This is a mod for the wind restraint system on the Ti Pro dome. The cables keep the middle shutter (which uses gravity only to stay on the dome unless in the fully closed position in which case it is locked in) in place during windy conditions during a close. I say during a close as you should not be opening the dome if its too windy. Sometimes wind does kick up during the night and the weather sensor (Boltwood, SkyAlert, AAG CloudWatcher) initiates the shut down command. The wind restraint does its job well but over the years we’ve had some issues as it wears.
What happens is as the shutter is opened and closed over many nights the cables eat in to the aluminum cable guides. Here is a image of the cable guides with cable doing their thing.
After a few hundred open / close cycles you can get wear on the guides from the cable dragging over them. There is no pressure as the cables are loose but the open / close action of the aluminum guides with the cable running through them as the shutter moves wears out a small channel in the guide as seen here.
If the cable happens to catch in the worn out channel on shutter close you can, depending on which shutter control you have, either snap a cable (new shutter control as of 2014) or pull (stretch) the close spring (right side front, looking in from home position) and rat nest the windlass screw on the old system. Here are before and after images of the spring on the old style windlass system.
Here is the close spring on the old windlass system in good condition.
This is a the result of the wind restraint catching and the close spring stretching.
On the new system the (one of two) cable snaps but the shutter still gets closed however on the old system once the spring is 4+ feet long (see image above) the windlass lose its tension and you get the rat nest with the shutter stuck about a foot from closed. Not good if you are remote and a long way away. Replacing the guides with regular maintenance works for the most part but we’ve been caught out with both shutter systems when it seemed we had a few months to go before guide replacement was required on the domes.
The mod is (at least for our domes) to use Polyurethane tubing and replace the guides with snug fit clamps. In our testing it will take many years for the cable to wear through the tubing if it ever does.
The clamps are 1/4″ ID and fit the tubing snugly. Going bigger does not seem to be an issue, 1/2″ or 5/8″ ID would be good as well (with the appropriate OD tubing). The clamps run a bit closer to the shutter lip but there is plenty of clearance and so far it is running smoothly.
This is 1/4″ OD x 5/32 ID Polyurethane tubing in white, very flexible and can handle -40 F ~ 160 F temps so weather should not be a problem.
Here is the shutter all together with the wind restraint mod.