Creating a perfect circle to cut on a laser cutter

Is there any way to create a circle without segments in Sketchup or Sketchup Pro? I am designing metal parts and having them cut out on a laser cutter. Because Sketchup builds circles in segments the laser cutter also cuts them in segments and my part ends up looking quite messy. I know I can up the number of segments but I am wondering if there is a different way to do this. I don’t want to spend lot’s of money on Sketchup if I can’t cut out nice circles on a laser cutter.

No, the only way to get a smoother circle or arc is to increase the number of segments.

Actually there is a way! Sorta. If you don’t mind exporting to an Autocad format, which I am guessing you might need to do anyway with your laser cutter. If you export your SketchUp model as 3D rather than 2D, the faces will export with the segments, but the edges of SketchUp arcs and circles will be converted to true curves. Just be sure to not export faces.


Edit --> You need SketchUp PRO to do this, I think.

Edit 2 --> Just imported exported .dwg into Illustrator. It also will honor the true curves. Will your laser cutter read Illustrator files?

3 Likes

Thanks for the detailed reply. It was very helpful. My laser cutter can read .dwg files but it works best with .dxf. Do you know if I can export true curves in .dxf format?

Yes it does.
Example:
2”r default 24-segment circle
Exported edges only from SU as 3D DXF AutoCAD Version Release 12
3D DXF imported into CadStd Pro
Entity query shown below:

-Geo

The DXF and DWG formats are identical in content, the only difference is that DWG is a binary format, and DXF is an ASCII (text) version of the same. SketchUp Pro can export both.

Anssi

1 Like

Hi. Thanks a lot for your detailed help! It was exactly what I needed. It worked perfectly. I should have replied sooner but I suddenly got really busy with the harvest crew.

What version of Sketchup are you using? I ask because I am running Sketchup 8 Pro, and exporting to AutoCAD formats does NOT create real curves or perfect circles. They are still segmented. Thanks for any info.

hey bob.
you have to do a 3D dwg/dxf export for it to work.


File -> Export -> 3D Model
…instead of 2D Graphic

(or, that’s the wording on mac at least)


add-- also, it’s not going to create real curves… only real arcs or circles (and even then, the arcs and circles which are being recognized as arcs and circles by sketchup… you can see if they’re arc/circles by right-clicking on the curve and choosing entity info)

Thanks for the response, Jeff. Yes. I understand we’re exporting a 3D model to a dwg format. I export without faces checked, as indicated in prior posts in this thread. Circles still look segmented when I view them in DWG TrueView, and importing the DWG file back into Sketchup still results in a segmented circle. That’s why I thought my results must be related to using an older version of Sketchup Pro.

hmm… see how this looks in TrueView:

fromSketchup.dwg (16.5 KB)

in sketchup, it looks like this:
(a circle and arc on the left… then copies of them on the right which were then exploded/welded)


i exported it with default settings:


then in rhino it looks like this:



edit-

but this part, yeah… there’s no tricking sketchup into displaying true arcs… they’re always* going to be segmented…

*well, maybe(hopefully) not always… but in all the versions up til now they will be.

Yes. If I look at your file, For Sketchup.dwg, the figures on the left look smoother, but when I zoom in on the figures to the left, the reason is that there are about double the number of segments. So yes, it seems to be a much closer approximation of a circle, but we can do that in Sketchup by simply increasing the number of segments in the entity info area. I was thinking we were actually getting a true circle (unless this is a limitation related to DWG Trueview).

yes, that’s what it sounds like… does trueview have measuring tools or is it simply a viewer?

some applications (like bonzai3D used to be) would have true curves but when displayed on screen, they can still appear as segmented. but if you measured from the centerpoint to any part of the circle, it would show true (as well as downstream cnc etc… the curves are true)

(and to a certain degree-- All applications do this… we’re trying to look at curves on displays which have square pixels)

if trueview has any measuring tools though, try checking the radius and you should find that the radius is proper no matter where you’re at on the arc.


add- fwiw, rhino which is one of the most accurate surface modelers out there, displays it’s surfaces as render meshes just like sketchup (and all of the ‘true surface’ apps do- that i know of)…

it’s a bit disorienting at first or it takes a bit of familiarizing with what’s going on until you fully trust what you see on screen… here’s a post i made a while back on scf which attempts to show the render mesh in rhino…

http://sketchucation.com/forums/viewtopic.php?p=511388#p511388

this same thing is probably what’s happening in trueview except it’s happening on curves also.

Trueview is basically a viewer, but fundamentally it seems to be AutoCad without any editing tools. I don’t actually have Trueview installed, but full AutoCad also displays circles as segmented polygons. It has always had a setting (VIEWRES) to control the number of segments. I found a reference to Tools menu>Options>Display>Display Resolution (Arc and Circle smoothness). The default might be a small number, increase it to, for instance, 500 (the default in full AutoCad) and see if circles look better.

Jeff, your arcs and circles look quite OK in AutoCad 2014.

Anssi

oh… i didn’t know that about AutoCad (i downloaded the trial once but only opened it once for a few minutes)… are the measurements still true even though it’s displayed as segmented?

fwiw, the blue screenshot above is Rhino… the autocad 2014 part is the export dialog in sketchup as that’s what i used for the example to make a .dwg to send to rhino.

segemented poylgon because of display output speed, a refresh may show a smoother display especially after changing the zoom scale. The entity is still analytic which can be evaluated by simply checking the AC entitiy info (probably in TrueView too).

thanks for the info. i imagine they could update that nowadays?.. hardware is a lot faster than it used to be and i don’t know how necessary it is to display curves as segments (not talking about polymodelers which have different reasoning for displaying segmented curves)

i don’t know if hardware is quite ready to display true surfaces instead of render meshes but the curves part seems ok to do.
?

having a model with several hundred thousands of ‘real’ circle/arc/ellipse and (worse) spline curve entities would require much more number crunching than outputting the polygonized equivalents with every move/pan/zoom/rotate etc… the 3D display output speed of the GPU by using OpenGL (and probably MS Direct3D too) is also calculated as facetted meshes because of performance issues.

yeah, maybe… here’s 500,000 circles in rhino… it does ok

i tried 10million but it got real sluggish then.

still, i don’t necessarily think it’s smart to program for worst case scenarios… how many autocad users need several hundred thousand circles to be displayed at once in a model?

seems better to aim for a more positive experience in most real scenarios as opposed to showing segmented curves to all users when there’s no reason not to display the true curve…


but like i said earlier… i don’t use autoCad… so i don’t really care what autodesk does with their curves :wink:

as Anssi already wrote, the resolution can be configured… not knowing the users system it seems to be resonable not to start with the ultra fine res imho