Damping the swinging cutting wire in my vertical hot wire cutter

My 3D printer has a detachable x-y stage, which makes it very easy to create a hot wire cutter. In fact, that was the first thing I did when I got the x-y stage working. The cutter is very simple: I hang a rope from the roof, with the cutting wire (a steel guitar string) tied to it, and a 12V supply to heat up the guitar string. I added a weight at the bottom to keep the guitar string under tension and vertical. The x-y stage moves the wire horizontally in any shape I want, and I place the foam just below the x-y stage.

A video of this in action:

The only problem with this arrangement is that the wire swings back and forth when I move it, since it’s basically a heavy pendulum. These movements take a lot of time to die down, so I have to slow down the cutter a lot to avoid having wavy cut lines.

I thought that putting the weight in a tub of water would dampen the movement, but that is messy and does not provide great damping.

After seeing one of those videos with magnets falling slowly through a pipe, I had an idea: Why not use a magnetic eddy current brake?

The design is simple: I just attach a strong magnet (scavenged from an old harddrive) to the bottom of the hanging weight, and put a thick piece of aluminium below it on the floor. This works very well: Any swings in the weight is damped out within a few seconds, and it still allows the wire to move freely.

I uploaded a video of it here:

I’m really happy with the result. This means I now have a hot wire foam cutter added to my tools as well.

Meetup report: 12 April 2018

Discussing deep maker things

Yesterday evening I hosted a Maker evening in my garage. We had some good discussions and even worked a bit on projects! The garage door was wide open most of the evening, so people had no trouble finding us. Nice warm evening.

Timelapse of almost the whole thing here: https://youtu.be/rVXQBAnWsEs

Discussions

Otto showed his very nifty 3D printer that folds up into an aluminium tool briefcase. He mentioned how much trouble he had getting the heated bed to work, since it’s a very specific smaller size. He first tried cutting down a heated bed circuit board and repairing/joining the cut pieces, which turned out to not work. Eventually, he built a heater out of nichrome wire with a 6mm aluminium bed that spreads the heat nicely. His mission for the evening was installing an inductive bed sensor. This required changing the firmware settings, which led him down a rabbit-hole of updating the Marlin version so that the newer Arduino IDE could compile it, and then figuring out what all the new settings needed to be. Not done, but good progress. Thanks to Luke for the tip about the older Marlin not compiling on the newer Arduino IDE.

Chris talked about his home automation efforts, getting his Raspberry Pi talking to his solar power inverter, as well as using a R600 gadget to measure water in his rainwater tanks. Interesting projects. Looks like home automation will be an ongoing theme, as I have some ideas for that as well. Otto has some entry control parts still to be done too.

Brad popped in for a short while, talking about the project to get kids in the Mitchell’s Plain area up and running on electronics projects. We mentioned Robotics Cape Town workshops as a great resource. We’re always willing to help too if anyone gets stuck. Very interesting project.

Luke talked about his latest 3D printer, an own design with linear rails, an H-bot xy top, and lasercut metal parts. Looks like an awesome machine. I’d like to see that in action, and also chat through the specifics of extruders and hotends. My 3D printer is due for an upgrade.

I had my pendulum wave set up and running, and managed to get the drawing machine to do one drawing before it refused to do anything else. That needs to be more robust.

I also managed to test a setup I thought of a while ago: When using the 3D printer xy stage as a vertical hanging hot wire cutter, the bottom of the hot wire swings around and causes ripples in the cut, since it’s basically a wire with a weight hanging free. I took a strong magnet, mounted it on the underside of the weight, and placed about 6mm of aluminium plate below it on the ground. The combination acts as an eddy current brake: It dampens the swinging of the weight very quickly and smoothly. This is a winner.

Lastly, I did get the 3D printer partly working. After a bit of oiling, the demo print (no extrusion, just the movement) works fine.

Future

Next week, I’ll see if I can upgrade the firmware and OctoPi for the 3D printer and actually do some prints. I’m thinking of doing some sort of bed sensor too. I also want to put Home Assistant on a Pi and see if I can do anything with it.

Takeaways

That was fun. I’m going to continue doing this. Anyone is welcome.

I need to take photos. I have a timelapse of the whole evening, which turned out OK, but no closeup photos at all. Ah well....

Home Automation seems like a big interest of quite a few people in the group.

That’s it!