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cura settings

Posted by broccolini 
cura settings
April 22, 2019 10:24PM
I've recently started using my printer after a couple of years. I dusted it off, checked the calibrations, and downloaded Cura. I added some silicone pads under the glass to replace the metal clips that held the glass on because i was having problems with the fan shroud hitting them.

After doing that, i rechecked the z offset because the glass sits a bit higher. I had to get an older version of the Arduino IDE because i couldn't get the new one to recognize the Melzi board. It seemed to work fine and I got a successful upload message.

When I printed some calibration cubes, they were off by .85mm on the z-axis. the 10 and 20 were off by the same amount so i don't think it's a cumulative error. If i print something, the thin skirt/brim Cura adds for adhesion looks fine. But the first layers of the object look like the print head is not actually lifting after the first layer. It seems like it's just dragging back through the previous layer. Once it starts the walls of the object, it's fine. So on small things, it's just causing them to not be tall enough. But on objects with a larger footprint, the hot end gets jammed because the plastic can't come out. I think.

Anyway, I don't know where i should start to rectify this. I think it might be a software problem, because it didn't happen two years ago when I was using the printer. Cura has a 'mendel 90' selection option. That's what I chose, but i'm not really sure if it's setting the parameters correctly.

Can anyone point me in the right direction for troubleshooting this?

Re: cura settings
April 23, 2019 08:24PM
well i went through and did all the calibrations again. now the first layer is printing at about .34, which is a lot better. i'm going to adjust the z offset again and see if i can make it better. I think i just did the math wrong the first time.

But now i'm having issues getting prints to stick. hopefully adjusting it again helps with that.

Cura also seems to forget to use the center of the bed randomly. i have to uncheck and recheck that option twice before i slice the print to make sure it doesn't print in the corner. it also randomly retracts all the filament after a print. i can't find a setting for that and it's not in the end g-code so i don't know what to make of that. Could be that Cura just doesn't work well with the latest Mac OS.
Re: cura settings
April 24, 2019 03:31AM
Seems like the Z calibration is too low. Print an outline and adjust so it is exactly the first layer height as per the Mendel90 manual. When it is a lot too low you get a thin first layer rather that zero thickness because the pressure of the plastic is enough to lift the nozzle but it then doesn't lift enough for the second layer.

Re: cura settings
April 24, 2019 11:44AM
Ok, thanks. that sounds like what was happening.

Right now my bed leveling calibration square is printing at .29-.31 all the way around. It's set to print at .30 so that seems good. It just won't stick well to the bed. When it was too close, it stuck really well. Should i leave it where it is and try different temps for the bed or tape, hairspray? something like that? Or slow down the print speed?

the bed is at 60C and the extruder is at 200C right now.

Right now it's printing the file that wouldn't stick last time. I put hairspray on the bed and slowed down the print speed. So far, it's staying on the bed. Am i just wrong in thinking that PLA should have fewer adhesion problems than ABS?

Edited 1 time(s). Last edit at 04/24/2019 12:24PM by broccolini.
Re: cura settings
April 25, 2019 01:59PM
Yes PLA should stick to plain glass as long as it is free from grease. I run the bed at 100C for the first layer and 70C on subsequent layers. Extruder 220C for Prusament, which is what I am printing at the moment. Never used hairspray or an form of adhesive. Just plain glass for PLA.

Re: cura settings
April 25, 2019 05:18PM
Ok, thanks. The hairspray has been working great, but i'm going to try changing the temp settings to see if I can get it to work with just the glass. I've been cleaning it with acetone so it should be clean. Other than the adhesion issues, it's been printing great. The z axis is making some squeally noises. I cleaned the smooth rods and lubed the threaded rods but it didn't help.

I also wanted to ask about replacing the hotend for one that works at higher temps. Is there an easy swap for the Mendel 90? I'm not sure i know enough to come up with my own solution. It looks like most materials come in the 1.75mm size now too. Is that better somehow?
Re: cura settings
April 26, 2019 05:28AM
Ethyl acetate is a better solvent for PLA. I use that to clean the glass when printing PLA. One thing I have been meaning to try is to dissolve PLA in it an try 'PLA juice' as a bed adhesive like ABS juice made with acetone. So far I have not needed it as a hot bed for the first layer works well for me.

I print ABS with a the J-head up to 255C. You can fit a E3DV6 to the standard Wade's block using an M8 washer as a spacer but the fan duct won't fit so you would need to find an alternative way to cool PLA prints. You loose a few mm of Z build height as it is a lot longer than a J-Head. You can get some of that back by printing the E3D version of the parts here: [github.com].

There are pros and cons to 1.75mm filament but no big differences. For example you can wind it on smaller spools and you need less force to feed it, but you need to feed it faster and flexible filaments are more likely to buckle.

Re: cura settings
April 26, 2019 08:57AM
ok. thanks for the info. The instructions say not to go over 240C for the hotend so i thought that was the limit. The PETG i was looking at wants to be around 250C.

Have you tried PETG yet? I was looking for a material that would work for parts inside an engine bay and PETG looked pretty good. Or nylon. I think the original parts were nylon.
Re: cura settings
April 26, 2019 02:51PM
I have printed E3D edge, which is form of PETG but it only needs 240C. I printed all the kit parts with ABS at 255C for the first layer and 250C for the rest, so J-Heads can definitely can handle that for thousands of prints, even in a chamber at 45C.

I know their spec says less but with the more accurate thermistor that I use I have not found it to be a problem.

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