Non perpendicular faces problem

Often I end up with rectangular objects with faces that are non perpendicular, creating problems in dealing with the surfaces; putting in holes etc. I use the ruler tools and axis lines to create my shapes and as far as I can tell they are done correctly. Then, somewhere in the design process, maybe doing a push pull somewhere, I find that the faces are just a bit off so when I try to put a circle for a hole I can see the circle outline is not constant along the plane. In fixing this, I have drawn orthogonal lines along the perimeters of the shape and have discovered a slight discrepancy between the lines of the rectangle, possibly caused by program approximation? Very frustrating! Help!

Can you attach a model that shows this.

non perp face problem.skp (203.7 KB)

The left side is non perpendicular. As seen on the right side, I drew a line across the smaller hole (take my word for it lol), erased the line and used the offset tool to make a larger circle around it. I then deleted the smaller hole’s face and pushed the larger circle in .040". When line drawn on left side, the circle did close up but when deleting the line to use the offset tool, the new face disappeared indicating it was not perpendicular. I’m not sure what is going on or how this problem occurred.

I scaled up the very small model and checked dims to see if everything was square and one end of the object is wider than the other end. The two long sides of your model are not parallel.

Your problems probably come from having length snapping enabled in Model Info/Units and your precision is quite low at 1/16".

When length snapping is on, you could think you were snapping to another endpoint but are actually snapping to the length which could be very close and cause lots of tiny errors. SketchUp has a certain tolerance for ignoring these errors around 1/1000 inch and when your face is non-planar by a tiny amount faces will still form. When the edges are less than this, faces you expect to form will not form.

Turn off length snapping and be careful to look for the coloured lines that show when your lines are going to be parallel with the axes. Use the arrow keys to force them to be parallel. Make sure you have the correct inference before you click to place each line.

I’ve placed text to show the coords of some points on your model. The style was changed to Color:By axis. This highlights some of the off-axis lines, but not all of them. For example the vertical line at the far left is shown in blue, but if you look at the coords (with precision turned up) you’ll see that the x and y coords are different at the top and bottom by a tiny fraction. I drew a new line next to it using the z-axis inference and the x and y coords are exactly the same at each end of the line. You can draw accurately in SketchUp, you just need to draw carefully.

I greatly appreciate your time in looking at this issue.

I actually copied and pasted this object into a new drawing with the units not set up, usually use mm, ruler, axis colored guides etc.

I see what you mean. The length snapping can cause minute errors which result in perp problems. I will turn it off from now on. Oddly though, if one is using the push/pull tool on an orthoganal shape it would seem it would pull all 4 corners out equidistantly.

This shape is not-quite a 100mm x 100mm square.

The bottom left corner is 0.01mm below the xy plane, but SketchUp still forms a face. The normal of the face is (5e-05, 5e-05, -1) or (0.00005, 0.00005, -1), so slightly off-vertical. When you pull it up 100mm, it will move each vertex exactly 100mm as you can see in the lengths of the vertical edges of the cube, but it is tilted very slightly off the plumb by 0.005mm towards negative x and negative y.

I created the first face with Ruby as its really hard to draw tiny lines like this. It could be done by drawing it scaled up, then scale down.

Ruby commands
> e = Sketchup.active_model.entities
> pts = [[0,0,], [,0,0], [,, 0], [0,,0]]
[[0, 0, -0.00039370078740157485], [3.937007874015748, 0, 0], [3.937007874015748, 3.937007874015748, 0], [0, 3.937007874015748, 0]]
> face = e.add_face(pts)
> face.normal
(5e-05, 5e-05, -1)
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How does one avoid this tiny ‘offness’? Is it by simply turning of length snapping?

Turn it off and leave it off. When you want a line a certain size, type the size. Just be careful to snap to the points you want to and draw parallel to the axis or line you need. Use the arrow keys or hold shift to lock the direction inference. Otherwise you could lose the lock just before you click and place a line off the parallel.

I’ve not been on this forum long, but every time someone has a problem like this and they upload their model, length snapping is on.

You are the first person I’ve found who has experienced this. Most of my questions re Sketchup are posted in the two major FB 3d printing groups where so many frown on SU and try to convert people to their fav-o-rite CAD program lol. I really love SU for the most part, so quick to use and fun.

Again, Thanks a lot for your help.

SR R&D Technician
Boston Scientific, Fremont, CA

This “slight offness” has been and is a problem for architects for many versions. As long time 'Power Users" it is the biggest problem we have with trying to use Sketchup as serious drafting tool. Sketchup is in effect too accurate? With complex modeling, this issue is driving us away to other products.

We need to be able to control position rather than have sketchup tell us we are innaccurate to a % of a mm! The issue is compounded when using color by axis, where it is misleading that the tolerances of the ‘on axis’ lines is such that lines are not necessarily parrallel.

We do snap to 1mm, but without doesnt improve the issue.

Would be good in version upgrades to have be able to control this, as Sketchup tries to become a more serious tool.

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