STL fails to slice properly

Box,
Thanks for this suggestion. To find out if my printer was the problem, I took both your stl file and mine to the local library where they have a Makerbot printer for public use and I printed both files. They both print the light covers, although with some thin extraneous lines that I can trim away. The prints are not as fine and smooth as I usually get on my printer, but I have mine set to 0.25 extrusion width and “High Print Quality” and they are used to printing larger objects with coarser settings. Based on this and the observation by IanT that the model prints when made slightly larger, I believe that adjusting my printer (or just accepting a larger object) should solve my problem.

I really appreciate the time that you all have given me on this, and I have learned several new things from you, including how to use section planes, more about what makes a model solid, and gained some confidence in SketchUp.

I will be on a trip for a few days, but when I get back I will adjust the printer (and model if necessary) and continue my design.

Thanks again,
Ken

I have done some experiments to determine if the size of the object is the source of my problem and I have evidence that the location where I start to draw it is the most significant. For this test, I drew a simple model as follows; A 10x1 (mm) rectangle with a 1x1 rectangle adjacent to the right side. I extruded the 1x1 up 3 and the 10x1 up 2. Then I removed the 3 lines between planes, one in the front, one in t back and one underneath. I did this ten times starting at different locations in the xy plane. Four came out solid and six not. For example, if the first point of the first rectangle is at 24,50, the figure is not solid, but if it is at 32,55 it is solid. I have also done this changing the size of the model but size does not seem to be important. This feels very much to me like a round-off condition resulting from floating point arithmetic. Is there something more I need to do to get the objects to be solid. Solid Inspector2 reports “Nested instances” on the ones that are not solid but I cannot find any.

StartingPointTest.skp (1.2 MB)

You may have accidentally deleted the underside face when deleting the extra lines. Did you check them for solid before deleting those lines? The six non-solid objects have the underside face missing. Hide the makerbot box and look underneath. Of the four that are solid, one has all faces reversed.

I don’t think its anything to do with round-off errors.

it’s not, it’s whether you start with a split 2d shape or if you draw in 3d…

draw the large base >> PP to height >> draw the small addition >> PP to height >> make group or comp…

if you start with a 2d plan you will lose the base of one or the other…

or you will add an internal face at the junction, depending on how you use PP…

better still, delete it and purge the model, it is useless and should have never been added to the shipped Templates…

use either the mm or meter template instead…

john

McGordon,
Both the solid and non-solid ones are non-solid before any lines are erased. I had in my notes that some of the models did not seem to have a line on the bottom to erase. I realize now that was because the whole bottom is missing as you discovered. The bottom of each rectangle disappears as soon as I extrude the rectangle above it - first one, then the other. This does not happen with the ones that turn out to be solid. If I erase a solid one and draw it again in the same place, it turns out solid. If I erase a non-solid one and redraw it in the same place, it turns out non solid.

John,
You are right! Changing the order of drawing for some of the models that were not solid (extruding each rectangle before drawing the next) made them solid. I thought I had discovered this before (I have spend many days trying different ideas and revising my models trying to get them to print) but at some point, I thought I had some drawn this way fail and some drawn the other succeed so I wasn’t certain that the order was relevant. The models I am working on are complex, so perhaps I have been mixing the methods or there is some other thing besides this that I am doing wrong. One of the things I tried before, was making solids off to the side and then moving or copying them next to extruded solids. Should that work?

McGordon and John,
What does it mean to have the faces reversed? I have been wondering why some of the faces in a model appear white and others gray. Even with John’s answer, that it works better to make each rectangle solid before drawing the next, I wonder why some of the models turned out solid. I have been making prints for a year and it is maddening that sometimes I get a print right away and sometimes waste days trying things in a different order or with a different technique before I get one that works, and then I am not really sure why.

This is a bit of a strange one. It’s nothing to do with drawing on top of the makerbot base. I can get this happening on an empty file.

As we can’t watch you draw it, I was guessing that you’d drawn the rectangles while editing the makerbot base. This is actually nothing to do with you drawing on top of another object. Sometimes this is a useful thing to do anyway, like taking a floor plan and projecting it up into 3D. As long as the floor plan is a group, it should work.

I’m using a style that has pink back faces to make them stand out more. When you draw a rectangle on the xy plane, it will be face down. Drag it up with push-pull and you’ll have a solid. You have to make it a group to get Sketchup to recognise it as such for boolean operations. Making a group or component early is always a good idea, even when you’ve only got one face.

You drew two rectangles next to each other. Dragging one up with push-pull creates a box with no base and all faces inside-out.

Yes, drawing it somewhere else will work as long as you don’t draw two rectangles next to each other and pull them up.

Each face has two sides, which have two different colours by default. For a lot of modelling it doesn’t matter, but if you want to do boolean operations or 3D printing then it does matter.
You want all the white faces pointing out, especially for 3D printing or it won’t count as solid. That’s why I’ve made them pink to make them stand out. I’m not a fan of pink, so if I see pink I know something is wrong. The default colour can sometimes be hard to notice when a face is reversed.

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Your demo is very clear. I will follow your advice and not extrude touching parts.

I am still wondering why I got 4 of my test parts to be solid when I made all ten by extruding rectangles that were touching along the short side, following the same steps in the same order for each one. And it still seems odd that when one of them worked, I could erase it and draw another that would also work and redrawing failed ones always failed.

Just now a friend brought me a broken part for his model train and asked me to make a new one. I have been building everything by combining separate parts, but this new one will be a good test of building a model by pushing part of a solid back down as in your demonstration.

Is there a list or document somewhere that gives advice on what other things to avoid or what are the best practices for drawing? It seems like there are so many variables that I have not been able to develop rules of my own to follow that will always work.

Ken

You can push-pull any way you like. Just be aware of reversed faces and rotate around your newly created solid to make sure there’s no holes. There’s no rule saying you can only push down.

If you could have predicted what was going to happen with your 2 rectangles next to each other(I couldn’t), you could have reversed the faces before pulling up.

Once you’ve got a 3D solid with no reversed faces, things are much easier.

McGordon,
I used your advice to make the part my young neighbor brought me last night, and I got a good solid model on the first try. I did not realize that the maker template was actually a part that I was modifying and I am happier drawing on the empty template. I would like to know how you set up a style so the back surfaces are pink. Thanks for your help.

CharliesPart.skp (132.4 KB)

Ken

Open the styles window, edit the active style, click the third icon at the top to get to the panel where you can edit the Front and Back colors for the default material. Update the style afterward. To make the change sticky, do this on an empty file and save it as your default template.

Another maddening test.

Following the advice above to get solid objects works much better, but I still am getting some results that act like software bugs or round off.

In this file, I am building a grid by copying cross rails against a side rail, placing each cross rail copy against the side rail at guide lines. This fails for rails 9 and 12, but works for the others. The following file shows the grid and guidelines for the ninth rail
RailsTest.skp (1.2 MB)
The partially completed grid and the cross rail are both solid. When I copied the cross rail, it opened hole in the side as shown in the following file
RailsTest1.skp (1.2 MB)
Then I tried drawing a rectangle (9.4 x 0.3) on the xy plane using the guide lines as shown in the following file
RailsTest3.skp (1.2 MB)
When I pulled up the rectangle 0.6 to match the side, it also opened a hole. So I tried drawing a rectangle (0.6 x 0.3) on the side panel (planning to extrude it horizontally to make a new rail), but a hole open right away in the side panel as shown in the following file.
RailsTest4.skp (1.2 MB)
Finally, I drew just one side of the rectangle - a single vertical line on the side panel - as shown in the following file

RailsTest5.skp (1.2 MB)
and then I copied the cross rail and it worked!. It also works if I make the cross rail a group and then copy it.

But it seems to me that all of these methods are equivalent. And the first method, copying the single rail against the side at a guideline was used for the other 10 rails and they all worked. It failed just for rails 9 and 12.

Another odd thing is that the zoom seems to stop working every so often. The mouse wheel just doesn’t do anything until I click on the “Zoom Extents” tool, and then it starts working again.

Should I be building my models 10x larger to avoid these problems? Is it OK to add groups together or will that cause nesting problems?

Ken

Each rail should be a component, even if you want this to end up as one big solid object for 3D printing. It will be much easier to work with. Then when you have them all in place, explode all the rails to make them stick together . They can still be contained inside another group to stop them sticking to something else in your model. So its ok to put them all nested inside a main group. When you explode each rail, they’ll still be contained in the main group.

You’ll have some faces to remove where the rails meet the end rail. Maybe have each rail open at the end and intersect them with the end rail to get lines so you can remove all the faces to make a hole for each rail. Otherwise your final solid will have internal faces.

You can place them quickly with Sketchup’s multiple copy feature. Do a move with copy by pressing the modifier key ( option on a mac, ctrl on window?) so you see the ‘+’ on the mouse cursor. Then move/copy one rail to the next by whatever the centres are, by typing ‘1.3mm’. Then type *12 to get 12 copies instead of one. If you know the overall length move/copy a rail from one end to the other and type ‘/12’ to get 13 rails with 12 equal spaces between.

Yes. Your model is perilously close to SketchUp’s small faces tolerance (the beams have width 0.3mm) and that is likely to cause issues. Also, you should get rid of the 3D printer volume component. It really doesn’t contribute anything but clutter!

But more fundamentally, you should learn about the Move tool’s array copy capability: you place a copy of the rail at one end, move a copy to the opposite end, and then type /12 to generate all the intermediate copies automatically.Edit: I should have read @McGordon’s post better - he says the same thing!

Yes, as @slbaumgartner said it is too small. I noticed random things happening when making multiple copies of faces on your end rail.

Making a copy of the component 10 times bigger solves the problem. This image is where I copied the face which is 0.3 x 0.6 from one end to the other of the rail using the ‘/12’ method. I get random results when working on the full size (small) component. Sometimes faces aren’t formed properly and its not the same ones every time. Its not my mouse work as Sketchup is doing the positioning for me. When I work on the 10x copy, it works every time. The one furthest from the camera was done with the 10x copy. The two nearest are examples of the random missing faces I get.

You could use this method to remove the small faces before placing your rails with no end face against them. Or you could pull these faces out from the end rail to form your rails. Double-click on every one after the first one to push-pull them the same length.

rail glitch

Use the Dave method when working small.

Thank you for your generous responses.

I have been trying to rework parts of a larger model that was not working, but given your advice, I will copy the parts into a new file to get rid of the Maker component, use my new plain template with the backs of the faces colored pink, make the parts into components and then put them together, and use Dave’s Method for making edits. I have used the array copy successfully for models where the copied parts were not touching, but as McGordon demonstrated, in the rails model the array copy also created holes. I was copying the rails separately in the test to find out what was wrong. I think it is time for me to review the tutorials again too, since I seem to have missed some things when I studied them before.

It only created holes when the object was too small. When using a 10x copy of the component, it worked fine.

Use Dave’s method.

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