Gravity is a natural phenomenon affecting everything on the planet we live. There’s no getting by it, we can only adjust our lives to cope with it.
Most often we do that without thinking, sometimes we need to be prepared.
Gravity is the original force of nature and, believe it or not, we should also consider this force when mounting equipment to wheelchairs.
The length of angled vertical poles on Mount Kits is one such consideration. It’s worth thinking about the forces that will come into play over time on the frame clamp assembly holding the vertical pole in place. The longer the pole, and the greater the angle away from pointing straight up, the greater the force directed at the parts of the frame clamp assembly. The weight of the device is also a factor and contributes to these forces.
The standard length of tubing for vertical supports suppled in most DAESSY Kits is 22” or approximately 56cm (24” or 61 cm in Rear Folding Mounts). These lengths are appropriate for most mounting situation, but what happens when a longer vertical pole is needed? Cases like this may happen when eye-gaze systems are in use of when the Frame Clamp Assembly is attached to the very bottom of the wheelchair frame.
The pole itself is held in place by the parts of this Frame Clamp Assembly. These parts that consist of a Frame Clamp Inner piece (the part that clamps to the chair) and a Frame Clamp Outer Piece (that holds the pole). Sometimes there’s a part or two in between the Inner and Outer Piece, like Offset Links, or a removable component like in the case of the Removable Frame Clamp variants where there’s a lock mechanism added to the Inner Piece. Never the less, all these standard options bind together using a unique and ingenious system.
To create a binding join, the adjoining faces of all the parts for a Frame Clamp Assembly have circular grooves to give extra friction against movement when assembled. The grooves on an Inner Piece engage with the grooves on an Outer Piece and when drawn together lock the Frame Clamp Assembly into place. The mechanism drawing these parts together creating the bind is the Swivel Clamp which runs through the centre of the parts. It consists of two halves; an unthreaded head and a threaded nut end and two 2.5cm bolts.
When the Swivel Clamp is tightened, the two halves, one the Frame Clamp Inner Piece, one in the Outer Piece, engage the circular grooves into each other and created the bind that holds you vertical pole in place. Very smart engineering. That also means the groves and Swivel Clamp is the central mechanical force holding your vertical pole at it’s angle and it’s the bolts in the swivel clamp that take the majority of the force that gravity imparts.
Parts With Teeth
When the vertical pole becomes longer, past 26” and the mounted device is of significant weight the stress on the swivel clamp holding a Frame Clamp Assembly together is magnified. It’s not critical at this point, the mount kit is not going to fail as these parts and components are engineered to the highest strength. Over time, it’s more than likely that bolts will need to be replaced, swivel clamps inspected more often, Frame Clamp Assemblies check on a more regular basis.
There is, however, a way to strengthen the DAESSY Frame Clamp Assembly such that these risks are alleviated and longer poles used without compromised. These parts have the moniker “Angle-Lock” and instead of circular grooves, they have teeth.
They replace their regular, circle grooved counter-parts and are installed in the same manner, you may not even recognise they are there once installed. The Inner Piece Adapter is replaced by an Angle-Lock Inner Pieces and is used with with Side Mount Clamps and Multi-Hole Adapters. The Removable Frame Clamp Receiver is replaced with the Angle-Lock Removable Frame Clamp Receivers and attaches in the same way as regular RFCRs, but this time to the Angle-Lock Inner Piece Adapter. There are also alternatives to the DAESSY Offset Links, called Angle-Lock Extender Links.
Rather than using the grooved circles, these pieces have tapered “teeth” giving a better bite when locked in place with the Swivel Clamp. It is nigh on impossible to rotate these pieces without disengaging the “teeth” and over time will provide less stress on the swivel clamp, the teeth spread the load around.
They don’t give you the rotation freedom the circle grooves do but the spacings aren’t too bad and we think you’ll still manage to find appropriate angles for correct positioning.
If you’ve after additional strength in your DAESSY kit to give you peace of mind with that really long pole holding that heavy AAC device then there is no question about it, these Angle-Lock parts are a must-have inclusion.