Computer Controlled Machining

Softwares Used

Make Something Big!

I was very excited when I started thinking about ideas for this week, I initially wanted to make a marimba and did quite a lot of research into this before realising it wasn't viable. It can take master instrument builders weeks to make one as tuning each wooden bar, which must be done by hand and ear by working out where the resonant nodes of each individual piece of wood are and sanding between them, is a fine art. You also need to craft the bars out of (very expensive) exotic hardwood such as rosewood, as this is the only way that they will be resonant enough. After moving on from this idea I decided to make a desk for the purpose of music production, encorporating speaker stands and a hole for cabling. This project better fits the use of a cnc machine and can easily be done using less expensive plywood, which is also conveniently un-resonant, making it well suited to the purpose of the desk.The desk will also be press fit, I will use no glue or screws, making it only really possible to make on a cnc machine. I am also hoping for the desk to be related in some way to my final gloves project, even if it is just the desk that I end up using during the time I am producing music using the gloves.

Designing the Desk

Before i started to design the desk I looked at lots of other press fit cnc furniture on the internet to work out ways that joints can be made strong without glue or screws. I first looked at Opendesk, then some related blogs, and Pintrest, and I finally just did a Google Image search in order to get inspiration for my design. My first design step was then to do a very rough sketch of what I envsioned the desk would look like. I then made some measurements of existing desks to get a good idea of the size that I would need to make it. After doing this, I started to work in Fusion 360 to 3D model all the different parts of the desk, starting with the top, then the legs, then adding speaker stands and a support bar to make it structurally sound. I wanted to make it look aesthetically pleasing, be sturdy enough to trust it holding expensive audio gear, but also be efficient with the amount of wood I used and make it able to nest well. I was working with two sheets of 1m x 1.2m ply and wanted to make a desk that was at lest 1m wide, 70cm deep and 75 cm tall. My proficiency in Fusion 360 has grown since the first couple of weeks and therefore, although more complex and larger, this design took about the same amount of time for me to complete as my FabPlax that I made in my Computer Contolled Cutting week. I used mirroring, construction lines and parametrics with much more success in order to make the design process faster and also editable. For instance if the width of my material or milling tool were to change. I designed all of the components in Fusion360

The original rough sketch I did before moving to CAD to precisely design the desk. It contains multiple angles and a few initial measurements.

The first thing I did in Fusion was to create a rectangle that would become the top surface of my desk. I initially made this 850x500mm, but later expanded it to 900x650mm. I had to slightly lower the size I planned to make the desk due to the constraits of our machine's size.

At this point I realised I needed to extrude the shape, but also be able to account for possible changes or variation in thickness, as I wanted the desk to press together. To make this possible I added a user parameter for material width.

I also had to account for the width of the milling tool if I wanted the desk to properly press together, so I made a parameter for the kerf of the machine. However I didn;t know the value for it at this point so I just left it blank. With parametric design it is possible to fill this in later, as long as you are consistent with inclusing it in your measurements.

After extruding my rectabgle by 'width' I then began adding the holes for the bottom of the speaker stand legs to press into. I had to ensure that they would be spaced well enough to have enough room for the speaker on the stand they would hold, but close enough so that I wouldn't waste any desk space. I later added a middle hole for extra structural support. Monitors are expensive, I don't want it to fall over...

The extra hole can be seen in this extrusion of the sketch. I purposefully only extruded half the width as I wanted the surface to still be useable if I was to remove the stands for any reason. This stopped there being too many holes that go all the way through. Although I did have to later scrap this idea as the plywood wouldn't have dealt well with this kind of milling and may have split.

These are the holes I drew for the legs at the front of the desk, I made sure to draw them along the same construction lines as the back hole so that they lined up precisely, especially because of the angle that the legs are set at. I then extruded them to my 'width' parameter.

Before extruding the holes in the tabletop I made use of construction lines to get correct anling on the speaker stands, which should form an equalateral triangle with the listeners head. I also added holes for the legs, and support bar to press into from the bottom. Extruding them to the opposite face of the original rectangle. I added a hole for cables later, at the back in the centre.

The original sketch for the back legs of the table. I did this by using the line tool to draw and then defining the dimensions of the sketch after I had achieved the shape that I wanted. This did however, prove difficult to edit later on.

The inspect tool is your friend! use this to measure your different bodies and make sure that everything joins up in the correct way. keep chacking because if you make a mistakw it can be difficult to work out where you made it.

This was a WRONG STEP but it is good to learn from. When exporting for cutting from Fusion you can only save sketches as .dxf files, NOT MODELS. This meant I had to remove the fillets I made to the models after they were extruded and redo them in the sketch. This does seem the easiest way to get a rounded edge though, as long as the curve doesn't have to be too specific. I filleted all of the sharp inside edges on the model, to form a wavy line. I then extruded it to 'width'.

Filleted curve on the back of the table leg model. Again, this was the wrong way to do this. If you want the fillets to appear YOU MUST DO THEM INSIDE THE SKETCH. Looks nice though if filleting is something you're only doing to the model for cosmetic reasons.

It lines up! My legs fit perfectly into their press-fit holes in the tabletop.

I then designed a bar to support the desk, to run across the back and line up with the hole you can see in the sketch of the tabletop shown earlier. This also required me to create a hole in each leg so that the bar would properly attch to and support the structure of the table.

My next piece was the bars that would hold up the speaker stands. I only made two in the 3D model so that I could check that the stand was properly aligned. I would duplicate these until I had enough for each slot in VCarve, for cutting later. They are just rectangles with tabs added for pressing into their holes in the platform of the stand.

The sketch of the platform for the speaker stand. I measured it to make sure it was the correct size for my monitors and then used the inspect tool to ensure the holes aligned with those in the tabletop. I then used the mirror function in fusion to quickly construct each hole in the platform and added the central one after this.

The model of the table after I finished modelling it. The other stand will be added in the 2D milling software. It would have been unecessary work to duplicate and move the parts into the correct place in Fusion360.

Prepping for Cutting

After I finished designing in Fusion, I exported each sketch as a .dxf file ready for prototyping and then milling. I then opened the files in Illustrator and scaled them to be 20% of their original size. I wanted to cut a prototype out of cardboard, to make sure that the table would fit together correctly. Howvwer this was nearing the end of the day on Monday and I didn;t have time to make the prototype of the desk which was less than ideal, as I had to mill it without knowing whether it would work. I then realised that I had not accounted for the fact that the milling machine would draw a curved path around the internal corners of the square holes being use for press fit, because of the size of the bit. This meant that I had to create t-bone joints. I did this the next day using rhino, as I find it easier to edit 2D drawings in this software. To make the t-bone I inserted circles with a diameter slightly laredr than that of the cnc tool and made sure that the centre met one line of the rectangle, and the apex of the curve the other side. I then removed the internal portion of the circle and the line of the rectangle across the remaining semi-circle. I did this on every corner and was left with t-bone joints that would work with my machine. It was an oversight not to have done this in Fusion360 as the parametruc properties of the software would have allowed me to make the joints editable for optimisation on other machines. After this I then saved the new .dxf files from Rhino and opened them up in VCarve Pro. Here i prepared them for milling, regrouping parts, defining the toolpath, adding tabs and saving the toolpath in a format compatible with the machine. As I was running out of time for milling and other people still needed to use the machine as well I only had time to mill one sheet of ply. This meant modifying my design, I had to lose the support bar, and the more complex arced legs. Opting instead for simple, straight legs on each corner, maintaining the slight inward angle to attempt to maintain some kind of structural integrity. I edited my .dxf files quickly and accordingly and exported again for milling. This was less than ideal but we only had access to one 1m x 1m cnc machine so it had to be done. I hope to make my priginal table design at some point when I get time as this is what is documented here up to this point and I much prefer it to my final product for this week. After my paths were ready to mill I zero's the x, y and z on the machine, select the correct job and hit go.

The menu in Vcarve, showing the group tool which is essential. You must rejoin lines from .dxf files in order to maintain scales and shapes of components.

The move tool in VCarve, you can use this to nest parts manually, however the best way to do it is to use the inbuilt nesting function in VCarve.

All the parts shown in VCarve, this is the changed design, made so that it would fit on one panel of wood. I made it as close to my orginal design as I could on the material that I had time to mill. After everything was in, you need to select all the components and select which toolpath you want (cut or engrave). I chose cut as I want the parts to be removed from the sheet of ply. I did however need to add tabs, so that parts that are cut weren't loose and dangerous during cutting. This is also done at the path selection stage. Then you press calculate and the software will display the toolpaths. You then save as Axyz Arcs(mm) and you are ready to send the file to the machine. To do this, open the AXYZ DNC software that comes with the machine and select AMC file mode, choose your file and press send. (apologies for the lack of screenshots here - I was using the computer for the CNC, which is on a different university campus to our lab, and forgot to grab my screenshots from thier desktop.)

To set x and y you must first move the tool using the 2,4,6 and 8 buttons. When you are happy with where it sits you must then press F and 3.

To check x and y move the tool again and then press F and 13, the tool should move back to the zero that you set for x and y.

The next step should be to set the z axis of the machine. Before doing this make sure that the milling tool is runnning already. Presseing the +/- button will provide different speeds of movement for the tool, so you can be more accurate as you approach the bed. You want to set z at the bottom of your material, so you can be sure that the machine will cut through the whole piece. Press F + 84 to begin tis process.

The macine successfully milled my design, it took around 45 minutes. You can see the rough speed of the machine in this video. You can also see that although tabs were present in VCarve they didn't transfer over to the cut in the holes for the speaker stands and the pieces were removed by the drill. For this reason I had to be very careful until these parts of the cut were over. Luckily there was a perspex shield infront of the machine a little further back.

After milling had finished the sheet was properly cut but the pieces were held in place by the tabs. This needs to happen for safety resons and the pieces are easily removable, either by hand or with a mallet and a chisel.

After I removed the pieces I had to sand the edges as they were very rough, and some little pieces of the tabs were also left on. I used loose sandpaper and a sandpaper block to do this and get a softer but still straight edge.

Here you can see the diffrence between a sanded edge (left) and one that hasn't been sanded yet (right).

Because I only had time to mill one sheet I didn't have space to mill the stands. I will make these at a later date. But here is my finished table for this week!

I made some test pieves using the stands earlier on. However I forgot to input the kerf before milling them so it didn't fit very well in the tbale. But at least here you can visualise what it will look like.

In all honesty I found this week a little frustrating to due to machine and time consraints (I had university deadline soon after, and the milling machine was on a different campus to our FabLab). However I have managed to produce a table that works and also a design that I am very happy with and hope to make in the future. I will update this page with the finished product if I do ever make it, I'll need to get some morre ply first though!

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