Start of print slows down heating print head

I often preheat the print head to the print temperature by setting the temp in the web interface.

If I am too impatient and start a print when the temperature is 2 degrees less (or lesser) than the print temp, the temp drops like 10 degrees and slooowly rises back up again.

I wonder if this effect can be avoided in any way. No major issue but annoying.

This is what the temp chart looks like. Heating up and then at the first red little mark I start the print, temp drops from 237 to 227 and slowly rises to 240 and the print starts at the second mark.



Colud it be the M301 in config.g

M301 H1 S1.5 T0.53
M301 H2 S1.5 T0.53

Or could it bee the M104 or M109 in the print g-code?

M107
M190 S50 ; set bed temperature
M104 S240 ; set temperature
; layer_height = 0.2
G1 Z5 F5000 ; lift nozzle
T0
M109 S240 ; wait for temperature to be reached
G21 ; set units to millimeters
G90 ; use absolute coordinates
M82 ; use absolute distances for extrusion
G92 E0
G1 Z0.400 F6000.000
G1 E-4.00000 F3000.00000
G92 E0
G1 X74.600 Y55.895 F6000.000
G1 E4.00000 F3000.00000
G1 X75.264 Y55.087 E4.08943 F1500.000
G1 X75.768 Y54.569 E4.15122
G1 X76.062 Y54.298 E4.18544

Perhaps the power supply output voltage is dropping when the motors turn on.

Judging from the undershoot you are getting, I think the PID values need adjusting. What are the rest of your M301 values? The default values vary between firmware forks.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
fotomas
If I am too impatient and start a print when the temperature is 2 degrees less (or lesser) than the print temp, the temp drops like 10 degrees and slooowly rises back up again.

This is what the temp chart looks like. Heating up and then at the first red little mark I start the print, temp drops from 237 to 227 and slowly rises to 240 and the print starts at the second mark.
[/code]

If you use Slic3r, have a look at what's in the Printer settings/Custom G-code/Start G-code field. It could be that you have a G10 command setting tool temperature to 225 deg C. When this command executes, it will wait until the tool temperature drops from your 240 deg C to within 2.5 deg C of 225, before it continues execution of the G-file. The print will then start and, assuming you have in the meantime been impatiently pressing Enter in the web interface tool temperature field, the nozzle temperature will slowly rise back to 240 (slightly slower than usual because you now have plastic flowing through the nozzle and removing heat).

If you don't use Slic3r, ignore the above....

Bart

If your nozzle is far away during the heating up process and it will be lowered then you also could have a problem with backwash of your fan. My Ormerod 1 suffers from this problem.

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Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

dc42;
A power drop when all the motors turn on could be it. How would one go about measuring that?
To check this in more detail I did a test print and when temp is high enough so that the print starts. It starts and then the temp dops slowly to about 234, so it seems it struggles to keep the temperature. But this is when pushing plastic through the nozzle. If I start the print too early I get an even bigger drop with no plastic going through the nozzle.

Furter in the print (layer two and forward) the temp is lowered to 235 and the printer it manages to keep it att almost exactly 234, it never reaches 235. Stopping the print and leaving the temp at 235 and eventually it gets there (235).
Firmware: 1.09v-ch (2016-03-02)

The M301's in my initial post are the only ones, see my complete config.g at the bottom of my post. Should there be more?
I wrote a post when upgrading to dual nozzles and not reaching the desired temp. That was due to the lower resistance of the dual nozzle upgrade kit. http://forums.reprap.org/read.php?340,491929,491981

bartdietrich;
I do use slicer but as you can see in the snippet from a print file there is no commands issuing a lower temp.

Treito;
During heatup the nozzle is a t Z10, and when starting a print it drops to Z5, at the corner of the bed so the backwash would be minimal.

M111 S0                             
M550 PEXETON		
M551 Preprap                    
M540 P0xBE:0xEF:0xDE:0xAD:0xFE:0xED 
M552 P192.168.0.65                  ; IP address
M554 P192.168.0.1                   ; Gateway
M553 P255.255.255.0                 ; Netmask
M555 P2                             ; Set output to look like Marlin
G21                                 ; Work in millimetres
G90                                 ; Send absolute coordinates...
M83                                 ; ...but relative extruder moves
M574 X0 Y1 Z0 S1					; set endstop configuration (Y endstop only, at low end, active high)
M906 X800 Y1000 Z800 E1200          ; Set motor currents (mA)
M563 P0 D0 H1
G10 P1 S0 R0
M563 P1 D2 H2 
G10 P2 S0 R0
;M92 E420:420	; org extruder ratio
M92 E420:420:105.4	; beltextruder ratio
M558 P1 F100 T2000 
G31 Z1.08 P500  
M305 P0 R1000 H0 L0					
M305 P1 R4700 H0 L0 X3				
M305 P2 R4700 H0 L0					
M301 H1 S1.5 T0.53
M301 H2 S1.5 T0.53
M201 X800 Y800 Z15 E1000            ; Accelerations (mm/s^2)
M203 X15000 Y15000 Z200 E3600       ; Maximum speeds (mm/min)
M566 X600 Y600 Z30 E20              ; Minimum speeds mm/minute
M208 X214 Y210						; set axis maxima (adjust to suit your machine)
M208 X-8 Y0 S1						; set axis minimum (adjust to make X=0 the edge of the bed)

You appear to have put all your config settings into your print file, which is unnecessary and some of the commands may cause issues.

Dave

Quote
dmould
You appear to have put all your config settings into your print file, which is unnecessary and some of the commands may cause issues.

Dave

I think you have misread my post. There are two codebocks, one with config.g and one with the first lines in a print file.

I have made some more observations and it seems like that the drop of temperature does not occur if the temperature is low enough when staring the print.

So it behaves the same if I preheat and start the print when the temperature is the desired first layer temp as when starting a print when the temperature is about 10-20 degrees below the desired print temp. And the behavior is that the temp steadily rises and the print starts.

What is odd is that when the temp is just a few degrees below acceptable print temp and I start a print, the temp drops and needs a few minutes to catch up.

I have have a theory that some other heating logic kicks in when a print starts, causing this. Could it be that there is a gap in the value of acceptable print temp (compared to desired temp) and the temp that makes the firmware go from rapid heating to maintaining a temp ?

I do not know if there is such logic and this is just guessing, I have nothing else than my observations above to back this up.

I think what may be happening is that you are getting a voltage change on the thermistor input when the print starts - the actual temperature is not changing. Check that the wires and connectors in the thermistor leads are all sound back to the Duet, and there is no short to the metalwork.

Dave