Cable instead of Belts

So I had made reference to this idea in previous posts but I felt it deserved its own topic. Up until a few weeks ago I worked in a machine shop that made medical tools. One part we made gave me great inspiration for a great reprap design. We all know belts can be expensive and more difficult to get, and there are many issues with getting a tight tolerance. The machine we made was a "pick and place" component for an automated test tube sampling machine. The main design feature that jumped out at me was a cable replacement for the current belt system. Instead of a toothed pulley on the stepper, they substituted a grooved cylinder. This grooved cylinder (much like the threads on a bolt) held the number of wraps necessary to permit a full range of travel. The reprap developer MadKite developed an almost identical system using a double pulley x-carriage to get better accuracy and faster speeds.

A cable double pulley system is not only possible, I've helped build and test them for other applications. The windings on the cylinder provide a smooth, powerful method of moving the x-carriage using simply friction. Gears are a very tough print, but perhaps this method can eliminate slack and produce better quality prints. The cable would be open and the ends could be secured with a spring mechanism to keep tension. So yea, that's my little idea I had I think could help us all get better prints and help new (and current) developers create more advanced machines.

could you please provide visual examples?

I think I'm having a slightly hard time conceptualizing your idea, but it sounds pretty cool.

I designed a printer that used wire rope in this way 10 months ago. I have never built it or even really experimented with it. [www.thingiverse.com]

---

FFF Settings Calculator	Gcode post processors	Geometric Object Deposition Tool Blog
Tantillus.org	Mini Printable Lathe	How NOT to install a Pololu driver

I recently dismantled a 20-ish-year-old Canon copy machine that had a cable drive for the scan head. I would have to go out to the shop to look at the parts to see exactly how it was set up but I think the cable ends were attached to the driven assembly and the cable was a single loop around the drive pulley. The cable was quite tight without any spring.

I would not use a spring in the cable, that would allow to much give and be very innaccurate if any sliding resistance were to occur. Better in my humble opinion would be a cable with a bit of slack, and a spring-loaded idler pulley taking up that slack on the return side of the cable (the length between the pulleys opposite where the ends are attached). That would keep the driving side of the cable tight, and therefore the linear movement of the driven assembly would always accurately follow the rotation of the driving pulley.

If I am not explaining myself very well, I can do a sketch.

pictures tell a thousand words

kenearlg Wrote:
-------------------------------------------------------
> I recently dismantled a 20-ish-year-old Canon copy
> machine that had a cable drive for the scan head.
> I would have to go out to the shop to look at the
> parts to see exactly how it was set up but I think
> the cable ends were attached to the driven
> assembly and the cable was a single loop around
> the drive pulley. The cable was quite tight
> without any spring.
>
> I would not use a spring in the cable, that would
> allow to much give and be very innaccurate if any
> sliding resistance were to occur. Better in my
> humble opinion would be a cable with a bit of
> slack, and a spring-loaded idler pulley taking up
> that slack on the return side of the cable (the
> length between the pulleys opposite where the ends
> are attached). That would keep the driving side of
> the cable tight, and therefore the linear movement
> of the driven assembly would always accurately
> follow the rotation of the driving pulley.
>
> If I am not explaining myself very well, I can do
> a sketch.
Yes, what you describe I can vaguely remember from ages ago. The rope and pulley system gave way to gears though (tons of gears that added way more complexity and costs for field techs to fix it).

... in this old post I've attached the drawings of the paten filing for my first laser-plotter wuth 3D-option (for LOM-fabbing)

You can see the wire-feeding with two stationary motors that move the head in XY ... in Z there was a separate stage, not shown here.

Most of my old XY-plotters have wires, newer ones belts - but the accuracy and dynamic is depending on the used motors and drivers ...

---

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

I miss those old HP X-Y plotters from the 80's. Built like tanks and as big as one too.

I built my heavy Mendel with cable drive and 2:1 pulley system, it works perfectly, I can print, engrave circuit boards and cut polycarbonate sheets without any slip.
The driving pulley is just a printed cylinder, way easier to print than a timed pulley. Other pulleys are also printed.