# Interesting Behavior While Using Fly Cutter



## prasad (Jan 18, 2016)

I bought a set of fly cutters for my mini-mill but never used them until today. Today I tried a test piece and I was very surprised by the finish I got. I am now hooked to fly cutters and I swear, I will never use an end mill if it can be done with a fly cutter. 



Having said that I want to share a picture of what I observed. I had my fly cutter set to about 2 inch diameter and running at about 2400 rpm. The test piece I picked up had two holes as you can see. After the run I noticed one pf the holes had a kind of a shadow in the direction the cutter moved. If you will please see the picture where I have drawn a red oval around this area. You will see a series of round shadows of the hole radiating in roughly 1 O'clock direction from the hole. These shadows are only visible in certain conditions of lighting. They are not felt when I touch the surface by finger. I do not see this pattern as a defect but I am curious what may have caused this. Is it due to the tool vibration? My machine was G8689 Grizzly Mini-mill, unmodified version. 

I milled the other side of the same disk at lower speed and I got better finish and no shadows. 

Thank you for your comments to help me understand
Prasad


----------



## mattthemuppet2 (Jan 18, 2016)

I'd guess it's from the interrupted cut due to the hole. I've often see that facing disks that have holes in. The tool tip springs into the hole as cutting pressure is relieved and then the impact and deeper cut flex it back again.


----------



## joshua43214 (Jan 18, 2016)

RPM = SFM*4/Diameter
This would indicate your stock has an SFM of 1200...

might want to slow that puppy way down, as you already noticed it will improve your finish. 180 RPM would be a nice starting point for steel, and 600 for aluminum with a 2" cutter.
Harmonics are another issue that is often not discussed with flycutters. When run too fast, they will vibrate and reduce finish quality. This is especially true when they pass over a hole.

Also, it might be a trick of the light, but I am not seeing the cross hatch pattern typical of flycutting. To get the best finish, you should completely pass over the work from end to end.


----------



## kd4gij (Jan 18, 2016)

:+1: RPM was way to fast. It also looks like your mill isn't trammed, You should get a cross hatch pattern as stated .


----------



## Wreck™Wreck (Jan 18, 2016)

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.


----------



## royesses (Jan 18, 2016)

prasad said:


> I bought a set of fly cutters for my mini-mill but never used them until today. Today I tried a test piece and I was very surprised by the finish I got. I am now hooked to fly cutters and I swear, I will never use an end mill if it can be done with a fly cutter.
> View attachment 119634
> 
> 
> ...



Did you grind your own bit? I've had my LMS fly cutter set for about six months but have not needed to use them yet.  Next free time I have I'll grind a bit and try the fly cutter on my mini mill. You've inspired me.  I assume the mini mill will require very small depth of cuts. It is not a very rigid machine.


----------



## Wreck™Wreck (Jan 18, 2016)

royesses said:


> Did you grind your own bit? I've had my LMS fly cutter set for about six months but have not needed to use them yet.  Next free time I have I'll grind a bit and try the fly cutter on my mini mill. You've inspired me.  I assume the mini mill will require very small depth of cuts. It is not a very rigid machine.


A single point flycutter will require small depths of cut regardless of the machine rigidity, heavy stock removal are what milti tooth face mills are designed for. A single point can only be expected to remove a small amount of material per revolution. A fly cutting OP is essentially a lathe OP with interrupted cuts, choose your feeds and speeds accordingly.


----------



## prasad (Jan 18, 2016)

I bought fly cutter from KBC Tools. That was an year ago. Then I read somewhere on one of the forums that mini-mill is not suited for fly cutters. They were sitting in a corner unused. On Saturday I was at Cabin Fever Expo and there was a demo mill being run by a guy at LMS stall. I saw him using a fly cutter and I was impressed by the finish. 

Yes, I ground the tool  bit myself. Tool bit from Harbor Freight. I am a beginner and my grinding may not be any good. Yet I am happy with the finish. I know I have to reduce the cutting speed by reading proper speed from speed charts. Today's attempt was a test run. I am very pleased with fly cutters. Of course the cut depth is small. 

Good luck to you
Prasad


----------



## prasad (Jan 18, 2016)

joshua43214 said:


> RPM = SFM*4/Diameter
> This would indicate your stock has an SFM of 1200...
> 
> might want to slow that puppy way down, as you already noticed it will improve your finish. 180 RPM would be a nice starting point for steel, and 600 for aluminum with a 2" cutter.
> ...



I agree. I was doing a test run to get a feel. Previously I had read somewhere that fly cutter is not suited for mini-mill. On Saturday I saw a guy at LMS Stall at Cabin Fever Expo running a demo (demo of a DRO) with a fly cutter. He had kept speed quite high. So I tried using similar speeds. Now that I am able to get good finish with fly cutter I will start using proper speeds. Thanks

Prasad


----------



## prasad (Jan 18, 2016)

kd4gij said:


> :+1: RPM was way to fast. It also looks like your mill isn't trammed, You should get a cross hatch pattern as stated .



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


----------



## prasad (Jan 18, 2016)

Wreck™Wreck said:


> 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 (Jan 18, 2016)

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 (Jan 18, 2016)

prasad said:


> 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 (Jan 18, 2016)

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 (Jan 18, 2016)

kvt said:


> 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 (Jan 18, 2016)

kd4gij said:


> 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 (Jan 18, 2016)

BGHansen said:


> 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 (Jan 18, 2016)

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 (Jan 18, 2016)

joshua43214 said:


> 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 (Jan 18, 2016)

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.


----------



## turnitupper (Jan 18, 2016)

I sometimes knock the mini mill out of tram a thou or so if i need a nice finish and a slight concave will not matter .
Also useful if bolting the cut end to another part as the high edges give an almost seamless joint.
Have used flycutters and 3/4"-2" face mills and end mills for this.
John.


----------



## prasad (Jan 20, 2016)

I ran the fly cutter test piece again. This time I used Niagara Cutter's "speed and feed slide" to estimate the speed at which I should run the mill as well as feed rate. I ran the cut all the way and got the "cross hatch". I now understand what you meant by cross hatch pattern. Final finish was truly superior. I did get those shadows of hole however, which really does not matter because I will not get the shadows when I cut a metal without any holes.  

Niagara speed and feed slide is great. Just got it yesterday. I don't have to use my calculator anymore. Oh, I also like the easy 400 rule recommended by Bruce.

Thanks everyone
Prasad


----------



## Bill C. (Jan 20, 2016)

I think you hit on problem, consider the new diameter and calculate for that speed and feed.  Yes Fly-cutter will show show you quickly if you are tramed of not.  If you use HHS tool bit as a cutter if there is enough space to add a stip of CRS or Alum for the cap screws can bite on.  I seen them slip out of the holders.  

Several shops I worked in they were banned as a safety hazard.  Sometimes a machinist would set up a knee mill with a flycutter with travel stops and turn his back to the machine.  A cutter could fly out and hurt the someone.

Just be careful


----------



## kingmt01 (Jan 20, 2016)

What is CRS? I have to check my fly cutter often to insure it hasn't slipped. I never considered putting something soft between the screw & tool. However I do realize that it is slipping because the screws are hard & so is the tool.

Another thing to watch out for is something that happened to me the other day. I'm not sure what happened but I crashed my mill. I was cleaning up the last side on a piece when the work was pulled up out of my vise, sheared the pin that aligns the R8 collet, & my fly cutter was bent. It did stall the motor but not fast enough. I did have 2/3 of the work above the vice so I don't know if this is what caused it out not.


----------



## prasad (Jan 20, 2016)

Bill C. said:


> I think you hit on problem, consider the new diameter and calculate for that speed and feed.  Yes Fly-cutter will show show you quickly if you are tramed of not.  If you use HHS tool bit as a cutter if there is enough space to add a stip of CRS or Alum for the cap screws can bite on.  I seen them slip out of the holders.
> 
> Several shops I worked in they were banned as a safety hazard.  Sometimes a machinist would set up a knee mill with a flycutter with travel stops and turn his back to the machine.  A cutter could fly out and hurt the someone.
> 
> Just be careful


Bill, 

Thank you, esp for the advice on using CRS or Aluminum strip. It is very timely because just last night I was thinking that my milling cutters will mostly remain unused since I have discovered the benefits of fly cutter. I checked my cutter for tightness of the screws. They are still tight but I will add a aluminum strip immediately. I dont want to get hurt. 

Thanks
Prasad


----------



## prasad (Jan 20, 2016)

kingmt01 said:


> What is CRS?
> 
> .


CRS = Cold Rolled Steel


----------



## kingmt01 (Jan 20, 2016)

Thanks


----------



## John Hasler (Jan 20, 2016)

prasad said:


> CRS = Cold Rolled Steel


To me CRS=Corrosion Resistant Steel  i.e. stainless steel (the latter is a trademark).


----------



## joshua43214 (Jan 20, 2016)

kingmt01 said:


> What is CRS? I have to check my fly cutter often to insure it hasn't slipped. I never considered putting something soft between the screw & tool. However I do realize that it is slipping because the screws are hard & so is the tool.
> 
> Another thing to watch out for is something that happened to me the other day. I'm not sure what happened but I crashed my mill. I was cleaning up the last side on a piece when the work was pulled up out of my vise, sheared the pin that aligns the R8 collet, & my fly cutter was bent. It did stall the motor but not fast enough. I did have 2/3 of the work above the vice so I don't know if this is what caused it out not.



CRS = Cold Rolled Steel

The crash can be caused by a number of things. Having the work pulled up is more common to end mills than fly cutters.
There are two basic causes of this sort of thing. Tool rake or pressure causing something to move, and loose machine parts.

I will hazard that you had one of two things go wrong. Either the work was not properly clamped, or the x-axis gib was loose enough to allow the table to tip as the center of balance went over center. Another possibility is the z-axis slid down from machine vibration. Always lock all unused axes.

Some general rules for vises:
Paper shims increase friction a lot, use them when needed.
Only place flat machined surfaces against the fixed jaw. You can break this rule a lot. Mill scale can damaged the jaw over time. Small irregularities will cause the vise to not clamp properly. Always check the surface for dings, high spots, and the like. Flatten with a file if needed. I usually put a piece of paper between hot rolled and the jaw to help gripping power and compensate for the irregular surface.

Only clamp parallel faces between the jaws. This one should be violated only at your own risk. Until this face is machined flat and parallel, a piece of soft metal such as heavy copper wire, or aluminum should be put between the moving jaw and the work. This will ensure the fixed jaw is the reference and compensate for irregular and out of parallel surfaces. Some stock comes pretty parallel, you can use paper on both sides. I use 10ga wire scraps. You can by some at the hardware store in the electrical department. Just buy what ever is cheap in 10ga or 12ga wire.

Only clamp in the center of the vise. Use a spacer or jack on the other side of the jaw if yo need to use just one side of the jaw. You can wrack a vise easily by using only one side of the jaw.

Curved surfaces need to be clamped using v-blocks.

Keep stick out to a minimum. To much stick out will cause vibration, vibration can cause the work to come loose.


----------



## kingmt01 (Jan 20, 2016)

The work was 2/3 taller then the vice jaw. I had machined the other 5 sides & after the crash I checked the sides for square which they were. It just had more surface then I wanted to use a end mill on. I thought I had it right but maybe not. I did consider putting paper in but I didn't.


----------



## prasad (Jan 20, 2016)

I had crashing of the mill when I forgot to tighten the clamp of Z axis. Vibrations made the mill creep down and finally it was simply too much for the milling cutter to handle. Motor over load acted and saved the mill. The job held in the vise got damaged. 

-Prasad


----------



## kingmt01 (Jan 20, 2016)

If my z creep it would move out of the work. I just about have to think I didn't have the vice tight enough.


----------



## Bill C. (Jan 20, 2016)

kingmt01 said:


> What is CRS? I have to check my fly cutter often to insure it hasn't slipped. I never considered putting something soft between the screw & tool. However I do realize that it is slipping because the screws are hard & so is the tool.
> 
> Another thing to watch out for is something that happened to me the other day. I'm not sure what happened but I crashed my mill. I was cleaning up the last side on a piece when the work was pulled up out of my vise, sheared the pin that aligns the R8 collet, & my fly cutter was bent. It did stall the motor but not fast enough. I did have 2/3 of the work above the vice so I don't know if this is what caused it out not.



CRS stands for Cold Rolled Steel.  I forgot to mention steel banding would probably be easier to find. At least back in my day if was common material used to ship small bundles of material. Might find some still used lumber yards to hold lumber together while shipping.  Search trash bins they likely give it to you.


----------



## Wreck™Wreck (Jan 23, 2016)

turnitupper said:


> I sometimes knock the mini mill out of tram a thou or so if i need a nice finish and a slight concave will not matter .
> Also useful if bolting the cut end to another part as the high edges give an almost seamless joint.
> Have used flycutters and 3/4"-2" face mills and end mills for this.
> John.


This has been practiced for the last 75 years in large manufacturing with face cutting mills, the light cut on the trailing edge rarely leaves a nice finish.
See it here https://books.google.com/books?id=S...epage&q=tilting a face milling cutter&f=false


----------



## turnitupper (Jan 23, 2016)

Thanks for the link to the book Wreck. Nice to see the theory behind the practice. 
Just spent over an hour of my Sunday morning (missed church, again!) reading the extract and thought "I need this book", then saw the price and thought again "No I do'nt". 
$US 95 would be wasted for the few hours a week I spend at machining.
Better to waste it on a nice bottle of Scotch.
John.


----------

