Mar 08: computer-controlled cutting

This week it was all about making something big on a cnc machine. At first we had a introduction to the Shopbot and the Precix. Ricardo showed us the process of changing the drillbits, sending the file (gcode generated) and start making something big on the cnc milling machines. After that we had a tutorial to learn Rhinocam.

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Making something big in Solidworks

I always thought that the FabLab in Barcelona is lacking a PingPong table. Everybody seeems to like the idea so I started making different measurements to build one on the big Shopbot. At first I sketched a lot of different possibilities for legs and also how I want to join (pressfit) all the plates together. I changed my design several times and decided at the end that it would make the most sense to have something modular that I can also use as a table for working, etc. For the final design I decided to make 4 tables that you can either join together to have a PingPong table or separate them to have 4 working spaces. I am really getting to enjoying Solidworks. Because its a tool for engineers I really like to can easy adjust the distances and dimensions. It was also my first project which I started to use "Assembly" to join all my parts together. At first it was a bit difficult but after some time I found out which sides should go together to make the joints and pressfit. I decided to use a 15mm wooden plate and a 6mm drillbit to mill it afterwards. I measured everything for that scaling and made a parameter for the "thickness" so I just can adjust it if I want to mill on an other size of board. After I was happy with everything I saved the file as a ".igs" to open it easily in Rhino.

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Setting up the file in Rhino and Rhinocam

I opened my ".igs" file in Rhino and started to ungroup everything and lay it flat on the topview and arrange it on the Stock I created in the right size of the board. Then I selected where I want to drill the screws that the board holds on the Shopbot. After that with the command "Offset" I set it to 0.2mm. You need to do this at the pieces where you have a join. But its enough if you have it on one of the two joints. I measured the distance afterwards and had 15.4mm which was what I wanted. After that I made the holes in the inner corner. You need to have them so the drillbit can move nicely around the inner corners. I used the "Point" tool and selected "END" to easily can make the holes. I also changed the inner layers to "Interior" and the outer layers for the "Exterior". After that put everything nicely on separated layers like one for "Stock", "Screws", "Holes", "Interior" and "Exterior". Then it was time to open Rhinocam and set the settings to generate the gcode. I downloaded the Shopbot Valldaura and the Milling bits settings to import them in Rhinocam. In Rhinocam I started making the first step for the screws and set the drillbit that it only drills 5mm inside. You just need to mark the holes that you see where you have to drill the screws in it. After that I just copied the step and changed the settings for the drill to 16mm so your sure you cut thru the whole board. Then just copy the steps for "Interior" and Exterior". To change the layers on the setup just go inside and to "Machining Features/Regions" and just say "Remove All" and "Select Drive/Containment Regions" go to your prefered layer make a right click and say "Select Objects" and press enter. Then it loads it directly back to Rhinocam. After that you can start to simulate how your mill will look like. After that you see on my picture that my simulation looked like strange pixels. I had a hard time to found out what was the mistake. At the end it was just changing in the "Preferences", "Simulation Model" to Polygonal Model. It doesn't interfere the mill but I like when my simulation looks like what I really get in the end. Also for the Shopbot in Valldaura I need to change the "Plunge" to 1000mm/min, the "Engage" to 30mm/min and the "Cut" to 15mm/min. Be also sure to make "Bridges" so the pieces that are already cutted don't move freely on the Shopbot. For making the gcode just make a right click on your folder for example "Screws" and say "Post". It will generate the gcode for the Shopbot. Be sure to make a separate gcode for the "Screws" and the other ones which has all the same dimension you can export all together as one gcode. Just remember to make folders in the order you like that the Shopbot will cut it. For example first the "Holes" then the "Interior" and afterwards the "Exterior.

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Milling on the ShopBot

At first you need to clean the whole surface of the Shopbot. Then measure your wood if it really has the dimensions you need. Usually they are a little bit off. After that you can put your wood on the Shopbot and start to align it nicely. Then open the Shopbot application and define your X and Y Axis. For the Z axis I would recommend to search for the flatest spot on your plate. Bog wooden plates tend to bend a little bit. If you move the axis be sure to put like 5mm for the Z Axis on because you don't want to scratch your nice board. After everything is ready you can upload your first gcode for the "Screws". In the Shopbot in Valldaura it's if you send your file there pops up a window. You have to press on the real green button next to the Screen and press "Enter" on the Keyboard. With that the drillbit starts to rotate. After the Shopbot is finished with the engraving of your screws just take a drill and some screws to put down your board. Then you can send the second gcode on the Shopbot and let it do the work. After my Board was finished I had to chisel away the "Brdiges" to put the pieces out of the board. Then I just sanded down the pieces and fitted it together with a rubber hammer. My first board took 55 minutes to mill. For now I mounted the legs in reverse so I already can use it as a small table. Next time when there are not that much people that wants to mill I try to finish also the missing parts and the other 3 tables. I also put a video in here to see the milling step by step. Enjoy! ;)

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Click here to download all the files.