Resin print artefact

[philipy]

Suggestions, advice or even remedies, more than welcome.

I'm having a problem with resin printing the DeWinton.

The Sketchup drawing is fine.
The Chitubox import shows no problems ( and I've also put it through Repetier Host).
When it prints, it produces what I can only describe as looking like a raised frame, all along the top edge of the footplate on both sides. I have printed it three or four times now and checked and tweaked between each one but the result is always the same and I have no idea why.

Sketchup drawing screenshot:

Chitubox screenshot:

Finished print - look at the row of rivets at the top of the sideframe between the water tank and boiler and you can see that they have a raised border underneath them. It goes right along both sides of the model EXCEPT between the brackets supporting the watertank. It appears to coincide with the edge/thickness of the footplate, which is printed as one pieces with the sideframes but which doesn't exist where the watertank drops between the frames.

[3 minutes of fame]

If you analyse the chitubox output layer by layer, is the artefact visible?

Best guess would be an inverted surface. What happens if you import it into Microsoft 3D builder? Does it suggest a repair is required?

[philipy]

Thanks for your suggestions.
I hadn't tried looking layer by layer in Chitubox previously but I have now and it shows nothing. The file shows as having no problems in everything I have: Sketchup, Chitubox, Cura 5.2, Flashprint, Repetier Host, MS 3D Viewer ( don't have 3dBuilder).
I've done layer checks as you suggest and also enlarged and zoomed inside the model and they all show as clean.

The only thing I can think of is that, given that the problem shows up at the same level as the underside of the footplate, it is somehow producing an "elephants foot" type effect which is distorting that layer and subsequent ones, outwards.

[3 minutes of fame]

I guess you could prove the printer artefact hypothesis by printing at a different angle, and seeing if the line disappears? It seems like a strange place to get pooling however.

[philipy]

It has crossed my mind to print at an angle, but I suspect that will create even more problems. I don't know if you have seen my build thread on this project,( viewtopic.php?f=54&t=14104&hilit=DeWinton&start=20 ) but for info I am trying to print the whole body in one go, leaving only the lower boiler, some small bits, wheels, coupling rods and the valve gear as separate items.
The theory being that this should (a) ensure that everything fits and is square and solid, and (b) leaves minimal supports to clean off where it matters. This means printing it upside down and parallel to the buildplate, and as soon as I angle it I'm going to need supports on the outside surfaces.

It all works perfectly EXCEPT for this *%$#@@# raised artefact!

Talking about it like this has made me think a bit further. The underside of the footplate is printed in thin air, which obviously can't happen, so I have a forest of supports to hold it whilst the thickness builds up and gives me a nice clean smooth, visible top surface - the quilted appearance of the underside doesn't matter once the model is the right way up. I'm now wondering whether the attachment of that many supports is actually swelling the layers with the support ends in and pushing them sideways.

However, if that IS the problem it seems strange that it doesn't also occur on the water tank which is printed similarly with a forest of supports, plus it also shows up on the curved section of the frames which doesn't have a forest of supports inside.