Critique my fly cutter surface finish

[MontanaLon]

I can't feel the swirls with fingernails. Before the cutter swept on the trailing side it was mirror like and then the trailing cut made the marks. Material is 6061. I'm thinking more radius on cutting edge and a touch slower on the manual feed.

 

[mikey]

Some thoughts:

• Check your tram. Many mills will have the trailing cut engage with a fly cutter but if the mill is in tram, this should be minimal.
• What was your speed? Looks to me like your feed is already pretty slow; not sure going even slower will fix this.
• Can you show us your tool? More nose radius = more deflection = limitations in the depths of cut you can take. Better to keep the nose radius small and adjust the other tool angles. You would be surprised at how a small change in one of the tool angles can make a huge difference in how the tool cuts. Show us the tool.

 

[SELBY]

View attachment 301876
I can't feel the swirls with fingernails. Before the cutter swept on the trailing side it was mirror like and then the trailing cut made the marks. Material is 6061. I'm thinking more radius on cutting edge and a touch slower on the manual feed.

Check tips or cutting edge/s of the tool and follow the cutting specification of the material to be machine.

 

[darkzero]

The volume is all the way down. I can't hear the fly cutter finish.

Well it looks like your head is trammed in well. As for the finish, It's hard sometimes with 6061 to see what the surface finish looks like in pics. Some lighting will make it look like a mirror & some lighting will make it look dull & make tooling marks look a lot worse than they appear to the naked eye.

 

[randyjaco]

Are you using a SHARP high-speed steel bit?
Randy

 

[Chuck K]

View attachment 301876
I can't feel the swirls with fingernails. Before the cutter swept on the trailing side it was mirror like and then the trailing cut made the marks. Material is 6061. I'm thinking more radius on cutting edge and a touch slower on the manual feed.

Yep....team looks spot on.

 

[Chuck K]

That should say tram!

 

[tjb]

View attachment 301876
I can't feel the swirls with fingernails. Before the cutter swept on the trailing side it was mirror like and then the trailing cut made the marks. Material is 6061. I'm thinking more radius on cutting edge and a touch slower on the manual feed.

Interesting post. I've actually been on the verge of posting a thread on this same subject. I made a fly cutter a few months ago that was a very good learning experience and turned out quite well (see photos below). But I have noticed a curious phenomenon that I, too, have wondered about. My fly cutter will mill about a 4 1/4" diameter. I've used it on both steel and aluminum and have noticed a consistent result: When I am feeding FROM the right - that is cutting the left side of the work piece first, the finish is beautiful. But when I feed from the other direction, I get a result similar to the photo shown above - not nearly as extreme, but the trailing swirl marks are visible. I am certain that my mill is correctly trammed. I am feeding at a very slow rate with an RPM of about 800 - 1,000 on 6061. (Played around with both feed rate and RPM's with no appreciable difference in results.) I wonder if perhaps because of the weight of the tool (it's pretty hefty), centrifugal force may be playing into the equation in one direction. I've accommodated for this by always feeding in one direction with very good results, but that seems a little like cheating. Any thoughts from our experts?

(Sorry, no pix of the result. That's why I haven't posted yet. The photo on the original post is similar, but not nearly as extreme.)

Regards,
Terry

 

[MontanaLon]

Interesting post. I've actually been on the verge of posting a thread on this same subject. I made a fly cutter a few months ago that was a very good learning experience and turned out quite well (see photos below). But I have noticed a curious phenomenon that I, too, have wondered about. My fly cutter will mill about a 4 1/4" diameter. I've used it on both steel and aluminum and have noticed a consistent result: When I am feeding FROM the right - that is cutting the left side of the work piece first, the finish is beautiful. But when I feed from the other direction, I get a result similar to the photo shown above - not nearly as extreme, but the trailing swirl marks are visible. I am certain that my mill is correctly trammed. I am feeding at a very slow rate with an RPM of about 800 - 1,000 on 6061. (Played around with both feed rate and RPM's with no appreciable difference in results.) I wonder if perhaps because of the weight of the tool (it's pretty hefty), centrifugal force may be playing into the equation in one direction. I've accommodated for this by always feeding in one direction with very good results, but that seems a little like cheating. Any thoughts from our experts?

(Sorry, no pix of the result. That's why I haven't posted yet. The photo on the original post is similar, but not nearly as extreme.)

Regards,
Terry

View attachment 304974View attachment 304975

That is very sharp looking. I ended up with something very similar after doing a couple with the angle. It works very well.

As you your question I have found as suggested above that the closer mill is to perfect tram the worse the results are. Knock it .001 out of tram and the marks go away or mostly anyway. .002 and they are all but invisible.

Also using HSS for the cutter give better surface finish that carbide when working with aluminum.

As to the trailing side messing up a good finish the forward side cut it seems to be 2 things with mill being trammed for 1 and needing a deeper DOC for carbide. If it isn't taking a big enough bite with will really never cut a good finish.

 

[mikey]

I wonder if perhaps because of the weight of the tool (it's pretty hefty), centrifugal force may be playing into the equation in one direction. I've accommodated for this by always feeding in one direction with very good results, but that seems a little like cheating. Any thoughts from our experts?

Terry, I'm no expert but it sounds like the reason you're getting better results when feeding from left to right is because you are climb cutting in that direction. It is not unusual for a fly cutter to leave trace swirls when feeding in the conventional direction if the mill is in tram. My theory as to why this happens is that the insert has taken the meat of the cut on the forward stroke and the insert is deflecting due to radial forces on the back side of the stroke. As you know, very light cuts with an insert will increase radial forces and the insert will deflect so it leaves marks as it skates over the surface. That is how I see it anyway.

The goal with a fly cutter is to obtain a flat surface that is accurately dimensioned. A fly cutter is not a finishing tool. Still, my Sherline inserted carbide flycutter that I use on my Sherline mill and RF-31 will leave a near mirror finish in steel or aluminum. It is a very rigid tool, much like a single insert face mill, so deflection on the back side is minimized. As expected, there is very little back side swirling. The insert I use has a 0.015" nose radius that is about the best compromise I've found for this fly cutter. It will take a 0.005" depth of cut and do so accurately.

In contrast, my Tormach Superfly insert has a huge nose radius and I always have back side swirls. I rough conventionally and do a finish pass in the climb direction to minimize the effect but its still there; you can see it but you can't feel it. I personally do not think it is worth the effort to throw the mill out of tram just to minimize the swirl marks; there are better ways to obtain a nice surface finish.

Bottom line: use the smallest nose radius you can find and experiment with feed direction. Use whichever works best and at least for aluminum, max out your speed and feed fast enough to actually cut. Feeding too slow with an insert increases deflection and will not finish as well.