"Cold spot" on my heated bed?

[old man emu]

I wonder if it is possible to get a "cold spot" on the heated bed? On a number of occasions I have been trying to print something and I get a corner lift at the left hand read quadrant of my heated bed. (Point 0,0,0 is at the right hand read corner of my bed, so I'm getting lifting near (-50, -50, 0).

I've tried slurry, hairspray, painter's tape or nothing at all, and I can't stop lifting in that area. The rest of the print sits down quite well. I've tried bed temperatures from 110 to 90 (printing ABS at 220).

Could the problem be caused by air coming off the extruder fan? Also, should the air pass over the extruder fan from the front of the printer to the rear, or vice versa?

I desperately need to resolve this as I have to print a minion for my daughter-in-law's birthday present.

Old Man Emu

[ciutateivissa]

Could the problem be caused by air coming off the extruder fan? Also, should the air pass over the extruder fan from the front of the printer to the rear, or vice versa?

Yeah, the extruder fan is ONE possibility. No mater from which direction the air comes, you should in any case prevent the print from any cool air. This was the reason I changed my hotend to a different type which needs no fan

Another reason could be, that a fan from the electronics (e.g. RAMPS or PSU) get sidetracked by the printer chassis and hit your print in this area. This was the case in my I3 as well, so I made a special box for my electronics where the fan is blowing in a direction away from the printer.

[printbus]

For the heater to be at fault, the "cold spot" would have to be a pretty large area. There are multiple circuit paths snaking back and forth on the heat bed - I think it was four. They go from left to right, so if a trace opens up, that entire 1/4 of the heat bed wouldn't be heated. ie, the back 1/4, etc. Shorting out an area of the board would leave unheated areas, but tougher to do. You have foil under the glass, right? Is the heat bed mounted logo down? That would put the heater traces up against the foil and perhaps allow the foil to rub through the covering on the board and short an area. If the heat bed is mounted logo up, look underneath where your binder clips go. Have any worn through the board covering so that traces are exposed? That could short out an area, but this would still be across the entire width of the heat bed. Now thinking of that, adding a layer of kapton along the heat bed edges for protection might not be a bad idea.

I remounted my extruder fan so that heated air exhausts the front of the printer. That's kind of annoying if you're down close trying to look at the print, but I read elsewhere this did a better job of cooling the hexagon hot end with bottom of the X carriage being so boxed in.

[old man emu]

I remounted my extruder fan so that heated air exhausts the front of the printer. That's kind of annoying if you're down close trying to look at the print, but I read elsewhere this did a better job of cooling the hexagon hot end with bottom of the X carriage being so boxed in.

I did turn my fan around so that it pulls air to the front of the X carriage box. My heat bed is "logo up". I will have another look today to see if there is a short circuit on the heating pad.

Thanks for your replies.

OME

[old man emu]

I turned the fan around. I resliced the object. I put slurry over printer's tape. This time the print lifted in the (+X, -Y) quadrant.

OME

[ciutateivissa]

Ok...

Now we now that your problem is connected to the fan on your hotend. Any chance to redesign the fan mount so that the air don´t hit the heatbed? Maybe a photo would help us to understand...

[old man emu]

How essential is it to have a fan on the extruder? I'm coming into winter now and room temperature is down to about 15C.

There are plenty of fan shroud stls on thingiverse I could print.

OME

[ciutateivissa]

That´s depending on the hotend you´re using and what material you´re printing with - PLA or ABS?

In most cases cheaper hotends needs a cooling anyway. The reason is that the insulator and/or the sleeve can´t withstand temperatures above 200 or 210 degrees C. On top of that there is no thermic insulation between the parts of the hotend and they are usually to short to do so.

There are some hotends out there which needs not be cooled at all, I know at least one which is J-head compatible. Costs about 70,- EUR + shipping, but believe me, that solved a lot of my issues with wraped prints.

Again, it would be good to seee a photo of your printer or at least an link to your extruder (incl. the hotend).

[old man emu]

Here is a photo of my printer:
Lights Off - flashlit.jpg

I have a Magma hot end and the recommendation is to run a fan with it.

OME

[gmay3]

OME, I also have an all metal hotend (hexagon) that has a recommendation to run the fan at all times. Not running the fan accidently caused my printer to fail after 30 mins of printing ABS. The problem is that without the fan, it heats up the aluminum mounting plate that holds the hot end in place, and the ABS extruder parts begin to melt which caused a really bad jam for me.