Wednesday, September 3, 2014

Documentation: Toolbox

So at this stage construction of the toolbox is well under way and I'm happy to report that while it's going a bit slower than I would like it's going quite well. While I promised a post detailing the 3D work I've done that will be saved for my next post. The post after that will show some of the construction work so far but for now I'd like to share an important part of the process that got me to this point.

While generating design documentation isn't a particularly sexy aspect of the work of design it is really important. You never really hear about designers being lauded for their magnificent spreadsheets but as a designer we spend a lot of time working on these sorts of documents and they are really valuable resources. They help keep costs lower, keep schedules shorter and most importantly ensure accuracy and correct detailing in the products produced. I also think this sort of exercise is often overlooked with bad consequences. The documents I'll be discussing today are a bill of materials or BOM, an aluminium extrusion calculation, an interactive ply cutting list and two simple cutting diagrams.

First below is a screenshot from my BOM. A BOM is a list of all the components of a build, the materials of those components and the quantity required of each. The BOM below has the materials details removed to demonstrate it's usefulness as a cost calculator. I used my BOM as a method for costing the components and compared pricing from three sources. The totals including postage costs were converted into Euro grand totals for easier comparison.

One of the options was abandoned due to the fact that the cost of postage would have been extreme and not all the components could be sourced there. While obviously there are more than three sources for these parts these were the ones that initially presented both the best prices and required range of parts. This BOM was since updated with details including the screws, bolts, washers and rivets to be used in the toolbox construction.

Next up is the Aluminium extrusion calculation, this is in essence a sort of cutting list but it serves a more important function than just that. The list was used to determine the smallest amount of aluminium angle extrusions and locator extrusions I needed to order to be able to build the box. Before creating this list I had to first determine the minimum lengths required for each of the cut extrusion sections. I calculated this and then checked those calculations off the 3D model which had the extrusions, made to the correct profile, fitted to it. This is a great example of how one form of exercise can inform or confirm the assumptions another.

With that calculation made and a second "ideal" value for the angle extrusions I determined how much I needed to order off each company to cover the box. As the two companies provided the extrusions in different standard lengths I used the tables at the bottom to graphically represent the standard lengths of the two companies theoretically split into the required sections. This told me the minimum I needed to order off each company, the waste left over and whether or not I could meet my "ideal" dimensions for the corner extrusions. The values from this table were used in the BOM for the costing.

The third document I'll discuss is a very standard cutting list. This cutting list is a little more feature full than some others but is essentially identical in presentation. Each section to be cut in this list is grouped by the parts they will be finally assembled to make up.

Each piece was also assigned a letter based on it's dimensions this was used to create a simplified cutting list which I'll talk about later on. The thickness of the plywood is a fixed dimension so this was simply arrayed down the list where appropriate. At the top of the list is the overall dimensions of the box and this is done also at the top of each part. Using formulae I was able to then get many of the parts to auto generate their own dimensions based on the box and part dimensions. This meant that should I need to change the size of one of the parts or of the box in it's entirety all the associated dimensions would automatically update themselves.

So as not to confuse myself when doing the actual cutting I made a more basic cutting list. This was literally a list with all the parts of the same size, grouped (using the letters from the previous list) and final numbers for each part tabulated. With this list I made three variations, shown in the three different colours below. The first was a straight forward listing according to the Letters assigned in the first cutting list. The second was sorted by the largest dimension of the pieces and the third was arranged by the number of each piece required to be produced.

Finally from the information in the basic cutting list I made a simple cutting diagram in adobe illustrator. There is software that I've seen used for CNC machines that can do this sort of arrangement of parts for efficient cutting however I didn't have access to such wizardry. Like a very complicated game of Tetris I arranged all the parts (to scale) onto representations of the Plywood sheets (to scale) attempting to take into account the width of my circular saw blade. After my first try I had the parts spread across nine and a quarter sheets of ply but after a couple of re-shuffles and many tea breaks I managed to reduce that number to eight sheets.

The green colour on this diagram was used when I was doing the actual cutting to remind me of the parts that were and weren't cut. The smaller pieces are highlighted in yellow as I kept the offcuts and created those later on.

While I stressed the importance of these documents earlier it is good to keep in mind that things don't always work out to plan. I'm not usually one for cliché but the whole "failing to plan is planning to fail" does spring to mind in this context. I ordered 10 sheets of ply as I got a discount on that amount but I had done this calculation beforehand and knew that would be enough to safely continue. While I did have two of the pieces I cut not work out very well having the diagram allowed me to mark them down as bad and move on knowing I had the contingency of other the other sheets of ply.

So that's it for this riveting round of boxes on a screen. The next post will hopefully make up for it with some 3D models and sexy renders.

John O'Shea

No comments: