Re: [CAD_CAM_EDM_DRO] I need some feedback on using wire rope for driving my x & y axis

Arnie,
Small mills and routers are available commercially, using wire drives. These include the small Roland MDX-15 and MDX-20 mills, which use an H-pattern wire drive for each of the X, Y and yes also the Z axis. In the past, they made flat-bed cutters with huge cutting area and wire drive, before they switched to toothed belt drive.

The upside of these drives is that by you can obtain zero backlash. Of course, every machine in the world has some elasticity in its motion system, but lash is not an issue with tensioned wire drives.

Multiple turns of the wire, around a precision drum, provides the grip for drive and it is amazing how five turns of tiny wire rope can grip so well. The driving force available is F equals e raised to the power of (mu times theta), where F is the force, e is the math constant 2.71828182845, mu is the coefficient of friction of the wire on the drum, and theta is the contact angle measured in radians.

The downside is that after thousands of back-snd forth motions, there may have been a tiny positional slip, due to wire compression and similar factors. In the 1980s many large plotters and cutting tables were made using this style of drive, with mind boggling position repeatability.

There's argument about the benefit of putting an encoder on the motor, due to the potential for slipped position over a few thousand vectors, so most of those machines were stepper motor driven.

Wisely, you mention the wire stretch issue. The wire drives always incorporate spring tensioning and they are always pre-aged by exercising them. The effective radius of the wire is established by test rather than measurement, because it "has a life of its own" to be added to the drum radius for your distance calcs.

Frankly, on the scale at which wire drives are practical, I'm a toothed belt man myself.

Mark Bingham
markb@...
http://www.fourth-axis.com


Arnie Minear <aminear@...> wrote: Hi all,

I am working on a cnc router I am building from scratch and was
looking for feedback on using aircraft style wire rope to drive my
axis. Anyone doing this or know of any machines using this?

I am not sure if there are any pitfalls to consider in the design.
Like stretch or thermal growth, or other things I haven't even
imagined.

Any feedback would be appreciated.

Arnie






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