bizarre heatbed temp spike

[Bill Schwanitz]

So, I've got a rather odd one. While running a 3-4 hour print job the heatbed spiked and marlin killed the print.

I've tried a few things, nothing so far has shown any improvement.

1. Checked wires, everything is secure
2. checked thermistor with multimeter, measures 50k ohm ( should that show 100? I did not record the actual temp )
3. Let the heatbed cool down for several hours

I just tried going from room temp ( basement ) to 50C. The temp rose steadily to 50 and sat there for a bit - then just shot up.

https://dl.dropboxusercontent.com/u/86313544/heatbed_wtf.jpg

I have put a thermistor/temp sensor which came with my extech under a towel. It measured ~15-20 below the target temp before it shot up. Its also never gone as high as the reading from marlin.

Something is odd here - any ideas?

here is the version string from repetier:

< 7:20:41 PM: FIRMWARE_NAME:Marlin V1; Sprinter/grbl mashup for gen6 FIRMWARE_URL:https://github.com/ErikZalm/Marlin/ PROTOCOL_VERSION:1.0 MACHINE_TYPE:Mendel EXTRUDER_COUNT:1 UUID:00000000-0000-0000-0000-000000000000

[Bill Schwanitz]

Here is a slightly more interesting view.

https://dl.dropboxusercontent.com/u/86313544/heatbed_wft_2.jpg

Seems it was pretty stable around 30. When I put it up to 50, its gotten pretty wacky

[Bill Schwanitz]

for grins, I moved the heatbed thermistor to the extruder therm input and it shot up the same way

anyone seen this before? Is this what happens when a therm goes bad?

I'm using the helios heatbed and used thermal paste to secure the therm head so I guess it'll be interesting getting that sucker out...

[Larry Knopp]

Replace the thermistor.

Betting the bead is faulty.

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[Bill Schwanitz]

Well, therm replaced. So far the bed is at 110 and no shut downs or other funky stuff.

Hoping its not the bed ;)

Also, no thermal paste this time. That stuff is a pain in the ass to get out of there. Does anyone else use that on to seal in the therm head?

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[Larry Knopp]

Good to hear!

We do use a dab of paste on the bead before taping in place.  On my personal machine I do not.  So....  imo, either way is fine as long as you ensure you have solid contact with the plate.

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[Bill Schwanitz]

For now, I have kapton tape on boths sides. The bead is pretty much stuck to the top layer of the kaptop with the boro right on top.

Now if I can just get this damned warping issue under control ;) Large objects printed in abs are peeling at the corner. I thought it was insulation under the board. I think I just need to build a case and have a little hole for the filament to get in through. I think thats basically what was done for the ic3d at the foundry yes? Or was that just for storage?

Baby steps to functional printer ;) I'm printing good stuff now. Other than a few wierd-o issues ;)

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[Ethan Dicks]

On Wed, Apr 2, 2014 at 8:59 AM, Bill Schwanitz <bil...@gmail.com> wrote:
> I think I just need to build a case and have a
> little hole for the filament to get in through. I think thats basically what
> was done for the ic3d at the foundry yes? Or was that just for storage?

That is a large case that encloses the printer _and_ the reel on top.
No hole for filament.

It's there because that location in the room gets drafts from the
ceiling vent, so when the AC is on, parts at the back of the build
plate are in a cold draft and they peel up during printing. It's a
draft protector not a thermal chamber. Folks usually print with the
front off. The front is a dust shield for storage.

I find that seasonally, I get more curling and lifting with *any* FDM
printer in the winter vs the summer (but my house is old and drafty
and has no AC, so my indoor temps fluctuate *wildly* between December
and July). When the room is 80F, there's less curling. Go figure.

Recently printing a Wade extruder body, I got good results with the
IC3D once I put down about 4 brim layers (there is a small (1mm x 5mm)
breakaway support post that wasn't sticking long enough to do any good
until I made the brim from it overlap the brim from the main body).
I'm sure Larry and others can chime in on what they do for large parts
curling and lifting on corners, but it's a perennial problem with FDM
printers of all makes.

-ethan

[Larry Knopp]

Google "mouse ears"

(basically you add little pads at critical spots that act much like Ethan's brim, except they are just at the corner or wherever that is lifting.  Very effective.)

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[Scott D]

I've done the brim that Ethan does in medium parts.

Mouse ears also work for part that just warp in corners but something to think about is over extruding filament, I find that if you are slightly over extruding you will build up more in the corners and can be part of the reason only the corners are coming up. Thingiverse has different mouse ears you can download adpnd add to your print if you search for them.

For this big parts, and I have a big heat bed plate. I recently started using 5mil kapton tape. The first sheet held up for about 30 prints before I decided to replace it. It's didn't tear, just started showing air bubbles and I like that flat surface. So it really didn't need to be replaced, it was more of a personal choose. Microcenter in Columbus sells 8x9 5mil kapton for $4. If they are out of stock the cheapest alternative I found for the same 5mil is printbots store. Sometime I sand it with a fine grain sheet to help the filament layer grab.

And last week I did the 5mil with a acetone slurry, it worked great for a very large part in ABS. I was impressed and should have tried this sooner.