<GenTooMan>
azonenberg, more fiddling around with mechanical components well when you are doing things like that it's probably the best route.
<azonenberg>
Yeah i mean i expect my probes to be largely hand built for the foreseeable future
<azonenberg>
it's not something you can really send off to a CM
<GenTooMan>
azonenberg, I had to deal with bad mechanical design before the consequences were lots of difficult assembly steps.
<azonenberg>
I mean the mechanical design is still being fine tuned
<azonenberg>
this is literally the first prototype i will be fully assembling
<azonenberg>
with amplifier, tips, and power
<azonenberg>
and the power supply is a bodged on hack until i get the usb-pd stuff done
<GenTooMan>
azonenberg, actually I was going to say if you have a friend who is good at mechanical design their advice might help.
<GenTooMan>
azonenberg, anyhow congrats for making it this far :D
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<azonenberg>
Just went back and put the second round of glue on the AKL-AD3 tip
<azonenberg>
to date i havent found out how to do it in one cycle, i need to partially hold it in place with tape while gluing one part then remove the tape and glue where the tape was
<azonenberg>
and it still isnt holding the pcb flat
<azonenberg>
i tried adhesive transfer tape before and it was difficult to get lined up because if you didnt have perfect alignment when you first made contact, you couldn't reposition it
<azonenberg>
best might be epoxy behind it followed by tape over the top or something, i'm not sure yet
<azonenberg>
over the next few prototypes i'll experiment with different means of attachment
<azonenberg>
idea: epoxy behind the flex and a bead of uv glue over the top
<azonenberg>
line it up just right then hold while the uv glue cures
<azonenberg>
uv glue will hold it until epoxy cures then remove the uv glue
<azonenberg>
I cant use uv glue for the final attachment because it's less strong than epoxy and the tip sees significant shear loads, it won't cure behind the opaque parts of the tip
<azonenberg>
and if i put it over the front it will mess with impedance of the line
<azonenberg>
But if it's only temporary while the epoxy cures it will basically act like a custom made fixture
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<Degi>
Hmm, there is some UV glue from UHU which cures a bit into the depth, but it is very pricy
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<azonenberg>
AKL-AD3 tip fully glued. One of the ends is slightly misaligned
<azonenberg>
so the needles are skewed wrt each other
<azonenberg>
This is definitely going to be something that will take a few iterations on the mechanical design to get right
<azonenberg>
I may also want to add a small spring to provide counterforce and/or move the tip jaws slightly closer together
<azonenberg>
the natural spacing with no force applied is a bit too far apart i think
<azonenberg>
might also stiffen the upper jaw a bit more
<azonenberg>
but i think some preload might be required
<azonenberg>
also gluing the tip in place before the amplifier was installed might have been a bad idea but we'll see how well i can squeeze it in
<azonenberg>
worst case i have more tip boards
<electronic_eel>
i don't remember all the details of the mechanical construction - is it still a outer plastic arm with a flex pcb glued inside?
<azonenberg>
Yes
<azonenberg>
I'll post some pics when i get a chance
<electronic_eel>
could you have some holder protrude inside from the plastic arm, for example above the flex pcb, to provide better alignment for the tip?
<azonenberg>
There is a single alignment pin
<azonenberg>
With the SLS process I currently use it's kinda rounded and doesnt stick out as far as i wanted
<azonenberg>
it also provides no angular positioning
<azonenberg>
So i will probably replace it with two pins
<azonenberg>
but the other issue is just keeping everything in place while the glue dried
<azonenberg>
dries*
<azonenberg>
things tend to move around
<azonenberg>
also the latest issue i'm seeing with this test is that some stuff might not be quite as centered as i want in a few spots
<azonenberg>
still playing around
<azonenberg>
But its hard to really form a complete impression until i have the pcb in it
<electronic_eel>
did you search for better uv curing glues, that will provide the same strength as the epoxy you are using?
<electronic_eel>
the dentists use uv curing Methyl methacrylate. i used some 2 component MMA in the past and it was quite good
<azonenberg>
So the issue is that i need the glue behind the flex
<azonenberg>
if it's on the front it will change Eeff of the transmission line
<azonenberg>
And if it's behind a solid metal plate aka the ground plane it won't cure
<azonenberg>
the fact that the stuff i use is mechanically weaker isn't the big problem
<electronic_eel>
ah, yeah, you are right. can't shine uv through the ground plane
<azonenberg>
Yeah
<azonenberg>
And tapes are hard because they grab as soon as you make contact
<azonenberg>
and if you're not perfectly aligned its hard to rework
<azonenberg>
So my current idea - which i have not yet tried
<azonenberg>
is to place a thin layer of epoxy behind the flex, then a few beads of uv urethane over the top
<azonenberg>
pinch it in place with tweezers and cure the uv glue
<azonenberg>
then let it sit until the epoxy cures and remove the uv glue
<azonenberg>
so the uv glue would basically be used as fixturing to hold the flex in place while the epoxy cures
<electronic_eel>
remove the uv glue as in peel off a tape it is on?
<azonenberg>
No, it has a very nice middling shear strength
<azonenberg>
if you pry it right it pops off without damage to the substrate
<azonenberg>
it will hold bodgewires in place just fine but if you need to reroute them you can do it
<azonenberg>
it's great for rework
<electronic_eel>
would using a not too sticky tape work to hold the flex pcb in place until the epoxy is cured?
<azonenberg>
over the top or behind it?
<electronic_eel>
over the top
<azonenberg>
I tried kapton tape over the top this time
<azonenberg>
it seemed to shift slightly
<azonenberg>
i think the uv glue would be better
<azonenberg>
anyway we'll see when i try it
<electronic_eel>
around the arms of the probe maybe
<azonenberg>
Yeah thats what i did
<azonenberg>
It's just a really awkward geometry to be working inside of
<azonenberg>
Main amplifier PCB is being fabbed so while i wait i'm gonna make a few tweaks to the mechanical prototype and respin it
<electronic_eel>
hmm, maybe it would work better if you had a holder jig you could clip the arm of the probe into. the jig could provide guidance for the flex pcb and also have a good flat face a tape sticks well to
<azonenberg>
my concern is that epoxy squeeze-out might attach the probe to the jig permanently
<azonenberg>
the uv glue is easy to remove and if a bit of it sticks its not horrible
<electronic_eel>
yeah, this could be a problem. especially the parts that provide guidance for the flex pcb could be an issue
<azonenberg>
exactly
<azonenberg>
a tiny spring clamp or something around the flex might work
<azonenberg>
like a paper binder clip but smaller
<azonenberg>
but the uv glue cures in a minute or so
<azonenberg>
so holding tweezers on it for a minute while i blast it with uv isnt that horrible
<electronic_eel>
or maybe the clamp jig as i wrote above, but the guidance-parts are covered in kapton tape or similar. the tape can usually be peeled off from cured epoxy
<azonenberg>
Yeah
<azonenberg>
Another thing to consider is possibly switching the probe body to a different material
<azonenberg>
in particular, something with better resolution than SLS
<azonenberg>
I'm just a little afraid that a SLA material would crack easily as those tend to be brittle
<azonenberg>
and i will be deliberately and repeatedly flexing it
<electronic_eel>
i wouldn't want to flex the SLA parts i have used in the past. but SLA has made some progress, so maybe there are SLA formulations that allow it now
<someone-else>
there are non-brittle SLA materials
<someone-else>
usually something with "tough" or "engineering" in the name
<azonenberg>
yeah i would be looking at accura xtreme or accura 60
<azonenberg>
those are pretty brittle afaik
<someone-else>
of all the available engineering resins I only tested Siraya Blu, but results were very much better compared to the normal SLA materials
<someone-else>
very comparable to quality injection-molded plastics
<azonenberg>
Nice
<someone-else>
so, depending on what printer is used (SLA/LCD/Formlabs etc), there are probably options for a decent material
<azonenberg>
At the moment I was looking at Shapeways's material catalog
<azonenberg>
as that's who i use for most of my mechanical prototyping
<azonenberg>
what about accura xtreme white 200?
<someone-else>
haven't tried Shapeways' SLA yet, but from the description, Accura Xtreme sounds like a good fit
<GenTooMan>
azonenberg, it is hard to have a guess at what you are doing with the tip without an image or two
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