On Lathes and Microwaves
The situation
I like making tools, but I'm always missing parts for them. Why?
- I live closer to Antartica than most of you.
- Things are expensive there, if available.
I am also a somewhat unreasonable, open-source philosophy maniac, obsessed with distributed manufacturing and technological freedom.
To me, these constraints are opportunities for empowerment.
Flowering Elbow explains the implications of this view in part 3 of his video on an "Idea to make ridiculous shelves from trash (& challenge the way you live!)". Limitations can make you strong.
The objective is to make parts for the micropipettes on my liquid handling robot.
I could have them CNC'ed by PCBWay, JLC CNC, a local shop, or the lathe at my friend's workplace, as I have sometimes done. Plastic injection is reasonable for large volumes, bot not for this niche case. These options are either not cheap, generally available, or adequate enough.
So.
Tree of Requirements
To make lab automation (fun) ubiquitous, the following is required:
- Develop a low-cost, hackable pipetting robot. ☑️
- Manufacture reliable micropipette tools, with their machined tip holders. ☑️
- Reliable access to a CNC lathe. 🏁
Work on the first two is not complete but rather done.
However, for a long time, getting a decent CNC lathe seeemed insane: too big, too expensive, too heavy. I really only needed a small CNC lathe to turn plastic into tip holders, I could not justify it.
Stuck, I spent many hours enjoying Tony's and Brandon's videos on machining, and dreaming of lathes and microwaves.
Then, a few months ago, I came across "The First Tool" lathe on Aliexpress. A cute little machine resembling a watchmakers lathe in size, costing 90 USD + shipping. It would need to become CNC to fit my purposes, which someone had already done of course: the Awesome CNC Freak, paving the way for the rest of us.
The tiny lathe now sits on my desktop, and I'm loving it.
The project
In brief, the objective is to make the lathe CNC and turn tip holders for micropipettes. I have some experience with stepper motors, am also interested in learning closed-loop motor control.
Excited by my ample ignorance in every other aspect of this project, I got to work.
Step 1: select components.
- LinuxCNC on a Raspberry Pi. ☑️
- Remora firmware running on a Pi Pico board. ☑️
- "First Tool" micro lathe. ☑️
All of this I already had. So far so good.
Step 2: define milestones.
- Spindle speed control and indexing. ☑️
- Motorization of lathe axes. 🏁
- Software and CAM setup.
- Test cut.
I had been playing with this desktop lathe for a few days, figuring out its limitations. I concluded that it can turn aluminium, but rigidity issues and vibrations easily appear. Spindle speed control was also missing, as it could only turn at max speed (2400 RPM approx.)
This was solved with Pi Pico, a rotary encoder (AS5600), and a DC motor driver (VNH2SP30).
New pulleys for the axes were still due, all of them uncommon. There is no GT2 "stock" I can get my hands on, and McMaster might as well be myth over here. This brings us back to the situation thing I described before: How could I get them?
Or perhaps I could make them instead.
What do micowaves have to do with a lathe?
The Microwave
It turns out you can melt metals in the microwave, use that molten metal to cast pulleys, and finally use those pulleys to motorize the lathe's axes.
All thanks to Denny from Shake The Future. I highly recommend chekcing out his channel out, and joining his patreon.
Dennys videos are great, so I'll spare you the details and share results:
There are four steps in this process:
- Make a mold of the GT2 pulley, using a pulley 3D printed in PLA and plaster.
- Lose the PLA from the plaster in a DYI microwave kiln.
- Melt the metal in a DIY SiC microwave crucible.
- Cast the pulley using a rudimentary vacuum machine system.
- Cleanup.
The cleanup takes as much time as the previous steps, but its very rewarding:
- Cleanup the pulley's faces and bore in the desktop lathe (might as well use it!).
- Tap threads for the setscrews.
- Cleanup the teeth by hand.
Results
A perfectly improvable 70T GT2 pulley, 10 mm bore.
It fits the lathe's spindle nice and tight.
Thanks Denny, a lot.