That’s a nice bit of Z axis bling.
I'm having evil thoughts of just selling my machine and upgrading those too.
I'd have a much better more rigid machine and probably money in my pocket from the sale of old machine.
This is good idea, and lets you jump over the rabbit hole rather than end up with a hodge podge
of mechanical\electrical\frame\software assembles that while work, are not really optimised to
work together.
I’m thinking that the Z axis is heavier than the old assembly, and if I recall correctly
your motors were 370-400 oz/in, you can get Nema23 4 amp (560 oz/in) motors that would bolt on
I have one on my lathe X axis and a Nema 24 4 amp on the Z, they are just longer.
If you use the original motors then you may have to back off the GRBL Acceleration values.
You can change these values by using one of the many Gcode senders, if your not familiar with the
process (there are plenty of examples on youtube) then GRBLaser has a very easy to use GUI
to do this as well.
For a little more cash than you can get closed loop steppers with their drivers, or clear path servo’s
but where do you stop, as you would then want to upgrade the controller to (32 bit GRBL) “Fluid CNC”(free) to be compatible with GRBLMachine
or Mach3/4/Linux or the software that comes with one of the many USB/Ethernet boards.
With the extra height and added weight there will be a greater turning moment on the Y axis assembly (and the beams)
so it wants to be linear rail and serviced (greased) regularly. (this is the most important thing to attend to and get right).
The linear rails will add some stiffness when bolted to the aluminum extrusions, I don’t know if this would be enough though.
Racks have their pros and cons, they are fast though, and if you are happy with the finish off the machine then I’d leave them until I had
measured the Y axis deflection, by running a test program which can be just a series of point to point G0 moves, I did this for my Z axis install
to check the Acceleration values Initially I set the values by running the axis and upping the values until the
axis started to miss steps then backed of the values 20%, I ran a few jobs and everything looked ok however I did a job which consisted of 500
drilled and tapped M3 holes, and after a couple of hundred holes I noticed that the clearance plane seemed to have closed up some (it was set at 0.5mm)
I then ran a test file with 1000 point to point moves (10 mm) and found that the axis had drifted 0.6 mm so I had to back off the Acceleration some more.
Once you have the acceleration sorted mount a dial indicator not connected to the machine frame (perhaps mounted up off the floor on blocks) with the
indicator point in the middle of the Y axis beam and apply some force and see what the deflection is. ( manufacturers do have this spec) but
it depends on the fixing conditions on each end of the beam.
Your machine manufacturer would have taken this into account (among other things) when deciding to use a rack or a
ballscrew as a rack is much more forgiving and durable when the mounting conditions and\or rigidity of the frame are not optimum.
ballscrews offer no backlash but are speed limited by their slenderness ratio.
For example a Module 1 rack and a 20 tooth pinion will for 1 revolution of the motor move
63.82 mm, a common 5 mm pitch ballscrew would need to rotate 12.76 revolutions.
long unsupported sections of ballscrew tend to whip about at high rpm.
To some degree this can be mitigated by using a rotating ballnut and putting the ballscrew under
tension you need a heavier built frame to do this though.
ps. I just use the windows built in app snipping tool to take shots of parts of the screen.
Dave