Flycutting 6061 Question

[michaelthomas]

I'm flycutting some 6061 plate, and I am getting a great initial cut.....but where the cutter overlaps the finish is kinda poor.

I am using a Leitz carbide insert two wing 2.5 " flycutter.

The machine is a Onsrud Panel Pro router.

I ran 2000rpm with a feed rate of 30 IPM. The stepover was 70%.

I climb cut each pass at a depth of .004"

The inserts are sharp cornered. I ordered some 1mm radius inserts, but I have not received them yet.

I would be ecstatic with the finish if I could complete it in one pass.....its just where the cutter overlaps that is the problem.

I cannot feasibly run coolant on the machine, but have an air blower directed in front of the cut.

It appears to me that it may be some chips dragging over the previously cut areas that are scratching it.

I thought about using maybe a 95% stepover instead to minimize the overlap.

I trammed the head to .0005 for a 10" circle.....I ran once with the pattern beginning in the back of the table and progressing to the front with a climb. This produced great results except for the overlap. I ran the other side beginning at the front and progressing to the rear in a climb. This way yielded a crappy looking cut everywhere. This seemed to point to a tram issue.....but I can't detect one.

Will the radius corner inserts solve this problem?

Any other suggestions?

[Geof]

Even though you cannot run coolant try just wiping a thin film on all over the plate. It is very likely your problem is due to the chip adhering to the cutter, aluminum tends to do this on carbide, and getting dragged around over the cut surface.

[michaelthomas]

Thanks.....Is there a specific type of coolant I should try? I'm hoping I can find something locally.

[Geof]

Automatic transmission fluid works very well as a cutting fluid for aluminum and you can get that almost anywhere. Just brush it or wipe it on...when the machine is not running.

[michaelthomas]

Thanks again.....I'll give that a try.

Is there such a thing as a maximum stepover?

[Geof]

Not really when you are taking a very light cut such as you are with this facing. When taking heavier cuts it is often necessary to limit the stepover simply because you run out of power.

[michaelthomas]

OK.....The spindle doesn't even seem to notice it is cutting at this depth.

Do you think there may be a significant difference in the cut grade with the radius inserts?

Thanks for the replies.

[Geof]

It depends on the type of carbide. Nearly all carbide inserts do not have a razor sharp edge. If you look at one under a microscope you will see the edge is slightly rough and rounded. This is because carbide tools are made by squishing together very tiny particles of carbide 'glued' together by cobalt. This means the edge cannot be sharper than the smallest particle of carbide and when the inserts are coated the edge is even less sharp because the coating is like a very thin layer of varnish.

When you take a very small cut of only a few thousandths of an inch with one of these inserts the rounded edge is larger compared to the depth of cut and so the metal sort of gets pushed ahead of the tool rather than flowing nicely up and away. With aluminum there is a tiny build up of aluminum oxide on the cutting edge and actually it is this build up that does the cutting. When this build up gets too large it breaks off and then starts building up again. This tends to leave an uneven streaky finish on the material.

Cutting lubricant minimizes this build up and can produce a much better finish but it may not prevent it completely depending on how rounded the tool edge is; in other words how large the carbide particle size.

For aluminum the best carbide tools to use are called micrograin. These have very small carbide particles and can be ground to a razor sharp edge and a mirror-like finish. With these inserts it is possible to get an extremely nice finish on aluminum, but the problem is they are not available in all styles.

[mopar]

Good ole WD-40 is what I use ,We deal almost exclusively in alum. in aircraft shop. Also try feeding in the same direction on both passes,If your not already doing that?

[michaelthomas]

I gave it another run today after work using something similar to WD-40 (I think).

It turned out very nice.....thanks for the suggestions. I also increased my stepover.

I'm pretty happy with it. The coolant made a dramatic difference, even on the part I was already happy with. I was surprised that it did much just being applied to the surface.

I did run the same direction in climb cut.....even before.

Thanks again!

[michaelthomas]

Here is a picture of the finished product. I'm pretty happy with it.

Thanks for the advice. I may be addicted to aluminum now....lol.

[Geof]

Nice, when you get clued in to all the tricks aluminum alloys are very nice to work with.