[sturgeo]

Over the past few months we've been converting our Chester Centurion 500 to CNC to allow us to partially automate runs and allow for more complex machining.

This was when it was new.



Here are some of the parts for the Y axis



And here with the new ballscrews and stepper motors installed



Electronics wise, we are using the following:

BOB
Drivers
Steppers

Its all controlled by Mach3 and we've ran a few thousand lines of G Code without breaking anything yet

We do, however appear to be having a few issues.

1. The dreaded backlash, whats odd is we appear to have different amounts for each direction of travel on each axis
2. Scaling, we used the "set steps per unit" wizard but although this appears to be correct, depending on where you are on the axis it moves varying amounts, sometimes 1mm will be 1.03, other times 0.98
3. When jogging up and down the axis, the motors appear to jolt, almost like the jolt when backlash comp is triggered so we are wondering if they are missing a step.
4. When pocketing, holes end up being roughly 0.2mm too small, and more ofthen than not, not quite circular.

Drivers are currently set to 4.2 Amps, Half Current, 1/10th Microstep. Mach3 has been set to 25k and 45k kernal speed and we've got the motor velocity set at 800mm/min.

We are making progress though and are already looking at changing to a VFD and installing some form of cooling system.

We've only been performing slow cuts (100-150mm/min) so far, hopefully there'll be more to come

You can see a few videos of it in action here definately not the most effective programming but we want to get familiar with everything first.

[katran]

Hi , nice and clean conversion you got there ...

By looking at the pics , it seems that you are using chinese ballscrews ?
If so , don't complain about the backlash ... Also , the bearing blocks ...
seems to be chinese too . Are there radial-axial bearings at the driven
end of ballscrew ? What kind of couplings are there ?

If the holes are smaller and not very round , that's because of backlash
and lost steps ... Probably stepper motors are a bit weak for this
aplication , can you upgrade to nema34 ? And the drivers ... there are
some new products now , based on DSP 32bits , advance control
algorithm ( kelingink ) , far better than any other on the market ...

If what I see in your pictures is corect ( RM1605 ballscrew , nema23
stepper motor / 200steps / 1,8deg/step , and 1/10 microstep setings
on the drivers ) your setings in Mach3/motor tuning should be :

steps per unit = 400
velocity = 800mm/min
acceleration = 100

I would recomend seting the driver to 1/4 microstep ( or maybe 1/2 ) .
That will give you a lot more power , and maybe less lost steps . There are
some heavy components moving in your build , plus the fact that you
don't have linear rails/bearings , but dovetail guides ... that is a lot of
friction involved .

Gabriel.