[czwalga]

I built a solsylva 25x25 machine. I used autocad/cambam/mach3.

I'm having some trouble when i'm cutting out these shapes it travels or starts to early. It's not always consistent either.

I thought it might be the flex on my router, since its only wood, but I slowed the cutting speed waaay down and still got the same result.


Anyway look at the pic you'll be able to see what i mean.

[metalworkz]

Hello,
It looks like the tool is not stopping at the same place for each direction change and I would think this is a result of mechanical backlash on the feed screw for the axis or perhaps a lose coupler from the motor to the screw? Check for backlash in the feed screws for each axis and fix if possible. Alternatively you may be able to use backlash compensation to help get better results if indeed it is from backlash. Also make sure there is no binding in your feed screws as they move.

[Frederic Gagnon]

I had a similiar situation on mine. If you are using flexible couplings to attach the screws to the motors, you need to add some shaft collars on the inside of the gantry and the other axises so the screws don't pull out when motion is reversed.

[czwalga]

I had a similiar situation on mine. If you are using flexible couplings to attach the screws to the motors, you need to add some shaft collars on the inside of the gantry and the other axises so the screws don't pull out when motion is reversed.

I'm using shaft collars, and threaded couplers. I initially thought that could be the problem but I checked the play and didnt seem like there was any.

[atwooddon]

Looking at the picture of the piece you cut, the overcuts are all in the corners where the bit is loaded on 2 sides. My guess is your machine is flexing as the bit digs into the corners. I also saw from your pictures the Z axis is extended a long ways down toward the table which makes any flexing more exaggerated.

Since you say there is no backlash, try this.... push or pull on the bit tip with the Z axis extended down toward the table (obviously with the router off). If you can easily move the bottom of the bit tip, even slightly, with minimal pressure, then it will certainly do that when cutting, particularly as it moves into a corner where the spin direction will make the bit dig into the corner. Now, retract your Z axis up to the point where the bit tip barely clears the bottom of the gantry. Now, try the same test, push and pull on the tip of the bit. The movement should be less. If so, try raising the piece you are cutting up to maximum height you can get it and still clear the gantry. Now recut the piece and see if the problem either diminishes or goes away.

If this is the problem, the only way you can fix this is to make the gantry more ridgid. Tighten bearings, etc.

Another test to check for flexing is to reverse the milling direction (change from conventional to climb direction). The if the overcuts move, then you are having a flexing problem.

Don

[czwalga]

Looking at the picture of the piece you cut, the overcuts are all in the corners where the bit is loaded on 2 sides. My guess is your machine is flexing as the bit digs into the corners. I also saw from your pictures the Z axis is extended a long ways down toward the table which makes any flexing more exaggerated.

Since you say there is no backlash, try this.... push or pull on the bit tip with the Z axis extended down toward the table (obviously with the router off). If you can easily move the bottom of the bit tip, even slightly, with minimal pressure, then it will certainly do that when cutting, particularly as it moves into a corner where the spin direction will make the bit dig into the corner. Now, retract your Z axis up to the point where the bit tip barely clears the bottom of the gantry. Now, try the same test, push and pull on the tip of the bit. The movement should be less. If so, try raising the piece you are cutting up to maximum height you can get it and still clear the gantry. Now recut the piece and see if the problem either diminishes or goes away.

If this is the problem, the only way you can fix this is to make the gantry more ridgid. Tighten bearings, etc.

Don

Thanks, I'll give it a try moving the stock up, maybe add another clamp to the router as well.

[czwalga]

Don, I tried your suggestions.

Raised the cutting surface, I added another clamp to the router. It is definitely much stiffer when you push on it, so that's a good thing.

Unfortunately didn't fix my problem.



I really think its the G-Code, that cambam is generating. On the cuts that are 'too long' in the Y axis, The router actually seems to go too far, then reverse exactly in it's tracks on the Y axis, then once it gets back to the location it should have stopped before, then it starts moving in the X axis.

After watching it close up, there's no flex/backlash, atleast that could be causing that big of a overcut.


I'm just not sure if cambam's code is not accurate, or I have some setting in cambam/mach3 not set up correctly.


Edit: I put the code into cutview and everything seems ok. Not sure what to try next.

[atwooddon]

Don, I tried your suggestions.

Raised the cutting surface, I added another clamp to the router. It is definitely much stiffer when you push on it, so that's a good thing.

Unfortunately didn't fix my problem.



I really think its the G-Code, that cambam is generating. On the cuts that are 'too long' in the Y axis, The router actually seems to go too far, then reverse exactly in it's tracks on the Y axis, then once it gets back to the location it should have stopped before, then it starts moving in the X axis.

After watching it close up, there's no flex/backlash, atleast that could be causing that big of a overcut.


I'm just not sure if cambam's code is not accurate, or I have some setting in cambam/mach3 not set up correctly.


Edit: I put the code into cutview and everything seems ok. Not sure what to try next.

I also use CamBam and would be happy to test your CB file or gcode if you will send me an email, then we can swap files back and forth. You should be able to go to my profile and send me an email. For CamBam to do that you would have had to select 'corner overcut' but that would have done the same overshoot on all corners. How do you have your CV (constant velocity) set in Mach3? One more thing, you can go into the Mach3 wizard and cut a rectangle/square pocket using the wizard. You might try that and see how the square comes out. If there is an overcut in the corners, it is not CamBam.

Don

[czwalga]

I also use CamBam and would be happy to test your CB file or gcode if you will send me an email, then we can swap files back and forth. You should be able to go to my profile and send me an email. For CamBam to do that you would have had to select 'corner overcut' but that would have done the same overshoot on all corners. How do you have your CV (constant velocity) set in Mach3? One more thing, you can go into the Mach3 wizard and cut a rectangle/square pocket using the wizard. You might try that and see how the square comes out. If there is an overcut in the corners, it is not CamBam.

Don

Never setup my CV settings (kinda new to this).

I do think it has something to do with my Mach 3 settings, the Y axis is actually reversing before the X axis starts. So I think the Y axis isn't over cutting, it's actually cutting the length it supposed to. The X axis is just starting late giving it the appearance that the Y axis cut too far.

[atwooddon]

Are your X and Y axis speed and/or acceleration set the same on both axis?

Don

[czwalga]

Are your X and Y axis speed and/or acceleration set the same on both axis?

Don

They are, I'll send you my files, tomorrow. The .cb is on my other computer.


I appreciate the help.

[czwalga]

Looks as though the machine is missing steps somewhere. When I cut out one of the shapes, it's supposed to return to it's exact same spot as the initial plunge point.

Seems to be off 1/16th or so. Not sure where i'm losing the steps though.