Flycutter blues....

[Highpower]

Well after sitting and collecting dust for a couple years now, I finally tried using a flycutter for the first time today. :-[

Cutting some 6061 plate, so I ground up a HSS blank (10% cobalt) similar to this one but with a bit fat radius on it since I was going for a fine finish. Approx 7 degree clearance angles ground by hand.



It all went horribly - horribly wrong.

So as a test, I replaced my HSS bit with a brazed C2 lathe bit and immediately got a beautiful mirror finish.
Needless to say it looks like I'll be wearing out a few grinding wheels trying to get it right. Sigh.......

To be continued:

 

[Tony Wells]

Many people fail to realize that when you have a large radius, your feed is typically relatively high. When you say horrible. what do you mean?

 

[Highpower]

Lots of smearing, and gouges - very rough surface. The finish looked similar to (but worse than ) the cut shown here that starts at 2:50.

[video=youtube;koYGLVGkRsI] http://www.youtube.com/watch?v=koYGLVGkRsI [/video]

Almost the same radius of cut and rpm, but only a .002 depth of cut and approx 3.5 IPM feed.

When I switched to the carbide bit - same radius and rpm, same depth of cut, but upped the feed rate to 7.5 - 8 IPM.
The finish was identical to the one shown on the last cut in that video. (4:18)

I had honed the cutting edge after I ground the HSS bit, so I know it was sharp - but I am thinking the geometry on my grind is probably WAY off.... :-[

p.s.
Used WD-40 when cutting with the HSS bit. Carbide bit was used dry.

 

[Tony Wells]

~1/16" radius. 500 rpm, 6 ipm.

If you have good bearings, and not much quill hanging out, you should get a good finish. When you have a large radius, the lead angle doesn't mean anything. You need 3-5 deg bottom relief, and just enough "end" relief to clear the swept radius of the cutter. WD40 or kerosene before the cut, but mindful that it "blows away" with the tool, so must be reapplied as you go, or use something a little heavier. The top or rake angle for Al should be nice and positive to get a shearing action, perhaps 12 deg or so. More wouldn't hurt, until it starts to pull into the work, or the work starts to lift.

Try hand feeding and varying it until you don't get any ship welding, which will give you the drag and swirl marks. Usually faster than people think, when you have a radius.

 

[Highpower]

~1/16" radius. 500 rpm, 6 ipm.

So noted, and will adjust accordingly.

If you have good bearings, and not much quill hanging out, you should get a good finish. When you have a large radius, the lead angle doesn't mean anything. You need 3-5 deg bottom relief, and just enough "end" relief to clear the swept radius of the cutter.
...............
The top or rake angle for Al should be nice and positive to get a shearing action, perhaps 12 deg or so. More wouldn't hurt, until it starts to pull into the work, or the work starts to lift.

This is where I get lost. I need to study more on what angles are what as related to a flycutter. I get turned around easily.... :depressed:

WD40 or kerosene before the cut, but mindful that it "blows away" with the tool, so must be reapplied as you go, or use something a little heavier.

That I DID notice! Dang cutter makes an excellent fan doesn't it? I doubt I could keep up with it without making a huge mess with my little spray bottle. Which brings up another question I had.

Some time ago I bought a jar of "Boelube" which is supposed to be a soft paste. But when I opened it I found a hard dry crumbly mess. I don't know if was just old stock or what - but I'm wondering if anyone here is familiar with the product? I'm wondering if I can bring it back to life by melting it or mixing something into it? I have REALLY got to learn to check items I get from Enco as soon as they arrive. Been burned a couple of times now, because I lets things sit unopened until I get around to using them. >

Try hand feeding and varying it until you don't get any ship welding, which will give you the drag and swirl marks. Usually faster than people think, when you have a radius.

Well I guess I'll try grinding a much sharper edge this time and see what happens. Thank you for the tips kind sir!

 

[Highpower]

Interesting video - I would have just wiped the magic marker off with some solvent. Wouldn't go to all the trouble of removing it with a fly cutter :

I assumed that was some kind of lubricant they "drizzled" onto the surface? :-[

I reground my HSS bit differently this time and just "broke" the cutting edge instead of trying to put a radius on it.
520 rpm, 6 IPM and brushed on some chunky peanu uhhh... Boelube. (I tried melting it with a heat gun and stirring it - but as it cooled it got all lumpy again and taking on it's dry crystallized form again.) Guess it's time to call the manufacturer. <groan>

Much better than my first attempt, but even after dropping the feed to 3 IPM I'm still getting a "groovy" surface. Running my finger over it - it feels like an old vinyl record album. Not at all "smooth". The plate cut with the carbide bit is as slick as a sheet of glass. Also getting a much more pronounced Damascus type pattern in the center of the cut with the HSS. No clue if that "means" anything or not. ???

Unfortunately I need both of these plates for a current project I'm working on, so I will just finish them with the carbide cutter and move on. I can't take off any more material without getting them too thin. I'll have to scrounge up some more material later to work on finding the right way to grind this bit.

 

[Pacer]

I only use those 'cheapo' brazed carbide cutters. for the very reason youre describing - much superior finish. I had/have several of those 'blunt' nosed carbide bits - otherwise pretty well useless - and clean up the pitiful factory edge on the diamond wheel. I do add a radius, I find that a radius keeps the "phonograph record" line from happening. Occasionally Ill have to revisit the diamond wheel and tinker with the cutting edge to get that mirror finish, but I can almost always end up with a really nice finish.

The finish on this table and the stand was from a flycutter - a BIG one. The stand is a piece of scrap yard 6" channel. In order to reach across that I melted a piece of carbide off one of those bits and re-brazed it to a 6' piece of 1/2" key stock. I did use some 500 grit wet/dry to finish up with, but it didnt take much

 

[Highpower]

My only concern with the brazed carbide is chipping them with the constant interrupted cuts. I've got a pile of them that are chipped / broken from doing those types of cuts on the lathe.

For some reason the finish on the part goes south quickly after they loose a little chunk out of them. :laugh:

 

[Tony Wells]

This is difficult to describe, I think, but I'll try.

To help the corner chipping problem (and this applies to inserted milling cutters also), make sure the corner of the bit isn't the first thing to hit the work. Think of the circle described by the tip of the tool like a compass, with N-S-E-W. Traveling from S to N, have your tool hit the work somewhere in the NW quadrant, close to the W extreme. Avoid the NE quadrant. This allows the angle of attack by the tool to present a much stronger part of the carbide than it would hitting close to the N point.

Harmonics play a role in the odd patterns that can be seen. Not much remedy for that, except finding the sweet spot for your machine.

I've achieved good finishes with carbide with a generous positive lead, and a small (0.015) radius. I don't use HSS for flycutting.

 

[Highpower]

Tony, I am assuming you are using insert tooling for your flycutting?
And thanks for the tip about the machine harmonics too. Unfortunately I don't have a VFD on the mill, so I can't dial in the spindle speed. It may be time to get rid of the factory v-belt and install a link belt though. Other than that, I guess I'm restricted to fiddling with the feed rate.

Well, yes and no. I use brazed carbide in shop made flycutters, along with multi-insert milling cutters. Perhaps the grade of carbide has an effect on the chipping also. Some are tougher than others.