cable drive

[vwhotrod]

old thread but whoever is following up, I suggest a cable spool like the ones found in your garage door opener at home, is about 5 inches in diameter and it has the threaded groove for the cable to sit on, it handles trememdous pressure from the door weight and springs and is already concentric with a hub. Im going to try it myself

[RICHARD ZASTROW]

This may be an echo: www.sagebrushtech.com/prod-rotolok.php

Dick Z

[handlewanker]

Hi all, we had a Cinncinnatti tool and cutter grinder at our works, and the table drive was by a 3mm multi strand wire cable....very smooth action, no backlash.

The aspect of using a cable round a drum to drive the carriage is probably well established so no need to hum and har about the design, the problem arises when the cable length increases, is unsupported and sags and vibrates with speed, but that can be offset by a damping arrangement that slides along the cable as the carriage goes back and forth.

The drive drum needs to be attached to the cable, not just wrapped round it with friction drive, otherwise you get slip, and so constant recalibration required.

As was pointed out earlier the cable wrapped round the drum and attached to it will form a thread as it winds on and off causing possible over laying but this can be guided so no problem in that field.

I machined many Telfers or cable drums for the mining industry in the 70's back in UK, that had rope grooves machined on them to take ropes about 30mm diam and more, and the wire ropes came out the side of the drum and were fixed with a wedge or a clamp to the side of the drum end outside face.

Some of the Telfers were a big as 2 metres diam and 3 metres long.

Having a cable hanging vertically, as in a mine shaft configuration has no problem, but when the cable is to be used horizontally, as in a router X axis drive mode, then sag and vibration will occur, but the accuracy and lack of backlash is without doubt, provided sufficient tension and cable support is present.

Without cable support you get a giant spring as the cable sags, and bang goes your accuracy, and the longer and so thicker the cable the more tension is required.

The problem of length and sag is also present in a lathe feed shaft and leadscrew, especially in lathes where the bed is long.

In that situation the is a folding down support that moves out of the way as the carriage gets to the centre of the bed.

Summing up, cable is go....provided you support it.

Cable drive and rack and pinion share the same bed, but one is DIY positive (cable), and the other is Engineering intensive (rack and pinion).

Using cable drive means you want to ensure travel dimensions occur according to the stepper motor drive over a considerable distance, and if you apply the Mike Everman principle in the toothed belt design to supporting the cable it probably would be a simple solution.

This implies a twin cable drive set-up, each side of the carriage, supported along the length as per the Mike Everman design, but using a wire wrapped round a largish drum (possibly grooved) and attached to it.

The wire is actually in two pieces, fixed to the drum and each end of the frame, and winds on and off the drum seperately as the drum/carriage moves back and forth.

The thickness of the wire would have to be strong enough to carry an accelerating load at a safety factor of at least 3.

So if the carriage with work weighs 40 lb and the acceleration inertia increases this to 100 lb and a safety factor of 3, we have a wire requirement tensile stress that will break at 300lb max, probably piano wire of about .8mm (.030") would be flexible enough for this to wrap round a drum of about 6" diam without fatiguing from the bending stress.

Using a multi stranded cable (motorbike clutch cable) of the same diam would introduce some undesirable stretch, but piano wire being a single strand won't as much once tensioned.

I wonder how much tensile stress a piece of stainless steel Mig welding wire at .8mm diam would take to break.

I would be inclined, if using that wire, to lay two pieces side by side and attached to the frame with a swivel compensating bar, like the old swingle tree on the cable brakes of cars around the 40's and 50's era, you'd never break that.
Ian.

[RICHARD ZASTROW]

Also, the cable can lay in a trough. This would negate vibration and sag etc.

Distance measurement on the cabled axis can be a separate. Another cable/resolver measuring device can be attached to that axis, such as the retro devices for HBM spindles Z axis.

I used all the above on a welding lathe. Not very critical but practical. LOL

Dick Z