<d1b2>
<DuncanHaldane> Looks like the mold loved the part too much and didn't want to let go
<d1b2>
<DuncanHaldane> Good filling though, don't see many bubbles at all
<azonenberg>
(18:25:59) azonenberg: So far, my postmortem takeaways are...
<azonenberg>
(18:26:05) azonenberg: 1) I forgot to actually use the mold release spray
<azonenberg>
(18:26:10) azonenberg: 2) thickness on the edges was too thin
<azonenberg>
(18:26:35) azonenberg: 3) the silicone has next to no adhesion to the PCB material itself. Meaning the board is gonna jsut be sitting there held in place by essentially friction
<azonenberg>
(18:26:44) azonenberg: and i need to rely exclusively on the edges to hold the halves together
<azonenberg>
(18:28:39) azonenberg: 4) The tip cavity around the solder terminals and resistors filled with silicone. So i need to probably fill it with sulfur-free clay (I have some on order already) to provide a seal
<azonenberg>
(18:29:01) azonenberg: 5 Cure time of 4 hours on the jar is insufficient, in fact 5 is insufficinent
<azonenberg>
(18:29:14) azonenberg: maybe my lab is cold, idk
<azonenberg>
(18:29:08) azonenberg: the puck i made last night and cured overnight was a lot less gooey than this
<azonenberg>
(18:29:39) azonenberg: 6) the SMA connector does not fit in the mold, i mismeasured somehow
<azonenberg>
(was just talking to somebody in another chan about this screwup)
<azonenberg>
DuncanHaldane: The actual PCBs are still on order anyway
<azonenberg>
So my current plan is to respin the mold with fatter sidewalls, correct the dimensions of the SMA cutout
<azonenberg>
actually use mold release spray next time
<azonenberg>
There was also a lot of flash due to flexure of the 3d printed plastic mold
<d1b2>
<DuncanHaldane> For this, a softer mold would help as well. Something like a 25-30 durometer rubber, either silicone or polyurethane depending on what you are casting into it.
<azonenberg>
the final mold will be cnc'd aluminum
<azonenberg>
I'm treating this as an injection molding setup
<azonenberg>
since that's effectively how i'm doing it
<d1b2>
<DuncanHaldane> Ah this is going to production then.
<azonenberg>
Well, i hope to be making these in some level of volume eventually yes
<d1b2>
<DuncanHaldane> Seems like the injection worked well!
<azonenberg>
I did have some aeration in the syringe, i think the luer lock fitting leaked
<azonenberg>
i ordered some larger needles to see if that helps
<azonenberg>
(drawing up the silicone faster)
<azonenberg>
But yes i think the method has promise
<d1b2>
<DuncanHaldane> Re: cure time. The platinum cure silicone s can be touchy about mix ratios, and the curing is highly temperature dependant.
<d1b2>
<DuncanHaldane> You can accelerate with higher temps, but beware the thermal expansion coefficient is huge, so too high and you get deformation
<azonenberg>
I measured with a milligram scale and tried to get within 1% of the 1:1 ratio it calls for
<azonenberg>
My lab is a controlled 70F +/- 2
<azonenberg>
I applied gentle heating to the red prototype, hot plate set to something like 40C
<azonenberg>
Just mixed up a second batch for another experiment. This time I am using mold release spray and curing overnight
<azonenberg>
I still need to respin the mold in order to get a better fit on the SMA, just need to identify the exact location it's hitting
<azonenberg>
so far it's not obvious where the clearance violation is
<azonenberg>
it's small, the mold is maybe 100-200 μm short of closing fully
<azonenberg>
(with the SMA in place)
<azonenberg>
it might even be a simple as me mistaking a nominal dimension for a max material dimension or something
<azonenberg>
or the 3d printed mold being at the extreme of some tolerance
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<_whitenotifier>
[scopehal-apps] azonenberg opened issue #297: Allow preferences to be reset to default values - https://git.io/JI2Nl
<_whitenotifier>
[scopehal-apps] azonenberg labeled issue #297: Allow preferences to be reset to default values - https://git.io/JI2Nl
<_whitenotifier>
[scopehal-apps] azonenberg assigned issue #297: Allow preferences to be reset to default values - https://git.io/JI2Nl
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<_whitenotifier>
[scopehal-docs] azonenberg pushed 1 commit to master [+5/-0/±4] https://git.io/JIaf0
<_whitenotifier>
[scopehal-docs] azonenberg d67e742 - Added new section for filter graph editor. Documented 64/66b decoder, major improvements to documentation of 8b10b and TMDS decodes.
<_whitenotifier>
[scopehal-apps] nshcat commented on issue #297: Allow preferences to be reset to default values - https://git.io/JIaJY
<_whitenotifier>
[scopehal-apps] azonenberg commented on issue #297: Allow preferences to be reset to default values - https://git.io/JIaTI
<azonenberg>
DuncanHaldane: turns out, upon some reading, that platinum cure silicone is incompatible with acrylic photopolymers
<azonenberg>
welp
<azonenberg>
Guess i need to make a new mold :p
<azonenberg>
I'll try fixing the SMA clearance issues, then reprinting it in SLS nylon. The surface finish won't be as good, but will hopefully be decent enough for a prototype
<azonenberg>
then i can move to cnc aluminum
<azonenberg>
Actually it looks like there is a surface treatment that might help
<azonenberg>
i might do that first
<azonenberg>
Since the photopolymer does have much better surface finish than SLS
<azonenberg>
also, next AKL-PT2 prototype received from fab
<azonenberg>
so i should have it by the weekend
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<d1b2>
<DuncanHaldane> Oh, interesting. I had hit the non-sulfur free clay issue before. Acrylic polymers is a new one.
<d1b2>
<DuncanHaldane> I was a bit stumped as to the issue because your method sounded quite well done.
<azonenberg>
Yeah i tried to do my research and was aware of the sulfur issue
<azonenberg>
I only discovered the photopolymer incompatibility after the fact
<azonenberg>
I ordered some Inhibit-X which is apparently some kind of petroleum based surface treatment that helps mitigate this problem
<azonenberg>
will see if it helps
<d1b2>
<DuncanHaldane> Machine wax makes for a great molding material if you've got a CNC around. Even something like the Othermill can do well.
<azonenberg>
I do not have a CNC. I have a 3-axis Sherline but it's full manual
<azonenberg>
geometry this complex would take forever to do by hand
<d1b2>
<DuncanHaldane> Yeah that would take some patience.