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Although I'm not too bad as a manual machinist, I'm interested in trying this CNC stuff and have a few questions for Those Who Know...
I'm planning on buying a middle-sized mill (something like an Abene, K&T No.2, Parkson 1N) once I've saved a few more pennies, probably a horizontal with a vertical head, as quills (and quill feeds) are pretty rare, I imagine I'll have to move the knee for Z movement - is this feasible? The main use will be smallish parts in aluminium (for motorbikes, mainly - think rearset footpeg and brake master mounts) and occasional steel parts (gear hobbing? sprockets?) and I realise I may have to mount a second, home-brew high-speed spindle for small work in ally etc..
I plan to mock up the CNC side before getting the mill (unless the workshop at work gets around to "releasing" a nice Deckel universal that they mothballed as a spare very soon...), so:
I've started collecting parts from evilBay, a 48v 20A PSU, two 400 Oz-in steppers (for X and Y?) and a 680 Oz-in (Z?), 5-axis cheapo breakout board, adequate PC for Linux CNC - next step is drivers, the motors are rated as 6A max current, is there a reasonably-priced driver board for this current level? The Chinese ones seem to top out at 4 - 4.5A, which would reduce the available torque, I assume. I have a few smaller, less-torquey (75 and 150 Oz-in) motors for things like a rotary 4th axis (and a 5th?) in future...
Microstepping... all the motors appear to have less problem with half (or finer) steps re resonance at speed, how badly will it degrade the available torque? Would it be best to (at most) half step and gear the motors for improved resolution?
LinuxCNC can do closed-loop, would 1 um linear scales be adequate for feedback? I picture using the "ref" outputs from the scales as home position indicators (and having physical limit switches) - I guess I could also have pulse generators for the three axes for manual machining, with the DRO replacing the handwheel collars - feasible?
What else should I worry about?
Any help very much appreciated!
Dave H. (the other one)
I'm planning on buying a middle-sized mill (something like an Abene, K&T No.2, Parkson 1N) once I've saved a few more pennies, probably a horizontal with a vertical head, as quills (and quill feeds) are pretty rare, I imagine I'll have to move the knee for Z movement - is this feasible? The main use will be smallish parts in aluminium (for motorbikes, mainly - think rearset footpeg and brake master mounts) and occasional steel parts (gear hobbing? sprockets?) and I realise I may have to mount a second, home-brew high-speed spindle for small work in ally etc..
I plan to mock up the CNC side before getting the mill (unless the workshop at work gets around to "releasing" a nice Deckel universal that they mothballed as a spare very soon...), so:
I've started collecting parts from evilBay, a 48v 20A PSU, two 400 Oz-in steppers (for X and Y?) and a 680 Oz-in (Z?), 5-axis cheapo breakout board, adequate PC for Linux CNC - next step is drivers, the motors are rated as 6A max current, is there a reasonably-priced driver board for this current level? The Chinese ones seem to top out at 4 - 4.5A, which would reduce the available torque, I assume. I have a few smaller, less-torquey (75 and 150 Oz-in) motors for things like a rotary 4th axis (and a 5th?) in future...
Microstepping... all the motors appear to have less problem with half (or finer) steps re resonance at speed, how badly will it degrade the available torque? Would it be best to (at most) half step and gear the motors for improved resolution?
LinuxCNC can do closed-loop, would 1 um linear scales be adequate for feedback? I picture using the "ref" outputs from the scales as home position indicators (and having physical limit switches) - I guess I could also have pulse generators for the three axes for manual machining, with the DRO replacing the handwheel collars - feasible?
What else should I worry about?
Any help very much appreciated!
Dave H. (the other one)
I'm using 1 um magnetic scales on both my mill and router, in both cases they will position to 0.0001 in all three axis.