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How to use a flycutter??

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Sanjay F:

--- Quote from: Charles Lamont on September 07, 2026, 10:53:35 pm ---On using the face mill for refinishing the cylinder and mouth piece bolting faces, the surface you have there looks fine for purpose, but when you want a better finish for functional or cosmetic reasons, a fly-cutter will generally do that, especially with a radius at the tool tip, and a sweep radius sufficient to cover the whole surface in one pass.

--- End quote ---

Charles gave me this bit of advice and I really do need to bite the bullet and learn to use a flycutter - I have a set which came with a load of other tooling years ago but have never tried it out! ::)

I found to 'bits' which fit, one 1/4" and the other 8mm" which fit into the medium and large size cutters respectively. I'm looking at the 1/4" Presto one and that looks like its tip is fit for purpose? The larger one looks very pointy and maybe should be radiused as Charles has stated?

How should I do that, with a file, emery, grinding wheel?

Any advice greatfully received as usual!

Also presumably I put it in collet then into the mill, but what rpm should I be running and what's an acceptable depth of cut?

Rledoux313:
No time like the present!

A fly cutter can be treated similar to the lathe in many ways. The tool grind is similar to a turning tool, but you may need a little more relief on the bottom edge to prevent rubbing depending on DOC. Speed will be set to achieve the correct feet per minute on the tool, only you’re turning the tool instead of the work as you would on a lathe. As for feed you likely want something small, maybe a thou or two. A fly cutter is a finishing tool more than a material removal tool so light cuts are probably best. I use the app “FsWizard” for speeds and feeds pretty often.

One other thing I notice is that you may have the tool backwards in the cutter. The “top” of the tool or the surface doing the cutting should be facing the set screws. This puts the cutting edge on centerline of the cutter.

The best part about a fly cutter is that the tool can be easily reground. So if you burn it up, or want to try a different geometry it’s an easy and low cost experiment. Good luck!

Jasonb:
You will only get a flat surface using a large cutter if the Mill tram is spot on. Many prefer a nice sharp small cutter and traverse the face many times which will give a flatter face.

I'm not averse to an angular corner but if it is shiny you are looking for then a small radius will do but does increase the length of the cut which can bog down a non geared/belted modern mill particularly as the swing diameter increases and rpm drops.

Speed will depend on the diameter the tip is rotating at. for HSS you want about 25m/min so 30mm dia 275rpm, 50dia = 142rpm, 75mm dia = 110rpm. Feed also needs to be slow as you only get one cut per rotation. start with 0.5mm depth of cut.

That's why I like insert face mills, you can run them much faster and feed even faster again. Hardly use my flycutters since getting them.

I saw this pdf drawing in a book some guy wrote about Milling for beginners ;)

ShopShoe:
I am one of many that believes a fly cutter should be in every cutter collection, even if you use indexable cutters for some of the jobs traditionally done with a fly cutter.

For general information, let your search engine loose and you'll find more information than any one of us can put together quickly. I just tried "making a fly cutter" and found lots of info easily.

From my experience, balancing cutting-edge geometry, feed rates, etc. is pretty much like using other cutters.

I grind my fly cutter tools old-school on a bench grinder, just like lathe toolbits. If you acquire more unground ones you'll have several chances to practice grinding them and cutting with them so you can contrast and compare. I have reground some chipped brazed-carbide toolkits with radii as well as grinding several all-metal cutters. (I have a green wheel for grinding carbide and typical stock wheels for steel.)

In use, I balance tip radius vs. sharp-pointed-ness and amount of cut vs. speed to cut efficiently without chatter and so the chips come out clean and as small curled pieces. I decide on whether or not to use lubricant/coolant based on material being cut and need to keep things cool and not abuse the cutting edges.

What have I done with my fly-cutter?  Mostly I have used it to clean up or dress large surfaces of material that will be further machined with other tools or machines. In smaller sizes, I have used a fly cutter to dress and square up small blocks for tooling I have made. It's great for making custom-diameter cuts for which I don't have a factory-made cutter. Material cut is mostly aluminum or ferrous metal. A couple of extreme examples include dressing a piece of 6-inch channel steel to make a base for a model and making a section of railroad iron flat on top and square before grinding it more flat to make a small bench anvil.

Have fun and let us know what you accomplish.

ShopShoe

P.S.: I like your restoration projects and I envy your ability to find the rough projects to work on.

SS

Sanjay F:
Thanks everyone, the tool bits you see are just out of a box of stuff, I'm not sure what they are or what they were for yhey just happened to fit! I have zero experience with grinding tools (bar a profile tool I experiemented with), but the picture Jason has sent gives a good indication of what is required.

If I started with a blank tool what should do? I have a bench grinder so that's a start, but it's the angles etc I'm not sure about?

EDIT: Hi Jason, presumably the diameter metioned is the diameter of the cirlce which the cutter will rotate/traverse?

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