Cable Management for Very Long Spans

[Pyronaught]

I'm building a fabric cutting machine which has a 16 foot long X axis. Originally I was going to do what everyone else seems to be doing in the fabric cutting industry and hanging the control wires off to the side so that they form loops that slide along a tight steel cable. I had zero luck getting this to work however and really don't see how they are doing this in the trade. There are four motor cables, a valve control cable, an AC cord, an air hose and three limit switch lines that have to hook into the gantry, and my tests using just a single motor cable resulted in the cable getting bunched up, twisting around itself and adding lots of resistance to the gantry. Some setups string the cable overhead instead of along side the table, but I can't see that working any better and just looks ugly.

So the trick is how to get a nine foot length of drag chain to work over that large of a distance. The problem you run into is that the chain will sag under its own weight once you get beyond about a four foot span on the upper portion. What I did was use a split shelf so that a higher shelf supports the cable on the top side once it goes beyond the mid point of the table. This seems to be working pretty good and looks a hell of a lot better than the hanging cable did (and was easier to install while using only half as much cable). There's a bit of friction once the entire chain is dragging on the upper shelf, but I think surfacing the top shelf with a low friction surface such as Formica should reduce the drag.

Just throwing this out there in case anyone ever runs into the same problem on long cable runs.

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[CarveOne]

Here's something to consider.

Lower the board that the drag chain is attached to by 4" or so to increase the bend radius of the chain. Then add a second board just above and ahead of where the cables come out of the chain, but position it just below the bottom of the gantry so the gantry can't hit it. Bevel the end of the second board so that the chain can't snag on the end of the board. Now the chain can slide onto the second (higher up) board to provide sag support for the chain only when the chain needs it. You'll need to find the right place for the second board by watching how the chain lays onto the board with no interference of any kind. The second board could even be installed on a shallow angle if it works better that way.

I have a 12' long DIY machine that has problems like this and cured it with just a piece of MDF stuck into the end of the cable channel I made for it from steel angles. It still sags too much and I have intentions of trying this second level of support idea after I finish building a heavier duty frame for the machine during the fall and winter months.

I have been into a manufacturing business near Fort Bragg that has a 20' laser cutter table for parachute cloth cutting. It appeared to be a commercial machine but I wasn't able to see how the cabling was supported. Could only see it from a distance.

[Pyronaught]

That is sort of how I did it actually. The higher shelf is slightly below the chain connection point, so when the gantry passes over it, the chain doesn't hit the shelf until about 12 inches later. I rounded over the edge of the shelf so that there is no corner to catch the chain on too. So at first there is no friction at all, then it gradually increases as the gantry gets closer to the end of the table as more and more chain is resting on the shelf. The resistance is actually not as bad as the amount of friction I was seeing with the hanging cable method as the cable was getting compressed and more and more hanging points were being slid on the wire. And that's with bare wood. Surfacing it with something smooth like glazed tile, glass or Formica would really make it slide easier.

Another method would be to use long support rollers instead of a shelf, with the rollers spaced 12" or more apart. A rubber roller with ball bearings would probably result in the least amount of friction. The wood shelf was just quick and easy to do so I went with that first.

I think this split support method is probably only viable for table lengths up to 16 or 18 feet, since the chain has to hold up under it's own weight for half it's length before it ever reaches the support shelf. Maybe with a more expensive metal drag chain you could get longer spans, but there is always going to be a limit. With the hanging cable method you can do longer spans. I'm using my cutter to make hot air balloon envelopes, so 16 feet is long enough for anything I would ever build as a hobby. A 60 foot diameter balloon with 12 gores is a worst case scenario, and that would be just under 16 foot panel widths at the widest point. Sail makers use really long tables though.

[CarveOne]

Ok, sorry, I didn't see the other shelf until you mentioned that it was there and I looked closer.

Seems like the higher shelf could be extended farther into the folded area of the chain though. I still recommend not having such a tight radius if you can help it. It puts more bending stress on anything inside the chain.

[Pyronaught]

Currently the bend radius is 3". I can see where opening that up would put less stress on the cables and reduce a little side force on the gantry plate. I'll have to do that.

I tiled the upper shelf with 3x6 ceramic bathroom tile and the chain slides much easier now. I just hot glued the tiles to the wood and it seems to work well.

[CarveOne]

My Igus e-chain has about 1.75" inside width (E4 series I think) and was donated by one of the kind CNC Zone members. It was enough to do the 5' gantry and the 12' long axis enough to cut a full 8' sheet. Later, I cut some 1/4" birch plywood links to extend the travel to the full 11' 4" travel. Those are where the white parts of the chain are in my photo. I never use the full travel, but it does work if I should need more than 8' of travel. I designed one of the links to mate with the last Igus link as a transition link to the wooden links. In the open source forum are some interesting ideas for making the chain links. My 3' x 4' machine uses 3" wide strips of vinyl siding and has been 100% problem free. It was made from vinyl siding cutoffs left from building my work shop.

With the Igus chain links, to cut down the sag requires going to larger links, larger bend radiuses, and higher costs.

[ger21]

You can't just raise the attachment point to change the bend radius. Each size of chain is usually manufactured in several different radii, and it's best to choose a larger radius.

Unfortunately, it seems that just about everyone just buys what they can find. I'm not sure if I've ever seen a single machine here with the chain having the correct radius for the application.
On the new machine I'm designing/building, the actual bending radius of the chain is dictating where the components need to go.

[Pyronaught]

Buying the cheapest drag chain I could find pretty much sums it up for me, which was the Amico chains sold on Amazon. There is not even a bend radius specified for them on Amazon. I could see a minimum bend radius being important when selecting a chain, but I don't see how anything above that would be an issue. If nobody seems to be designing to the manufacturer specified bend radius for these chains, what are the consequences?

I'm pretty new to CNC and this is my first machine, and have not even scratched the surface of the vast amount of information on this forum.

[ger21]

If nobody seems to be designing to the manufacturer specified bend radius for these chains, what are the consequences?

Chains that sag more than they should.

Chains mounted with the proper bending radius will be better supported, have smoother motion, and less kinking.

The downside is that you'll most likely pay more.

I'm using new Igus chains. You can get Chinese knockoffs with the same specs as the Igus, but they didn't offer as many bending radii and widths that Igus does.

[Al_The_Man]

I had zero luck getting this to work however and really don't see how they are doing this in the trade.
.

The name of the festoon idea is a Catenary wire system, and usually works well, although once you get to a certain weight, it can be a problem on long runs.
I have seen Burny Plasma tables that use this method with the heavy torch cable.
A couple of sources.
Catenary Wire Festoon Cable Systems
Metreel Suppliers of Enclosed Track, Pre-Built, Ibeam & Catenary Wire, Cable/Hose Festoon Systems
Al.

[underthetire]

The Japanese use the plastic cable track for long lengths. Agv tracks are 125 feet long, so they need to span at least half. Don't remember what brand they use, but they certainly sag.

[Pyronaught]

The name of the festoon idea is a Catenary wire system, and usually works well, although once you get to a certain weight, it can be a problem on long runs.
I have seen Burny Plasma tables that use this method with the heavy torch cable.
A couple of sources.
Catenary Wire Festoon Cable Systems
Metreel Suppliers of Enclosed Track, Pre-Built, Ibeam & Catenary Wire, Cable/Hose Festoon Systems
Al.

That's what I was referring too, thanks for the link. Now that I can see the details up close of how they work I can see why mine failed. I didn't have trolleys with the wheels like what they are using, I was just hanging the wires from keychain rings so there was a lot more friction. I can see there has to be a lot of excess wire too so that you have uniform loops arranged so that they can not twist around themselves. Due to how the wire all bunches together at one end it appears that you would have to make the support wire run well beyond the end of the gantry travel though. That combined with the excess wire used for the loops and the fact that you have to run wire for the full length of the table means you are really going to be using more than twice as much cable and air hose compared with the drag chain method. I don't see how it could be any cheaper either. I only spent $80 for my 9ft of plastic drag chain, while I bet having to buy a few dozen of those special trolleys and the cable hardware would come out to around the same amount and then you have the cost of the additional lengths of cable/hose. Perhaps their price comparison was for premium drag chain or something.