Hi Martin@Paul Boyd
I've been doing battle with Cura 5 on my new Neptune 2S.
The problem for a long time has been the width of the sockets in plain sleepers in 4mm scale. The plugs are 2mm wide, plain track sleepers are 3.33mm wide. That means the wall each side of a socket needs to be about 0.6mm thick, or a bit more. That's a problem using a 0.4mm nozzle.
Using a narrower plug on the chair isn't an option -- it wouldn't be wide enough to contain the slot for the loose jaw pins, and the delicate thin chair base surrounding it would be wider than is good for reliable resin printing. It would also make CNC-milling the sockets more difficult.
So the choice is to do a single wall and over-extrude from 0.4mm in the hope of creating a thicker wall; or do two walls and under-extrude in the hope of creating a thinner combined wall.
Neither was working -- the most I could get with a single wall was 0.5mm, making the wall unnecessarily fragile, and the chair was able to twist out-of-square in the too-wide socket.
With two walls the thinnest I could get was 0.7mm, making the chair too much of a bash fit in the too-narrow socket.
Then hidden among the 10,000 Cura 5 settings I found Flow Equalization Ratio:
View attachment 4614
Which applies where a wall width needs to be modified to fit the model.
That's normally set in the range 0-100%. So I set 200% .
And that seems to have worked! A single wall but now 0.6mm thick. What that setting does is to cause the forward nozzle movement to slow right down, while continuing to extrude filament at the normal rate, so creating sufficient over-extrusion to create a 0.6mm wall from a 0.4mm nozzle. Cura was already doing that at 100%, but not enough and creating only a 0.5mm wall. Setting 200% increased it to 0.6mm. Why Cura couldn't have done that by itself I have no idea.
The Prusa gcode viewer is showing the effect of the over extrusion.
What that setting is % of only Cura knows, and it seems odd that 100% isn't the usable maximum. But it's working, and by changing this % I can now fine-tune the wall thickness.
Every day is a schoolday with Cura. The next mystery is why the same settings which produce nicely-fitting brick connector clips on the BIBO, are now producing a tommy bar which won't fit in the claws on the Neptune.
How are you getting on with the Anycubic Mega? I see it is now discontinued, just like my BIBO. It's difficult to keep up.
That's a useful tip to know, thank you. Somewhere in the back of my Covid-befuddled brain I seem to remember trying to adjust a wall thickness that wasn't a multiple of the nozzle width - can't remember what it was now - but that tip may work there as well.
The Mega is doing fine! I tend to use it mostly for printing functional things such as circuit board mounts or adapters, and will shortly be printing some alternative spacers for the DCC Concepts rolling road to suit my narrow gauge stuff. I've even printed prototype parts for work before committing to expensive machining. I've learnt to wait until it's nicely warmed up before levelling the bed, and then cleaning the bed with IPA immediately before printing - I've put a 3-second warning beep into the code so I can keep cleaning almost right up to the point at which the head starts to move for printing. It's now essentially a process of uploading the sliced model to OctoPrint (the trouble I had finding a Raspberry Pi!!) and setting it off.
I do still have a few timber bricks to print for my narrow gauge layout when I get back around to that. No sockets though, just the rail head guide indentation.
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