Drawing an offset angle in an isometric grid
This is about constructing an isometric vector drawing correctly when part of the drawing is at an angle that is not 90º. This post is mostly here to remind ME how to do this. I figured this out one night, but didn’t complete the drawing, then came back a day later to finish it and . . . I had no idea what I did to make it work. Maybe I’m old and losing it, or on too many medications or, perhaps, not enough. After an entire afternoon being hard on myself, I remembered what I had done and I thought I’d share it.
I’ll be using Affinity (vector studio) to create the drawings here but other tools will work as well (Adobe Illustrator mostly); I just find Affinity’s implementation of isometric drawing tools the most productive for me. YMMV.
I’ll assume you know what an isometric drawing and/or grid is already. There are many other places to get a good primer on them. Affinity’s tools are explained here.
The 10 parts after the cutting process prior to assembly
The example I’m using here is a project I designed for my laser cutter/engraver. It’s a rack for my various sanding sticks I have for model building that’s made out of 3mm thick MDF. All of the parts were designed in flat plan view since that’s how they will be cut using the cutter’s software, Lightburn. Because I wanted to sell the design eventually I wanted to include assembly instructions to make assembling it simple. An isometric diagram seemed perfect, but I had inadvertantly made that prospect complicated by not designing the pieces with that in mind at the beginning. The shelves in this design are tilted up at a slight angle so the sanding sticks won’t fall out easily. The angle was something arbitrary and doesn’t really matter but it complicated making isometric versions of the shelf parts.
Converting the angled shelf panel to a cross-section is the first step
The trick to getting this to work is to figure out what plane of the angled object (shelf) you are creating meets one of the three planes of the isometric grid (top, side, or front). In this case the edge of each shelf falls on the “Side” plane. Therefore the first step in this case is to construct a cross section of the shelf part (see above). Next, rotate it to the angle you need (in this case it was 17.6 degrees. I told you it was arbitrary). You now have the basis of the correct offset angle to construct the isometric version of your object.
Take the rotated cross-section and first change its bounding box so it keeps its new orientation for the following steps. In Affinity select Layer>Select>Cycle selection box. When you see “Regular Bounds” appear over your object, stop. Now you need to convert your object to curves and nodes so you can move the corner points around. In Affinity select Vector>Geometry>Add.
Line the two parts up and set them to the isometric grid together.
Place the cross-section object in the position it will appear on the flat side panel (above) and group them. (see above).
The angle of the panel B isn’t right yet, but now you have all of the points necessary to construct the correct version.
Next, take the flat view of your piece (A) and use the “Fit to plane (Top)” command to make a basic iso view (B). It won’t be at the right angle but it will provide you with the correct “width” and all of the nodes needed for the next step.
Select all of the nodes of object B and snap a corner of it to a corresponding corner of your angled “Side” cross section (step 1 above). Proceed selecting the various node sets as shown above, continuing until all of the nodes are connected to their points on the cross-section object. That’ll give you the top of your offset angled object with a correct isometric perspective. Duplicate it to create the bottom, and then connect the dots to create the sides. The snapping settings will help you get it all nice and tight looking. Done!
The finished sanding stick storage module.