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Archive for January, 2018

4
Jan

3D Stud Thermistor – MG Chemical Fix

Having toasted, and not that I mean that literally, more like broke, wore out, shorted, and just plain destroyed any number of those fifty cent hot end thermistors, I went in search of something a little more robust.

The keyword being robust. Except you can leave off the “ro”. Thus, bust.

Stud Thermistor

When I found was a bunch of these little guys. Essentially a typical brass standoff, with a thermistor (yeah one of the fifty cent glass bead marvels) glued inside.

Stud Therm

When I started using these, they seemed really handy, easy to change, didn’t break any wires. I was rather elated.

Within two months, I was deflated.

Whatever sort of epoxy or glue used to hold the glass bead into the brass fitting is designed like a tail light warranty. I.e. when they can’t see your tail lights your warranty is up.

Now if these cost fifty cents it’d be annoying but not a big deal. However, on average these are $5 USD. If one is going to shake loose every month or so, tis a bad omen.

Repair

To fix these, trying to get high temperature epoxy or some kind of car muffler goop that isn’t going to melt, stink, or be ugly to apply is a challenge.

And equally pricey. I tried some quick fixes, all failed, some far more spectacular than others.

High entertainment value, zero usable results.

MG Chemicals Solution

MG Chemicals has this magic silicon goop (and that’s my technical term) that is the weirdest stuff I’ve ever used. It’s called RTV106, comes in a tube, red goop, very strong silicon smell.

And. It. Never. Seems. To. Dry. Out. And. Harden. In. The. Tube.

Yeah, you got that right. I use it, screw the cap back on, go back in a month, uncap it, use it, screw the cap back on. I’ve done a few dozen times over the last year. Stuff is still the same as the day I cut the tube open. So, yeah. Weird.

According to the datasheet it will run all day at 260C with brief jumps to 315C. I primarily print PLA so I’m running 204C to 216C depending on the PLA.

RTV106

This stuff doesn’t burn, no odor, doesn’t flake off, sticks like, well like that “baby’s” brown stuff to a blanket. According to the data sheet it can corrode the brass so you wouldn’t use it on electrical circuits, but I’m using it on the OUTSIDE of the stand off.

I wouldn’t put any on the inside where the glass bead is.

Taint Purdy But It Works GREAT!

When the last stud thermistor popped out, I shoved it back in. Grabbed some RTV106, slathered up a toothpick, gooped it on. Wasn’t too neat about it either, as you can see…

Fullsizeoutput 2c49

And it’s been sitting like that for 5 months. Truthfully I have been waiting for it to fail. I think it’s going to be a long wait.

Side Effect

Something else I found was that after I, ah, “insulated” with the RTV106, the temperature held a little better. My guess is the thermal transfer of the RTV on the brass stud is shielding it from the fan right above it. That would be a win – win as far as I am concerned.

Summary

When you build a 3D printer, you don’t really think out of the box much.

You just build like everyone else and when something doesn’t work, you kind of look at what everyone else might have tried. I know I did in trying to fix the thermistors on these studs, but when I was talking with one of the MG guys they off handedly mentioned the temp range for the RTV106 a long time before there even was stud thermistors.

At any rate, my spongy brain absorbed that little nugget of info and I found that’s the easiest way to fix these things.