Begin print cycle time reduction - calibrate while heating  

Re: Begin print cycle time reduction - calibrate while heating

You can do this, by adjusting the Start GCODE in your slicer.

BUT you DON'T want to. The calibration is temperature dependent, and you want to measure it when the system is at printing temperature.

Re: Begin print cycle time reduction - calibrate while heating

Thanks for pointing me in the right direction on how to make that change.

But can you elaborate on why you wouldn't want to? I get why in theory you'd want to wait for the temps to stabilize as the heated bed and extruder could expand a bit under heat. But is the temp change really going to result in a measurable difference in Z axis distances that would affect a print?

Bed Thickness (@ room temp): 3.3mm
Bed thickness (after heat to 55deg C): 3.3mm

So no appreciable bed thickness change from heating.

Here is the modified Start G-Code:

M115 U3.0.12 ; tell printer latest fw version
M83 ; extruder relative mode
M104 S[first_layer_temperature] ; set extruder temp
M140 S[first_layer_bed_temperature] ; set bed temp
G28 W ; home all without mesh bed level
G80 ; mesh bed leveling
M190 S[first_layer_bed_temperature] ; wait for bed temp
M109 S[first_layer_temperature] ; wait for extruder temp
G1 Y-3.0 F1000.0 ; go outside pritn area
G1 X60.0 E9.0 F1000.0 ; intro line
G1 X100.0 E12.5 F1000.0 ; intro line

I ran a print test and the print was fine.

So just curious to what your reservations would be? What else am I missing?

Thanks,
Chad

Re: Begin print cycle time reduction - calibrate while heating

I am not worried about straight thickness expansion. As you point out that would be minimal.

I would worry about the bed flexing when it heats. Recall it is attached at 4 points to a thing that is NOT heated and thus does not expand. Thus when then bed does expand (in X and Y), but is constrained at those points, it will flex in Z.

I would also worry about the PINDA probe which is measuring the points, which is known to be temperature sensitive.

All of these MIGHT be okay at PLA with a 50deg bed, calibrated at 25deg, but will cause much more issues at PET or ABS with 100deg beds. Make sense?

--- You cans stop here unless you like math. ---

The CTE of Aluminum (Coefficient of Thermal Expansion) is (fractional expansion per deg C) 24e-6.
For a 25 deg shift that is 6e-4 (fractional).
So agains a 3.3mm thick board, it will shift by 0.00198mm (nothing).
but across a 200mm width, it will change by 0.12mm. Not much, but enough to make the bed bend and bow.
For a 75 deg shift it will be 3x that, and clearly enough to cause calibration issues.

--- End Math ---

That all said, I am experimentalist at heart. If you find your new start gcode is still resulting in good prints (I would at least do a 9 patch one layer test at the edges of the bed with and without your settings change as a comparison) and the few minutes of savings are important to you, then by all means go for it. Since my prints average 12 hours (and have gone has high as 55 hours) the few minutes of heat up time really don't affect me.

Since the "differences" you would be looking for are bed leveling issues, run one of these: https://www.thingiverse.com/thing:29028 with the original start g-code and your new start g-code and see if you can find a difference.

Interesting discussion anyway. Let us know what your experimenting results are, many here would be interested .

Re: Begin print cycle time reduction - calibrate while heating

Thanks Aaron for the explanation. I had not accounted for the flex 🙂

I am doing multiple smaller prints at times, and in those instances, the timing can be a bit frustrating, but I was more curious as well.

The prints I've done so far have been fine, but I'll try the test patches to help detect the issue specifically.

FYI, I'm just south of Boulder in North West Arvada...hello neighbor!

Re: Begin print cycle time reduction - calibrate while heating

Hello neighbor!