxis]

A Shell Mill with Radii of 1/6 on the flute tips will provide a good finish at a low RPM 400-800. If this is for Roughing you will be better off with sharp corners.

[mhtom]

If micro finish is what you need do this, it's allways worked for me. Have two shell mills, one for roughing and one for finishing. Leave 0.010 for the finish pass. Use max RPM'S , feed rate at 0.002 PR. I allways get a miceo finish of 8 or better, just like a peace of glass. Remember rigidity of holding the part is very important. Good luck.