Sunday, March 30, 2014

Research: Toolbox

So it's been a long time since my last update and I've been working on a few projects recently I thought I might share. Primarily I've been looking for a workshop space and I'm currently working on some portable workshop units that can be easily moved or re-arranged. This will provide for a more flexible workspace and has the added advantage of providing a secure and orderly place to store all my tools when not in use.

The units need to be flexible and portable but also durable for transport. I decided to build them in the style of flight cases (US: road cases) as would be used for touring shows, which I've worked on in the past. These cases have a lot of hardware already designed to stand up to the rigours of a demanding transport schedule but are flexible enough to facilitate almost any size, shape or weight of equipment required for a large production. Building these cases will also provide a high level of security and protection for my tools.

Portable Flight Case

The general make-up of these cases is normally a plywood box with added aluminium edge and corner protection. There is a large range of aluminium and plate steel hardware available to seal and secure the cases and a range of surface treatments and coverings to give them good mechanical and chemical wear resistance for prolonged use.

The first stage of designing these cases was identifying the method of construction, materials and capacity requirements. The cases also had to provide ready access to the tools and have compartments that would be flexible enough to suit my current tools and likely future requirements.

As regards construction there are two common methods that currently prevail. The first is the use of so called "case-maker" extrusions. This method uses preformed aluminium double-angle extrusions, into which plywood panels slot to create the outer shell of the case. The second method calls for the box's outer shell to be built separate to the protective extrusions, which are then fixed in place to the finished box. I decided to opt for the second option for a number of reasons. Firstly I believe the outer shell of the case will be more rigid using this construction method. Secondly I think the final dimensions of the case will be easier to determine using this method which is important for me as I will be putting a lot of internal divisions inside the structure to hold the drawers and other compartments for the tools. Finally, though possibly only a small if actual advantage at all, I believe this could give the box slightly better protection against moisture intrusion.
Double Angle "case-maker" Extrusion

Plywood is generally regarded as the best material for the construction of flight cases for a number of reasons. While slightly more expensive than MDF plywood is generally more flexible and so less prone to break. It is considerably stronger than MDF while also being lighter and so more suitable for transport. Another material occasionally used for flight case construction is OSB which is a material more commonly used on construction sites for hoardings or concrete formworks. Again OSB is cheaper than plywood however again it is nowhere near as strong. In terms of lightness it is probably the lightest of the three options but has less flexibility physically and in regards to it's surface appearance it is very low quality. Plywood can be acquired in a range of finishes, surface treatments and internal treatments, including high quality outer veneers (often birch), plastic outer laminates and marine environment treatments that make it less water permeable.

Of the plastic laminates available some of the most common are phenol resin coating, high pressure laminates (HPL) which I think uses polypropylene, and PVC. These pre-made panels have the advantage of being an all-in-one solution to providing the outer layer with a water resistant protective coating. The phenol-coated panels give the case an attractive and slightly grippy surface, however this finish lacks good mechanical wear properties being very thin and susceptible to scratches. The HPL finish is strong and rigid with both good mechanical and chemical resistance. This is an attractive option as it also lends rigidity to longer spans of panel. The PVC coating again has good chemical resistance though possibly lower than the HPL and wouldn't add as much rigidity as the HPL. I eventually discovered a product which meant I could laminate the cases myself which comes as a thin sheet of ABS. The reason this is attractive to me is the fact that I could apply it after the shell of the case has been built but before applying the aluminium extrusions. As I decided against the case-maker method of construction this means the outer coating could be applied to the case in such a way as to cover the exposed edges of the plywood panels, which is a feature of this method I like. Also ABS has similarly high mechanical and probably even better chemical resistance than the HPL option.

As was already mentioned the outer protective edging is made from extruded aluminium profiles. There is also aluminium "locator" extrusions available to make up the connective surfaces for the openings of the boxes, which makes them water tight to a fairly high degree. There is also cast aluminium protective corner "balls" available. These are all standard hardware for flight cases. Continuing with the use of standard hardware the case will feature retractable recessed handles and butterfly latches for connecting them together. The most common material used for this hardware is 14-16 gauge plate steel often coated in a protective layer of zinc. They are also available in aluminium, ABS and (for the more glamour inclined flight case builder) polished stainless steel. Finally hard wearing castors will be used on the base of the box to make them more transportable. These again will be made predominantly from steel and generally have either polyurethane or rubber wheels. The rubber used is synthetic rubber which has been engineered for longevity and heavy use though polyurethane is generally regarded as having better wear and weight-bearing capacities than the rubber equivalents.

Protective Aluminium Corner Ball

Finally as regards capacity and size I done a couple of exercises to determine the must-have qualities and dimensions for the boxes. My first concern was with regards to facilitating my current tools but also having enough space to take any tools which I'm likely to require in the future. Currently the largest tools I own and am likely to own are a pair of sash clamps. These are over a meter in length and are heavy and awkward to carry around. Finding a good place to store these was essential so this helped to determine the minimum dimensions of the largest compartment in the case.

As regards the depth of the cases, there were a few factors accounted to determine this. As I would like to be able to use the top surfaces of the boxes for workspace (more on that in a later post) they needed to be deep enough to be comfortable to use. My rough initial guideline for this was that I could comfortably lean on the surface while reading a from a notebook or sketchpad and also be able to reach to the back of the work surface without moving from this position. This requirement also informed the overall height of the top of the work surface. This helped to roughly determine the depth and height of the case which was later tweaked for other more practical considerations regarding the standard widths of MDF available.

The final factor that determined the dimensions of the case was security. The boxes are going to be built such that once closed they will be relatively secure from outside intrusion. However because the cases are mounted on castors this would be a rather useless feature if it was possible to simply wheel the cases away. I decided to make the overall widths of the case such that it would not fit through a standard width European door frame (800mm) when the case is closed. There are other security features to the case which will come into play when it's being kept in places with larger door openings, as many workshops might have, but again that is a detail for a later post.

So these were the initial determining factors for the construction of the case. This post gives a flavour of the types of research conducted for this phase of the project. At the end of the project I might write up a more comprehensive guide for anyone who wants to undertake a similar project and I'll link to that here if I do. In the mean time a great source of information I found was the youtube video series of tutorials by which are an accessible and informative series of videos that demonstrates very well many of the basics of flight case construction.

John O'Shea

1 comment:

  1. I simply want to tell you that I am new to weblog and definitely liked this blog site. Very likely I’m going to bookmark your blog . You absolutely have wonderful stories. Cheers for sharing with us your blog. nuts and bolts