Z Offset for better first layer control

[rupert]

I want more control over my first layer in order to improve adhesion in PLA (lines should be flat and wide not tall and thin) and was advised to use Z Offset and Bed Roughness by @Isaac_alaska viewtopic.php?f=13&t=74

I want to print 0.2mm layers, but 0.1mm on the first layer so the ratio to my 0.35mm extrusion width is good. This is possible with a Z Offset of -0.1mm, but it doesn't change the amount of material extruded, so the layer is too fat and bumps in to the head causing judder.

Bed Roughness doesn't seem like the answer as this will increase the amount of material extruded without really changing anything else.

What am I missing? It seems this would be easier and more discoverable with a first layer override for thickness.

[PenskeGuy]

So, you don't go so far negative. Make incremental adjustments in Z-Offset until you get a satisfactory result. May not end up being half the normal layer thickness but who cares?

[rupert]

@PenskeGuy Thanks for the advice, but I don't really like heuristic fixes like these. On their own they are fine, but they quickly multiply with other compromises until you have no idea which setting is influencing which feature of the result.

I'm not entirely sure why there is a reluctance to accept the need for an explicit first layer thickness override, especially as it appears impossible to achieve it in other ways and keep everything else the same.

[PenskeGuy]

Hey, all I can tell you is that it works for me and I don't need yet another feature that is handled very well by the capabilities that are already present. Liking heuristic solutions or not, there are solutions available. If it is all just handed to you on a silver platter, where you do zero exploration on your own, you learn nothing. There's a word for that. For me, I appreciate learning each and every facet of the software that I am using by trial and error -- sometimes discovering aspects that no one knew existed -- as it enables me to extrapolate a path to a future solution that no one has encountered but me.

[Isaac_alaska]

have you tried offset of zero and bed roughness of -.1mm?

i've never tried putting negative values for bed roughness, but in theory it should work, as most boxes allow negative values (thanks Jonathan!)

bed roughness should really be called "first layer additional thickness" because that's exactly what it's doing. it increases the layer height and increases the plastic flow rate to achieve a layer that is this much thicker. the idea is to account for small imperfections in the bed height.

[Dreide]

have you tried offset of zero and bed roughness of -.1mm?
i've never tried putting negative values for bed roughness, but in theory it should work, as most boxes allow negative values (thanks Jonathan!)

Unfortunately, negative values for bed roughness give basically the same results as 0 (v1.5Beta1.17). "Basically", because the XY and E coordinates change a tiny bit, but not the Z values. When having sliced with bed roughness 0, entering a negative value doesn't even trigger a new slicing. Yet, if forcing KISS to re-slice, it shows some effect in the G-code. Weird.

[PenskeGuy]

Without taking time to test, I would wager that, like other settings in KS, negative values (other than to disable something) are illogical to include. IOW. you can't have a bed that is "smoother than smooth".

[duaneh]

FWIW, I have used the Z offset to force the first layer to print wider and thinner and have had very good results with it. PLA seems to want the extra pressure to adhere in the first layer. Also,I have tried a wide variety of materials to help glue the print to the bed, and so far the very best I have found is Aquanet super hold hairspray. Yep. It works better than Cube's "Super Glue" (and it's a WHOLE lot less expensive), blue painter's tape, etc. Just spray a thin layer on the print bed and let it dry, and then you can print 3 or 4 prints before having to renew it. When I do the Z-gap, there is a slight sharp edge at the bottom of the print that I have to sand off, but I consider that a good tradeoff to have the print stay in place.

Also, use a raft if you are trying to print something with a small footprint. It's sometimes a pain to remove, but it makes a big difference in the stability of the print.

[Mikk36]

FWIW, I have used the Z offset to force the first layer to print wider and thinner and have had very good results with it. PLA seems to want the extra pressure to adhere in the first layer. Also,I have tried a wide variety of materials to help glue the print to the bed, and so far the very best I have found is Aquanet super hold hairspray. Yep. It works better than Cube's "Super Glue" (and it's a WHOLE lot less expensive), blue painter's tape, etc. Just spray a thin layer on the print bed and let it dry, and then you can print 3 or 4 prints before having to renew it. When I do the Z-gap, there is a slight sharp edge at the bottom of the print that I have to sand off, but I consider that a good tradeoff to have the print stay in place.

Also, use a raft if you are trying to print something with a small footprint. It's sometimes a pain to remove, but it makes a big difference in the stability of the print.

Been printing with the same layer of PVA (white wood glue) for tens of prints. If it starts to wear out (ie, not stick as well), I just use a wet brush to freshen it up again. Easy to wash off with water and apply fresh again, if necessary.

[duaneh]

I wonder if that would work with my PolyPro print bed. I only have the yellow carpenter's glue, but I could get some of the white and try it.