Small circles NOT round

[kennected]

Hi Everyone,

I am having trouble cutting small round holes in 5/16 birch plywood. My machine is running Clearpath motors, UB1 and UC300. My bit is a very small .028 end mill.
I have successfuly worked through this issue with Mach3 with steppers in the past but am having difficulty now with UCCNC. I am using 2017 Screenset but don'y think it is the issue. The toolpath is a profile cut of a 1/4" hole. I am cutting inside the line. I am getting very odd shaped cavities that are not close to smooth circles. I think in the past this was an acceleration issue but I have played with that by changing from a setting of 10 to much higher to where the machine jumps abruptly. I am now at 18 in acceleration for both X and Y axis but still not getting what I need, although I think it improved a little.

Ken

[cncdrive]

Try to adjust the CV settings on the general settings page. (left side of the page)
They are to control the path blending and tolerances.
The UCCNC will only make the path error as much you allowing it to do so and it is defined by these parameters.
What these parameters do is that you can define with them how to do the constant velocity control, how much path error you allow the software to do on the path in order to maintain the feedrate.
If the path error is set high then you allow the software to go off the path with high distance, so the software is allowed to go off the path if it can't maintain the speed otherwise e.g. if it is physically impossible to do on the original path.
If you set the tolerance low then the UCCNC is forced to follow the path more closely and so it is allowed to make less path error.
The optimal values depend on the job, the allowed tolerances of the job.
If the job allows high tolerances then you can set the parameters high and so the UCCNC can maintain the feedrate and can finish the job faster, but may create large errors on the path.
And if your job requires tight tolerances then you set the parameters low so the software will run with tight tolerances, it will follow the path closely.
Small circles are one of the most complicated to maintain the feedrate, because with a circle the movement direction and the direction of the axes changing and when they are small then the direction changes rapidly and so it is hard to maintain the feedrate, but if you set the tolerances low enough the UCCNC will not create larger error than that and so the circles will be round. The software then may not be able to maintain the feedrate you setup (depends on the settings), but will make nice circles.
The exact meanings of the CV parameters are described in the UCCNC manual (G64 code). I suggest you read them through to understand how to set the parameters for the different jobs.

And accelerations also plays a rule in how the feedrate can be maintained. The higher the accelerations of the axes of the circle the faster the software is allowed to accelerate and deccelerate and so the software can maintain the feedrate better in many cases. Also note that with the UCCNC you can setup higher acceleration than with Mach3, because Mach3 has a never fixed bug in it's motion planner which causes to over accelerate your settings, but the UCCNC will not do that, so you may setup the acceleration higher in the UCCNC than you did in Mach3 and so you will get a better overal performance.

[skrap]

Are you running your machine in inches and using constant velocity mode and using the default settings?

UCCNC is unit-less so you have to make sure the settings that go along with CV mode make since for your units. By default these are values that work better for millimeters. For example - linear error max is defaulted to 0.03 - which is not precise enough for inches, but works for mm.

There are some threads on this forum and CNC Zone which I can't seem to find at the moment.

[cncdrive]

Yes, Skrap is correct, that the default error values are 0.03 which is small enough for the avarage millimeters jobs,
but 0.03 inches is 0.762 millimeters which is a high tolerance and you may visually see that on the workpiece.
So, if your units are inches then for first round try to simply set the linear error and corners error parameters to about 25.4 times smaller to value of about 0.001.

[skrap]

Try to adjust the CV settings on the general settings page. (left side of the page)
They are to control the path blending and tolerances.
The UCCNC will only make the path error as much you allowing it to do so and it is defined by these parameters.
What these parameters do is that you can define with them how to do the constant velocity control, how much path error you allow the software to do on the path in order to maintain the feedrate.
If the path error is set high then you allow the software to go off the path with high distance, so the software is allowed to go off the path if it can't maintain the speed otherwise e.g. if it is physically impossible to do on the original path.
If you set the tolerance low then the UCCNC is forced to follow the path more closely and so it is allowed to make less path error.
The optimal values depend on the job, the allowed tolerances of the job.
If the job allows high tolerances then you can set the parameters high and so the UCCNC can maintain the feedrate and can finish the job faster, but may create large errors on the path.
And if your job requires tight tolerances then you set the parameters low so the software will run with tight tolerances, it will follow the path closely.
Small circles are one of the most complicated to maintain the feedrate, because with a circle the movement direction and the direction of the axes changing and when they are small then the direction changes rapidly and so it is hard to maintain the feedrate, but if you set the tolerances low enough the UCCNC will not create larger error than that and so the circles will be round. The software then may not be able to maintain the feedrate you setup (depends on the settings), but will make nice circles.
The exact meanings of the CV parameters are described in the UCCNC manual (G64 code). I suggest you read them through to understand how to set the parameters for the different jobs.

And accelerations also plays a rule in how the feedrate can be maintained. The higher the accelerations of the axes of the circle the faster the software is allowed to accelerate and deccelerate and so the software can maintain the feedrate better in many cases. Also note that with the UCCNC you can setup higher acceleration than with Mach3, because Mach3 has a never fixed bug in it's motion planner which causes to over accelerate your settings, but the UCCNC will not do that, so you may setup the acceleration higher in the UCCNC than you did in Mach3 and so you will get a better overal performance.

cncdrive,

This seems to be a common issue that is hurting the performance of machines ran with UCCNC.

Most people are just going to start using the software assuming the defaults are a good place to start.

Adding more clear detail to the manual (which likely most people don't read) could be a good starting point. Even though UCCNC has no units, the values in the config reflect the unit the machine is working in so maybe there could be a inch-default and mm-default configuration. Something that will alert uses to determining the best values for their machine. There could be some hints in the 'configuration -> general settings' screen saying what good starting values are for in or mm. ex - Linear error max: in = 0.001, mm = 0.03. Another idea is to leave them blank and force the user to set them, directing them to some documentation to guide them.

Somehow people need to be aware that those settings are important.

[Gary Campbell]

If the control has no units and is shipped with metric settings, shouldn't there be a supplied doc that provides similar recommended settings for imperial units?

[kennected]

Thanks everyone. Almost all of your replies make perfect sense to me (scarey). I do use inches and can see that choice in setup will require some tuning. I will make the adjustments tomorrow and report back.