4 Attachment(s)
Arboga Manual to CNC Conversion
I've completed the first stage of my manual to CNC Arboga mill conversion, I decided to use a ball screw hung off the side, a 700N gas spring is mounted on the other side to balance/reduce the weight, IF - and that is a big if - this works OK I can lock the quill in place for CNCing and still have the use of the quill if I need to. The other option was utilise the existing rack and pinion, this would have relied somewhat on gravity to eliminate any backlash - a ballscrew seems to be a more positive system and any backlash would be from the ballscrew and nut plus any flex in mounting system/drive belt.
I initially mounted just the gas spring on it's own and found that it more than balanced the weight and had a slight positive affect on the system - once the stepper and ballscrew (which are not light) were fitted I estimate the overall weight of the Z axis system that the stepper has to lift is around 5-10 Kg plus any friction, the gas spring unfortunately does not reduce the mass so the stepper still has to contend inertia plus the weight + friction.
The ballscrew is 25mm x 5mm pitch the drive belt is 18mm wide 5mm pitch with a 2.5:1 ratio - the stepper is closed loop Nema34 12Nm 1.8deg per step, these are not a full closed loop system but a sort of hybrid system in that the stepper provides feedback to the stepper driver so the driver can try to regain lost steps should these occur, if the lost steps can not be made up the driver can alert/signal the motion controller - how the motion controller handles this depends on the motion control software and is a bit of an unknown for me at present. The 2.5:1 ratio multiplies the motor torque - it can easily be changed with different pulley sets and possibly removed altogether if I mount the motor directly above the ballscrew for direct drive.
The ballscrew nut mount is a section of 70mm square tube that was left over from a long ago carport build, the ballscrew top bearing and motor mounts are made up of 100mm wide Al plate, 15mm thick for the bearing mount and 10mm thick for the rest.
With everything bolted up tight and a DTI placed under the quill I could not detect any backlash when I rocked the drive pulley back and forth by hand, next step for me is to temporarily wire up the motion controller, bumble my way through the setup procedure and do some tests on backlash and possibly speed tests as well.
This all new to me, while I think I'm headed in the right direction with what I'm doing, I may well not be - I did vow at one time that I would never venture into 3D printing or the CNC world - I've had my 3D printer for over a year and now this.
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