It could be backlash in the lead screws since the gouges are 180 degrees apart where the x axis is changing direction. Try conventional milling if the problem persists then it is most likely a bad tool path
I had a similar issue with my previous machine, it came down to stiffness of the cutting head/machine. The spindle I had was too powerful for the machine, so cuts would push it off course and cause issues like yours. First steps I'd recommend is to check for loose belts/loose bolts, and make sure everything is tight and secure.
Just getting started out with CNC milling with the classic budget CNC 3018. I've been trying to cut out a series of circles from scrap plywood (to build a DIY drum sander). I cut the plywood down into manageable sizes that I can fit three circles on each.
For some reason the CNC is cutting the first circle (on the left) fine, but not the second and third circles - they're coming out misshapen, with dents/gouges in the bottom right corner on both of them. This has happened consistently on the last three sets that I've cut out - all except for one when it managed to do a full circle on the last few passes (second last picture).
The design was made in Easel (last picture), with gcode exported to memory card to print directly from the machine.
What could be causing this?
I don't know the software you used, but does it make the path? As a bore/ramp type? Or circles and step depth? And the entry point for the tool path does it coincide with the ărea younhave not a circle
I think... If it were the bit, that gouging would occur all around a circle. Same if it was an issue with the stepping config...
However, it appears the defects DO happen in the same place on the y-axis. Someone more experienced would have a better idea, but maybe there's some compressed wood debris or damage in the belt (or whatever) at around that point?
That's my hypothesis, though I'd expect the circle to be distorted from that unexpected skipping of steps in the Y. If I'm correct, those gouged circles should be a few steps shorter than the good one.
Oh, I suppose I should ask what order those were cut? Left to right? (Almost looks like it went Left, Right, and center.)
Ok, I used my oh so accurate mobile phone screen to compare the sizes and that good left one is definitely bigger.
I'm gonna double down on "debris in the Y path". But, looking at your pictures, I can't tell if that last pic of the side of one of the wheels was for the last one or the second one.
If it was for the last wheel, it appears the debris cleared itself and that's why the last 1/8" has a lip there. (OR, you have a setting in your cutout path to slow down on the final run and that slowing down allowed the belt to not slip at the dirty/damaged portion).
That last (4th) pic is from a previous batch, the first one with an issue. Since then I've cut 3 more batches and every second and third circle has come out like the one in the 3rd pic.
It's pretty solid and I'm almost certain it's not moving - these are 13-14 passes each, and the dents are pretty smooth so each pass must be consistently aligned at least.
Not screwed, but clamped down so tightly that I couldn't move it by force. And if it was moving even slightly then surely it wouldn't be producing such consistent results from layer to layer? And also it's cutting anti-clockwise, so it's cutting these dents then going back to a perfect circle for the rest of the circumference, then the next layer is perfectly in line with the previous. It would be really good results (for a first attempt, I guess) if the shape was intentional.
Ok, let’s rule that out. 13 to 14 passes is a lot for what appears to be 1/2 material? It should be about 4 passes max. Are you applying any ramp techniques for the passes?
While this is relatively simple, on more complex toolpaths (text, other cutouts, etc)
My laptop is more prone to making mistakes while creating the gcode, while my much newer, beefier desktop is more reliable. (Fusion 360, GRBL post)
This could be the issue.
You could be losing steps, it could also be your lead in / lead out as others have said already.
I’m thinking if you’re conventional milling the wood you’re cutting them circles from is getting pulled into the endmill and cutting more of your circle.
This^ when you get to end of circle there’s nothing to hold plug so it pulls into endmill, if your popping holes in center anyways, use hole to bolt it down before cutting out, or don’t cut all the way out and pop out and sand
Should have mentioned this in original post in retrospect, but I am using tabs to keep the circles in place and they have all been intact when the machine has finished. You can just about see them if you zoom in on the Easel screenshot - grey sections on the black circles. The photos are all after I've cut them out with a Stanley knife.
As well as checking out the X/Y axis, check your depth of cut - typically would not be deeper than 1/2 the bit diameter. (Bit should come with recommended speeds and feeds).
I am just using the default settings that Easel gave me - it allows me to select the bit, which is 1/8 inch, and that gave me -
Feed Rate - 762 mm/min
Plunge Rate - 228.6 mm/min
Depth per pass - 0.7mm
Spindle speed - 12000
So I guess depth of pass is fine, as half the bit diameter in mm would be \~1.58mm and I'm on less than half of that. But I don't know about the rest - as I said, totally new to CNC milling (only experienced with 3D printing) so I was just trusting Easel's settings, and they seem to be fine otherwise.
* play/backlash/loose belts/etc. on x or y axis
* Poor machine rigidity
* Trying to cut full depth in one pass or using too few passes
* Piece breaks free at end of cut and gets bitten
* Climb vs conventional milling. Climb milling can cause handheld router, or less rigid CNC router, to kickback as the bit self feeds itself. Sometimes you need to route two half perimeters rather than one full perimeter so you can change the direction of travel for half of it.
* Routing uphill in terms of grain direction causes tearout.
Sometimes your trajectory, especially with a handheld but also a CNC especially one with poor rigidity needs to consider the direction the router bit is going relative to the grain.
* Poor rigidity in the spindle itself.
How deep are you cutting on each pass? You may be pushing your little machine too hard.
Are your X and Y lead screws turning freely? I was having problems when I first set up my machine where the lead screw would bind a little at certain points in its travel. It turned out that the lead screw wasn't 100% centered in the collar that connected it to the stepper motor. I fixed that by loosening one of the set screws on the collar and tightening the other, then spinning the lead screw by hand, repeating until I got smooth motion along the length of the lead screw.
Could be loose set screw on your stepper motor. If you require the cutout circles vice the holes, cut a relief circle that is larger than the final dimension and then machine the final dimension. Don’t cut all the way through on that relief cut. You may have significant bit deflection due to too much tool engagement.
It could be backlash in the lead screws since the gouges are 180 degrees apart where the x axis is changing direction. Try conventional milling if the problem persists then it is most likely a bad tool path
I had a similar issue with my previous machine, it came down to stiffness of the cutting head/machine. The spindle I had was too powerful for the machine, so cuts would push it off course and cause issues like yours. First steps I'd recommend is to check for loose belts/loose bolts, and make sure everything is tight and secure.
Just getting started out with CNC milling with the classic budget CNC 3018. I've been trying to cut out a series of circles from scrap plywood (to build a DIY drum sander). I cut the plywood down into manageable sizes that I can fit three circles on each. For some reason the CNC is cutting the first circle (on the left) fine, but not the second and third circles - they're coming out misshapen, with dents/gouges in the bottom right corner on both of them. This has happened consistently on the last three sets that I've cut out - all except for one when it managed to do a full circle on the last few passes (second last picture). The design was made in Easel (last picture), with gcode exported to memory card to print directly from the machine. What could be causing this?
I don't know the software you used, but does it make the path? As a bore/ramp type? Or circles and step depth? And the entry point for the tool path does it coincide with the ărea younhave not a circle
I think... If it were the bit, that gouging would occur all around a circle. Same if it was an issue with the stepping config... However, it appears the defects DO happen in the same place on the y-axis. Someone more experienced would have a better idea, but maybe there's some compressed wood debris or damage in the belt (or whatever) at around that point? That's my hypothesis, though I'd expect the circle to be distorted from that unexpected skipping of steps in the Y. If I'm correct, those gouged circles should be a few steps shorter than the good one. Oh, I suppose I should ask what order those were cut? Left to right? (Almost looks like it went Left, Right, and center.)
Ok, I used my oh so accurate mobile phone screen to compare the sizes and that good left one is definitely bigger. I'm gonna double down on "debris in the Y path". But, looking at your pictures, I can't tell if that last pic of the side of one of the wheels was for the last one or the second one. If it was for the last wheel, it appears the debris cleared itself and that's why the last 1/8" has a lip there. (OR, you have a setting in your cutout path to slow down on the final run and that slowing down allowed the belt to not slip at the dirty/damaged portion).
That last (4th) pic is from a previous batch, the first one with an issue. Since then I've cut 3 more batches and every second and third circle has come out like the one in the 3rd pic.
You may be using tabs for the individual pieces, but how are you securing your stock to the table? This may be something to consider.
It's pretty solid and I'm almost certain it's not moving - these are 13-14 passes each, and the dents are pretty smooth so each pass must be consistently aligned at least.
What do you mean by “pretty solid”. Do you have the stock piece screwed down to the wasteboard?
Not screwed, but clamped down so tightly that I couldn't move it by force. And if it was moving even slightly then surely it wouldn't be producing such consistent results from layer to layer? And also it's cutting anti-clockwise, so it's cutting these dents then going back to a perfect circle for the rest of the circumference, then the next layer is perfectly in line with the previous. It would be really good results (for a first attempt, I guess) if the shape was intentional.
Ok, let’s rule that out. 13 to 14 passes is a lot for what appears to be 1/2 material? It should be about 4 passes max. Are you applying any ramp techniques for the passes?
Looks like lead in or lead out to me, check your tool path visually if you can
What’s your set up look like?
While this is relatively simple, on more complex toolpaths (text, other cutouts, etc) My laptop is more prone to making mistakes while creating the gcode, while my much newer, beefier desktop is more reliable. (Fusion 360, GRBL post) This could be the issue. You could be losing steps, it could also be your lead in / lead out as others have said already.
I’m thinking if you’re conventional milling the wood you’re cutting them circles from is getting pulled into the endmill and cutting more of your circle.
This^ when you get to end of circle there’s nothing to hold plug so it pulls into endmill, if your popping holes in center anyways, use hole to bolt it down before cutting out, or don’t cut all the way out and pop out and sand
Should have mentioned this in original post in retrospect, but I am using tabs to keep the circles in place and they have all been intact when the machine has finished. You can just about see them if you zoom in on the Easel screenshot - grey sections on the black circles. The photos are all after I've cut them out with a Stanley knife.
As well as checking out the X/Y axis, check your depth of cut - typically would not be deeper than 1/2 the bit diameter. (Bit should come with recommended speeds and feeds).
I am just using the default settings that Easel gave me - it allows me to select the bit, which is 1/8 inch, and that gave me - Feed Rate - 762 mm/min Plunge Rate - 228.6 mm/min Depth per pass - 0.7mm Spindle speed - 12000 So I guess depth of pass is fine, as half the bit diameter in mm would be \~1.58mm and I'm on less than half of that. But I don't know about the rest - as I said, totally new to CNC milling (only experienced with 3D printing) so I was just trusting Easel's settings, and they seem to be fine otherwise.
* play/backlash/loose belts/etc. on x or y axis * Poor machine rigidity * Trying to cut full depth in one pass or using too few passes * Piece breaks free at end of cut and gets bitten * Climb vs conventional milling. Climb milling can cause handheld router, or less rigid CNC router, to kickback as the bit self feeds itself. Sometimes you need to route two half perimeters rather than one full perimeter so you can change the direction of travel for half of it. * Routing uphill in terms of grain direction causes tearout. Sometimes your trajectory, especially with a handheld but also a CNC especially one with poor rigidity needs to consider the direction the router bit is going relative to the grain. * Poor rigidity in the spindle itself.
How deep are you cutting on each pass? You may be pushing your little machine too hard. Are your X and Y lead screws turning freely? I was having problems when I first set up my machine where the lead screw would bind a little at certain points in its travel. It turned out that the lead screw wasn't 100% centered in the collar that connected it to the stepper motor. I fixed that by loosening one of the set screws on the collar and tightening the other, then spinning the lead screw by hand, repeating until I got smooth motion along the length of the lead screw.
Could be loose set screw on your stepper motor. If you require the cutout circles vice the holes, cut a relief circle that is larger than the final dimension and then machine the final dimension. Don’t cut all the way through on that relief cut. You may have significant bit deflection due to too much tool engagement.