CNC - A Question of Resolution

[GBCues]

For those of you running CNC machines of various types and for various tasks, what resolution do you find preferable?

For example, a common 10 tpi screw turned with a 1.8 degree (200 steps per revolution) stepper motor will resolve .0005 inches per step. That would seem pretty tight.

Using a 20 tpi screw or implementing micro-stepping in the control board will give even finer resolution.

And finally, do you use the same resolution for a taper machine as you do for a spindle?

Just wondering.

Thanks in advance for any info.

Gary

 

[RBC]

Gary,

Actually, you didn't include any microstepping.

Running a stepper at full step is just asking for mid-band resonance issues and stalling and poor performance. Most common drives, like the Gecko G540, use microstepping to reduce the noise issues that are a part of life with stepper motors. The G540 is a 10x microstep drive. So, your 10TPI screw with a 200 step motor yields .00005" per microsteps. I strongly suggest to anyone that hasn't already done it to read the various documents on Gecko's website. They are a wealth of information.

Now, when it comes to machine accuracy, I think the biggest problem is with the backlash found in the screws and the mounts. Most everyone will pay close attention to the backlash between the screw and the nut, but often overlooked is the backlash found in the screw mount. If the screw moves end to end when you change directions, the affect is the same as backlash in the screw and nut. Your mount really needs to have more than one bearing, and they should be preloaded against each other to eliminate any play they may have.


Keep in mind that the resolution of your cnc control is going to be much smaller than your machine will be able to produce.

 

[DanO]

Gary,

often overlooked is the backlash found in the screw mount. If the screw moves end to end when you change directions, the affect is the same as backlash in the screw and nut.

This conversation is a bit over my head but this is a great point here. Tony & Mc2 preached this to me when I was building my machine & I can't thank them enough. Your machine is not a team sport. You cannot make up for your weakest link. Every component has to be held accountable.