Advice on setup / speed / feed for 1/2" Radius corner rounding end mill

[peter.blais]

Hey guys... I have a bridgeport series 1 cnc, its probably an honest 2hp spindle, 4200 rpm max.

I'm cutting 6061 alu, and I need to cut some large radii so I bought this 1/2" radius corner rounding end mill. Its a 4 flute design with a 3/4" shank.

Anyways, I have lots of questions...

Should I cut the pockets first with a standard end mill, leaving steps along the radius, then just use the corner rounding mill to knock down the steps and leave a smooth finish?

Option 2 would be to pocket the holes straight down, then use the corner rounding mill like a standard end mill, working down till half an inch or so in .100 DOC passes. This would be hogging off all the material of the radius with this endmill alone.

Option 3 would be to pocket the hole then switch to the rounding mill and work outwards till the full radius is reached. This also would be removing all the material from the radius with this endmill alone.

I'm not really sure which approach to take on this? I was gonna maul some scrap and just see what works, but I figured I'd ask first and maybe save some time...

Second, this bugger is like 1.5" OD at the largest and .3" or something ID at the smallest... First off, how do you set this guy up so it actually cuts a perfect 1/2" radius corner? Second, what speed and feed would be a good place to start with this tool- its plain HSS.

I'm not sure because the varying radius and such throws me a curve.

TIA

Pete

[HuFlungDung]

I think you should try a test cut first to see if you can safely load the motor for a full cut. Depending on the finish desired, if you use a moderate feedrate, it may be adequately powered.

Such a tool does not remove a huge amount of material. It would be roughly equivalent to 1/4 of the load of a 1/2 endmill cutting 1/2 inch deep on a full width cut.

I'd try 1500 rpm and 20ipm to begin with, climb milling, of course.

As for locating the tool, again trial cuts would be in order if you must have exactly the full radius. One would have to know the actual tool sharpening data before making any assumptions about the location of the tip or body features, ie, there could be a small amount of tangent lead in to the full radius curve.

For general appearance purposes, I would tend to run such a tool two or three thousandths less than 'exact dead nuts on full engagement' because the blend in curve is easier to achieve this way, than to risk getting a tiny ledge caused by overcut or burring. Those last couple of thousandths has a fairly disproportionate effect on how large the radius cut looks, so for that reason, a test cut is in order if your job is critical.

[peter.blais]

sweet, I'll give that a shot. I may start a little lower rpm and lower feed (to match). I didn't do the math to figure out exactly how large that cross section is but- I usually cut 30-35ipm with a 1/2" EM .125 deep, should be ok.

I'll just setup a long piece in the vise and fool around with it, I just can't stand accidentally exceeding the power available, bogging the spindle, and chattering the hell out of things, and its not all that hard to do with this little power, so I like to have a rough idea where to start with a new tool.