Interesting Behavior While Using Fly Cutter

[prasad]

Interrupted cut when passing over the holes, this will happen EVERY time you do such an operation whether with a mill or a lathe. If a uniform surface is required produce the holes after facing.

Thanks. I understand. I was using a piece from scrap and it had holes.

-Prasad

 

[BGHansen]

I primarily work with brass, aluminum and steel. From Tom's Techniques, the boiled down formula for steel is 400 / diameter of the cutter for RPM. 1" cutter/drill/chucked work in the lathe is 400 RPM. For a 2" fly cutter that'd be 400 / 2 or 200 RPM. Frankly, don't remember the numbers for brass or aluminum, but recall them being at least doubled. Check out Tom's Techniques (google it for the link), really informative guy.

Bruce

 

[kd4gij]

I agree, the speed was high. But my mill is trammed good. I did it just a few days before Christmas and I had not run it until today. What do you mean by cross hatch pattern?

Thanks
Prasad

If you look at the arc's in the finish there should be a second set 180 deg. You should run the fly cutter all the way across till it clears the part.

 

[kvt]

Agree with both the speed and the fact that you will get a difference any time the cutter comes off of the edge and back on. I have found this even when doing small cuts trying to provide a fine finish.
The cross hatch that they are talking about is where you bet a slight pattern from the cutter on both ends of the movement. When you go the first one would produce a ( arc across the surface then as it hits the other side of your 2 inch then it would produce a very light ) across it thus giving you a slight cross hatch design. If you are not getting it then something is not quite in line. I have seen this on my mini mill. It does not take much to be out where you will not see it. In fact that is one test I do on scrap just to check my mill when I get a chance. Another cause is a tools that is out of round, etc. That does not take much from that either. In fact I had a chip get stuck in the taper and it caused me to go through the thing retramming it until I found the chip stuck on the taper of my fly cutter. That was a pain. Oh, by the way mine is a Sherline mill so they do work on small mills.

 

[prasad]

Agree with both the speed and the fact that you will get a difference any time the cutter comes off of the edge and back on. I have found this even when doing small cuts trying to provide a fine finish.
The cross hatch that they are talking about is where you bet a slight pattern from the cutter on both ends of the movement. When you go the first one would produce a ( arc across the surface then as it hits the other side of your 2 inch then it would produce a very light ) across it thus giving you a slight cross hatch design. If you are not getting it then something is not quite in line. I have seen this on my mini mill. It does not take much to be out where you will not see it. In fact that is one test I do on scrap just to check my mill when I get a chance. Another cause is a tools that is out of round, etc. That does not take much from that either. In fact I had a chip get stuck in the taper and it caused me to go through the thing retramming it until I found the chip stuck on the taper of my fly cutter. That was a pain. Oh, by the way mine is a Sherline mill so they do work on small mills.

OK, I think I understand what you mean. I did not run the cutter that far. Cutter was set to approximately 2" diameter and the test piece was about 1 inch. I ran the cutter to go over once only i.e., I did not take it further until it goes over once again to create the cross hatch pattern. I will do it again tomorrow and see how it comes out. Of course, I will do it at proper speed.

Thanks
Prasad

 

[prasad]

If you look at the arc's in the finish there should be a second set 180 deg. You should run the fly cutter all the way across till it clears the part.

I got it. You are right I did not run it all the way. I will do it again tomorrow and see how it works.

Thanks
Prasad

 

[prasad]

I primarily work with brass, aluminum and steel. From Tom's Techniques, the boiled down formula for steel is 400 / diameter of the cutter for RPM. 1" cutter/drill/chucked work in the lathe is 400 RPM. For a 2" fly cutter that'd be 400 / 2 or 200 RPM. Frankly, don't remember the numbers for brass or aluminum, but recall them being at least doubled. Check out Tom's Techniques (google it for the link), really informative guy.

Bruce

Thank you Bruce

That is an easy to remember number. I will use it.

Regards
Prasad

 

[joshua43214]

I am not sure how viscous rumors like mini-mills not being suitable for fly-cutters come from. Mini-mills will run fly-cutters just fine. You just can't run big ones or take deep cuts.

There are a number of sources for SFM's online. The Machinery's Handbook has them of course. There are also a number of placards and the like.
I just start with steel = ~100SFM, and Aluminum = 300-500SFM and go from there depending on the toughness of the material. The tougher the material, the lower the SFM, this is why bronze and cast iron both have lower SFM than steel even though they are softer.

 

[prasad]

I am not sure how viscous rumors like mini-mills not being suitable for fly-cutters come from. Mini-mills will run fly-cutters just fine. You just can't run big ones or take deep cuts.

There are a number of sources for SFM's online. The Machinery's Handbook has them of course. There are also a number of placards and the like.
I just start with steel = ~100SFM, and Aluminum = 300-500SFM and go from there depending on the toughness of the material. The tougher the material, the lower the SFM, this is why bronze and cast iron both have lower SFM than steel even though they are softer.

I completely agree. As a beginner I have been depending and trusting info I find on the Internet. I know plenty of it may be urban myths. That is where I ask here and I get great answers. Thank you for everything, very helpful

Thanks
Prasad

 

[kingmt01]

For steel I use 120 sfm with a fly cutter. A fly cutter can be ran a little faster then the end mill. A fly cutter is easier to run on a small mill then a large end mill. A 1" end mill will pull your machine down much more then a fly cutter will. The fly cutter tool will be much cheaper then the end mill also.