Designing for 3d printing in Sketchup

[BS4Boy]

Can anyone please help, I am asking for advice from anyone who has designed and printed something using sketchup.

I have started tinkering with sketchup in an attempt to learn a bit of 3d design (It is easy to learn, compared to the other 3d programs I have looked at, which would take far too much time and effort to learn otherwise)

As I understand it Sketchup does not handle small curves too well. Advice I have seen suggests designing at up to 1000 times actual scale then rescaling to print size before exporting. I am primarily interested in designing for 1/76 scale, but I would ideally want to print at any scale, so long as the detail would hold up.

My questions are this, Is this advice really correct, does it make any difference to the level of detail? Would simply increasing the number of segments in curves not have a good enough effect? Scaling is incredibly easy in sketchup so does it really matter what size you design at, as you could rescale to 1000 times if you initially designed at 1:1 or 1:76 then rescale back down. Would this have the same effect?  Is there no external software that would automatically increase the models resolution to improve detail, perhaps when being exported to an stl file?

So far I have been designing at 1:1 scale which is only 76 times my target scale, but surely that would be enough to create a  detailed print!

[mgbusa]

I use 10 times bigger since it just easier to calculate while drawing. It seems it works most of the time. Some smaller details I use 100 times the size just to get the radius right. I would not use a odd size like 1/76 or you will go crazy with the calculator. It does not matter which scale you use since Sketchup has only problems when you draw the radius, etc but after that you can resize it to any scale and it will hold the shape.

[Marbelup]

I don't use Sketchup, but I understand that the number of segments used to form a circle is limited, regardless of scale. The default is 24. I don't know what the maximum is.

 

On some models, such as a locomotive boiler, facets on a cylindrical shape are visible after printing due to this restriction.

[Multiple identity account]

Scaling in SketchUp just looks easy. But I doubt it is. You need a rescale drawing top refer to when you scale. I don't think it's straightforward.

[Quarryscapes]

Scaling in SketchUp just looks easy. But I doubt it is. You need a rescale drawing top refer to when you scale. I don't think it's straightforward.

 

Correct it's not. Scaling in sketchup, especially say scaling up to create a small curved part then scaling it back down introduces small errors which lead to flat surface no longer being flat and that can no longer be further manipulated.

 

Work at least 10x the model size, that works well for most things, though you will find if you're working with very complex curves (think running a pipe around objects and making Y junction of the same etc) you'll need to increase the size further. With the STL plugin export it's also very convenient as you simply export in Centimetres instead of mm and your model comes out correctly sized. 

 

There is no connection whatsoever between number of sides used to create a curve and how small it will go. I will personally tend to use 64 SIdes, but anything over 48 is normally smooth enough. The default is 24 which is nowhere near enough. Remember the more sides you use the more complex the model becomes slowing down processing time and bulking up file sizes. 

[Rabs]

This is why you need to draw at bigger than model scale in Sketchup:

Curves with a radius <~0.5mm simply don't work (such as you'd use for rivets).  If you try to draw one directly you'll get this message.  If you draw a bigger one and scale it down it will just break the model without telling you.

In my experience this doesn't relate to the number of segments.

 

Also, sketchup will try to merge points closer than ~0.1mm.  So features that you thought were separated will suddenly get joined, even if it means moving a point out of the plane of the face it was in.

 

I've tried playing around with different precision and unit settings but it seems to be a global limitation.

 

When using sketchup I now set the units to meters and draw the model where 1m in Sketchup will be 1mm on the model and 148mm on the prototype (for N).  I then use a different program (meshlab) to do the scaling after I have exported the model.

 

it sounds very clunky, and it's certainly annoying that Sketchup has this problem, but the workaround is actually very easy.  Set the units to meters and then whenever you see a measurement mentally add a second 'm'!

[BS4Boy]

Thanks very much guys.

 

The thing I don't quiet get though is that in sketchup it does not seem to matter how big a model you make, it will always create curves with the same number of segments (manually adjustable up to 99, with commensurate slow down in processing) So even 1000m radii circle would only have the same by default, 24 sides, as a circle of 1mm. In effect that is actually a reduction in resolution. For some unknown reason as Rabs said  Sketcup has a limit in how small it can draw a circle. That gives me a very good reason for drawing things much larger. However without changing the radii of and curves in sketchup, would it not export low res 24 sided based curves, giving just the same effect as if designed at scale (not withstanding the 1mm limit)

 

Rab do you change the resolution of the curves doing it your way or leave them at the default?

Can the default drawing of 24 sided curve be changed, or do they all need to be done manually.

 

So based on what I think I now know it seem that this would be the workflow I need to follow

 

1. Setup to draw at least 10 times larger(simply to avoid the 1mm curve limit and proximity errors as Rab  describes. My existing project at 1:1 (76x scale should be plenty to avoid any problem apart from awkward scaling possibly later)

 

2. draw all curves with between 40 and 64 segments (what would be the optimum to avoid processing slowing, and best resolution at 1/76?)

 

3. Export to stl

 

4. Rescale in Mesh.

 

 

Would this be correct?

[Marbelup]

Netfabb Basic is another software package which is good for scaling and free!

[Rabs]

You are absolutely right. That process is how I work around Sketchup's quirks.  If it draws the circles as 24 sides then that is what will get exported so you definitely want to increase that number.  Sketchup usually remembers the number of segments that you last chose and will use the same number the next time you use the arc or circle tools.  

[BS4Boy]

Thanks very much guys,
I now have a better understanding of how Sketchup works.