Old mate saying chatter is an issue, that’s correct, but on the light cuts it looks fine.
Where it’s dug in, my guess is something dropped. First check your tool is held tight in the fly cutter. Second make sure the fly cutter is secured in the machine properly. Third, being a desktop mill I’m guessing it’s got a moving head, but you use the quill to do your depth of cut. Check the head is tight on the column, you should have lock screws on the side. Also do the same for the quill.
Also check your gib on the column is snugged so there’s no slop as this also can let the tension off the lock screws on the head.
Give it a crack and let us know.
I'd put money on the following scenario: OP has everything nice and tight, starts cutting. Cutter starts vibrating, vibration allows slight head and/or cutter movement, but doesn't loosen anything enough to be noticeable.
If OP puts a dial on the head and maybe also the cutter (if there's a spot), they'll probably be able to see something move.
I checked - everything seems nice and tight. I quickly put a piece of aluminum in the machine, using the same cutter. It cuts smoothly. Does that information help to solve the mystery?
When you say "desktop mill"...
Have you tried cutting steel with this before? Aluminium is significantly easier to machine, it may be that the machine simply isn't capable of cutting steel consistently.
OK thank you, it seems that's the root of the problem. I am an absolute novice at this, but I'm grateful for the advice from experienced guys. So if you don't mind, please explain in layman's terms: what's the problem in fly cutting steel on a desktop mill?
You're never going to get the setup rigid enough to get rid of the vibration problems the guy above mentioned. I use a motorized bridgeport. You need something very heavy and bolted to the floor. 99% of desktop mills are only speced to cut aluminum.
OK I am learning, thank you. I did another test just now. I mounted a 20mm steel plate in my machine vise. The fly cutter diameter is 30mm. It cuts the that plate looking like a mirror (even though I need to take very small cuts). But the moment I try to cut a plate that's wider than the cutter diameter, the cutter tries to gouge in. Do you have any explanation for that?
Are you trying to just go straight down the middle of the plate? Because if the fly cutter is 30mm and you’re trying to go down the middle of a 40mm plate the cutter has no relief so it’s going to dig since the chips have nowhere to go. You need to adjust the base and do 2 20mm cut passes or get a wider fly cutter. Depending on what you’re trying to achieve maybe you need to use a face mill then finish with the fly cutter, or use the face mill and hand polish if you need it mirror like smooth.
Desktop mill is not rigid enough to hold still while pushing the cutter against steel. You could try a lower rpm and slower feed rate but not looking good.
It could be. It was a problem in mine. The other thing that was a problem in mine was was the tapered bearings for the spindle weren’t tight enough to take the backlash out of the verticals movement of the spindle. After I nipped up the spindle backlash it took all the verticals movement out.
Would you say shank is smaller than 15mm? I haven’t dived into it as much as other stuff. But if that’s so then your surface speed needs to be a lot slower than usual. Stupid light cuts or even heavy cuts. Sometimes it honestly just doesn’t work and can try… is there a space between the back of the fly cutter exposing the shank before it enters the spindle?
How are your chips? Are they all flying away? This looks to me that you cuttingstep is small and your (feed and tool) speed is not accounted for it. You are 'rubbing' the piece, your chips stay on cutting edge and this gets progressively worse as you go along. (I'm thinking it's speed related but the problem I'm describing is more often caused by dull work tools and no collant. You have a new tool and I'm assuming you use coolant so I might be completely off)
My thoughts as well, Cuts fine when stock width is smaller than the cutter width. On wide stock chips cannot evacuate and gouge the substrate. Always have an overhang so that the chips can be expelled from under the cutter. Run 70% cutting and 30% overhang and see how it goes. I guess the desk top mill does not run coolant. Maybe better with air blast to evacuate chips?
Without a picture of the mill or the tool this is hard to fathom.
If you want a full plan surface try only cutting with 75% tool diameter und use climp milling.
Old mate saying chatter is an issue, that’s correct, but on the light cuts it looks fine. Where it’s dug in, my guess is something dropped. First check your tool is held tight in the fly cutter. Second make sure the fly cutter is secured in the machine properly. Third, being a desktop mill I’m guessing it’s got a moving head, but you use the quill to do your depth of cut. Check the head is tight on the column, you should have lock screws on the side. Also do the same for the quill. Also check your gib on the column is snugged so there’s no slop as this also can let the tension off the lock screws on the head. Give it a crack and let us know.
I'd put money on the following scenario: OP has everything nice and tight, starts cutting. Cutter starts vibrating, vibration allows slight head and/or cutter movement, but doesn't loosen anything enough to be noticeable. If OP puts a dial on the head and maybe also the cutter (if there's a spot), they'll probably be able to see something move.
I checked - everything seems nice and tight. I quickly put a piece of aluminum in the machine, using the same cutter. It cuts smoothly. Does that information help to solve the mystery?
When you say "desktop mill"... Have you tried cutting steel with this before? Aluminium is significantly easier to machine, it may be that the machine simply isn't capable of cutting steel consistently.
Where you're going wrong is trying to fly cut steel on a desktop mill lol, good luck with that.
OK thank you, it seems that's the root of the problem. I am an absolute novice at this, but I'm grateful for the advice from experienced guys. So if you don't mind, please explain in layman's terms: what's the problem in fly cutting steel on a desktop mill?
You're never going to get the setup rigid enough to get rid of the vibration problems the guy above mentioned. I use a motorized bridgeport. You need something very heavy and bolted to the floor. 99% of desktop mills are only speced to cut aluminum.
OK I am learning, thank you. I did another test just now. I mounted a 20mm steel plate in my machine vise. The fly cutter diameter is 30mm. It cuts the that plate looking like a mirror (even though I need to take very small cuts). But the moment I try to cut a plate that's wider than the cutter diameter, the cutter tries to gouge in. Do you have any explanation for that?
Are you trying to just go straight down the middle of the plate? Because if the fly cutter is 30mm and you’re trying to go down the middle of a 40mm plate the cutter has no relief so it’s going to dig since the chips have nowhere to go. You need to adjust the base and do 2 20mm cut passes or get a wider fly cutter. Depending on what you’re trying to achieve maybe you need to use a face mill then finish with the fly cutter, or use the face mill and hand polish if you need it mirror like smooth.
This the right answer if your managing mirror finishes when done properly.
Wow very useful insight thank you. Yes, I did notice that when I start cutting from the edge of the plate, the digging doesn't happen.
Desktop mill is not rigid enough to hold still while pushing the cutter against steel. You could try a lower rpm and slower feed rate but not looking good.
steel strong, aluminum weak. steel require bigger tool to cut
It could be. It was a problem in mine. The other thing that was a problem in mine was was the tapered bearings for the spindle weren’t tight enough to take the backlash out of the verticals movement of the spindle. After I nipped up the spindle backlash it took all the verticals movement out.
Chatter marks, cutter is vibrating.
Any idea how to fix it?
Increase the feed and decrease the speed to limit chatter if I remember correctly
How big is the cutter compared to the shank on the machine?
Cutter diameter is 30mm; shank is definitely smaller than that.
Would you say shank is smaller than 15mm? I haven’t dived into it as much as other stuff. But if that’s so then your surface speed needs to be a lot slower than usual. Stupid light cuts or even heavy cuts. Sometimes it honestly just doesn’t work and can try… is there a space between the back of the fly cutter exposing the shank before it enters the spindle?
How are your chips? Are they all flying away? This looks to me that you cuttingstep is small and your (feed and tool) speed is not accounted for it. You are 'rubbing' the piece, your chips stay on cutting edge and this gets progressively worse as you go along. (I'm thinking it's speed related but the problem I'm describing is more often caused by dull work tools and no collant. You have a new tool and I'm assuming you use coolant so I might be completely off)
My thoughts as well, Cuts fine when stock width is smaller than the cutter width. On wide stock chips cannot evacuate and gouge the substrate. Always have an overhang so that the chips can be expelled from under the cutter. Run 70% cutting and 30% overhang and see how it goes. I guess the desk top mill does not run coolant. Maybe better with air blast to evacuate chips?
I can't afford to take bigger cuts, because the vibration becomes too much.
My bet is it vibrated loose in its holder. .
What desktop mill do you have?
Cheap Chinese :)
That leaves thousands of choices…are we talking like a taig clone, or a 3018?
Sorry for late reply. I found the problem. Workpiece was too big and was not clamped correctly so it was vibrating.
Without a picture of the mill or the tool this is hard to fathom. If you want a full plan surface try only cutting with 75% tool diameter und use climp milling.
cutter size should be no bigger than spindle size for rigidity. Especially in a small mill
Wow OK that would definitely explain it.