First Layer

I keep having problems with the first layer very, uneven and lots of blobs. The print will finish off absolutely fine but starts very poorly. Printed the parts last night no problem at all. Print exactly the same part, same settings same gcode this morning and I have this blobby first layer. Any ideas what could have changed overnight. I have observed this several times over the days and can't find an answer. If I print it again it will probably be okay.
PLA, temperatures first layer bed 64c extruder 200c then 57C 190C. I have tried moving the temperatures up and down with no improvement. Just can't predict how the first layer will go.

John

it MIGHT be that the Z is a fraction too low - so the plastic can't leave the nozzle until enough pressure is built up, then a blob comes out,and so on - I got similar when I replaced my glass and didn't level it correctly (I'd put the front over the soldering so it sloped up quite a lot)- the high side didn't print, then as the nozzle reached a lower part of the plate the backed up stuff came out all in one go, then flow stopped as it reached a higher point in the slope and so on. once it had raised high enough over the bed, the print contiunued properly, just as happens for you.

Ray

I often get a blobby first layer on the first print attempt of the day. It gets better after a few attempts. Next time I will try extruding 100mm or more of filament first.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I agree with dc42 that that is most likely the reason. I zero the Z axis and find the bed set figures by hand before every print. It is a PITA, but I find the bed slope changes slightly between prints so if I use a fixed "setbed" file I do not get consistent results. I do it while the bed is heating, so at least it doesn't cost any extra printing time. The blobby first layer is very typical of the nozzle being too close to the glass (as is the extruder skipping). As you say, the rest of the print is usually OK, so you can get away with it after a quick run over with a needle file if the finish is not too important.

Dave
(#106)

Is there anyway to have a wizard open when you want to do the bed compensation?
Example, when you open the wizard it homes all axis, then you set the nozzle hight and click next, it moves to the next point. you change nozzle height and click next then it moves to the next and then the next?

Ray, DC42

I have just tried to higher the extruder a little more but it is a disaster the layers are not sticking so obviously too high. I think DC42 maybe right about first prints, because I have continued to print and the first layer is again just fine. I don't normally print consecutively but subsequent prints are all fine. I had already extended the skirt to 20mm and a double lap but still not any good.
John

Make sure the bed is getting to the working temperature before zeroing the Z axis. If you zero when it is stone-cold, it will be out slightly after it is heated. I print the first layer at 100 deg, and wait until the bed has reached at least 80 deg before zeroing and doing bed compensation measurements. A wizard would indeed be great - I do it all by hand by raising the nozzle 2 mm, entering the G code for the next position, then bringing it down until it just grips a sheet of paper, then entering "M114" to see the Z level at that point. I have my "setbed.g" file open in notepad, and enter the readings as I take them. At the end, I save the new setbed file, load it with Pronterface, and print it. I then move the nozzle to the middle of the bed and enter "G1 Z0" and check that the nozzle at 0 (M114 will not report zero, but that doesn't matter). If way out, I've done something wrong (gross error check), if only slightly out I adjust the zero height. Once you've done it a few times it is quite quick.

Dave
(#106)

Dave
Thanks for your help. I have consecutively printed a further 5 pieces and all have been perfect. So it is clearly a start up problem. In the morning I will follow your procedure and see what happens
John

Quote
johneato
Dave
Thanks for your help. I have consecutively printed a further 5 pieces and all have been perfect. So it is clearly a start up problem. In the morning I will follow your procedure and see what happens
John

I should add that I am printing ABS - don't use such a high temperature with PLA, but still wait for the bed to heat before zeroing the Z.

Dave
(#106)

I always heat the bed to 60C before doing z-homing or bed compensation, and I still get a blobby first layer on the first few print attempts of the day. So in my case, it isn't for lack of preheating.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Hi John, I see you have some replies already. I had a similar problem. The skirt in-particular would be affected. Next time your about to print, have a feel of the PTFE tube just above the Extruder. I found mine was really cold with the fan and heat sink cooling it down. I also had problems with the skirt breaking away from the bed and being dragged in to what ever I was printing because it was almost setting before reaching the glass.
In Slic3r you can up the temperature for the first layer, so try adding another 5' or 10' to it. Also I've insulated about 40mm or so of the PTFE tube with bubbly kitchen roll wrapped around it. It's helped a great deal.
Another thing, was I found that even with the extruder hot but standing idle I had a hard pip of plastic at the orifice. When I took the extruder assembly off I found one of the fan vents was blowing directly on to the tip, so I have blanked that one hole off with Kapton tape, and things have improved dramatically... I hope that helps... My problems seemed to stem from this cold plastic, but just incase the skirt breaks free again I now move it further away from what ever I'm printing. (I also found that when the printer was starting to print, it would miss say the first 30 to 40mm of skirt, as the PiP would interfere with the stream of plastic, so making a snotty ball of goo that eventually got stuck to the skirt. When the printer got to printing the object I was printing, the extruder was getting lifted up when it got to the snot ball, and messing up my print. Once the extruder was clear of cold plastic, it was fine.

What I might start adding to my STLs is a few lines at the edge of the table to let the printer use up the cold stuff just moving back and forth out of the way of everything before getting on with the actual job in hand. That way if it does make another snot ball, then it won't interfere with the extruder when it's on the job.

Good Luck,
All the Best,

Kim..

Make sure you wipe down the bed with acetone each time. I found doing this solved the non stick problem. The second thing I found was that manual Z0 with the bed was better using an A4 page folded over or two A4 pages. I needed that extra height. When setting Z0, it's like setting car tappets, the paper must not grab but also night just slide out. When move the paper around, it must just just feel like it is touching. Do the Z0 in the centre of the bed.

Dieter

#257

Just one word on acetone - it is much more aggresive against plastics than isopropanol. The latter cleans good enough and costs the same, but be sure to work in a well ventilated area when you apply either of them, because both could irritate skin or mucous membranes (use gloves or other saftey measures). Also both are easily flammable - so watch for not having a 100°C hot bed and then applying (lots) of those substances. Isopropanol has also an advantage here - the boiling point is at 83°C compared to 56° with acetone.

Markus

Edited 1 time(s). Last edit at 01/27/2014 03:16AM by markbee.

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XBee & electronics blog: [lookmanowire.blogspot.com]

Quote
PaulHam
Is there anyway to have a wizard open when you want to do the bed compensation?
Example, when you open the wizard it homes all axis, then you set the nozzle hight and click next, it moves to the next point. you change nozzle height and click next then it moves to the next and then the next?

Communication with the Duet using USB is basically exactly the same as with an old fashioned serial port. All the commands and responses are text, so its not difficult to communicate and therefore writing an app or a Python script is pretty easy. (If you dont know programming then Python is a good intro ) I started writing one (in C++ as that is my favourite language) but it wont be finished any time soon due to long list of other stuff to do!


regards
Andy

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Ormerod #318
www.zoomworks.org - Free and Open Source Stuff

1) Make sure your table is as level as possible. Do this mechanically. Don't rely on any Z axis compensation. Put some adjustable nuts or screws on the bed so you can visually tune it.
2) Generate Slic3r code to make a few more skirts.
3) Manually zero the Z axis as close as you can before printing.
4) During printing watch the skirts and manually turn the Z axis thread. Anti clockwise goes down, clockwise goes up. The extra skirt lines will give you enough time to get it right. Remove any loose pieces quickly before the print starts.

You want the height just right where it squishes the plastic flat onto the glass/Kapton. Too low and the plastic does not extrude. Too high and it makes nice and round, but loose print (blobs as well). This way the plastic (1) will stick, (2) will give a gloss finish to the bottom of the print and (3) give a good foundation for the rest of the print.