• The Genesis of the National Gallery Case Roller

    Submitted by Mark Slattery
    Originally published 1/15/09

    One of the perennial problems for preparators in the museum and gallery context is the repeated flatting and raising of picture containers many of which can have considerable heft. At the National Gallery, London, we routinely used to place foam blocks on the floor and manually lower the containers onto these pads. Depending on size and weight, additional staff would be required to ‘foot’ the container to avoid it slipping out at the bottom as the case tilts. Typically, these operations will tie-up five technicians and result in sore backs for all concerned. The repeated raising of the cases and the lifting of the lids from close to floor height takes its toll on the backs of the staff; who will by the end of a shift, be complaining of muscle strain and tiredness.

    We felt that we needed to protect staff against this risk and started looking at ways we could semi-mechanise this operation. Some obvious solutions were quickly dismissed as too cumbersome, for example the use of a gantry with chains. It was felt that the use of heavy rigging equipment alongside and over paintings was incompatible with museum best practise.

    For some time, we had considered the use of sturdy wooden boxes at each corner as supports for the flatted containers in order to raise the level of the container, thus easing the removal of its lid and contents. This measure in itself presented its own handling difficulties as the case would have to be handled from both top and bottom and effectively lifted onto these platforms.

    There was also the risk of instability and the case toppling during the removal of the lid or the contents, but this principle was also considered to be a prerequisite of part of the functionality of any new piece of equipment. The desire was to deliver flatted cases at a height that was optimal for ease of lifting, after casting around our team of technicians for ideas, one concept emerged as worthy of investigation.

    The Proto Roller

    The principle of levers as most of will be only too well aware, is the spreading of an input in the form of effort exerted at one end of the lever to deliver a much greater effect at the other end. This is achieved by increasing the distance through which the lever moves at one end in order to see the desired, smaller degree of movement at the other. Thus the input at one end is more progressively applied and the relatively small effort is spread out over a great distance resulting in a far greater force exerted at the blunt end. The point at which this force is transferred from the lever to the object is called the fulcrum. That is the point where the forces are converted into progressive motive force. It is the point at which all the combined forces of the effort at one end of the lever, the weight of the object to be moved and of course the weight of the lever itself, lets call it a ‘J’ Bar for arguments sake; comes to bear. This will usually be the floor. As some of will know, this operation is best avoided on unprotected tongue and groove flooring as the combined forces can easily add up to several hundred pounds per square inch.

    Lightweight all welded aluminum case roller

    This fulcrum can rotate and even move if we so desire. Sack barrows rely on at least two wheels not only to transport heavy loads but also to act as a fulcrum when the barrow is laid on its back. It is this principle which was adopted as the basis of the design of the Case Roller.

    Heavy Case Roller flatting a large container. Aluminium construction with sub-assemblies.

    The aim was to develop a tool which could be easily moved about the gallery, had no moving parts to break or get lost and would be optimised for the best results both in terms of ease of operation and final resting height of the cases. A simple drawing outlining the basic shape and dimensions was transferred to a timber prototype. This was then used to establish the actual leverage effect on test cases and the optimum height for the cases to be delivered to for servicing of their lids and contents.

    Lifting the container and roller to raise the undercarriage.

    Inevitably, this involved a degree of compromise. If we had all been 6’ plus in our stocking feet, the diameter of the cam we chose would have been larger than we finally settled at, thus alleviating a greater degree of effort in the lowering and raising phases. The determining factor was the horizontal resting height of the case. Since we had an in-house team of technicians ranging in height from 5’ 3” up to 6’ 2” that height was determined to be just under 24 inches.

    Removing the cam extensions (Prime Ribs).

    Another factor which determined the diameter and therefore the height of the tool was its astonishing effectiveness. Small to medium sized containers, depending on their weight and height would sometimes perfectly counterbalance the weight of the tool, and so rock back and forth like an easy chair. We would have to push the roller down then drag the case towards the top of the lever to stop them from rising back up again by themselves! It was during this development programme that we realised that one tool would not suit all sizes. We would have to look at two versions to service our needs, one for small to medium size picture containers and one for the real whoppers.

    Retracting the extendable prop arms

    We had already established that the leverage effect we could achieve was considerable over the sorts of distances that we were working to. By increasing the diameter of the cam by just a few inches; the mechanical benefit increases almost exponentially. To this end, we conceived of a much larger version that would be capable of lowering much bigger containers. This was achieved through adopting a similar design to the first all welded construction with no moving parts to a more complex structure with collapsible legs and removable additions to the cams which increases the diameter for larger, taller cases.

    The working method for this device was different insofar as the height that the cases were delivered to was impractical for lid removal. With the case lowered, the lid was around chest height. In order to overcome this, the roller was made with extendable legs and removable cam extensions. Once the case had been flatted the entire ensemble is lifted just clear of the floor using two stackers. The extendable legs are retracted and the cam extensions are removed. The roller with the case on board is then lowered back to the floor and the stackers wheeled away leaving the case at a more workable height.

    Since we adopted this method of handling picture containers four years ago we have had many other parties interested in the Case Roller. We have supplied drawings to colleagues here in the UK and overseas, notably the national Gallery of Sweden, Stockholm. They in turn, have recently passed the drawings onto colleagues in Holland, where the Van Gogh Museum have recently taken delivery of their own Roller, so it is spreading across the museum world along with its manifest benefits.

    The Case Roller is of course not a unique tool as we have discovered through looking for similar devices. We have subsequently discovered that some sound mixing equipment manufacturer fit a portable sound desk into a flight container that has a radiused side, thus enabling it to be stood upright for transport. The same principle is applied to a specialist tool for the transport and flatting of upright pianos. Often it is the simplest solutions that are the best and most reliable. No one is aiming to re-invent the wheel but the more things we can attach them to the smoother things will run.

    Mark Slattery