Securing autopilot sprocket

[ThereAndBack]

I am new to boat auto pilots so please forgive any sort of terminology I get wrong.

I have wheel steering on my catamaran. The steering column or shaft has a sprocket which connects to a chain-to-cable arrangement that then turns the rudders. More forward on the same steering column is where there is supposed to be a sprocket which connects all chain to a motor for the AP.

The problem is this AP sprocket fell off the end of the shaft. I'm not sure what happened the first time except that it worked its way forward on the shaft and fell off.

I inspected the parts and found the shaft has a keyway for a woodruff key cut and the sprocket has a hole drilled for what I assumed was a set screw.

Attempt #1 at repairs was to replace the woodruff key, slide the sprocket onto the shaft and over the key, and then put a cup point set screw into the hole and tighten it down against the shaft.

This repair worked for approx 4 hours before the assembly again worked its way off of the shaft and fell.

I'm wondering if I am doing something wrong or if there is a "right" way to do this. Should I loctite the set screw? Should I use a pin tipped set screw? Should I drill a divet in the shaft if I do? Forgive my ignorance. Please help.

[Sailmonkey]

If the set screw is on the shaft, a divot will help immensely.

Is the sprocket a loose fit? Meaning is it able to wobble slightly once the screw is tight?

Do you have the ability to drill a hole in the end of the shaft to put a screw and washer there to prevent the sprocket from coming off of the shaft?

[ThereAndBack]

Originally Posted by Sailmonkey

If the set screw is on the shaft, a divot will help immensely.

Is the sprocket a loose fit? Meaning is it able to wobble slightly once the screw is tight?

Do you have the ability to drill a hole in the end of the shaft to put a screw and washer there to prevent the sprocket from coming off of the shaft?

The sprocket is not what I would call a "loose" fit, but there is def play in it. It is better once the set screw was tightened.

As far as getting to the end and drilling a hole, I don't believe that is possible unless I disassemble the whole thing and bring it to a machine shop with a proper drill press. The space is very confined and the shaft is stainless, so drilling in place is out of the question.

I might be able to make a divot though and use a set point set screw instead of the cupped screw I attempted.

[Sailmonkey]

With a little play I’d suspect that the sprocket is wobbling a tiny amount while in use and just walking off of the shaft.

I’d do the dimple, and possibly even fit the sprocket with some epoxy inside to remove the loose space. Removals involve heat in the sprocket, but that’s better than it falling off.

[ThereAndBack]

Originally Posted by Sailmonkey

With a little play I’d suspect that the sprocket is wobbling a tiny amount while in use and just walking off of the shaft.

I’d do the dimple, and possibly even fit the sprocket with some epoxy inside to remove the loose space. Removals involve heat in the sprocket, but that’s better than it falling off.

Interesting. I've never done epoxy in that manner. What is the process? Just slather the sprocket inside with JB weld and slide it on? Or West system?

Also, is there a preferred way to create the dimple? Keep in mind space is very limited. I'm guessing a drill but was wondering about a punch and hammer?

[Sailmonkey]

You’ll need to drill it, start with a center punch and hammer to keep the boy from wandering.

I’ve had success with plain old neat epoxy just slathered on the shaft and inside the sprocket. Slide it on, tighten the set screw (generously greased so it can be removed) wipe up the squeeze out and wait for the cure.

Is it ideal? No.

Does it work in a pinch for a relatively low speed not extremely loaded loose fit? Yes.