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alaris2

perfect first layer..

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I'd be interested in how people are tackling the 'first layer' problem with PLA and the print quality they get. (i'm assuming no heated bed)

for those not already aware, the problem is that if the bed is perfectly levelled using:

1) the tin foil method - the nozzle is too close to the bed for the first layer. if you have Cura on default settings of 0.3mm for first layer, you'll get a mess. I have mine set to 0.2mm and backed off the bed by a quarter screw turn.

pros: this results in perfect adhesion and no warping,

cons: it's almost impossible to get the print off the bed without destroying the blue tape it sticks so well, and the first layer is (measured) 0.05mm not 0.2mm since it's been squashed into the tape. this is not only a problem if you want a really accurate part made, but it means there's lots of excess material when you print the second and third layers which can lead to a lumpy bumpy ride for the head as it runs over the excess pla and grinds against the print.

regardless of this, the print quality is excellent, so it's my current setup.

2) the just slide a piece of card under the nozzle method - the nozzle is a little too far away. I'm guessing Daid uses this method, since when I do it this way I find I need the first layer to be 0.3mm and the fan switched off to get better adhesion.

pros: slightly more accurate part, no bumpy rides

cons: prone to warping, doesn't always adhere, especially with support

so I'm curious what methods people are using and whether anyone has found a 'perfect' solution?

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2) the just slide a piece of card under the nozzle method - the nozzle is a little too far away. I'm guessing Daid uses this method, since when I do it this way I find I need the first layer to be 0.3mm and the fan switched off to get better adhesion.
I'm using the "adjust the bed during the first layer" method, combined with a 0.3mm first layer and the fan off on the first layer.

What I do is, I first level out the bed using one of the 6mm wooden spare parts. First you home Z, and then move the head up 6mm. Move to all corners and level those. Next, start a large print, slowly. During the printing of the first layer, see if it sticks, if it doesn't stick, quickly turn all 4 screws by half a turn, repeat until it sticks. If the first layer is too squashed, turn the screws the other way around.

It requires some getting used to, but I've been using this method for a while now, and now I only need the "during print adjustment" after I moved my printer or removed the bed.

I'm also using "gamma painters tape" which sticks properly to PLA, but doesn't stick very well to the bed. The default blue tape is better.

I used to have a 0.1mm start layer, with a very level bed. But after replacing the tape so many times I switched to the 0.3mm start layer.

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I use both the "paper method" and the "tinfoil method" depending on how tired I am... I always use the same thickness for the first layer as the rest of the layers, I don't want to start with a fat layer first, never got the reason for that. As the first layer is printing I manually adjust the height by turning the axis by hand a click or two. If you've tuned the height correctly this isn't needed most of the time but I like to keep an eye on the first layer regardless.

On very large solid bottom layers I sometimes let out the pressure a bit so to speak by lowering the bed a click or two for just a few seconds, this gives any pent up pressure a chance to release. This helps when you want to avoid popping your bowden.

Generally though, on small to medium prints with a properly levelled bed I just make sure the first few lines go down clean by making sure the print head doesn't drag any pre-extruded material with it etc and then I just let it run.

As for the parts being hard to remove. I've found that if you're able to get a utility knife in a few millimeters in a corner you can twist the blade and just hold it there for a few seconds. After a little while you can hear stuff moving (crinkling noises from the tape) and you can apply a bit more twisting pressure, eventually the part pops off. But for me that problem only happens on large solid bottom layers. On medium to small objects I can usually just snapp it off from the platform cleanly with my hands.

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Once you've got the bed level what you can do is home the head, then use the ultipanel controls to move the head to the middle and lower it down until it just touches the bed. The ultipanel will tell you how far down (or up) that is, then just remember that level and put it into your slicer. That has worked well for me before I started using a heated bed. With the heated bed you have to remember that the bed moves upward a bit when it heats up because of expansion. So just wait for it to heat up and do the same thing. As long as you are always heating to the same temp and waiting a bit before printing (or your heating takes a long time) you should be fine.

I was using acrylic to print PLA which was working great but now I've switched to kapton and that works well too (PLA and ABS).

For leveling I use my 1" travel indicator and this

http://www.thingiverse.com/thing:16630

Just maneuver the indicator so it is almost directly underneath the nozzle, then move the head (via software!) to the four corners and adjust until the needle doesn't move much. My aluminum platform is not very flat so that approach doesn't get very far but at least i know that the curvature is evenly distributed.

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well the method Daid is using to fine tune the position with a slow print is similar to what I've been using. I did some experiments today with fans and thought I'd share the results.

fan on for first layer - requires a skirt to work, because the fan comes on after the Cura 'warm up routine' which causes the nozzle to cool down, so no plastic will stick to the bed for about 20seconds.

fan on second layer - first layer is much better, maybe the first 3-5 seconds of plastic doesn't stick to the bed, so some cleaning up still required. but the second layer now suffers the cooldown and the perimeter of the second layer suffers as a result.

note, this is not the stock fan. my observation with the thermal camera is that the head is very close to the bed, so most of the air is bouncing straight off the bed and cooling the nozzle. this problem may also occur on subsequent layers with large flat surfaces. the cooling effect exceeds the rate at which the nozzle can heat up again and causes thermal fluctuations. switching the fan off on the first layer doesn't really help this (in my case). it may work if the bed is slightly further away (Daid's 0.3mm suggests this is the case) or with different fan shrouds.

so I think 'the answer' is the fan should vary according to the properties of what's beneath it (bed and model), but that's not really an easy thing to do. so my solution was to modify the start g-code. I now switch the fan on near the beginning of the warm up routine.

result? far less pre-extruded material being dragged around (yes I was plagued by that too Robert) and excellent sticking. I can recommend this but I'd be interested if others find the same results or if it's very bed-level and fan shroud dependent.

cheers, nik

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note, this is not the stock fan.

Pray tell what fan shroud are you using, and what fan? I am using gijs' fan shroud (

http://www.thingiverse.com/thing:21182

) with the stock fan. I haven't had any problems with my fan cooling the nozzle too much but I am running KISSlicer which turns the fan on ONLY when making outlines and turns it off during infill and support. Oh the fan is off for the first layer too. I did have an issue with the fan cooling my heated bed too much when printing with ABS resulting in warping, but I re-started that print with no fan and it came out ok.

So I guess some prints (ball-like object with support) want the fan on and some prints (rectangular object with no support and a lot of outlines) want the fan turned off?

You know what would be good is turning the fan on only for overhangs and bridges, as well as for small layers. Because I can't see why you would need it on, for instance, the third layer of a cube build, since the adhesion there is fairly good.

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I agree with you there destroyer. the fan is currently treated as a binary thing (tho I note Cura does let you change the percentage the fan is on) whereas it really ought to be far more intelligent and take what you're printing into account.

that fan you're using is quite a broad one - should be great for large objects but probably not so useful for fine or tall objects (eiffel towers). I'm using

http://www.thingiverse.com/thing:17768

which is great for the latter, but does suffer some design flaws (fan is too big and blows half the air back out the inlet).

I should swap fans depending on what I'm printing really. but i'm too lazy so leave this one on all the time now...

note how since the air exits immediately beneath the nozzle, it's prone to being reflected by the bed and cooling the nozzle - I think the larger one you showed me won't be so susceptible to that - but I can print some awesome overhangs and bridges from any angle.

I think the fan shape and control really should be selected on a per-print basis..

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