My experiments continue.
I've been working on building a modular synthesizer...which includes a LOT of knobs. At $0.50-$1.50 each knobs can add up quick. One module I built has 23 knobs alone. I've built 12 modules and have 5 more in the works with even more planned...so saving money on knobs can really help.
The white modules are 100% DIY. I designed and 3d printed the panels on my Mk3 with the MMU to do the labeling. The circuits on them are all built on stripboard either from published designs or which I just found schematics for and created my own stripboard layouts. The black panels are modules that people have created PCB's for and I've bought their panels/PCB's to speed construction.
5 of those are just panels that don't have modules built yet (one looks almost finished just to the left of the mixer.)
Anyway .. the point is I'm trying to print my own knobs. You'll notice the grey knobs and one blue knob - those are SLA printed.
It's tricky though. Some of the potentiometers are smooth shafts and some are knurled. Either smooth or knurled I can't just print knobs in normal resin and have them work. They're too still and brittle and either break getting pushed on or are too loose.
So I tried printing some in Siraya tenacious flexible resin.
(I also tried dying this one red after printing...that almost kind of sort of worked but the color wasn't what was expected.)
The problem is....again they're either too tight or too loose. And on this one I broke one of the soft flexible bits inside. Plus they just don't feel right in the fingers when printed in flexible material.
So...I noticed one of the commercially made knobs that came with some of my potentiometers used a 2 part approach. It's a plastic insert with a metal body over it. So why not try the same idea. I designed a knob with an inner flexible core designed to grip the shaft, and a hard outer housing that feels/looks right and compresses the inner core to make sure it stays tight even on smooth shafts:
This works REALLY well, the inner part is a center section that's very slightly undersized for the shafts surrounded by 8 legs connecting to the outer shell which is sized to have an OD the same as the ID of the outer case:
The outer case can be anything I want. So I can print a bunch of the inner cores and then put them in various knob shapes/sizes/designs to fit my whims/needs. This first design is just modeled after the commercial knob that gave me the idea to try a 2 part approach:
Printing the inserts is easy - they don't have to look perfect and I can print them with the open side down. In 100% tenacious they come out great.
Printing the outer bodies...that's trickier. They have to look and feel "just right". And if I print them with the open side down the marker on the top gets obscured and the top just never looks good. If I print them other other way a lot fail because of the suction when printing a hollow tube. So I had to add a small hole to them to allow them to vent while printing:
With that little hole they mostly print well....occasionally one will still fail but for the most part they come out usably.
But...I don't want grey. And I'm almost out of black resin but have too many other resins to justify buying more right now.
What if I could make my own colors of resin?
Hmmm.. Apparently you can use epoxy dyes on resins. I did a search on amazon and found some UV transparent epoxy dyes and ordered a set:
Of course...the blue color I was most interested in had to be the one to leak in the package during shipping. Oh well. Can still experiment!
I found a blog post that talked about dying resin and suggested starting with white base resin and adding 20% siraya tenacious to help compensate for the way the dye affects the exposure. So I mixed up 80ml of white resin with 20ml of tenacious then added 15 drops of "sky blue". That got me a light blue color but I still wanted it darker...so I added 3 drops of the leaky blue. Still lighter than I was hoping for...but decided to give it a try:
For comparison that rook was printed in the white resin I used as a base. And the lion is printed in Phrozen aqua blue. My knobs...weren't exactly a success...but taught me a lot so I don't consider them a failure either.
One odd thing is that the color seemed to shift as they printed with the open end that was against the build plate being more grey and the top being more blue:
It's less obvious in the photo than it is in person. I think this may just be because of how thin the caps are at the bottom though.
You'll also notice a lot of damage on these. None of them completely failed when printing...but a lot of them broke at various points and had some layer adhesion issues.
So for the next try I increased exposure, slowed the lift speed, and added another 12 drops of the darker blue:
The 8 in front are from this second batch. Still a few small issues with a couple of them but overall much better results. And the blue is getting closer to what I want. The elephants foot on the first layer is really bad now though so I need to ease off on that exposure a bit. I think another second or two on the normal layers and 3-4 seconds less on the first layers should be about right. Might slow down the lift speed a tiny bit more too.
The back row is the original set of dyed prints...so you can see my color is getting better. I don't want to add too much dye too fast and cause problems so I'm creeping up on how much to use. Will probably add another 15 drops of the dark blue and see where that gets me next.