Fly cutting info

[morrisman]

Hi

I found this while searching for info re fly cutting

Fly cutting « Start Model Engineering

[cba_melbourne]

Fly cutting can indeed produce beautiful smooth fininshes that look very flat and accurate. But looks can be deceiving. The very smallest alignment error of your milling head will be magnified and ensure that beautiful surface ends up concave in feed direction. You will find, that the same surface made up of several passes with an endmill will come out flatter. Considerably flatter. And more reliably and repeatably flatter. Despite the surface finish looking stepped, the deviations from flatness of each step will always be much smaller than with a flycutter on the same mill.

Do not get me wrong, I like using fly cutters where it makes sense - and that is usually where appearance matters most. Chris

[morrisman]

Fly cutting can indeed produce beautiful smooth fininshes that look very flat and accurate. But looks can be deceiving. The very smallest alignment error of your milling head will be magnified and ensure that beautiful surface ends up concave in feed direction. You will find, that the same surface made up of several passes with an endmill will come out flatter. Considerably flatter. And more reliably and repeatably flatter. Despite the surface finish looking stepped, the deviations from flatness of each step will always be much smaller than with a flycutter on the same mill.

Do not get me wrong, I like using fly cutters where it makes sense - and that is usually where appearance matters most. Chris

Ok that is interesting Chris

I have tried that fly cutter as described in that link - It appears to be more suited to softer metals like alum and brass. It does not do a mirror finish on mild steel , for me anyway .

What is the favourite or most suitable tool shape for steel ? Mike

[cba_melbourne]

Ok that is interesting Chris

I have tried that fly cutter as described in that link - It appears to be more suited to softer metals like alum and brass. It does not do a mirror finish on mild steel , for me anyway .

What is the favourite or most suitable tool shape for steel ? Mike

I look at a fly cutting tool very much like I look at a lathe tool used for facing. The conditions are about the same. Also both have to cope with interrupted cuts. Think of a rectangular workpiece held in the lathe's independant 4-jaw chuck, being faced square on all sides. And if talking light hobby machines, both light lathes and mills suffer from rigidity limitations.

I have never tried to grind these tools with a rounded cutting edge as described in your link. I understand why the author recommends it, in theory a round cutting edge makes for the smoothest surface. But only on a rigid machine. On a hobby machine (lathe or mill) a rounded tool cuts on too large an area, the cutting forces are too high and cause deflections. These deflections can cause a wavy cut, especially on interrupted cuts. These "waves' can be seen on surface finish, especially in the first 10mm or so after entering the workpiece. I prefer to cut a light V-shape into the cutting edge, and slightly rounding off the tip of this Vee, something like a 1mm tip radius will do.

I get near mirrror finishes on stainless steel and some othe steels. But being a hobby user, I do not always know what this or that piece of steel that I "found" somewhere many years ago exactly is. Some steels just do not finish well, they cut to a matte finish that feels like a cat's tongue when I slide over it with my finger. No matter how I grind the tool, no matter what insert I use, no matter if milling or turning. In general, I find steels that are good for welding are not ideal for machining, and vice versa.

In any case, fly cutting is a slow and messy affair. But you do not to have to spend money on fancy cutters that are toss away or need a cutter grinder to sharpen. The tool bit for a fly cutter can be sharpened freehand hundreds of times and will last an eternity. One more reason to buy only a good brand quality HSS-Co blank - it stays sharp for longer and since you measure its life in decades, its price is really irrelevant. Chris

[morrisman]

Maybe a few forum members could upload drawings or pics of your fly cutter tool , this would be a very good thing for all of us .. the more the better .

Mike

[morrisman]

Discussion on aspects of fly cutting

Fly Cutter?