Nice, thanks for digging all that out. Beautiful machine!
Did you use a toothed belt or one of those mini-v belts for the spindle drive?
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Did you end up getting the accuracy of the c-axis kinematic to where you wanted/needed it?
How many watts is your spindle motor and is it 1:1 geared onto the spindle?
Not sure what the belt is called - its flat, 25mm wide, about 7 or 8mm thick and has 8 V's on the inside. The pulleys on motor and spindle are self made, 80mm O/D with the V's machined in.The spindle motor is a servo motor ( of sorts..) - its from TEKNIC, a Clearpath NEMA-143 motor 240/315VAC 3 phase, driven by step/direction inputs, 2800rpm max, 33NM, and with positioning accuracy of 0.03deg - pdf attached. Ratio is 1:1.
The C axis accuracy is still not where I want - The encoder I use I made - it is a magnetic encoder with a 4096 PPR output, which is around 0.09 deg. Since the servo does 0.03, I would prefer am 16000PPR encoder, with 0.023 deg position, and with a dead band or 2PPR - gives me around 0.04deg position repeatability, which would be 100% better!
Why have I not pursued that? Well, for me the C axis is a live one,ie , I intended to use is in milling shapes on the ends of a shaft type of thing. That means the C axis is moving all the while, synced with X/Z, with no brake on C. But...That 25mm flat belt has 'some' elasticity in it and on a large OD workpiece - say 40mm, taking a respectable cut near the edge of the periphery with a 14mm end mill, rotates the workpiece 6 or 7 hundredths of a degree...which negates the Hi-Res encoder. I can limit it to less than 2/100 of a deg by REALlY putting tension on the belt, but thats hard on the bearings. The belts has ( I think) nylon thread all its length, which is no good - I am looking for one with steel wire, or preferrably, carbon fibre or Aramid/Kevlar.
So, you get started on this and you will go down so many paths its not funny.
Oh wow, 3kW spindle . I've only got a 750 W servo on my (planned) lathe/rotary. It has a brake (though that is not 100% without play) and i wont be doing much simulaneous milling. I'm planning on a 12 groove mini-v belt (what you have, but a bit wider) I was contemplating a toothed (timing) belt but I fear the noise.
Really I could have done with just a normal 3phase motor on a VHD as I mostly aim to be able to do lathe work on my mill but as usual the want is bigger than the need.
Just out of curiosity, how cold does it actually get where you are?
Not cold, really...Winter is centered around August or so, and the coldest is around 7 or 8degC, but rarely - mostly its down to 13deg to 16deg, which is not cold by any means. However, I am 50m from the edge of the Atlantic and we have lots of heavy mist in the winter - so that you don't see houses two removed. Humidty at 15deg C around 80 to 85% and that makes it cold to the bone! The workshops are brick and concrete, unheated and all the machines are covered in plastic an sheets so they don't rust. Not conducive to winter work.
The motor is oversized soley so that is has lots of low rpm torque and holding power at stop, specifically for C Axis milling. Now I know less would have been ok, but its a schlepp to get another here if I underestimated - it was too complicated to try calculate!
A motor on VHD - is that the same a VFD - variable speed drive? Great for spindle work, but does lack positioning for your C axis...
Took most off a year for mine to work - although that includes the build from scratch.
VFD is what I meant.
I guess the best would be to have some kind of gear (low for c-axis and high for lathe work) with some way to electrically switch from one to the other.
13deg and damp is not nice to fiddle with things. I remember reading something about a beetle in some coastal desert that can gather it's drinking water by catching the mist on it's body.
I tried to come up with a geared arrangement with a servo activated pawl that slid a locking gear between 2 gear trains - a 1:1 and a 5:1, but since that had not been thought of from the start, my layout, mechanics and structure was just too small to accomodate the concept. I suppose had there been a purpose for the machine then I may have maintained the interest!
You are right about the beetle - does hand stands on the dune windward side and the mist condenses on the trailing edge of his wings and runs down the central ridge to his mouth...Mother nature is a smart Cookie....
