Finding the right extruder temp

What are the signs I should be looking for to get the right extruder temp for PLA? Are there subtly different things that will happen at different temps?

 

Man, you are helping me all over the forums this evening! Hah, thanks for the tip!

 

So should I shoot for the lowest possible temperature that it can extrude at?

 

This is where having good test/calibration objects are useful. One thing to keep in mind that the same settings may not be valid for all spools of PLA. Changing manufacturer, color, etc. may cause settings to change. Same PLA from same manufacturer, if from different batches, may have different settings.

Thus, when you start using a new spool, keep notes, especially if you tend to switch from one spool to another before it's all gone. This way when you switch back to it you'll "remember" what the previous good settings were.

As for calibration objects, here is one I love. It's three circles and can be found on thingiverse at http://www.thingiverse.com/thing:12259

The three circles, one is a solid, another hollow but with the top filled, and the last is hollow. Printing this will give you a good idea on how well your printer bridges and how badly the filament strings at your settings. If you read the description you can see some of the things it tests for and definitely read the comments.

Another calibration object I really like is the hollow pyramid which can also be found on thingiverse at http://www.thingiverse.com/thing:8757

It also can test how badly you're stringing and the top of the pyramid is very difficult to print well.

Here's one I printed several days ago (before my Z axis motor controller died)

 

Thanks! I had seen the temp test that was basically a stick with different number markers on it but these are far more interesting! When using the calibration objects do you basically just print out multiple versions at different temps?

 

Yes, but you should understand what it is you're going for. Layer adhesion? Less stringing? Experiment and have fun.

 

I used http://www.thingiverse.com/thing:66175 to find the ideal temperature -- Higher temps tend to make strings everywhere. Lower temps make the surface finish on the ball part get grainy. 30 mins per temp, and you can fit 3x3 on your printbed (start with back corner -- and remember to have a gap big enough not to run into the fan).

Then I fine-tuned the speed/cooling settings by using the racing vase.
http://www.thingiverse.com/thing:113440

 

I had the filament shaving problem and it's because the temperature is too low. Fortunately, I have a Flir thermal imaging camera. I checked the nozzle temperature and found it to be 20C below the setting. I set the first layer temp to 240 and others to 230, which is actually 220/210 and all my problems went away. I also slowed the print speed dramatically, will have to try speeding it up now.

Robo needs to invest in a thermal camera and calibrate their sensors. As an EE, I know part tolerances add up! -5% plus -5% = -10%!
Also, the heated bed is a lot hotter by its connector. Thermal imager shows a weird looking pattern. Could send imager photos?

 

even then there would be differences. the camera is also not 100% accurate.
the electronic and the terhmistor can have a little shift
and from one spool to another (different colour, or just a new one) can have little bit different optimal temperature
and also the room temperature can have an influence.

so all in all, even if once calibratet, there can be plus/minus 5-10°C

easiest thing to do, start with a educated guess and increase or decreae in steps, till the right temperature is found.

 

I am having an extrusion issue where the first layer or two are great every time, and then, when the printer speeds up, I start having sections with lower extrusion/no extrusion, and then it picks back up. In the lower areas, the bolt starts shaving filament. I am printing at really slow speeds, 25mm/s or less.

I am replacing the hobbed bolt and will try a higher temperature.

Smaller objects that take only small amounts of filament at a time are no problem, and I don't have much stringing on calibration objects, either. Is it as simple as temperature too low? Maybe the hobbed bolt will fix it. I think the Robo one isn't quite perfectly round.

 

I had this problem with the stock extruder -- the PTFE tube gets mangled really easily (if printing ABS, keep the speed up and don't let it sit -- the heat from the block will go upwards and melts the PTFE tube) and causes this.

The other thing that I've seen cause this was heat-soak -- if you aren't moving filament fast enough through the extruder (even PLA plastic), the heat works its way up the tube, causing it to get too soft at the top of the PTFE tube and then it makes a S-Shaped thingy between the drive and the extruder. I was only able to fix it by disassembling and then pushing the filament out of the PTFE tube with a drill bit shank (on just the tube -- it made a mushroom shape so I had to push it "backwards".

E3D and other metal hotends don't have these problems as much because they're actively cooled to make a clean heat break zone -- the new Prusa hotends have a fan on them blowing on the PEEK to keep it happier.

That being said, I still have problems with the stock hobbed bolt eating instead of pushing.... but with the E3D hotend, it's been a lot easier. If it starts giving you fits, open up the drive and blow out the hobbed bolt. rotate it and blow it out again. I also have 3 washers under each spring for more tension; for PLA and ABS, it works like a champ. For XT, it still jams periodically because I run it cold (210) so it doesn't sag when it covers gaps.

 

I was having issues finding extruder temp as well and PrintedSolid was helping me out. He linked this test on Thingiverse and it was a great idea. See example below; what you do is modify the Gcode to change the extruder temperature every 10cm so it matches the section printed on the actual object. When you are done you can clearly see what temperature your brand/type of filament extrudes best at.

 

Wow... I like that. I think I'm going to fix/remix it so you can see bridging ability on the backside and then I'll post the gcode so you don't have to modify it...

 

Keep in mind the posted Gcode will only work with people that have the EXACT same setup as you; same hotend nozzle diameter, etc.

 

Thanks for the info - my issue is when the filament is going quickly and not slowly, so I don't think it is heat getting up into the unit, more like the nozzle isn't staying hot enough as more filament tries to get through. I have a fairly new Robo so the PTFE jamming issue shouldn't be an issue. I have the newer stock hotend so hopefully it continues to be jam-free.

 

Ack. good point. Maybe I'll have to figure out a way to put "tags" into the STL that Slic3r will obey...

 

Tried the new hobbed bolt, sped things up, same issue.

Maybe try a lower temperature this time?

 

I tried the calibration circles, and after about a third of the print, shaving and bad extrusion. I'm on PLA and printing at 215 - maybe my sensor is low, but I guess I will clean out the extruder and up the temperature some more.

I can print small things just fine - as long as it is really slow.