Careful with Ultra Copper RTV!

[JohnStack]

gestalt73 wrote:
Ok everyone, repeat after me, so I don't forget this again.

"Ultra Copper High Temp RTV Silicone Gasket Maker is NOT a thermal conductor. It is not an adhesive. It is actually a thermal insulator. Stay far away from it. Do not use it in the thermister hole, do not get it between the thermister and the hot end block, and for goodness sakes, DO NOT fill the thermister hole with it and then stuff the thermister into it"

I've been fighting what I thought was PID auto tune problems, with a +-5c temperature oscillations, which shows up in smaller prints as rhythmic ridges on the perimeter of the print, and other perimeter sloppiness.

After I moved over to screw in thermisters, everything is back to normal.

The end."

Thanks to Flateric for commenting so this would come up again.

[bvandiepenbos]

I never have liked the Copper RTV either. Screw in thermistor and heater cartridge in a J head works fantastic.
Screw-in thermistor in a SeeMe hot end works better and safer to.
All that RTV around the heating resitors does not seem like the best way either.
Would JB Weld be OK to fasten in resistors?
Probably could JB weld the stock thermistor in place if you did not want to buy a screw-in.
I have not used heater cartridge in a SeeMe hot end yet, but think it should work fine. I am thinking just 1 cartridge and milling off the other side.
Anybody tried this?

By the way, I recently built 3 machines with SeeMe hot ends with screw-in tmist and stock RTV'd resistors.
I was unable to get the hot end auto tuned or LCD to read correctly.
John Oly at SeeMe told me what was wrong... screw-in tmist from RP One Labs is different than the stock one.
There is a value in firmware that needs tweaked called "GENERIC_THERM1_BETA 4450"
4450 is the value for the stock thermistor
I understand that this value is a way to shift the temp reading into the right range.
Adjust it up or down by 50 until your LCD matches thermocouple reading.
Through trial and error I found 4250 work correctly for the screw in. LCD value was within 2 degrees of my meters thermocouple pinched between nozzle and heater block.
Re did autune and WooHoo! we are happy... temp holds +- 1 degree.
By the way, leave the thermistor set at type 97 as stock.
And at 220c

Thanks Oly

[gestalt73]

Looking at f15sim's youtube video about screw-in thermisters, it looks like all the cool kids are using jbweld or jbquick to fix the thermister into hex standoff.
Then they're tap and threading the original thermister hole to take the threaded hex standoff with the thermister epoxyed into it.

I suppose you could jbweld the resistors and/or the thermister directly into the hot end, but then they're pretty much stuck there unless you destroy them to remove them.

The jbweld itself kinda just chips away if you ever need to remove it, but holds really well, (and I would assume) conducts heat rather well.

[bvandiepenbos]

use JB Weld original NOT the JB Quick version, it does not withstand high enough temps.
I know this from a friend who made his own screw-in tmist using the quick version, it smoked and failed.

[bdjohns1]

John Oly at SeeMe told me what was wrong... screw-in tmist from RP One Labs is different than the stock one.
There is a value in firmware that needs tweaked called "GENERIC_THERM1_BETA 4450"
4450 is the value for the stock thermistor
I understand that this value is a way to shift the temp reading into the right range.
Adjust it up or down by 50 until your LCD matches thermocouple reading.
Through trial and error I found 4250 work correctly for the screw in. LCD value was within 2 degrees of my meters thermocouple pinched between nozzle and heater block.
Re did autune and WooHoo! we are happy... temp holds +- 1 degree.
By the way, leave the thermistor set at type 97 as stock.
And at 220c

Easier way than that - the rp_one_labs screw in thermistor is type 1 in the Repetier firmware (epcos 100K). Mine holds +/- 1C easy. No need to do the whole trial-and-error thing John suggests.

Personally, I wouldn't even bother with the stock hotends - that and the U joints are in my opinion the only subpar things to the kit. Wrapping resistors with foil and having to glue stuff together with RTV seems a little hackish. It was fine in the early Reprap days, but it's a kludgy solution vs a cartridge heater that already has suitable insulation, wire long enough to get the disconnect mounted up on top of the machine, and just needs a set screw to put in. That, plus having to muck about with those non-insulated crimp splices.

I printed exactly 2 things with my stock hot end:

1) A calibration cube
2) A groove mount for an e3d

Since then, the stock hot end has been relegated to sitting in the back of a drawer in the unlikely event my e3d bites it. If I were designing the kit, I'd just spec an e3d and be done with it. Otherwise, I'd at minimum re-do the hot end to ditch the resistors for a cartridge, go to a screw-in thermistor, and switch to groovemount like most other hotends.

[AEK]

The Rostock MAX v2 manual says to use the "Ultra Copper High Temp RTV Silicone"... So is it safe and/or better to use the JB Weld instead for the stock Hot End?

What do you use on the Heated Bed?? Says to use the "Ultra Copper High Temp RTV Silicone" there too for the thermistor right in the center.

[geneb]

Follow the docs as written.

JB Weld will simply guarantee that you have to throw the whole hot end out if the resistors or thermistor were to fail.

g.

[KAS]

JB weld has a K factor of .59 for thermal conductivity.

Water: .58
Air: .024
Asphalt: .75
Earth, dry (dirt): 1.5
Copper: 401

I'm not saying the Copper RTV is the best, but JB Weld is not the replacement answer. Can't find the actual value of the Copper RTV, or any vulcanization silicone products.

Thermal conductivity of some common materials and gases
http://www.engineeringtoolbox.com/therm ... d_429.html

[geneb]

JB Weld is an epoxy. Anything you do with it is permanent.

g.

[Mac The Knife]

:roll

[geneb]

JBWELD IS EPOXY! IT'S PERMANENT. YOU AIN'T GETTIN' THEM PARTS BACK. IT'S FOR-EVER! WHAT TEMPERATURE IT CAN TAKE IS TOTALLY IRRELEVANT.

*drops mic*

g.

[KAS]

JBWELD IS EPOXY! IT'S PERMANENT. YOU AIN'T GETTIN' THEM PARTS BACK. IT'S FOR-EVER! WHAT TEMPERATURE IT CAN TAKE IS TOTALLY IRRELEVANT.

*drops mic*

g.

I can feel the frustration in your words. But I think you got the point across.

[Mac The Knife]

[geneb]

*sighs theatrically, bangs head on desk*

[AEK]

I've built one Rostock MAX v2 already and have no problems thus far. I followed the manual to the letter. Very well done BTW!

I just ordered a second Rostock MAX v2.5 and came across the thread(s) about the RTV etc... That's why I asked just in case there was some new "thinking" or "development" in securing the thermistor to the Heated Bed & Hot End.

Didn't mean to get anyone upset over this.

Sorry.

[geneb]

Don't worry about it. It was just me waving my cane and getting shouty about kids on my lawn.

If you bought the kit after 7/17 or so, grab the new manual - it's got revised instructions for the new carriages. (and a LOT of new content!)

g.