Roughness only on Outside Shell?

[ssashton 2]

I printed these little cups and I'm getting a strange result.

Same Cura (4.0 Creawsome) settings I printed a single cup with a great result. I multiplied the object in Cura and printed 9 of them.

I checked the print half way and there were little blobs around the perimeter. The weird thing is, it's only on the outside wall. The inside wall is smooth and so is the support material being generated. Weirder still, one object in the bottom left corner was all smooth as it should be.

The top curved surface is also smooth, it's only a problem on the vertical wall section.

More photos here

https://photos.app.goo.gl/58e8DdeNTxTmpHfL6

Can this be hardware related? I'm not convinced because the support material is perfectly smooth and so is the bottom left object and the curved tops.

Help and advice appreciated!

 

Edited August 31, 2019 by ssashton

[gr5 2,173]

The only thing I can think of is print speed is too high.  When cura prints circles it prints slower for smaller circles.  but only if your print speed is quite high.  When you see those bumps/vibrations, try lowering the speed - most printers let you lower the speed live.  Typically in a "TUNE" menu.  Try printing at half speed for a few layers to see if those bumps go away.

 

You should also consider trying a different color.  White is the most difficult filament to print because of the heavy amount of additives (e.g. chalk).  It might be better to print some darker color (like gray) and then paint the parts white afterward.

 

Is this PLA?

[ssashton 2]

47 minutes ago, gr5 said:

The only thing I can think of is print speed is too high.  When cura prints circles it prints slower for smaller circles.  but only if your print speed is quite high.  When you see those bumps/vibrations, try lowering the speed - most printers let you lower the speed live.  Typically in a "TUNE" menu.  Try printing at half speed for a few layers to see if those bumps go away.

 

You should also consider trying a different color.  White is the most difficult filament to print because of the heavy amount of additives (e.g. chalk).  It might be better to print some darker color (like gray) and then paint the parts white afterward.

 

Is this PLA?

Thanks. I thought white was natural PLA so the easiest to print.

 

I only printed at 80mm/s so not exactly fast. I guess I'll just try again and see what happens. Also I'll switch to black PLA.

[ssashton 2]

I might have found the problem. Yesterday I got these strange rough prints. Today my CR10S Pro turned itself off in the middle of a print and wouldn't start again.

I did a little bit of investigation and found the screen board was only getting 2.8V where the board was marked as 5V. The screen board is fed from the main board. When I unplugged the connector to the screen board the voltage on the connector went back up to 5V as it should be. This suggested a broken screen board and possibly a short circuit that made it draw too much power and cause the voltage to drop.

I disconnected the screen board and tried to power it with 5V from an external supply. It drew a couple of amps which seems like a lot. I'd have expected a few hundred milliamps.

Where there is power, there is also heat. I put some isopropyl alcohol on the PCB and connected power again. I could see the alcohol evaporate quickly in one location. There were come capacitors nearby so I tested their DC resistance (which should be in the kilo-ohms range). I found one larger ceramic capacitor that had a very low resistance of about 100 ohms. So I removed it.

Going by the size and fact the PCB is only running at 5V this is probably in the range of 10uF - pretty large for a ceramic surface mount capacitor. I replaced it with a 15uF tantalum capacitor. Powered up the board from an external PSU and the current draw was far lower now.

I connected back to the printer and it all came alive again! Yay!

So moral of the story here is - Ceramic surface mount capacitors can fail short circuit (often due to flexing such as on this touchscreen). Also you can often times follow heat to find the cause of a broken circuit.

I guess this excess current draw as the part was failing will have put the main board under stress and caused the strange results I was seeing. I'll let you know if the problem persists!

I've added some photos of the fault in the album.

https://photos.app.goo.gl/58e8DdeNTxTmpHfL6

Edited August 31, 2019 by ssashton