Orcinus' Build Log (was: Thermistor insanity)

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Re: Thermistor insanity

Postby orcinus » Sat Jul 07, 2012 1:33 am

1kg+ isn't that micro. Not that big either.

I've also got a tiny 300-sized traditional (collective pitch) heli.
That one tried to attack me with the tail rotor once. The design is kinda wonky, it's a downscaled 450 size, meaning all the shafts are just proportionally scaled down, more or less. Which is stupid, because they're too weak to handle the RPMs (or, rather, they need to be perfectly straight, which they never are).

The tail rotor was acting up. I was testing the heli while holding it in my hand (stupid, i know, but at least i was holding it above my head and directed off the rotor plane). The tail rotor spun up, worked fine for a little while, started vibrating all of a sudden and then the straight line of the shaft blurred into a cone about 2cm in diameter. I had about enough time to go "Ohshi..." and then the shaft snapped, whistled by me and dug a little hole in the wall.

Sorry for going off topic :)
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Re: Thermistor insanity

Postby orcinus » Sat Jul 07, 2012 10:47 pm

I was slightly bored and decided to try and macgyver something to replace the broken SS tube.

I took a cylindrical ceramic fuse, attacked it with a torch (yes, i really like to torch things) and removed the end caps, ending up with a ceramic tube with a cca 3.6mm internal diameter. I've epoxied that to the lower threaded block that screws into the nozzle, but first, i've sanded off the remains of the tube and used a rotary tool with a conical sanding attachment to give a slight fillet to the hole in the block (reasoning being that should reduce chances of filament getting stuck on the edge on its way in, due to different IRs of the block vs. the ceramic tube).

Then i took a big, chunky washer and epoxied that to the middle of the tube, to increase its surface and act as an additional heat sink. The internal diameter of the washer was much bigger than the external diameter of the tube, so i've filled it in with epoxy. I've been using thermal epoxy for all of this, in case of the washer, with a slight more filler than normally suggested (should be 1:1), hoping that would increase the thermal conductivity at least a bit.

Finally, i've epoxied the tube to the upper screw block, while taking care not to mess up the threads (unlike the lower block, the upper screws inside the heat sink all the way).

I honestly doubt this will work, because of two factors - the epoxy doesn't stick that well to the ceramic tube (it flakes off, i tested it first on another tube, but didn't wait for it to cure all the way from gel phase); and the tube's internal diameter is much bigger than the filament, meaning lots more space for it to bloat and get stuck, if the heat creeps too far up the tube. But hey, like i've said, i was bored and trying can't hurt :)
Last edited by orcinus on Sat Jul 07, 2012 10:55 pm, edited 1 time in total.
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Re: Thermistor insanity

Postby orcinus » Sat Jul 07, 2012 10:49 pm

(Also, i found out today there's someone local selling reprap parts, including hotends, heatbeds, RAMPS kits and other stuff needed to build Mendels. Wish i knew that before ordering nearly everything from abroad, LOL)
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Re: Thermistor insanity

Postby Liberty4Ever » Sat Jul 07, 2012 11:49 pm

The ceramic tube sounds like a potentially good idea, even if the McGyvered implementation isn't optimal.

BTW - I've often said that "trying can't hurt", only to learn a bit later that it can in fact hurt a lot!

:o
Apparently, I didn't build that! :-)
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Re: Thermistor insanity

Postby orcinus » Sun Jul 08, 2012 2:26 am

Can't wait for that ceramic tube to explode in my face :lol:
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Re: Thermistor insanity

Postby Liberty4Ever » Sun Jul 08, 2012 3:18 am

orcinus wrote:Can't wait for that ceramic tube to explode in my face :lol:


Experimental 3D printing has gotta be safer than quad copters shedding parts at relativistic speeds.
Apparently, I didn't build that! :-)
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Re: Thermistor insanity

Postby orcinus » Sun Jul 08, 2012 5:04 pm

Behold!

Image

The FrankenArcol!
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Re: Thermistor insanity

Postby orcinus » Wed Jul 11, 2012 12:26 am

So that didn't work out all that well... :lol:

The epoxy flaked off, basically.
It held on to the ceramic quite nicely, but the SS side just fell off when i gave it a test nudge.

Good thing i've heated it up and cooled it down a few times (5 cycles) before trying to extrude anything.
The first 2 were to see if it'll endure the temps at all (it did, but got a little soft, which i thought would eventually cure out).
The last 3 were with poking to see if it can endure the mechanical strain. It fell off on the 5th cycle.

I'll try with one of those "putty"-like metallic epoxies next.
Supposedly, they work for up to 300 deg C and stick to both metal and ceramics better and with less flaking.
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Re: Thermistor insanity

Postby Liberty4Ever » Wed Jul 11, 2012 5:27 am

It might help to scuff up the stainless with sandpaper or other abrasive and then clean off any residual oil or other contaminates with 90% isopropyl alcohol (from the pharmacy or the pharmacy aisle of a large grocery or department store). The acetone that's sold for solvent is recovered from industrial processes, and even after reclamation, it contains a small amount of oil that remains after the acetone evaporates. Alcohol is a cleaner solvent.

If you could find a compatible epoxy, painting the textured metal part in pure epoxy (mixed resin and hardener with no filler material) should also improve the bond with whatever filled epoxy you're using.

It's probably still a doomed project though. :P
Apparently, I didn't build that! :-)
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Re: Thermistor insanity

Postby orcinus » Thu Jul 12, 2012 2:12 am

Yeah, tried all that, and cleaning with 96% alcohol.
Still no luck.

Same thing with epoxy putty, it just fell of.

Incidentally, my workload went up dramatically in the past few days, so i don't have any time to play with that project anyways, so i guess i'm gonna wait for the replacement :)

If Laszlo (Arcol.hu) sent the new one mondayish/tuesdayish, it should be here by weekend (his last package arrived within 3-4 days, Hungary is right across the border from here). Failing that, i can get give the ebay hotend from the local guy a try.
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