Fly Cutter Eating Cutting Tools

[walterwoj]

I build a fly cutter and made a cutter for it but every time I test it the cutter just gets eaten by the material. I made the fly cutter head out of 2 1/2" 1045 mystery metal I got from a local supplier. It is one piece and is made in the standard way, I didn't do anything clever or weird so I doubt that is the issue.



I ground the cutter with ~10-12 deg of relief and a slight radius on the cutting edge following several guides online. I have tested it on some 1 x 1 cold rolled 1018 but it always chews through the tip in the first fraction of an inch of the workpeice. I had always read that fly cutters were easy but this one is anything but. Does anyone have any Ideas?


This view let you see the chewed up tip (that angle on the end was not there when I started):

 

[great white]

I had the same issue, but my HSS grinds lasted a bit longer than what you're describing.

After a couple different (recommended) grinds with the same results, I switched to some old brazed carbide inserts I had rolling around in the back of the drawer.

Ive been running the same junk brazed carbide now for a little more than 6 months without issue....

 

[Chewy]

Try this. Your fly cutter is set so the bit goes down at an angle to the piece. Install a bit and bring it close to the piece. Use a square and mark vertical. Using that as a reference grind to that line with a little face and back rake. Leave the point sharp and try a cut, the add radius as desired. If you are breaking the tip, my guess is that the angle is too sharp, not enough supprt, or that you are trying for too deep of cut. I have also used the carbide brazed bits and they work. Make any changes about 1 degree at a time and watch the results. It takes some time and studying to figure out was is going wrong.

 

[Aukai]

Would the grade of HSS, or RPM contribute to this?

 

[benmychree]

I would suspect too much cutting speed. Also as above, what grade of HSS, China or good USA?

 

[mikey]

I suspect part of the problem is the shape of your tool. It has no side cutting edge angle and is therefore cutting purely with the nose radius. Naturally, that radius is going to go away very quickly. A flycutter bit cuts just like a lathe cutting bit except that the tool spins. Like a LH lathe tool, your flycutter tool should be contacting the work just aft of the nose radius along its side cutting edge. Such a tool, when used this way, will last a fairly long time and give a superb finish. Maybe look for examples of a LH turning tool and make your tool look like that.

 

[ttabbal]

I use a LH square tool at about 15 degrees for most fly cutting. Made from good quality HSS. I believe that the current one is a Rex cobalt bit. The only time I have killed the edge that fast was forgetting to adjust speed from aluminum to steel.

When calculating RPM, remember SFPM is based on the diameter of the fly cutter tip. For steel, that puts HSS at about 150 RPM for a 3" diameter set cutter. Deep cuts can also cause issues, don't try deeper than you would go on the lathe. With sharp HSS start small, to get a feel for it.

 

[MrWhoopee]

Most likely RPM too high. How fast are you running?

 

[markba633csi]

Agree with Mikey, shape of tool (or poor quality blanks)
It should be sharp, sharp enuf to cut you- check that (but be careful, don't actually cut yourself
And run very slow for cutting steel, use cutting fluid
I would recommend cobalt HSS blanks for steel cutting
-Mark

 

[Flyinfool]

Ok, Someone has to ask the stupid questions.
Is the geometry of the fly cutter that you made correct?
IS the tool slot on the correct side of the center line?
Is the cutting point exactly on the center line?
Are you spinning the fly cutter in the correct direction?