Hello,
I've been working on my CNC router, built from a Fine Line Automation kit about a year and a half ago or so. Everything is going great, aside from some backlash issues with the Z axis.
My problem is odd- I hope others have expereineced it and can give some input. The backlash is being caused by the spiral cut motor to shaft coupler. With the Z axis carriage not attached, just the coupler shaft and upper bearing block, everyting turns fine. With Mach3 set to a .001 step per keystroke, everything moves fine with each step. When I attach the acme rod and Z axis carriage, there's .001 backlash- the motor turns with every keystroke, but the bottom of the motor coupler tied to everythin else stays stationary for one step- .001- of movement before it starts moving. With the router and dust collection shoe on the unit, there's a .002 takeup before it starts to move. You can visibly see the top of the spiral cut motor coupler turn and tighten the spiral like a spring before the rest of the assembly starts to move.
The problem with this, is that it's not repeatable backlash. The amount of "spring" being introduced by the motor coupler is variable when the motor is running, depending on if the Z axis is making a fast decel to reverse direction, etc. The problem is not exibited on the X and Y axes- I believe it's an effect of gravity and the weight of the motor and carriage on the coupler.
Any ideas? Would I lovejoy 3 piece type coupler be better for the Z axis?
Thank you,
Michael