Help with fly cutter tool please

[boatmadman]

Help!
This is my flycutter tool after one cut of less than 0.1mm on cast iron. I re ground the tool and tried again, but got the same flatspot.
I used this cutter successfully on a previous piece of C I with good results, so what is going wrong?
The tool didn’t get too hot when grinding – dipped in water every couple of seconds.
The only thing I can think of is, have I reground the angles shown by the arrows in pic 3 too deep?
Any ideas please?   
Ian
 

 

 

 

[John Hill]

Hi Ian

Is that a chip?  Maybe your angles are just a little too 'sharp' and the cutting edge is not getting enough support.

I read that on some types of tool material dunking in water gives the hot tool a thermal shock which causes tiny cracks and I presume chips,  of course I can not say if that is the problem in your case.

 

[boatmadman]

Hi,

I have ground another tool, with shallower angles, tried again, but still got the same problem, this is weird, cos I was successful with this a few weeks ago on another piece of CI cut from the same block!

I think it started out as a chip and then rubbed smooth.

Ian

[Darren]

You might have too high a spindle rpm, remember a bigger arc has increased cutting speed over a smaller arc.

Try slowing it down 

[websterz]

CI is finicky stuff, especially if you are cutting near the outer edge of the material. That hard outer skin is a bear on tooling!

[Jasonb]

I'd also say its the CI, either a hard skin or chilled casting as the tool has worked OK previously.

Don't know what you are working on but I've heard a lot of Stuarts stuff is comming out chilled.

Jason

[spuddevans]

It could well be just a hard spot.

I have had something similar happen to me recently. I had a chunk hacked off a a cast iron bar, or it might well have been a large sash weight. Having roughly squared the "chunk" up, I set about sizing it to thw desired shape using a flycutter that was sharpened to pretty much the same profile as yours. I got 1 side flycut to a lovely smooth finish, turned over and got the opposite side smooth. I kept on cutting it down with the flycutter, until it hit a tough spot and it flattened the cutter exactly like yours is.

I re-sharpened the cutter, and tried taking a shallower cut but the same thing happened. At this I broke out an end mill and it went thru it like it was butter (all be it cast iron butter )

I guess that there can be some harder spots buried in CI that flycutters dont like. Have at it with an end mill and see if that cuts it better.

Tim

[boatmadman]

Tim,

You could be onto something there, I have gone at it with an end mill and it cut through ok, leaving the usual end mill machine marks.

For this item I am thinking I might leave the machine marks as a finishing pattern as they are regular in spacing.

Ian

[Darren]

Is the end mill also HSS?

If so why didn't the hard spots damage it's cutting edges?

[spuddevans]

Is the end mill also HSS?

Yup

If so why didn't the hard spots damage it's cutting edges?

I really dont know 

I did try the hard spot with a file and it wouldnt file well at all, kinda skipped across it. Yet the end mill didnt blink when cutting it  And I used the endmill to size the remaining sides of the "Chunk" and it left a finish that looked just fine ( for a end milled piece ) ie, no seeming indications of a blunt mill 

It's a mystery to me, answers on a postcard please...


Tim

[Darren]

I'm only guessing Tim and merely offering a suggestion...

My thinking is the surface speed of the flycutter is much higher than the end mill cutter. The flycutter is simply being pushed too fast through the hard bits to cope and it's taking the edge off.

What do you think?

[GordTopps]

What sort of speeds are we looking at for fly cutting, (depending on radius of flycutter of course)?
Thanks
Gordy

[spuddevans]

The flycutter is simply being pushed too fast through the hard bits to cope and it's taking the edge off.

What do you think?

I think you might have hit the proverbial nail on the thumb. I was using the smallest of a set of 3 flycutters, it has a cutting-edge-diameter of about 1.5" and I may well have been running the speed a little hot ( not having a rpm meter I set the speed on what seems to give the best finish along with what feels and sounds right ) Then I changed over to a 14mm 4 flute end mill.

What sort of speeds are we looking at for fly cutting, (depending on radius of flycutter of course)?
Thanks
Gordy

On my little flycutter mentioned above ( I havent yet sharpened up the other 2 larger ones ) I would run at a max of just under half speed on my belt-drive-converted-X2, ( that's about as fast as I can get it without it causing vibrations to set in ) without a meter to tell me the exact rpm I would guestemate that would be about 1300-1500rpm. However ( and that's a big however ) that would be on taking light ( and I mean light for a flycutter ) cuts on soft materials like brass and Ali. On harder stuff you need to slow down even more.

A handy little online calculator for working out just what the actual surface-feet-per-minute is  Here And near the top of This page there is a basic table of cutting speeds for different metals.

Looking around, there seems to be a lot of variations in what people say should be the cutting speed you should use on a particular metal, I guess the best you can do is to get it roughly right and then let the machine ( lathe or mill ) tell you if it is too fast.

Tim

[Darren]

OK,

You used a single cutter 1.5" at 1,400 rpm.
Then at the same speed a four tipped 14mm cutter (lets call it 1/2")

That's a surface speed comparison of 550/183 inches per min

Now take into account that the end mill has four cutting tips, that means theoretically you can up the speed by a factor of four over a single tip cutter.
To look at it another way, the 1/2 end mill had a surface speed of 183/4 = 45.75 inches per min per cutting edge compared to the single cutter of 550.

Quite a difference ....

I tend to use twice the rpm for alloy over steel and while I'm not saying this is correct it seems to work.

[spuddevans]

Just to clarify, I didnt run the flycutter at 1400 rpm when surfacing the CI, ( it was probably about 7-800 rpm which was most likely still too fast ) but I do use that sort of speed on brass, and find that it leaves a real silky smooth finish.

I tend to use twice the rpm for alloy over steel and while I'm not saying this is correct it seems to work.

That seems to be a good rule of thumb , just from memory ( which is not all that reliable  ) it seems that I work on steel at half the speed of brass and ali.

Then, just to confuse matters further, things change again when you use carbide tooling, arrrrrrrrrrrrrrrghhh

I'm off to lie down in a dark corner 


Tim

[boatmadman]

I did a bit of experimenting yesterday and found my problem.

I was running the cutter too fast, 1000rpm on 2" dia cutter

I now find I get a pretty good finish on about 300rpm and a slow feed, and the tool lasts through several cuts before touching it up. 

Ian

[Darren]

Just to clarify, I didnt run the flycutter at 1400 rpm when surfacing the CI, ( it was probably about 7-800 rpm which was most likely still too fast ) but I do use that sort of speed on brass, and find that it leaves a real silky smooth finish.

Sorry Tim, I incorrectly made that assumption from the info given. But hopefully the illustration will help someone realise how diameters and numbers of cutting edges effect the equation.  

[spuddevans]

Sorry Tim, I incorrectly made that assumption from the info given. But hopefully my illustration will help someone realise how diameters and numbers of cutting edges effect the equation. 

No worries, I am amazingly gifted at not quite saying all that I need to say 

Tim

[michael3fingers]

I got this finish at around 100rpm with a nice rounded cutter. I fed by hand as slow as I possibly could..



I cant find the insert image icon?

[Darren]

I got this finish at around 100rpm with a nice rounded cutter. I fed by hand as slow as I possibly could..

Nice, have you any pictures of the tool used, esp the tip

I cant find the insert image icon?

It's in your Photobucket links 

[Jonny]

Looks like tool and or machine flex to me considering the worn edge is a lot deeper than put on if cut. Slowing it down tended to reduce the movement.

Have used big single point non rounded hss flycutters on chinky variable speed Bridgeport copies at max 2000rpm, power feed very slow and you can see the grain. If there was any movement either tool would have gone like like first piccy and or job left with chatter marks!
Now i cant do anything like that at home on either of the mills a Super Lux and a Clarke, i often have to slow it down or use carbide cutting implements even on wood- Its movement.

Nice job on the head Michael, they usually come off rough via an engine centre.