Over cutting corners problem.
Over cutting corners problem.
I am cutting letters out of 3mm acrylic, using a 1/8" dia by 1/64" tip radius 10degree (20 included) bit. I am using profile toolpath, with sharp external and sharp internal corners selected, machining outside.
I find that the internal corners are always overcut. The bit lifts as though to make a sharp corner with the point of the tool, but the cut is as though the fatter part of the tool has not only cut it out, but gone into the corner a little extra as well.
I suspect the geometry of the tool may be half a degree out - 20.5 not 20, and I am cutting .25mm below the 3mm, so I get a clean edge on the bottom, not a rounded one. Could these be the cause?
They may be factors that are vastly outweighed by some other stupid error I have made, but I can't think where to look.
thanks for reading
Jim
I find that the internal corners are always overcut. The bit lifts as though to make a sharp corner with the point of the tool, but the cut is as though the fatter part of the tool has not only cut it out, but gone into the corner a little extra as well.
I suspect the geometry of the tool may be half a degree out - 20.5 not 20, and I am cutting .25mm below the 3mm, so I get a clean edge on the bottom, not a rounded one. Could these be the cause?
They may be factors that are vastly outweighed by some other stupid error I have made, but I can't think where to look.
thanks for reading
Jim
- TReischl
- Vectric Wizard
- Posts: 4589
- Joined: Thu Jan 18, 2007 6:04 pm
- Model of CNC Machine: 8020 48X36X7 RP 2022 UCCNC Screenset
- Location: Leland NC
I had a similar problem over a month ago. In my case it was the machine. Not even close to being rigid enough. Just finished my new machine and do not have the problem. If all else fails, you might want to take a look at your setup on the machine.
"If you see a good fight, get in it." Dr. Vernon Johns
- TReischl
- Vectric Wizard
- Posts: 4589
- Joined: Thu Jan 18, 2007 6:04 pm
- Model of CNC Machine: 8020 48X36X7 RP 2022 UCCNC Screenset
- Location: Leland NC
Even at a crawl mine did it, like at 5 inches per minute. A dead sharp tool did not help either. What I finally did to figure it out is work the math.
I used my CAD program to interpret the numbers in the G code, it was dead on. So after that, it has to be the machine or tool. I simplified things by programming a single pass cut, so I did not have to look at bunches of numbers.
Good luck, things like this are why I am bald!
I used my CAD program to interpret the numbers in the G code, it was dead on. So after that, it has to be the machine or tool. I simplified things by programming a single pass cut, so I did not have to look at bunches of numbers.
Good luck, things like this are why I am bald!
"If you see a good fight, get in it." Dr. Vernon Johns
- dighsx
- Vectric Wizard
- Posts: 939
- Joined: Tue Nov 01, 2005 12:36 am
- Location: Royal Oak, Michigan USA
- Contact:
This looks like a bit geometry problem to be. Like VCP thinks the bit is a vbit but the bit is round. If you look at the inner corners you can see where it pulls up but cuts a round notch. Have you tried doing this with a vbit and see if you get the same results?
If it isn't that then my next best guess would be you've got a backlash problem. But just looking at those pics I bet it's something to do with the shape of the bit and how you've got it setup in VCP.
Take a pic of the bit and a screen shot of the setup page for that bit if you can.
If it isn't that then my next best guess would be you've got a backlash problem. But just looking at those pics I bet it's something to do with the shape of the bit and how you've got it setup in VCP.
Take a pic of the bit and a screen shot of the setup page for that bit if you can.
Take it easy.
Jay (www.cncjay.com)
Jay (www.cncjay.com)
- BradyWatson
- Vectric Craftsman
- Posts: 136
- Joined: Fri Jan 13, 2006 5:57 pm
- Location: South Jersey, USA
- Contact:
braidmeister
Your right, it's not a v bit. I think if it was it would be spot on. I will test this asap as dighsx suggests.
pic of bit setup follows.
I had a good look at the z axis this am, because I guess if there was backlash, the tool has continued into the letter thinking the z has started to rise, but it hasn't, hence it's cutting into the letter. There was some backlash, .03mm at worst. Would this cause it?
But even on the first pass .5mm, it is starting to cut a notch out
dighsx the bit is from Menlo-USA.com , tool no 02971, if you want to look at their spec.
The whole bit is only 1.5" long, so I don't think deflection is a problem
thanks for the attention
Jim
Your right, it's not a v bit. I think if it was it would be spot on. I will test this asap as dighsx suggests.
pic of bit setup follows.
I had a good look at the z axis this am, because I guess if there was backlash, the tool has continued into the letter thinking the z has started to rise, but it hasn't, hence it's cutting into the letter. There was some backlash, .03mm at worst. Would this cause it?
But even on the first pass .5mm, it is starting to cut a notch out
dighsx the bit is from Menlo-USA.com , tool no 02971, if you want to look at their spec.
The whole bit is only 1.5" long, so I don't think deflection is a problem
thanks for the attention
Jim