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| Rotary (4th) axis for my cnc mill |
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| stefang:
Ahoi, tomorrow I will meet a friend, where we are going to cast the clamping bracket and a tailstock for the rotary axis out of alumium. --- Quote ---The other is your tool post. I've never seen one like that --- End quote --- Pekka is of course right, its a Multifix Style toolpost, they are over here in Europe very common, almost every lathe in a professional shop here in Germany has one mounted...and also on very much lathes in hobby shops :) Not very cheap, but pretty precise..there are chinese clones (mine is also a chinese one), that are not to bad. --- Quote ---Forgive my ignorance but why is the harmonic drive neccessary? Is it just a simple case of the steps are too large without it? --- End quote --- The Harmonic Drive multiplies the torque of the stepping motor by 50, and also increased the precision by facor 50. --- Quote ---I would be even more impressed if I know what it was. --- End quote --- Think of a rotary table on a conventional milling machine, only computer controlled. Stefan |
| loply:
Do you mind me asking how much the harmonic drive was, and which seller it was from? |
| stefang:
Hello, The seller was "xyza.part", and it was about 80$ if I remember correctly.. Yesterday was a good day, as I had the chance to cast the clamp to mount the rotary axis and the tailstock from alumium. The mould with the sand-core: The finished cast of the clamp and the tailstock: The rough casting of the clamp is not very nice, but seldom...it will be machined on all sides, so i can live with that crappy casting. On the other hand, the tailstock came out pretty nice. greetings, Stefan |
| Pete.:
That dividing head is jaw-droppingly nice :) |
| John Stevenson:
--- Quote from: loply on August 16, 2011, 05:48:08 PM ---Forgive my ignorance but why is the harmonic drive necessary? Is it just a simple case of the steps are too large without it? --- End quote --- You need some form of gearing in a 4th axis to prevent the cutting forces winding the stepper back. Work gearing like in a rotary table at 60:1 as an example is ideal as it can't be back driven. There has recently been an article in MEW that describes building a 4th axis that is nothing more than a stepper driven spindle with a timing belt reduction. I built on of these some years ago and had to scrap it as when doing splines for instance it was impossible to keep a straight cut, you could see and feel it notching over under cutting forces. John S. |
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