Failing tower calibration

I'm commissioning a Durbie Prusa Mendel, using the calibration procedure in Calibration. The thin wall is okay, and the block is very clean. It had one wavy edge, but once I tightened the Y belt a little, it came out as I expected.

But the 50mm tower won't print. I'm using 3mm PLA, and I started at default filament temperatures (first layer/successive layers) 190/180, and it printed a couple of layers square, then started rounding corners. I tried 190/175, and it improved slightly, then 185/170. At that point, it prints about 8mm fairly square, then begins rounding corners. It prints the whole tower, but it's clearly distorted. Just to be crazy, I tried raising the temperature, to 195/185, and that made one corner a little better, but didn't help the rest. The tower stays more or less a tower, but the corners are rounded, not sharp.

This isn't just a problem with the tower: I tried printing an extruder pulley, and it came out looking sort of blurred in the the upper parts: the round base is okay, but the gear part is no good. This doesn't just seem to be temperature: once the z axis moves up, the x and y registration seems to go wrong.

Post a picture of the tower,

This image here shows the towsers at two temperature settings. I think you can see the behavior.

Thanks;
Rick

Looks like the layers are not cooling in time for the next layer. The slicer can attempt to fix this by printing more slowly, but you really need a part cooling fan to print small details in PLA.

perhaps a bit temp, but also overextrusion. you need to calibrate etruder steps lower.

alj_rprp Wrote:
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> perhaps a bit temp, but also overextrusion. you
> need to calibrate etruder steps lower.


Would it have printed the previous calibrations correctly if the steps were wrong? The thin wall was pretty good, and the 20mm cube was great.

Also, is the extruder steps something settable in the slic3r settings, or do I change that in the firmware? I see STEPS_MM_E in Marlin Configuration.h. I'm willing to try it.

Thanks!
Rick

Andrew Smith Wrote:
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> Looks like the layers are not cooling in time for
> the next layer. The slicer can attempt to fix this
> by printing more slowly, but you really need a
> part cooling fan to print small details in PLA.


I have another small fan, like for the extruder. I'll hook it up to some power and hold by hand, and see what happens.

Thanks!
Rick

Yup, more cooling is needed on the layers before the next layer is printed.

A fan worked well, after a little experimentation. First try, I cooled the extruder right down and stopped it.

But then I figured out to move it away, and get it to where the extruder temp stayed stable, and got a very nice tower. I'll have to set one up with a variable voltage for better control.

Thanks very much for the help!!

Regards;
Rick

Are you using RAMPS? If so the middle of the three mosfet outputs, where your extruder heater and heated bed are connected, can be used to control a hot end fan with PWM, so no variable voltage required. I think the connection is called D9 from memory

mnturner Wrote:
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> Are you using RAMPS? If so the middle of the three
> mosfet outputs, where your extruder heater and
> heated bed are connected, can be used to control a
> hot end fan with PWM, so no variable voltage
> required. I think the connection is called D9 from
> memory


I'm using gen 6, specifically gen6.d, according to the board. It doesn't seem to be vanilla gen 6, but there's at least one connector similar to the extruder fan. I'm looking for the schematics.

Thanks;
Rick