Fly Cutter Surface Finish Issues

[DeusExMachina]

So I got an order Carter Tools the other day (excellent service), and in it was the small 3/8" shank fly cutter (1224ER). Tonight I got my mill all trammed (5 tenths over 6 inches) and decided to play with the Fly Cutter...

I've tried a variety of speeds and feeds, but not having any luck with the surface finish, its coming out fuzzy.

Spindle is set to the lowest speed (1000 rpm), tried between 1 IPM and 8 IPM, and about 3 thou depth of cut. Nothing, everytime it comes out fuzzy. Also tried climbing and standard, both end up with the same finish. Felt the spindle while it was cutting the last pass, it was smooth and steady no vibration, I don't think the spindle/column are flexing as these are really light cuts.

The bit was pre-ground, and quite sharp and, well, brand new so I don't think thats the issue.

Anyone have any experience running fly cutters on a Taig? What am I missing?

[Geof]

"Fuzzy" is a very imprecise technical term. Can you post pictures so we can see what your definition of fuzzy is?

It could be the tool; sometimes preground tools are not ground correctly.

It could also be the rotation; you do have it rotating the correct way?

[Hirudin]

If you haven't already, check out this: Flycutting Aluminum on the TAIG. The whole blog is very cool and there are a lot of videos.

Oh, here's another blog entry: Fly Cutting.

A quote from the blog...

FYI - the final cut was 0.001” DOC (one thou) per pass, 2800 RPM on the spindle and 4 IPM.

I assume he's talking about the first cut shown in the video (which was the last cut he had done chronologically).

[DeusExMachina]

Didn't have a chance to get a picture, it seems to cut a mirror finish on the leading edge of the circle but when the trailing edge comes around it seems to grind off a bit more leaving a rough surface, almost like 400 grit sandpaper.

The tool is mounted in the right direction, and spinning in the right direction -- I've read enough post about boring bars/heads and flycutters on backwards to double check

It may be the tool, the preground shape looks like the cutting edge only has a rake of 15 degrees, but I'm not exactly any good at grinding bits, don't have enough practice yet I don't think.

I'll try some other speeds and feeds tonight, didn't really want to run the fly cutter at 2800 rpm, seems a little fast considering the diameter.

[Geof]

.. it seems to cut a mirror finish on the leading edge of the circle but when the trailing edge comes around it seems to grind off a bit more leaving a rough surface, almost like 400 grit sandpaper.


...... didn't really want to run the fly cutter at 2800 rpm, seems a little fast considering the diameter.

2800 is a bit fast unless your cutter is well balanced and the toolbit is secured so it cannot come loose; often a lot of simple flycutters meet neither of these conditions.

It might sound a bit contradictory but you may have trammed your head too well. Sometimes when the cutter is very true, on the trailing edge it just hits the high spots but it is not really taking a cut so it does fuzz things up. If you are finding the same thing happening with both directions of table travel then it is very true.

If you read through posts about using flycutters you might see some people mention they deliberately leave the tram very slightly off so the cutter is minimally above the cut surface on the trailing edge. Before you give it a nicely calibrated whack with a hammer to knock it slightly out of true try using a bit of cutting fluid.

And I suppose I should make the comment for other readers who chastise me; the whack it with a hammer comment is not meant to be taken seriously.