Black mark on prints  

Re: Black mark on prints

It's not dirt, it is burned filament i.e. blobs of excess plastic that have collected around your hotend and nozzle and have burned black. Then they detach at the worst possible moment and ruin an otherwise flawless white print.

Printing white can be frustrating. I have four beautiful white PETG twin wheel rims here for an RC truck I am making, and yep, one of them has one of these skanky blacks blobs embedded in it. Grrr!

Re: Black mark on prints

Is there any way to prevent or at least minimize this? Do I need to clean out the nozzle before printing?

Re: Black mark on prints

Is there any way to prevent or at least minimize this? Do I need to clean out the nozzle before printing?

Cleaning the nozzle between material changes is a good idea, but this is most likely caused by accumulation of melted material around the heat block and nozzle. Remove the part cooling fan with the single front screw and inspect the block with a good light. If you see material accumulated on it, that's likely what is flaking off mid-print. Think of it like a dirty oven.

You can heat up the block and give it a brush with a soft brass brush. This will knock off a lot of junk, so he prepared to catch it and to clean your print bed afterwards. Be careful around the heater cartridge and thermistor wiring as they are fragile.

Re: Black mark on prints

Would this level of accumulation happen after only owning it a week? Is it hurting anything or can I leave it for another week or 2? Basically, how often should I do that?

Re: Black mark on prints

Would this level of accumulation happen after only owning it a week? Is it hurting anything or can I leave it for another week or 2? Basically, how often should I do that?You only have to do it if you don't want random black bits falling into your prints.

Re: Black mark on prints

I have had the same problem before. Would silicone socks, e.g. http://e3d-online.com/v6-sock-3pack , or a non-stick nozzle, e.g. http://e3d-online.com/v6-nozzles-plated-copper-175 help with this? Or is this kind of stuff marketing hype? I know the copper nozzle is also for high-temp stuff but they also advertise it as non-stick.

Re: Black mark on prints

Hi Lars,

Peter PJR has used the plated copper nozzles and says he didn't see a significant improvement in quality.

I used the original sock, and got a blob of doom inside it... 🙁 the later socks have a wider mouth around the nozzle to prevent this sort of issue.

but the nozzle still sticks out and can collect bits of filament.

A Brass brush is useful for clearing waste off the nozzle!
https://www.ebay.co.uk/itm/Wire-Brush-Nylon-Steel-Brass-Cleaning-Brush-Wire-Rust-Sparks-Wheels-Scruber/142878802288?var=441865814213&hash=item21443d8170:m:mir4qFK2kQZtlSuKaWcWm6w

I think the most important bit is to know that there is a possibility of contamination, and keep the nozzle and heat block as clean as possible

regards Joan

RE: Black mark on prints

I’m having the same problem aft a week or two printing on my new Prusa.  I was able able to scrape of some burnt filament but it just keeps happening.  I will silicone cover to see if that helps.  

RE: Black mark on prints

Posted by: @gmj43

I’m having the same problem aft a week or two printing on my new Prusa.  I was able able to scrape of some burnt filament but it just keeps happening.  I will silicone cover to see if that helps.  

Take a good look at the heater block, specifically the gap between the block and heatsink fins. Be sure you don't see any filament leaking out the top of the block and down the sides. If so, you have most likely got a leak between the nozzle and heatbreak (inside the heater block) that you will need to address. It's not a big deal, but if changing nozzles, correct reassembly is critical.

If not, you may just have accumulations of old filament on the block. Clean it periodically with a soft brass wire brush, being careful to avoid the wires. I use a strip of cardboard around the wires to scrub away filament accumulations while heated. The silicone sock is the best method of keeping the block clean.

RE: Black mark on prints

So how helpful is such E3D sock in preventing black dots from forming on printed surfaces? I recall that when I considered this option awhile ago, Prusa Support did not recommend putting any sock on.

RE: Black mark on prints

The "Pro" socks only have a tiny nozzle opening, so there was a danger of it shifting and creating a mess. The "non-Pro" version has a larger cutout for the nozzle.

I've seen a couple of people complain about reduce cooling fan coverage with the socks, but I use a tweaked nozzle fan design anyhow.

The sock only prevents filament from accumulating on the block. Any stray filament still goes somewhere, but the hope is that it falls aside somewhere outside the print that is easier to clean up. You still want to avoid any over-extrusion to reduce excess filament as much as possible.

Also, do be sure you don't have a leak above the block due to improper nozzle tightening. If so, you'll have burnt filament dripping down the block, inside any sock, and still making a mess.

RE: Black mark on prints

Chuckling - "Do I have to clean my printer head?" - sort of like taking a shower.  Every single print, look at your printer, clean the bed, clean the nozzle (there are some good "ultimate nozzle brush" prints that use felt pads).   Every single print will leave some residue on the print head - especially if you haven't been cleaning it after every print.  Or not.  If you don't mind blobs of burnt stuff falling on your nice white prints - print in black.

RE: Black mark on prints

Had the same issue, fixed by reducing the flow by a few percent. The extra goo was sticking to the nozzle because there was excess filament extruded and nowhere else for it to go.