Surfaces are suddenly missing

I hope I can make myself clear. I am constructing rails for a model trainway. For a bending rail I have to creat a curved surface wich I pull up to creat the rail, So the rail has a top and bottom surface, After doing some modification to the rail it sometimes happens that either the top or bottom surface is sudenly missing without any change toe the surface or boundery lines of the surface. It is hard or impossible to get the surface back. It seems that for one or the other reason the points on the bounderlines or no longer in the same plane, though I did not change any of these points. Can somebody tell me what creates this problem, thanks in advance?

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It’s hard to say exactly without seeing an example SketchUp file but two reasons for that come to mind. One is that in your modification process you are creating non-co-planar edges. The other is that you could be working at such a small scale you are running afoul of the short line segment/small face issue. Working at a small size can result in missing faces because end points of lines are too close together.

Can you share a sample SKP file that shows the problem?


In the attachment you see the rails I made.
The problem of disappearing surfaces does occure many times when moddeling this railway switch. I first tried to make one model of rails and sleepers in order to faciltate 3D printing so that the slicing programe sees one closed volume. For making one volume I used the intersection tool, witch in it self did succeed. When removing the waste lines then suddenly the top and/or bottom surface disappeared whereas the line I removed was not in the plane of these surfaces at all. It seems that when recalcutlating the model after a change, that the boundery lines of a surface, whitch are in one plane originaly, are out of plane after the recalculation. It is not only when doing an intersection, surfaces do also disappear in cases of other modifications, whitch is very anoying.

I cured the problem by copying the top or bottom surface (only the surface and not its boundery lines) and placing it on the location of the missing surface. By doing so the the copied surface is recogniced as being in the sameplane as the bounder lines of the disappeared surface. How this is possible I do not know.

In the end I made different groups of the rails and sleepers, fortunately the slicing programm sees these two items as one volume, whitch is not always the case. So for the moment the problem is solved.

Why surfaces disappear even when not being touched I do not understand, maybe somebody can explain?

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Could you share the SKP file? It looks like it has to do with the order and method you are using to draw the parts. I see reversed faces and overlaps which would prevent the model from being considered “solid” and printable.

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WisselrechtsForum (2).zip (1.9 MB)

Dave, Attached is the compressed file of the skp and skb file you requested

Thanks in advance

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Your model has a number of problems. I’ll try to fix it up for you when I get home from work but before I do, I need some accurate dimensions. You’ve got Precision set to 0mm and Length Snapping set to 1mm. Both of those are going to create problems for you considering the dimensions of the part you are attempting to draw. You’ve also got small portions of the model misaligned reversed faces, and the axes have been screwed up.

Do you have some dimensioned drawing you’re working from? Can you share that? Anything that shows what the dimensions are supposed to be would be a big help.

In addition to what Dave mentioned, here are some thoughts:

Right now your model has a main group containing four nested groups. Although some 3D printing apps may accept this, SketchUp will not recognize it as a solid. But, on top of that, various portions of the groups occupy the same space at the same time, such as where the rails meet the sleepers. They pass through each other without either of them having an opening! If they are to be merged as a single object for printing, you don’t need to model the notches and overlaps. But if they are to be printed separately and then assembled, you need to decide which one cuts through the other.

It’s not clear to me why you changed the working axes to upside down and far from the base model axes. Was this due to drawing a portion from a larger plan or a model in which this switch was far from the origin? In any case, I’d reset the axes and then move the part to the origin.

You are indeed working at a size perilously close to SketchUp’s nearby vertex tolerance. On the curved sections of the track, some of the faces are pretty small. I don’t know whether that was causing the issues you saw, but as a precaution I’d scale the whole thing up by a factor of 100 while editing and then scale back down.

Dave, I Attached one sketch showing the units I worked to during the design. For an experiment I changed the precision and forgot to set it bag. The 2nd sketch yous see the dimensions.
The most impotant is the rail height 5 mm, the width between the two rails 17 mm, the rail width 2,2 mm. Also important is the railend of 10,5 length, though the length itself is not so important but all other dimensions of the end are important as that is the connection to the other rails. The bended rail is 30 degrees. An example I do not have as the design I made is more or less from the top head, though I looked at the HO dimensions of model railways.
Thanks for helping me

I’ll take a look when I get home.

Thanks for your remarks,
The nesting of the items, I do for two reasons. As a lot of the designed items need changes after having tested in practis. Then it has an advantage that on one single item I can work without interfering with other partsc of the model. The second reason is that I treid to make it one solid design but I did not succeed due to the mentioned problems of disapearing surfaces.

The reason to let eg. the sleeper protrude into the rail is that during printing my experiance is that items whitch match each other at their surface can get loose during printing. Now that items protude into each other the slicing programm made it a sold item. I know that is not always true, but in this case it is.

Indeed this switch is part of a bigger design, and I agree it is a better idee to move it to the original position of he axis. That the axis is upside down is for reason hat I was working on matching the bottom of the sleepers and rail.

To uposcale the design and later downscale again is a good idea,

I am awaiting the results of Dave very kind of you people to be so helpful.

I did some more poking around. There is a very slight twist in the surface of your rails that may be causing problems as you edit. See the figure below and look at the third value (z) in the coordinates. Did you create the rail by extruding a rectangular section along the curve of the rail? Sometimes SketchUp twists a profile as it goes around a curve (architects who do arched doorways see this a lot).

I started from scratch because it was easier than trying to fix the original. I noticed other problems than the ones already mentioned. For example, the curved rails should all have the same centers but they don’t.

On the left are the individual components. I added point rails but not the tie rod between them.

In the center is the right hand turnout as a single solid component and on the right, the same as a left hand turnout.

I’m curious about the rail ends. Will the wheel flanges clear them?

Turnout.skp (295.5 KB)

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Thank you for redrawing the switch.
Best I can tell what I learned from it. First of all I made the error that when moving the axes, I had the Idea to move the origin as well, now I learned, it is not the case. Second thing, to find the coordinates there is the utility plug-in tool, I was not aware of. This facilitates to see where things go wrong. Now I see the impotryance to start a new model, in an existing sketch, from the origin and not moving the axes to a new start point, so that all points in the X-Y plane are at zero level, and the coordinates of all points in the model refer to both the origin and the models starting point.

In answere to the question how I extruded the rail, indeed I used a rectangular, which I thought to be a plane in the zero X-Y plane (being not the case I learned now), the rail shape in that rectangular I extrude by using the push-pull tool. Tthat is the reason why all points on the rail top and bottom face have different Z levels, as the rectangle was not in line with the zero X-Y plane.

Quetion: is there a repare option available to repare an item such as this rail when it is slightly out of line wth the zero X-Y plane, sothat it comes in line?