Starting the journey

[JAZZCNC]

For a machine this size I,d have bearing plate 225-250mm. This gives a good balance between ridgidity and maximising the travels.

Regards your first post and you mentioning 3200 resolution then let me just clairy something that you may not be aware of.? (Think I've said this before, if not I started writing then got disturbed.!!...Lol)

Don't class micro steps as resolution because it's false, MS are mostly to help with smoothing the motor rotation and they do come at a cost in that you lose torque and require a much higher number of pulses from the controller for the same RPM causeing it to work much harder and with more chance for missed steps. Also much above 2000Ms is wasted on most steppers because they cannot resolve to those fine amounts. 1600 MS is more than good enough for most stepper systems.

If you want higher resolution then either buy smaller pitch screws or use a gear ratio then this will be your true resolution that can be trusted 100%.

Regards step errors and closed-loop then again don't rely on the closed-loop.? Step errors are often caused by over tuning the motors or binding axis etc and this is no different for a closed loop system.! The errors will still occur but the encoders will ensure the motors catch backup at some point. However the error will still have occured and will possibly show on your part, depending on what it is your cutting. The only way to ensure that you don't get step errors is to size and tune the motors correctly.
When tuned correctly and provided everything on the machine is aligned and sticktion free then you will never get step errors on a correctly tuned machine and it will perform just as good any Closed loop system that use the same type of motors.
Where Closed loop systems differ and are better is in the fact you can get 3 phase motors with a finer 0.9 or 1.2deg step angle, these run much smoother and provide more power at slightly higher Rpm's because of being 3 phase.

But if you have Steppers already that are the correct Size then with good Digital drives and correct PSU they will match any 2 phase closed loop system on performance and accuracy provided they are tuned correctly.

[ian]

Don't class micro steps as resolution because it's false, .....

Thanks - noted on MS. When people refer to "resolution" in general, what does it refer to then?

But if you have Steppers already that are the correct Size then with good Digital drives and correct PSU they will match any 2 phase closed loop system on performance and accuracy provided they are tuned correctly.

Thanks. How do I tune it correctly?

[JAZZCNC]

Thanks - noted on MS. When people refer to "resolution" in general, what does it refer to then?

It should refer to the true resolution of the ball screw pitch. But because MS does divide each step up into smaller steps then a slight amount of resolution is gained, however, it's not to the degree people believe and claim, or I should say it cannot hold that level of resolution accurately and repeatably. The keyword being repeatability, only the true pitch of the ball screw can be counted on to repeatably give the same resolution.

Thanks. How do I tune it correctly?

Well every machine is different and motor tuning settings etc are different based on each machine. However, the method of tuning is pretty much the same in that you find the limit of where it stalls the motors and then back it off a certain percentage. How high that percentage is will depend on many variables and how you want to use the machine.

For instance, If your mostly cutting 2D with the odd 2.5/3D work that doesn't have small tiny movements and speed isn't of great concern then you'll tune the machine with Velocity and acceleration in a 50/50 balance. However, if you are mostly cutting 3D or doing engraving etc that consist of 10,s of 1000's of tiny short moves then you'll tune biased more towards acceleration.
The reason you would do this is that each move as got to accelerate up to commanded speed then travel at commanded velocity then slow down before the next move comes along. In reality with tiny moves you can never hit the commanded speed before the brakes have to be applied for the next move and the whole process starts again. So tuning for high acceleration gets you up to a higher velocity before the brakes come on and it can drastically shorten the cycle time on these types of Job.

Another tuning scenario comes up for 2D profile type work where the moves are not so short so the commanded velocity is easily reached, however, if this velocity is high then it can cause issues with corner rounding when using G64 CV mode (constant velocity) because the opposite of 3D type work happens.!
Now we are at full velocity and tramping along nicely then a corner appears, but CV says we must maintain the commanded velocity but the laws of physics say there's no way we are getting around that corner at this speed so the controller as to do something so it cuts across the grass. This is no good to us because we wanted a 5mm radius not 50mm.
So we need to tune the motors to help with this, again acceleration comes into play, if we set a higher acceleration it means we can leave the point at which we need to cut across the grass until much further down the road and closer to what we wanted.
Now in practice the controller provides a few tools to help with this, like specifying when CV can be turned off for corner angle degrees then turned back on again. But motor tuning plays a big part into how well the machine can be set up. A properly set up machine can shave hours off cycle times.

This is where people go wrong and they try to tune the machine for all situations and it's just not possible. The other thing they do wrong is failing to realize that it's a simple equation in that you basically CANNOT have both high, it's either high Accel with lower velocity or vise versa or a balanced setup. The balanced setup will work for mainstream work and machine setups but if you want to do 3D type work or the high feed type work then a different tuning setup is required.
When they get this wrong is when you get missed steps or stalling motors.

Now the crazy thing is that most don't realize you can create profiles with different tuning setups and just load that setup when doing that type of work. It's easy really.

But the basic rule of thumb for a general tuning setup is to tune velocity until the motors stall then back it off 25%, then adjust acceleration to a level which you are happy with. Often the machine will tell you when it's enough. If you want higher of either just know that the other as to be lowered and you shouldn't have any trouble.
Obviously there are other parameters that come into play like Pulse rate, MS, Voltage etc that affect how the motors can be tuned and then there's the machine it's self and the Mass, sticktion etc which get thrown into the mix. Which is why every machine is tuned differently.!

It's not rocket science but it's not an exact science either with fixed settings so a lot of feeling your way and tweaking comes into play. then machine also loosens up over time and will need tweaking as it settles down.