How To Make A Wooden Drag Chain General Woodworking
I got a new CNC from STEPCRAFT and have been doing a series of progressively more difficult projects to train myself to use it efficiently. The goal is to be able to quickly draw a part in SketchUp, export that to the CAM program that generates the toolpaths and then run it on the machine. I know from experience that the only way to get there is through practice. And I know that the best way to solve the problems more complex projects present is to do those projects.
The CNC didn’t have a drag chain on the top of the gantry, so I figured that would be a good opportunity to make a double sided part. A drag chain keeps the cables orderly and prevents them from getting tangled or snagged while the machine is running.
My first step was to look at plastic drag chains and see how those are made. I figured that there’s really only one part that I need to cut on the CNC: the sides for the links. I drew one in SketchUp and then copied and flipped it so it was oriented the opposite way. I then copied that pair into an array until I had enough:
In fact this turned out to be more than enough. The chain itself only needs to operate over a limited distance, and that’s not the full width of the gantry on the CNC. But no harm done – I actually like the way the extra links look.
Out in the shop I screwed the material onto a temporary spoil board. The parts will be made from 1/4″ plywood that came from the crate the CNC was shipped in, which I thought was appropriate. I’ve made several projects from the plywood, including the mobile cart the CNC is set up on.
I spent a lot of time figuring out how to set up the toolpaths to get all of the cuts made in the right order. Much of that was research on doing a double sided part. But I eventually figured it out and fired up the CNC to make the first passes: drill the dowel holes that key the material to the spoil board, and cut the recesses on the top:
As you can see it’s not just cutting the recesses. It’s trying to surface the entire part while cutting the recesses, which took a long time. I guess this is where my inexperience shows, because there has to be a better way to do this. Problem was that I really couldn’t find a good example of making a part like this to learn from, so I’m sure there is a better way to set up the toolpaths.
Here’s the preview from Vcarve showing that surfacing pass:
But when I ran the preview, it kind of skipped that surfacing part and went straight to milling the recesses, so I assumed it would do that on the machine as well. Well, as shown above that wasn’t so and I spent the best part of 5 hours cutting out these parts. That includes redoing a toolpath run where I forgot to reset the Z axis.
Here’s the bottom with the final cut, the profile, done on the first part:
At some point I got tired of holding the vacuum hose and taped it on while the machine was running. A testament to how solid the machine is – it didn’t even care that a 230 pound human was lashing a hose to it:
Not perfect (my fault) but it looks pretty neat. I could have done a better job of nesting the parts and positioning it on the sheet closer to the corner. But these are lessons learned for the next time:
And while this took hours to do on the CNC, I can’t even calculate how long it would take to do this with traditional tools with this much precision.
Satisfying to see that the parts link as predicted:
But as it turned out the recesses on both sides could have been deeper. On the end with the hole I used a 3/4″ forstner bit to cut it a bit deeper, and I show that in the build video at the bottom of this page. On the pin side, I had to make a special sanding tool to grind it down a bit:
Just a hardwood dowel with a hole in the middle and self adhesive sandpaper stuck on. The drive shaft is just a 2″ Philips driver bit stuck in a tight hole in the end and I used the impact driver on a very slow speed to do the sanding. Still, I had to replace the sandpaper 5 or 6 times to finish the lot.
Assembly started by gluing together full links – two sides and the bottom – and half links. I let those dry for about an hour then glued the sections of three together – two full links and one half link:
The bottoms (and tops) are just straight parts and I cut those on the table saw.
From there I glued this triples together with half links to complete the chain:
I then went back and designed the straight end that will be bolted down to the machine and cut that out:
That took less time!
The tops are removable and held on with #4 screws:
The top of the gantry isn’t flat, it slopes down, so I cut and angled strip to fasten the chain to:
And with the cables inside it rolls perfectly and looks pretty cool doing it.
Here’s the build video: