Help Please. Bad Prints With Prusa Mendel

Hello, I'm currently trying to complete my first print with my prusa mendel but unfortunately I've had nothing but bad luck. Im trying to do a basic 40 mm cube print, the first couple layers work out fine but when it starts to do the sides it just clumps up. I'm using 3mm pla and the extruder is set for 185. Photos are attached of the print, any assistance would be greatly appreciated.

Thanks,

Do you happen to have a fan blowing on the hotend?

No theres no fan installed on the printer anywhere. I currently got assigned to work on the 3D printer but someone built it a couple years ago. The fillament seems to be coming out of the extruder in little balls .

i am new to 3d printing like you, just one advice.

read wiki about calibration, maybe start with higher temperature, like 200, then lower it step by step....

it worked for me, if everything is calibrate as it should be with default slicer software settings print will be fine..

Here's the page you are looking for :

[reprap.org]

If you run through this step by step, your prints will come out looking solid. I would advise a fan for PLA.

raeliean Wrote:
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> ... I would advise a fan for PLA.

If you don't mind, may I ask you why? You mean a fan to cool down the printed object, right? Is it to make the lower layer more rigid therefore make the whole object less prone to shaking/curling/lifting?

PLA needs a fan to cool the thermal break on most hotends. Without it, the PLA in the thermal break melts, expands, and then causes a jam.

I was having trouble with the PLA too. When I first started the print, I would already notice it spewing out, hitting the bed, then working its way up the side of the nozzle. I lowered the temperature to 165 and it seemed to work.

You could also try calibrating the extrusion speed. It's toward the bottom of the config file in Marlin I believe. First, measure out 100mm of spooled plastic above a reference point on your extruder. Mark it with a pen. Then, extrude 50mm. Measure the new distance between the reference point and the mark. It should be 50mm. If not, adjust the config file and re-upload to the arduino.

(I also have essentially a Prussa Mendel - though it's a slight mod)

I've been reading other people's postings about the temperature, and like many people say I don't think the temperature reading necessarily is the actual temperature of the inside of the hot end - where the filament is melted.

Wissing apparently can have the PLA extruded at a low temperature like 165C, but with my printer at that temperature I cannot squeeze out any no matter how hard I try. As a matter of fact, I have problem with extrusion even at 185C, so what I had to do was the opposite of what Wissing did - I had the temperature set at 205C...

I guess there can be three things which can contribute to wrong temperature reading:

1. Location of the thermistor:

The thermistor cannot be placed at the nozzle hole, where the plastic is melted, because that's where the plastic should be. And, even though we are going to try our best to place the thermistor as closely as possible to the spot we want to take the temperature reading at, the temperature would be slightly off.

But then again, I think the key word is "slightly". I think the difference of the temperature reading caused by the fact the thermistor being at a few mm away from the nozzle tip should not be that much. Only a degree or two? Well, even if it's 5C difference, I don't think that's that bad.

2. Wrong thermistor configuration:

This is what I am looking into with my printer right now. Someone advised me to check the termperature table (as a reply to my another posting). Well, I didn't even know there was such table before I read that. Anyway, so apparently there are different tables, which is basically an array with pre-calculated numbers the controller will reference to determine what the temperature is (based on the resistance reading it gets from the thermistor).

I built my printer from a kit, so I didn't shop each individual parts myself. I've contacted the vendor about my thermistor, too, and all I know is it is (or it is supposed to be) Epcos 100K thermistor. Well, there are a few different versions of Epcos 100K thermistors... All Epcos 100K thermistors may have similar characteristics so I may not need to know the exact specs (specs are always not exact anyway), but it won't hurt to know the specs and use the correct table, even if the difference is small. Also, I know it's not very likely that the vendor made a mistake like this, but it always is a possibility that my thermistor was not Epcos 100k - maybe the supplier of my vendor mixed up the order, maybe the vendor happened to include a wrong thermistor in my kit by a mistake..

3. Not all PLAs are the same:

Well, this won't really be a "wrong reading' of the thermistor. But I wonder how correct it really is to say "ideal hot end temperature for PLA is 185C". Maybe some PLA (because of the coloring and other factors) works best at lower temperature, while some other may work better at a higher temperature.


If we got a combination of all three than we may explain why some people print PLA at 165C while some need to set it at 210C.

A hypotheical case:

Perason A has -
1. The thermistor reading is 5C cooler that the actual temperature of the nozzle because of its location
2. The temperature table used in firmware is off by 15C (cooler than actual) at high temperature range
3. The PLA he is using works best at 190C, not 185C.

So the person A would have to set his hot end temperature at 210C (= 185 + 5 + 15 + 5).

On the other hand Person B may be in an opposite situation-
1. The thermistor reading is 5C hotter that the actual temperature of the nozzle because of its location (it's closer to the heat resistor than the nozzle)
2. The temperature table used in firmware is off by 10C (hotter than actual) at high temperature range
3. The PLA he is using works best at 180C, not 185C.

Now the person B would have to set his hot end temperature at 165C (= 185 - 5 - 10 - 5)


Well, my example is a bit exaggerated for the sake of illustration, but my point is that I really think this temperature reading should be just used as a reference, but not as the key reference to go by.

I've once read it from someone's posting on how he/she did find the right temperature, well it's actually right temperature "reading" for his/her particular printer/extruder. He/she basically kept on increasing the temperature in small step, until getting a good extrusion (by hand), and tag that temperature (reading) to that particular filament. So, basically you would do this for all different filament roles you have (if you have more than one), and if you have more than one printer or extruder, then you would also have to repeat this test with the other printer/extruder.

Edited 2 time(s). Last edit at 08/10/2013 11:13AM by Yamster.

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Edited 1 time(s). Last edit at 08/10/2013 11:11AM by Yamster.