Machining Strategy Question

[MetalShavings]

I'm getting ready to mill 10 concave-funnel-shaped pockets that will be .125" deep at their lowest point and .30" wide at their widest point. (6061 aluminum)

I'll be using an 1/8" ball nose carbide end mill to do this pocketing on my 770 mill.

Here's my question:

I'm wanting to mill these pockets so that I don't have to go back and smooth out any machining marks. If possible, I'd like to get a smooth finish the first time around. Otherwise I'll have to make my pockets small and go back and polish to size.

I've done pocketing before but not this small and not on a CNC Mill.

Laying it out was no problem and running the simulations was no problem but, never having done this size and shape of pocket, my expected outcome is the problem.

Any tips or insight from those of you who have first hand knowledge of such projects?

Please forgive any rudeness that may come across from the following statement. Rudeness is not the intent but, the simpler the answer the better.

Some of the folks here have such a vast amount of knowledge that the simplicity of the answers tend to get lost in the explanations of the answers.

I realize that some answers require some explanation but, if you can help it please, no lectures .

Thanks very much for your help.

MetalShavings

[flick]

Here's my generalized "finish critical" approach:

Roughing method doesn't matter (depends on geometry), but leave a skin for finishing.

Finish in two passes, taking half the thickness of the skin with each pass.

Use high RPMs, a light CLPT, a small stepover/stepdown, and very long ramping transitions between cuts.

Start cutting at the inside/bottom and work your way to the outside/top.

Lots of lube, flush those cuttings away.

[MetalShavings]

Thank you flick:

This is just the type of reply I was hoping for.

My initial setup strategy was to forgo the roughing cut and just do the entire pocket using very shallow cuts as I went from top to bottom.

I can see the logic in the, "Bottom-Up" approach. I'm assuming that it aids in spitting out the metal shavings as the cutter works its way up and out; as apposed to having them work their way down to the bottom of my funnel-shape as the cutter goes down to the bottom of my funnel. (I think)

I'll have to change a few things now before running this part.

I do have another part that I'll be making that's basically the same except that my funnel-shaped pockets will be even smaller. I've tried making these same pockets with simple carbide burr tools similar to the ones we see used in Dremel tools and such but, no matter what my feed and speeds they all seemed to leave chatter/machining marks on finish. These smaller pockets may require a little more finessing.

For this particular part it's important that I have a fairly smooth finish. A mirror smooth finish would be even better but, I can live with "fairly smooth."

Thanks again.

MetalShavings

[kevinro]

Any chance you could send a picture or a screen shot of the job? Just curious is all. I think I understand the shape, but not really!

[MetalShavings]

Hi kevinro:

I ran the part yesterday and it turned out OK. I still would like a smoother finish but, I think that for the most part I got it licked. (Thanks to the input of a couple of the guys here)

Being a newbie to all things CNC I'm slowly but surely gaining ground on this new hobby. I'm just glad I can come here with questions when I run into problems.

I also had trouble initially on drawing the funnel shapes I've eluded to. A picture of the part in question can be viewed in the SolidWorks forum of this site at the link below.

http://www.cnczone.com/forums/solidw...rother_up.html

MetalShavings

[Gundawg]

It seems like you could have a custom cutter made to create your shape with a drilling toolpath or a pocket. You could probably start with a ball mill and have the geometry changed for your finished profile.

Mike

[David Bord]

Can you use a larger ball mill? .25 to .375? Even .1875 may help.

The larger the ball mill the less deflection and the smoother the finish overall. Are you climbing? Have you checked your tool holder and tool runout?

How about roughing to to bottom with the largest mill that will work, and doing the finish pass, starting at the bottom and working your way up and out as was recommended earlier.

David

[MetalShavings]

Can you use a larger ball mill? .25 to .375? Even .1875 may help.

The larger the ball mill the less deflection and the smoother the finish overall. Are you climbing? Have you checked your tool holder and tool runout?

How about roughing to to bottom with the largest mill that will work, and doing the finish pass, starting at the bottom and working your way up and out as was recommended earlier.

David

Hi David:

I thought about doing it exactly the way you've mentioned but I'm afraid that the radius of even a 1/4" ball nose would have given me more of a Bowl-Shaped pocket rather than the Funnel-Shape I was looking for.

I do have an upcoming project that's basically the same but a little larger that may benefit from a slightly larger diameter ball nose to make my initial rough pass.

I finished this present part last night. It's far from perfect but fully functional for its application.

Thanks for the input.

MetalShavings