ShopBot Introduction

03/19/2015

Ismael gave us a basic lecture on working with the Fab Lab’s ShopBot.

Some notes

• The machine has no lubrication that means no hard materials can be processed!
• Always know what you do, never guess! No rush, no hectic, triple-check. The machine can be dangerous.
• Drilling bit vertical (z), milling bit horizontal (x, y).
• Bits: ball end, flat end, bull nose end et al.
• Bit’s flutes:
  • Less flutes (e.g. 2) for soft materials
  • More flutes for hard materials
• Upcut, downcut that means climb cut for soft materials, conventional cut for harder materials

Further notes

1. Tightly fix the material using e.g. screws
2. Turn on ShopBot machine, vacuum power as well as the connected computer
3. In ShopBot’s software, press K to open the navigation panel in order to move the machine
4. Press the software’s Z icon in order to start the Z calibration
5. Press the software’s XY icon in order to move back to the machines XY origin
6. Move the machine to a point designating your XY origin and take a photo of the shown coordinates (you need the coordinates if the job crashes)
7. Choose the set XY function from the software’s menu and set your XY origin. The XY coordinates should show 0 now.
8. In PartWorks, open a DXF or AI file (Inkscape doesn't work well)
9. Type in your material’s thickness and material size
10. Place your paths
11. Choose and adjust a tool path
12. Choose a required bit and cone, tightly fix it to the machine’s head
13. Turn on the vacuum and the mill—start the job. It’s advisable to do an air job first.

Redesigning Gerrit Rietveld’s Chair With Low Back

03/19/2015 - 04/07/2015

One or two years ago, I stumbled over a book: How to Construct Rietveld Furniture by Peter Drijver. The book shows some furnitures designed by Gerrit Rietveld including measurements and technical drawings. I wanted to redesign Rietveld’s Chair With Low Back.

I started with a test for the flexures which I wanted to use. Due to a quickly and wrongly drawn concept, the first test wasn't a success at all. The test piece broke. The second test was a full success. I was very astonished that a bending of more than conceived 180° was possible!

Flexures test and sketches

I drew the seat using Inkscape and the chair’s sides using Rhinoceros. Rietveld screwed planks together—I used the ShopBot to machine one piece. Rietveld glued several bended thin layers of wood together—I used the ShopBot to machine flexures. Instead of screws, I used joints to fix the chair.

I milled a piece to test the joint concept. The 10 mm wide joint’s tenon tongue tightly connected to the 9.7 mm wide joint’s mortise hole.

It took a while to draw the chair with exact original measurements. I had to calculate the right lengths, curves and angles. To get the right lengths of the bended seat, I had to calculate half of the offset. My material was 15 mm thick. So, half of my offset was 7.5 mm. This line gave me the right length of my bended seat.

I found very nice stable wood and started milling the chair. Milling the chair worked fine. Unfortunately, the joints didn't fit at all! I was very disappointed. I wasn't able to fix the chair.

I tried it a second time. I adjusted my drawings and set the width of the joint’s tenon tongue and mortise hole to 1 cm—an offset 0. I was told that this should work. I milled the chair and tried to fix it. I had to crazily hammer. I got one side super tightly fixed. Fixing the second side, one of the seat’s flexures broke! It was just to much hammering. Many small zero tolerance joints weren’t optimal.

Finally, I calculated an offset of 0.1 mm and used just a few big joints. I bought some new wood. Milling worked well but the wood wasn't the best quality. The flexures were milled and got splintery. I didn't care and finished the production hiding the splintered surface upside down. I milled another leftover piece of wood and got a nicely milled seat. Due to bumpy wood, the bottom side wasn't completely cut and I had to use a cutter in order to untuck it.

Photos of setting up the production

ShopBot settings

Original design and cut files

Please download selected original Rhinoceros design files here.

Photos of production

Finally, I got two chairs ready to test comfort and footing. It's a very small chair!