While enjoying a Sunday morning at the coffee shop a few weeks ago, I found myself daydreaming about a concept for a small easy to build Parametric CNC chair.
I've been playing with Fusion 360's Parameters section for awhile, and this is the perfect project for a parameter driven design!
A Parametric Design is driven not by fixed values, but but variables and mathematic relationships. It gives you the ability to quickly change elements of a design without needing to redraw it completely.
Need a child sized chair? No problem, set the seat hight lower and make the seat smaller! Need a seat for NFL Linebacker? Better raise the seat height and use thicker material for all the parts!
Download and Build Your Own!
If you'd like to download this project, you can follow along to see how the file is put together! If you have access to a CNC Machine, you can even use this file to make your own chairs!
This link will take you to the projects A360 Page, where you can view it in 3D and download the file from my Fusion 360 Account. https://a360.co/2m7g30w
For the file to work properly, you will need to download it as a 'Fusion 360 Archive' and re-upload it into your own Fusion 360 account.
If you download this, aggressively market it and make untold millions from my design, all I ask is that you donate some of the proceeds to charity... and buy me a large yacht.
The Input Parameters
The design of this chair is driven by seven input values.
- Material Thickness - The nominal thickness of the sheet material the chair will be cut from
- Seat Height - The height of the surface of the chair's seat off of the floor
- Back Height - The height of the top of back the chair's back off of the floor
- Width - The width of the seat. (This value is also used for the seat's depth, for simplicity sake)
- Bit Radius - This is the diameter of the CNC bit that will be used to cut out the parts, this is used to drive the dog bones that make assembly easier.
- Rail Thickness - The thickness of a typical rail element. This controls the thickness of the legs and two rails that support the chair's back
- Allowance - This is a general value added to the width of slots where one part needs to slide into another one. If we cut out a chair and find the part are just slightly two tight or loose, we can fix that by tweaking this value.
Each of these values in a variable that can be adjusted in the Fusion 360 'Change Parameters' window, which is accessible under the 'Modify' menu in the 'Model' workspace
How a Parametric Design Works
In a parametric design sizes and relationships between elements are not driven by fixed dimensions, but by mathematic relationships based on the input parameters.
For example, look at the sketch for the chairs back
Each of the dimension values read something like fx: 7.50 or fx: 2.50. The fx: prefix before a dimension denotes that it is a computed value, not a fixed value.
If I open one of these Dimensions we can see whats going on.
The value of this radius on the upper corner of the seat back, which shows in the sketch as fx: 2.50, is dimensioned as Width/6. So Fusion looks up the value of 'Width' from our parameters, divides that value by 6 and make the result the radius of the arc.
Most of the dimensions in this chair are driven this way, with the exceptoin of the screw holes, which are all a fixed diamiter.
Fun With Parametrics!
Here is our base chair with the original design values
Now lets make a version of the chair for those short wiggly kindergarteners! We'll lower the seat height from 18 inches to 12 inches, and the back height from 32 inches to 24 inches.
Next lets make a wide version, for when the in-laws come to visit!
Going to Production
With our chair sized, copy all of the chair's bodies into a new empty component. The duplicate parts will maintain there relationship to the original parametric bodies, but we can use Fusion's 'Align' and 'Move' Tools to lay them out onto a flat sheet and cut them out on our CNC!
We ended up building these chairs is an 'Introduction to Fusion 360 CAM' Class we teach here at Hammerspace Workshop. 18mm Baltic Birch plywood we used is amazing stuff. Well made, dimensionally accurate, and fantastically strong!
None of these class participants were small guys, and all the chairs came together awesome and strong!
Thanks for Reading! I hope you are building something Awesome!
-Michael