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Pockmarks on surface

Posted by blt3dp 
Re: Pockmarks on surface
November 28, 2016 04:25PM
I already found the source of the ticking.

It's an 8mm id washer used as a spacer on a 5/16 bolt that is my Hobbed Bolt. So it's eccentric. It rotates with the bolt as it should, but sometimes falls and ticks against the bolt shaft. I'd actually count this issue as resolved, after inspecting gcode and changing my slicer settings regarding keeping flow more constant, pockmarks are gone.

I do need to do a fine tune of E steps per mm though. I originally set steps per mm in firmware using ABS
It's quite a bit softer than PLA and can be pressed on the drive gear, changing it's diameter.

Setting stepper driver currents, this does raise a question however.

Previously I was using a Printrboard, and had never adjusted the stepper driver voltages.

I switched to a RAMPS board over the weekend, I had to lower the voltages from what they came factory set at, so everything works.

But, I'm having a problem figuring out what vref to set on the drivers. Would someone check my assumptions.

The drivers are Pololu A4988
and the motors are https://ultimachine.com/products/kysan-1124090-nema-17-stepper-motor

Looks if I set VREF to .280v then I end up with about .7A for the motor which is below it's rated limit of 1.5A per phase.

I figured best not run the Pololu at their max of 1A so I chose .7A

Edited 3 time(s). Last edit at 11/28/2016 04:51PM by FA-MAS.
Re: Pockmarks on surface
December 12, 2016 05:10PM
So, still kind of struggling with this one.

I ended up taking apart my hot end completely again and visually inspecting it. I didn't do so well the first time, apparently there was still quite a bit of carbonized filament in the threaded part of the throat past the heat break and in the nozzle. I heated it up again and with a smaller than 2 mm drill bit just by hand pushed it in and turned it against the sides until it was clean, did the same to the nozzle orifice with a .35 mm bit (smaller than the .40 opening). Heated it up and hit it with compressed air. I also sanded the mating surfaces of the nozzle and throat. Dunked them in alcohol and blew them off with compressed air. Put it all back together. The hotend is completely clean.

I also tore apart the extruder and arranged it so that there are no more washers, and used a nylock nut. No more tick noise from that.

I also made sure it is perfectly calibrated. I ask for 100mm and it does exactly that. Down to the .01

But I still get top layers that are not solid.

I'm starting to wonder if Cura is dong something with the flow rate on those layers.

I've got line width of .67 for everything
I mean bottom layers, perimeters, infill

I measure those and the line width is pretty much right on (considering measurement error)

But those on the top solid layers are .40 roughly

I've attached a truncated gcode file that includes layers in this scenario
open | download - frame_trunc_2.gcode (88 KB)
Re: Pockmarks on surface
December 12, 2016 07:17PM

I've had a look at your gcode in Repetier host, and in all the layers that you provided only every other run of filament is being printed. It is something to do with your Cura settings and not the extruder nor the calibration.

I encountered a slight wierdo like this a bit back when I was using a first layer extrusion width greater than 100%. This spaced the filament runs in the first layer further apart and seemed to affect the infill layers above. I think the problem stems from your having set all line widths to 0.67 mm. This will work for wall thicknesses as the slicer will add runs based on your nozzle size to get the required width. I don't think that it can perform a similar exercise for proportional or solid infill. Therefore each line will be printed at 0.67 mm centres, but the extruder simply cannot squeeze the filament out that wide in one pass. Hence the reason for the gaps showing in Repetier.

I suggest that you leave your wall thickness as it is, and set all other line widths to the nozzle width of 0.4 mm then try again. I strongly suggest that, if you don't have Repetier Host installed, you install it and use the included Cura slicer. Repetier will allow you to step up through the print one layer at a time and view the effect of your settings before printing (saves a lot of filament).

The Cura manual that I have recommends that you set wall thicknesses as a multiple of your nozzle diameter, and I know that the general assumption for the max successful width from a 0.4 mm nozzle is 0.48 mm.

Edited 1 time(s). Last edit at 12/12/2016 07:32PM by Supermec.
Re: Pockmarks on surface
December 13, 2016 02:21PM
Yeah, I eventually ended up thinking along those lines.

I did end up setting all the line widths to .40, set the wall width to 1.2, and number of perimeters to 3

I also took Cura's "advise" (highlighting things in yellow that may be incorrectly set)
It never did like that I was telling it 2 layers for top and bottom layers

I originally had the layer height at .20, I had the top and bottom thickness set to .40 and 2 layers

I was thinking maybe the lines I was getting were a slight pillowing effect because of the "sparse infill" underneath
I wouldn't consider 30% infill sparse, it looks like more than enough to support the solid layers

But I went with Cura's advise and I changed them to get rid of the yellow warning.
Changed to .20 layer height, top and bottom thickness to .80, and 4 top and bottom layers.

I also payed attention to another little indicator which was the "difference from calculated value"
Specifically for the top and bottom layer speed . I originally had it set to 30mm sec, I let it go to the calculated of 15 mm/sec
Though I don't think this had an effect, and slowed down the print ALOT. I'll probably experiment with 3 top/bottom layers and set it at 30 mm/sec

The result was:
The bottom shell was perfect as always

After the layers of infill, it went to do the first solid layer for the top and it still had lines in it
Odd, inspecting the gcode, it looked different than the top solid infill
Almost like an interface layer, or maybe slight pillowing. I let it go knowing more layers were going on top
The subsequent solid top layers were perfect

I'd say the print was perfect in that aspect

That's interesting you mention viewing the gcode in Repetier Host
I actually posted this same issue on Curas' github and was given that advise too
There I did comparison between the successful first 2 layers on that print and the 2 top solid layers

I saw the line widths were consistent, but on all the layers showed equal spacing
I just assumed that it was not giving representation of the actual extrusion width rather than the tool path

Guess I was wrong
I loaded the gcode from after I made the changes and Repetier showed exactly what I got

I'd say I need to incorporate Repetier and visual inspection of the gcode in my workflow

Only issue I have with the print is that now with the different line width, i need to tweak the retraction
I currently have it set at 1.5mm and no extra on restart

I notice that at the start of perimeters, it's starved for filament for bout .50 mm
Nothing to worry about, I'll back off my retraction or add extra length on restart.
Re: Pockmarks on surface
December 14, 2016 03:38PM
apparently there was still quite a bit of carbonized filament in the threaded part of the throat past the heat break and in the nozzle

I put Teflon tape on my heatbreak and nozzle's treads to prevent this. The nasty carbonized filament would mess up my prints otherwise...
Re: Pockmarks on surface
December 14, 2016 05:55PM
I haven't had this problem but I have the code for a 4mm retract in my ending code (I put this back in the start code for the next print). I leave the printer on with the cooling fan running until the extruder drops below 120.

The other thing to do is to clean the back end of the nozzle and the bottom end of the throat tube. When re-assembling, don't screw the nozzle completely in by say 0.1 to 0.2mm. Using your fingers screw the throat tube against the back of the nozzle as hard as you can, and then holding the heater block in an adjustable spanner, tighten the nozzle hard against the throat tube. This give a good tight contact between the back of the nozzle and the throat tube and prevents leakage, It's impossible to do this any other way without risking snapping the throat tube.
Re: Pockmarks on surface
December 15, 2016 11:29AM
I'm all sorted out.

Dropped my retract to 1.0 mm and added extra length on restart of .2 mm
No more gaps on layer start
And Cura does do things better, I'll probably switch over to the Repetier/Cura combo.

Edited 1 time(s). Last edit at 12/15/2016 11:30AM by FA-MAS.
Re: Pockmarks on surface
December 15, 2016 11:36AM
Cura 2.3.1 seems to do most things better, but I do run into the occasional STL file that Cura can't handle properly for one reason or another that slic3r handles quite well.

On the slic3r note, I've been having better luck with the Prusa version from www.prusa3d.com and just telling the installation to only install slic3r. I can't remember if I've seen this version crash yet.
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