Unable to control extruder temperature

I have built a 3d printer of my own design as a learning experience. I've used mostly available off the shelf parts with an Arduino MEGA running Marlin, Ramps 1.4, Pololu boards, nema 17 steppers and a RobottDigg Stepstruder extruder. The extruder came with a thermocouple so I added a AD595 board. I have written a handfull of Arduino sketches to test axis movement, endstops (min & max) and calibrate the extruder feed rate. Got the 100mm feed interval perfectly. (bypassing the extruder nozzle) I even tried to stall the extruder stepper by holding back the filament with my hand while it was doing a test feed. Seems to pull very strong and work great.

However, when I do a test print, Marlin shows on the LCD2004 display that it overshoots the desired temp of 210 by a few degrees, then drops below 210 a few degrees, then goes back up to 210 and begins the print by homing everything. I think that is all normal. Just after homing when it tries to extrude a line around my actual object, the temperature drops to around 135C. I told Cura to print the first layer at 5mm/sec. I was trying to give the extruder enought time to reach temperature and it sort of works. It does not extrude anything while drawing the outside line, but just after the beginning of the object extrude, and its up to temperature, the extrude only outputs during part of the line. It starts and stops extruding during each pass. So I just get a bunch of dots and short lines. In one test I increased the extrude feed rate to 3 times normal. It printed my rectangle cube test, but it was very rough and pourous. During all my test prints the temperature is constantly jumping around with values at least 10 degrees off. If it reads 205 one instant, it may immediately read 191, then 197, etc. It just keeps jumping around constantly, averaging about 10-15 degrees lower than defined (210). When I test the temperature with my Arduino program by putting ice cubes in a rag and then hold the extruder head with my hand I got slowly moving reading from 66F to 88F as expected. Marlin keeps flashing numbers all over the place. I did wiggle all the wires and connections during my Arduino testing to see if all the connections were ok. I got no bad reading.

I don't kown what to try next. I have done about 20 tests with varying Cura settings and nothing seems to change. I used some temperatures that would "brown" the pla at the beginning of the extrude, but they were only drops, never a complete line. When I first start the print and I'm waiting for it to warm up (Marlin already went throught the several minutes of warm up) it seems to start extruding at about 190C but it never keeps a constant extrude.

Short of ripping apart the extruder and replacing the thermocouple with a thermister or buying a different hotend, I don't know what to try next. I'm very patient and willing to try most everything, but I'm not sure what to do next. Too bad. I was really on a roll and pleasantly surprised how well it was going.

Any ideas or help would be appreciated.

Thanks. Bruce

Sounds like your power supply doesn't have enough oomph to drive the hot end and steppers at the same time, hence the temperature drop.

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Calibrate your PID settings by following this, if not already:
[reprap.org]

Arrrrhhhhh......

I think I found the answer to my problem. I read somewhere to try cleaning out the nozzle with a drill bit in case it is clogged. So I heated up the hotend and started trying drill bits until I found one that perfectly fit the nozzle. It didn't seem dirty, so I tried another print, but still the same problems. But as I was cleaning things up I noticed that the drill bit I used seemed rather large. I'm fine with fractional sizes, but metic sizes keep me in a tailspin. So I checked the drill bit with my digital calipers and low and behold .... 1.96 mm !!!!!!!!!. Why someone would send me an extruder with that size nozzle instead of the advertised .4mm, I have no idea. But I see now why I actually made some progress during my tests when I upped the feed rate 3X. Maybe 5X would work even better. But if the nozzle is larger than the filament I can't see how it would ever develop backpressure to do an extrusion. It is just going to "dribble" out the nozzle. I'm actually surprised the filament doesn't pass through the nozzle and never even melt.

Anyway, now I need to order some .4 nozzles and wait to see what happens next.

Thanks to all for responding to my problem.

P.S. My PS is a 450 watt ATX and I'm not heating the bed yet, so I think it's ok. Still don't understand why the temperature drop so much during homing before starting the print and why it jumps around so much during.

Bruce

Also, I did the PID calibartion and the numbers are the same as in my Marlin config.h file. P22.20 I1.08 D114.00

Bruce

I was able to source a new nozzle locally, albeit it's a .2mm nozzle. But my print problem persists. I manually warm up the hotend to 190C. Once it reaches temp I push filament by hand into the hotend and it does extrude material.

But once I select a file, and it homes the axis', the temperature drops to below 140C and nothing extrudes while it tries to make the outside lines. I'm running the first layer at 10m/sec to it has time to warm up before trying to print the actual part.
But even after it reaches temp, it fluctuates by 15-20 degrees and the extrusion is erratic. I have tried every temperature from 180C to 240C (in 5 degree steps) and nothing seems to work. On one try I got a pretty good 1st layer at 200C,, but the perimeter was all blobs and skips.

Any ideas why the temperature fluctuates so much. (Never having done this before, I'm not really sure what to expect)

Thanks,

Bruce

Thermistor could be an issue.

I've been running PID auto tune everyday with a cold extruder. I seem to get way different results every time it runs (6 times so far). From 28.28 1.79 111.79 to 43.16 2.88 161.76. I enter the results each day into marlin config.h and reflash my Arduino. I was running all my prints just from CURA with an SD card, but yesterday I installed Repetier Host so I could see the temperature graph. If you look at the attached file you can see that once the printer "homes" and begins printing after coming up to temperature, the actual temperature is 30-50 degrees too low and nothing extrudes for 20-30 seconds until it reaches temp. I added "brim" to all my prints to give it time to warm up. It usually makes 2 or 3 passes around the perimeter of the brim until it starts extruding. Then, regardless of my PID settings the average temperature is about 10 degrees below target and the oscillations are at least 10 degrees in either direction.
I'm running the latest download of Marlin on an Arduino Mega 2560 with Ramps 1.4. My extruder is a direct drive "stepstruder" from Robotdigg. It came with a thermocouple, so I wired to through a AD595 board. It seems to give reasonably correct readings, so I don't suspect it as the problem since it is supposed to be more accurate than a thermister. I've asked around to some friends with 3D printers and no one has seen the dramatic temperature drop at the beginning of a print. I been told to work on the PID settings to get the oscillations down to a resonable amount. Is that +- 1-2 degrees? I seem to get the best print results at 205 degrees with 1.75 PLA, Although actual running temp. is about 195.

Any suggestions as to what to try next?

Thanks for your help.

Bruce

Is your amplifier own made or did you buy it?

I've made it by myself and had this problem. After 2 days of intensive googling I found that you can add 1 uF. Capacitor at thermistor inputs (SIgnal + Ground). It helped me

Give me a note if it helps

Edited 1 time(s). Last edit at 01/16/2015 01:37PM by KarolisL.

I bought two of them from ebay. They took forever to get here and one of them didn't work correctly from the start. The second one seems to indicate the correct room temperature and in general it seems to be working correctly. They were apparently parts for an Ultimaker printer since it says Ultimaker.com/tc1 on the board. The board has a SMD resister and capacitor plus a led. The chip on the board is a AD597A.

I can understand how the tempeature might be off based on the supplied 5 volts variance, and I don't have a problem requesting 220 degrees to actually get 210, but why does the temperature oscillate by over 10 degrees + and - ?

Any why does the PID values I get vary so much every time I run it?

And finally why does the temperature drop 40 - 50 degrees during the 7 or 8 seconds it takes to home and start printing? I select PREPARE and heat the extruder to 180 PLA temperature before I select a file to print from my SD card.

Edited 1 time(s). Last edit at 01/17/2015 03:51PM by Macarduino.

I had exact same problem. I found schematics of that board, i soldered everything but amplifier didn't work like I wished to. Probably noises from steppers influenced everything. After searching Russian forums I found out that capacitor is often used to filter external noises. And it helped me.

Just try this:


Best regards

Ok, I had the same prob with erratic tempatures, to the point it was dropping below room tempeture. I could heat it up, but as soon as I started a print, the temp would drop. I swapped the thermocouple wires over on the board and mine works perfect. I found a website and it stated this

" If you insert it wrong, it will simply report the reverse of the real temperature.
Please note: the v1.0 board has a silkscreen error, and the +/- signs on the board are reversed. Sorry!!!"

In other words the green wire needs to be swapped over because the + marking on (I assume some boards) are printed on the wrong side of the terminal. All I had to do was select -1 for ThermoCouple in Config.h and change Pin settings and works perfect!!!!!

Sounds like the heater cartridge doesn't make proper contact with the hot end. See if there's too much room inside the hole. Stuff some aluminium foil in the hole for a snug fit.

The temperature can only drop so much if the heat capacity is too low or the feedrate is too high. Since you're printing at a speed below 80mm/s my guess is that the heater cartridge can't tranfer its heat well enough to keep up with demand. I've only noticed at 280 degrees, 0.5mm layer height and extrusion width of 0.75 at 80 to 100mm/s it will drop 10 to 15 degrees centigrade. This is with an E3D v6 bowden on 12V 40W heater.

Edited 1 time(s). Last edit at 02/26/2015 07:37PM by imqqmi.