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Hello,

I found that bending the leads on the heating resistors at about 10 to 15 degrees, the same distance from the body, allows you a better perspective of where the center of the body of the resistor is, once it's covered in RTV. You do want it centered in the hole it is too be mounted in. Just grasp the lead next to body with needle nose pliers, then bend the wire on the needle nose side, repeat on the opposite side, and you'll be able to move that around and know where the center of the body of heating resistor is, even covered in the goopy RTV.

James.

You shouldn't be covering the body of the resistor with RTV. Just filling in the ends to secure it in place.

bdjohns1 wrote:You shouldn't be covering the body of the resistor with RTV. Just filling in the ends to secure it in place.

RTV doesn't conduct heat very well, but it has ten times the conductivity of air:

Conductivity of RTV (http://www.sciencedirect.com/science/ar ... 759700146X) is 0.27 watts / (meter * degrees K)
Conductivity of air at STP (http://www.engineeringtoolbox.com/therm ... d_429.html) is 0.024 watts / (meter * degrees K)

So, if you don't have anything better to use, then filling around the resistors with RTV is far better than having an air gap.


Dan

I believe geneb's build guide recommends cutting a ribbon of aluminum foil and wrapping it around the resistor body (being careful to wind straight so the foil doesn't contact the leads). I got a decent light-press fit with foil, then RTV'd the ends.

bdjohns1 wrote:I believe geneb's build guide recommends cutting a ribbon of aluminum foil and wrapping it around the resistor body (being careful to wind straight so the foil doesn't contact the leads). I got a decent light-press fit with foil, then RTV'd the ends.

In at least the recent Rostock Max manual, he recommends coating the resistor in RTV; no aluminum foil.

I dropped the foil for the v2 build. All the production Orions go out the door without the wrap and don't seem to be the lesser for it.

g.

I drilled a hole and put in a set screw to hold the thermistor in. I used RTV to seal the keep in and then took a small drill to the RTV to provide some relief so that when the air heated up, it didn't blow the RTV off or burp.

I just used as carefully constrained a blob of RTV as possible. I do remember, though, when I heated the thing up, there was this POP and concurrent puff of smoke that had me yanking out the power cord. Never happened again; I'm guessing it was indeed a "burp".

I added a very small piece of heat shrink tubing to end side of the resistor, and then wrapped it foil until it was a tight fit. Then just enough RTV on the ends to make sure it didn't move around.

I cooked my first set of resistors when I just had RTV there. So I figured I would sink the heat away as fast as possible, and it decreases the delays in the termistor picking up the change.

I just went thru my original resistors ( 9 months of daily operation - 6-10hrs daily of printing).. Was pleasantly surprised they lasted that long.

However, RTV is a terrible thermal conductor.
Yes, it's 10x's better than air... But it's still terrible..

I've been considering putting some RTV on one end, then filling around the resistor with a thermal paste, then putting RTV over the other end.. I'll probably do that on the next set (assuming I still have this printer in operation - i've got another SLA system inbound right now)...

I'd be concerned about the thermal grease shrinking and separating, leaving you back with an air gap. The stuff is designed to be installed between to very flat parallel surfaces; it may not do well in irregular spaces.


Dan