Blender as CAD

Hello again! As mentioned in a previous post, I decided to use Blender to design my table. Blender is not designed to do CAD. It’s more geared toward 3D modeling and animation. Blender is to Maya or 3ds Max what GIMP is to Photoshop. That said, folks are using it to create designs for 3d printing and milling. I used it to create this pendant for my fiancee last Valentine’s day. I had it printed at Shapeways.

I’m not going to get into the basics of Blender here. There are tons of great tutorials out there. Some of my favorites are at Blender Guru and Blender Cookie. I did have a difficult time getting Blender set up to use real world measurements though, so I’ll give a brief explanation of how I finally got it working.

Step 1

Go to the Scene menu and click on the Units drop down. Then click on Metric or Imperial depending on which units you’re working in. Scale of sets the scale to 1 foot in imperial or 1 meter in metric.

Step 2

Hit the ‘N’ key to bring up the Transform Properties menu.  Under ‘Display’, make sure that ‘Grid Floor’ is checked. Set the scale to 1 for meters of feet, 1/12 (.08333) for inches, .01 for centimeters, etc.

Easy, Right?

WRONG!! Say you’re a goofy American like me and you want to use imperial units. You’re Trying to model a leg for your table and you want it to be 12″ tall. You’d hit shift + A to add a plane and ‘e, z, 1′ to extrude the plane along the z axis 1 ft. However, due to an apparent bug, your new leg will be 3.2808 feet tall. This happens to be 1 meter. Therefore if you insist out of national pride, ignorance, or practicality on using imperial units, you must convert your z measurements into meters. For example, if you wanted to extrude a 2′ long leg you’d type ‘e, z, 2*.3048′

Alternatively, you can click the little magnet icon on the bottom of your screen and instead of entering a distance to extrude you can drag your mouse the direction of extrusion and it will snap to the nearest grid line. If you set 1/12 in your grid floor scale window, you’ll be extruding 1″ at a time.

Don’t forget to name the pieces that you model. I found it helped to name the piece its length and orientation, i.e. ’3_ft_vertical’ or ’50_in_horizontal’. This helped later when I went back to add up how much steel I was going to need.

Here’s what I ended up with for a frame:

Catching Up

Well hello. I started researching this project several months ago, so there’s a bit of catching up to do on documenting the process. As such, this post is meant to start bringing you up to speed on where I’m at and where I plan to go.

The Goal

The goal of this project is to build a CNC table. CNC stands for Computer Numerical Control. Basically, the idea is to be able to put a sheet of material (metal, wood, vinyl…) on the table and have the machine cut out a two dimensional design from a computer file. This is accomplished by moving a cutting tool over the material using a gantry (sort of like the one that moves the printer head on your inkjet printer except with another axis or two). Stepper motors or servo motors move the gantry and the tool mount. A motor controller interfaces with the computer to interpret a CAM (computer aided manufacturing) file. Don’t worry, I intend to delve into all of these components in much more detail as I come to them in the process of building my table.

The Motivation

My reasons for taking on this project are few and nebulous. I’m fascinated by the possibilities of locally manufacturing digital designs delivered via the web. Part of this is due to my living in a place where almost everything is shipped in on a barge or an airplane. I suppose this is true of America in general. The difference in Juneau, AK is that we don’t have the economy of scale in shipping that others enjoy. It seems like local manufacturing could be a boon in isolated places such as this. Raw materials are still required to be shipped in to the extent that they aren’t able to be produced or recycled locally. I still see a couple benefits to local production though. One is that products can be made more speedily than they could be ordered and shipped. Another is the benefit of just-in-time manufacturing. If less inventory is required, fewer resources will be wasted by shipping goods in quantities beyond the actual demand.  All of this is just to say that I think a machine like the one I’m building has the potential to add a lot of value to the local economy.

In addition to making stuff for locals, I want to be able to make stuff to sell to tourists. According to this report, over 1.1 million tourists came to Juneau in 2007-2008. I think a subset of these visitors see the environmental and economic value in purchasing locally made souvenirs. I have some ideas of things I could make to help these folks remember their trip to Alaska.

I am enormously fortunate to have a job where I have a fair amount of time on my hands. I feel a responsibility to make good use of this time. I’m going to have to learn a lot of new skills, from welding to gcode, in order to complete this project. If you follow this blog, I can guarantee you’ll have a front seat for a lot of mistakes. Hopefully we can prevent your making the same mistakes if you start down this road later on.

The Process

I started by looking at pre-built systems like those offered by Torchmate and Gotorch. I decided I had more time than money, and based on what I’ve read I’m hoping to be able to build my table for about half of what I would have to spend for a turnkey system.  Reading other build logs on forums such as CNCzone helped me wrap my mind around the process. I’m also looking forward to actually building the table and learning all the requisite skills. In time, we’ll test the soundness of this logic.

Once I chose building over buying, I looked around at different kits and plans. I’m planning a future post that will give an exhaustive comparison of the different offerings. For now I’ll just say I decided on a gantry kit from Shopdroids. I’m planning on using a comprehensive electronics kit from CandCNC. Shopdroids has plans and parts lists available for download after you purchase one of their gantry kits. The plans are fairly generic and it is expected that the builder will customize them for his/her needs.  I used Blender 3d modelling software as a free CAD substitute for designing my table. I had quite a bit of experience with this software from previous projects. I’ll go into detail on the workarounds required for this in a future post.

One of the obstacles I’ve had to overcome is the fact that I live in an apartment. I love almost everything about my seaside apartment. One thing it lacks, however, is a garage/workshop space. I’m insanely fortunate, however, to have been granted access to one of my coworkers’ hangars during the build process.

Once I had a workshop lined up and I’d finished my design I started gathering tools and equipment as well as getting quotes for materials. Another post to look forward to is a description of the tools and equipment I’ve acquired and how I decided what to get. Going forward you can also expect to read about how these items worked out for me.  I’m currently awaiting delivery of this tool before I can begin construction.

That’s all for now…

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