"Cold spot" on my heated bed?

[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

[printbus]

Some random thoughts...

Have you tried repositioning the clips for the glass? The MK1 I got with my i3v kit wasn't very flat, which I assume is typical. It could be that you've got a spot on the heat bed that bows away from the glass as mounted, and repositioning clips might help. Or add a few more?

Another thread mentions your use of kitchen foil between the heat bed and the glass. I'm curious on the reason for that. It'll add more required soak time before printing, won't it? I remember a picture somewhere showing ripples in the foil. Couldn't inconsistent ripples in the foil lead to variations on how heat is being conducted to the glass?

You mentioned the room temperature being 15 degrees C. Is that adding a challenge to ABS printing? I haven't done anything in ABS, but printing in a cool room seems contrary to reading how some people use a printer enclosure to keep the print area warm for ABS.

[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]

You raise some good points, Printbus. I've put aluminium cooking foil between my heat bad and glass, and cork sheeting underneath the heated pad. This was in response to thoughts in a thread. I think that the aluminium foil would distribute the heat across the glass.

If I remember correctly, my heater pad was bowed in the middle a little. I did try to take the bow out by putting some 1/4 x 1/4 stick under the centre of the bed, but then I took it away because I figured that the glass was flat. I don't think the stick helped much.

The more I think about it, the more I approach the conclusion that the best way to stop this lifting problem is to:
1. Give the heated bed some time to stabilise its temperature. Perhaps it would be wise to let it heat for about 10 minutes before starting a print.
2. Lay down at least 2 layers at 0.2mm at a speed of about 30mm/second
3. Put a raft under the print, and a skirt around it.

OME

[Roxy]

4. Print big parts in PLA.

Incidently... When you get your Auto_Bed_Leveling going... And we add the enhanced G29 code to produce the Topographical map of your bed... You are going to be amazed at how not flat your glass is. There will be parts of your bed that you avoid on certain types of prints.

[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.

[ciutateivissa]

OME, looking at your picture makes clear what the problem is: This seems to be a huge fan at your extruder, approx. 80mm in diameter? Maybe it would help to have a smaller one... I´ve used a small 30mm fan for my old extruder and it was more than enough. With a smaller fan it will be a lot easier to control the flow of the cool air, with your big one it is simply impossible.

[RobH2]

If you have a laser thermometer you can measure a bunch of spots and see if you to have a large cold spot. The thermometers are pretty cheap at some tool stores. We have Harbor Freight here in the US. I'm not sure what you guys have OME.

[RobH2]

OME, I think your new approach will work better but if you can get things to stick without the raft your life will be easier. Rafts are hard to remove cleanly.

I don't know if you have 3d modeling capabilities but you might try something I've been doing. I put long 2.5mm thick tabs on corners. It's holding my parts down and keeping them from warping. I use borosilicate glass with 3 coats of Aquanet hairspray. Spray the Aquanet let it dry and repeat twice more for a thick coat. Pet and ABS are sticking very well to it. I posted last night in this thread http://3dprintboard.com/showthread.p...e-to-ABS/page8 which shows the tabs on a part. They are easier to cut away than a raft and don't waste much material.

We have the same printer, if I'm not mistaken, so I think that your new process of using your #1 and #2 above will begin to give you better results. Adding tabs like I have done might be helpful too.

I also agree with 'printbus', I'm dubious about the aluminum foil. I'd remove that. Finally, if you do decide to pick up a laser thermometer, you can measure the glass to see what "dialed in" temperature actually reaches the glass. Mine is about 2 degrees C different. So if I want a bed of 120C I dial in 122C.