Printer Flexible Cable Installation

Had an interesting time with my Prusa i3 style printer (Factory 3D) today. Trying to print a part that is essentially a 100mm dia cylinder but every time I tried the left hand side would print and the right hand side would be missing or very poor quality. As I am a newby at this lark I quickly decided that it must be down to an unlevel bed. Re-levelled and tried again - same result. After about 3 goes at levelling with the same result I decided it must be something else.

Watching very carefully I noticed that the extruder motor was turning (I have a line drawn on the spindle) when the print head was on the left but not on the right. Just to confirm I went into the move axis mode and could extrude on the left but if I pushed the head over to the right I just got a very faint click from the stepper motor. Checked the plugs which were firmly on and concluded a broken wire which I confirmed with a test meter.

A lot of faffing about later having undone the wiring loom to the print head and replacing the stepper motor cable I tried again. This time no extrusion at all. "Oh bother!" I said and went and had a cup of tea before something terminal happened to the printer.

It turns out that standard stepper motor cables are all different, a bit of swapping the terminals in the Dupont connector around and all was eventually working again. Having spent most of the day being in turn confused, annoyed, frustrated and annoyed again I was wondering:-

Is there a better way of cabling up the moving bits in particular the print head which needs to up and down and left and right. At present I have all the witres in a braided nylon sheath with spiral wrap to give it some stiffness. The wire broke somewhere near the termination point on the head but to me it doesn't seem to bend much at that location. I was thinking of using a cable chain or is there something else that can be done to prevent future breakages?

John

Could that stiffness be the problem? Unconstrained bendy wires have more room to flex which distributes the movement along the length of the wire. Bundling them together might focus the stress at a particular point whilst the added weight also increases the potential energy of the wiring loom as it moves about. Not good if the combination of extra energy and stiffness is relieved by snapping something expensive.

Dave

I'm going to print a clip on support arm from the back of the print head to hold up the wires, and keep flexing to a minimum.

Solder and crimp terminations are known failure points for wires if they're not supported properly. You need a cable tie or clip some way above the termination, so the wire doesn't bend, even a small amount, at the termination.

Andrew

It's not unusual to include an over length piece of filament (3mm is ideal, but I've seen a few pieces of thin filament used) within the bundle of wires to the extruded which is held in a clamp to the back of the extruded block- this give flexible bouncy stiffness, with all load taken on the filament (cheap enough to replace if it does break) but creates instant cable strain relief.

Thanks for the ideas gents. I have managed to keep all the crimps on the fixed side of the cable clamps so no movement near plugs or sockets. Seems strange that just one wire should break completely, perhaps I managed to pinch it when tightening up the cable clamp on the extruder. I think the moving wires are always going to be liable to failure but I would expect them to last a little longer than this one has.

Neil is the cable support on Thingiverse or your own design? I am still leaning towards cable chain (cos I think they look good) but I have never used one and don't know if they are any better than the stiff loom style I already have.

John

Hi John,

I haven't designed it yet... I imagine a simple 'cradle' with a point at the back for a cable tie. heater and thermistor cables would have connectors supported on the cradle.

On industrial robots that I've worked on the cables are fixed in flexible cable trays on all axis so the whole cable moves as one, when the cable gets close to the motor it should then be held rigid to the motor with no chance of it moving to the connector joint, the cable should be kept straight as possible as well.

Martin P

If you can arrange it constrain your cables in energy chain rather than bundling with ties wraps or spiral.

Definitely use cable clamps behind connectors so the the clamp to connector length cannot move.

Keep bend radii as large as possible for the sections that flex.

Probably a little over the top to use robotics cable which is designed so that the cores can slide a little over each other but if you so wich the Lapp Cables are your friend.

regards Martin

Whilst re-doing the wiring I also swapped out the hot end nozzle and tube. My latest print effort has a top surface that looks like a ploughed field!

I was wondering if this could be down to the nozzle width, the new ones are much more pointed. The old one has a flat end approx 2mm dia the new one has less than 1mm flat.

Should I make the flat bit bigger, easily done on the lathe?

John

No, the smaller nozzle will work fine.

Check your cura settings, especially filament width, that problem may be under-extrusion

Neil

Cable on moving parts of commercial machines use a cable tray/chain to guide the wires and cables. These provide protection and control the minimum bend radius. Similar to that shown below.

Lots of 3D models available for download to make your own.

**LINK**

Paul.

Edited By Paul Lousick on 27/09/2017 14:18:00

I already said that.

Martin