Resin print "bridging"

[philipy]

Guys I have a problem and I have no idea why or how to cure it.

I have been drawing up a standard Midland Railway V-shape running-in board ( station name board) in 4mm scale for somebody.

I've done a single sided one which prints perfectly, but a double one bridges across the inside of the diamond shape outline, at the bottom of the board faces. I've drawn and redrawn, and sliced and resliced several times but the same thing happens each time. Any idea's?
I should say that the vertical posts seem to be deforming inwards at the same location, so I assume that is related somehow.
Plus, when I chopped the posts off the drawing and just printed the boards, it came out perfectly


SketchUp drawing

Screenshot 2024-07-04 14.28.17.png (183.67 KiB) Viewed 43578 times

Chitubox image ready to slice

Screenshot 2024-07-04 14.28.58.png (191.15 KiB) Viewed 43578 times

Chitubox sliced file with the bridging which has appeared from nowhere.

Screenshot 2024-07-04 14.33.22(2).png (215.36 KiB) Viewed 43578 times

Printed with bridging and deformed end posts.

IMG_0837.jpg (263.38 KiB) Viewed 43578 times

Printed without end posts and no bridging.

IMG_0841.jpg (333.13 KiB) Viewed 43578 times

[ge_rik]

I'm not familiar with Chitubox but there is a setting on the slicer I use for Anycubic which automatically adds supports. Is something similar to that switched on in your slicer?

Rik

[philipy]

I'm not familiar with Chitubox but there is a setting on the slicer I use for Anycubic which automatically adds supports. Is something similar to that switched on in your slicer?

Rik

There is, Rik, but that isn't the problem here, unfortunately.
Auto supports have to be selected each time if they are wanted but I rarely use the automatic supports and when I do I normally take most of them out anyway.
Either way, the version without the end posts was Ok, but with them it had the problem.

[ge_rik]

Have you tried a different slicer - or would you like one of us to try?

Rik

[philipy]

No, it's the only one I have. Thanks for the offer but I think I may have found the problem anyway - won't know for sure until the current test print finishes at midnight though.

If I'm right its an issue between Sketchup and the size of the model, but I'll explain in detail once I'm sure.

[philipy]

OK, folks I found the answer to my problem, so just in case anyone else comes across it, this is what I've worked out.

SketchUp is really intended for large scale architectural projects like houses and blocks of flats, etc, and as a result doesn't do well with very small dims. and that was the fundamental issue.

I had decided that the only way out of my dilemma was to separate the components and print a kit of parts rather than a complete item, but when I pulled out the centre leg complete with its 2 ironwork brackets, it was leaning noticeably to one side, although I hadn't drawn it like that. .
Now if you look at the picture with no legs in my original post, that didn't have a bridging problem. Which implies that the legs are the problem, or at least are causing the problem.

Eventually I realised that when I put the temporary bar across the bottom of the three legs it was about 0.5mm inside the face of centre leg, which is actually about 1mm wider than the outside two. SU has a 'snap' function which is very useful most of the time, but on this occasion I think that it grabbed the leg and shifted the bottom sideways to snap it to the line. This then twisted ( not moved) the whole centre leg together with the fancy scroll brackets at the top, sideways. Not sure exactly what happened subsequently, but I suspect that because the various components and faces were then out of line, when I sliced it the Chitubox auto repair attempted to join the dots and thus filled in the gap.

To avoid any other errors, I redrew it yesterday at 10x magnification and then reduced it to correct scale, ( which is the easy workaround for SU's dislike of small dimensions) and that has cured it. It is a peculiarity of SU ( one of many!) that it can display very small small items, it just can't handle actually drawing them!

This is a picture of the finished items, which I'm happy with. Given that the signs are only 50mm high o/a, I'm particularly pleased with the way the fancy ironwork scroll brackets have come out.

IMG_0844.jpg (368.25 KiB) Viewed 43480 times

[ge_rik]

That is impressive. Well done for sorting it out

Rik