My drag chain setup.
Looks like it is actually from the front left screw of carriage plate, not the back centre screw like I originally thought.
So you have an X loop on the gantry and just let the Y loop run down the side of the gantry? Is there another drag chain along the right bottom side?
@donkjr No other drag chain. Just the one above the X-rail. Not really sure what you mean by X loop & Y loop.
@Yuusuf_Sallahuddin_Y the drag chain only goes left-right (X). What managed the cables up and down (Y)? Do they just lay on the floor?
@donkjr The cables on the Y-axis just feed through that hole into the electronics bay. There is enough slack on them to allow it to go from centre of Y (around where the hole is) to top of Y or bottom of Y. I’m assuming by “up and down” you are referring to “front and back” of the machine?
Personally I mounted it the other way around, like that never in the ray path :
@StephaneBUISSON thats a rediculously good idea … duh!
@Ashley_M_Kirchner_No That’s a good method too. I tried that on mine & for whatever reason it was slapping the roof of the machine when it moved to the far side (right).
That’s because you weren’t using one with a tight radius. This is a 7x7mm chain, and I have a good 15-20mm clearance before it hits the cover with the gantry all the way forward where it’s closest to the cover.
Mine’s a 7mm chain too. Probably something to do with how/where I was trying to mount it on the right of the rail. Maybe a bit high.
edit: actually, you have nice end attachment pieces that hold it properly. I just dodgy’d up a solution with a bit of plywood haha.
Custom designed and 3D printed plate. 
@Ashley_M_Kirchner_No design is ideal but I am not sure that I can get all my “stuff” through a 7mm chain. I have plans for a auto focus head later on (sure:)!.
@donkjr As you notice with mine, I managed to fit 1x 8mm OD airpipe through the chain & had to zip tie the other to the chain since I couldn’t fit it in. Best to go with a bigger size if you need more space.
On my 7x7 chain, I have a 5mm tube through it with plenty of room for wires. Several pairs of wires for that matter. I can run a CAT5 cable through it, alongside the air tube. That gives me 4 pairs of wires. Easy.
Update: thanks for all the help from this group @Bob_Damato .
I ended up keeping the approach I started with including some modifications.
… added a sheet metal plate under the screws on the chains head end attachment. The screws wanted to pull thought the chain.
… removed some links and now at 24 links not including mounting links, this got the chain out of the beam path.
I ordered a 7mm x 7mm chain to try out a laser cut version of @Ashley_M_Kirchner_No 's approach.
I tried @funinthefalls 's clever approach and had binding problems, perhaps I am using a bigger chain.
…
All in all, so far, I am pleased with its operation and how it cleaned up my cabling to the gantry. I was previously using a shop made “coily cord” but was having problems with it not having repeatable tension.
I also updated the blog post: Don's Laser Things: K40 Gantry Cable Management
Note: the movement is jerky because I am using the jog function from the panel.