fly cutter

[AdeV]

Yup.
It looks rough, but it feels smooth - I'm assuming my lack of flycutting experience contributed to the look of it.

BTW, that block is aluminium.

Whaddayamean "rough"? That surface looks almost glassy. You'll be there for hours with the ultra-fine wet&dry, polishing compounds and other paraphernalia trying to get a better surface than that...

Seriously, that looks really good. And great idea to use the button insert tool, that should be good for steel and even this lousy ali-bronze stuff I'm using just now.

[wongster]

That's a good idea!!! No need to rely on my grinding skill, or the lack of it...

Are you able to give me the angle of that holder of yours?  The part that is slanted to the horizontal.

Regards,
Wong

[No1_sonuk]

I'm not sure of the exact angle - it looks like about 20 degrees off horizontal.  It's a body I bought that came with an unground HSS tool.  I just took that out and put the lathe tool in instead.

I should think just about any angle would do, though, as the cutter is circular.

[j45on]

Yup.
It looks rough, but it feels smooth - I'm assuming my lack of flycutting experience contributed to the look of it.

BTW, that block is aluminium.

I was not criticising the finish it looks great  
I dont have a fly cutter yet and grinding a tool has put me off but you post made me buy a glanze profile tool to complete my lathe set
And now i'm shopping for a fly cutter to fit it

[No1_sonuk]

As I said - lack of experience.  That's the largest area I've ever fly cut.
My comment about it being rough was because of Bogs' photo and comment about a "mirror" finish on the first page of this thread.
Mine's kind of a very scratched or smeary mirror. 

[wongster]

I found that I get nice finishes when the cutter is cutting at the trailing end of the circle. In my case, from right to left.

Wong

[cidrontmg]

No1_sonuk,
Iīve also tried a similar round- tipped tool, an exact copy of yours. It works rather well with steel, ali, cast iron (chips fly even straight from the cast surface), less well with brass/bronze. The surface finish is rather scratchy, though. An HSS tool bit gives a better surface, but it must be really razor sharp. The classic test for a keen edge is to check if it will cut hair from the back of your hand. With a carbide tip, no chance. A sharp HSS bit, no problem.

And in general, the ready-made fly cutter shanks have usually far too little an angle for a Bogs- style ground tool bit. The angle should be at least 20^o, but it wonīt hurt any if itīs 40-50^o. Obviously the sweep will get less with a steeper angle, and thereīs less "air" above the workpiece.
 

[No1_sonuk]

Last night I discovered a flaw in my cunning plan...

Be careful if you try fly cutting up to a shoulder using an insert lathe tool.  Depnding on the design of the tool, the support behind the insert might not have enough clearance to get round.

Mine didn't

On the tool I showed above, the support goes straight down/back with no angle.  It was designed as a lathe tool, which doesn't need a relief angle.  Of course, one could always make or modify an insert holder specifically for the job with sufficient undercut.

[Bogstandard]

Having read this post all the way thru, it seems I caused some confusion with regards to 'TOP'. If you actually go to the first page, and find where I put up the grind pics with the pretty red lettering on, directly under the last pic, I explain what is meant.

Another couple of points that do need to be brought up. The radius of the cutter should be the width of the cutter blank, so for a 6mm blank, the radius should be 6mm, not elongated as some of you have done.

The other point is the direction the faces need to be ground. The direction should be with the grind marks at right angles to the cutting face. Do the radius grind first, then the front of the cutting face. Doing it that way, you are doing just two grinds. You sharpen by rubbing your stone against the vertically ground angled face, not around the radius grind.

I have done a C-o-C to try to explain what I mean.

Bogs

[wongster]

Hi Bogs,

Glad to "see" you in here.  Hope you're better.

I did the radius about the size of the tool width but it seemed that the cutting action was at (or almost) the shank.  So I "lengthened" the cutting edge but grinding it longer.  It could be the angle of my holder being too shallow.

Regards,
Wong

[Bogstandard]

It just might be that Wong. You are not getting the correct edge shape presented to the work.

I do in fact use the back cutting face as well. If I see my tram is slightly out, I use that to my advantage, as the return cut (without putting any further cut on) can just take 'wisps' of material off, and that is what gives you the mirror finish. I will run my fly cutter fairly fast, well above 500 RPM most times, but at a very slow feed.

Plus lubrication always works well, especially with ali, as that is liable to pick up on the cutter and swipe it across your nice mirror finish, I use WD40 for lube on ali, brass or phos bronze and cast iron doesn't need it, and for normal steels (I wouldn't recommend a fly cutter on really tough stuff) I just use normal water based coolant/oil mixture from a squeezy bottle. Basically, to obtain a very nice finish, you have to attempt to keep the removed material from being carried around to the next cut, so by using a lube, the fine swarf is thrown away by the liquid being thrown around by the cutter, the ones that require no lube, automatically eject from the surface by themselves.

Bogs

[wongster]

Thanks Bogs.  I'll redo the grinding.

Regards,
Wong

[Xldevil]

Hello.
I did my first free hand fly cutter grinding today.Btw.,my first tool grinding ever.
I followed the "Bogs way" and after "only" 3 hours of intensive grinding, I succeeded
Then I tried the cutter on a piece of aluminum.The surface looks smooth and shiny.
Thank you, Bogs.
Ralph

[luke_duke]

Sorry for picking up the old thread.
I tried to grind one myself and tested it out. The result is really awful. I guess I missed something with the angles. In the drawing No.3 there is a angle of 10-15 degrees. But when i look at the last picture I can't see any angle. Could someone explain to me how the second angle is grinded? I spent a few hours figuring out how to do so.

Thanks in advance!

Luke