|Topic Review (Newest First)|
|06-03-2008 05:35 AM|
The term "fret" is used to describe the steady build-up of play from very small clearances to noticeable play. It is normaly a problem for splined shafts delivering power where the lubrication cannot be assured all the time. The clearance gradually enlarges with time. I heard the term to describe the build-up of play in a BMW motorcycle final drive shaft, so I used it. It is not dissimilar.
I trust that a new key will help. It cannot worsen it, for sure.
A stepped key, properly radiused is a possibility. They are not universally popular as the step is a weakness. Still, if it avoids dropping the rudder post, it will be welcome.
I wonder is the shaft solid section? I trust it is? If so, if I have to, I will grind two flats on the shaft (slowly), change the steering head to thick walled steel, and put two of the most enormous bolts in there to lock it, and fit a new key. I am not dropping that rudder post unless I have to, and I will over-engineer a steel (or stainless) rudder head before I have to drop the post. I simply cannot face that one, as yet.
I will measure up for the fitting of a big torque arm on the rudder shaft too. I really need to have some aux steering capability. I can send a man below to operate it, using a pitch-fork handle and shaft or something similar....just enough to be able to control the ship. I plan to cut a wee aperture for the handle and a wee inspection hatch to be able to connect it quickly. It sounds a reasonable project.
|06-03-2008 01:04 AM|
I would think the key being bronze will hopefully have absorbed most of the wear and replacing it will restore to a tight fit. As you know the only way to find out is to remove it and take your lumps. If the rudder shaft keyway is OK but there is wear in the head you might be able to have the heads' keyway enlarged and use a step key. If the post is worn; well, you know what needs to be done in that case.
Good luck, John
|06-03-2008 12:50 AM|
I am having a problem with the term "fret".
I am guessing the box drops down over the rudder shaft after the cover is removed and mount to the hull unbolted. You migh want to put a hose clamp around the rudder shaft to keep the housing from going down to far.
You may have to rotate the wheel to get the gears to release.
I bet just replacing the key with a new one will take the play away. If not all then look for shims on both sides of the pinion gear. Since the gears are captured once the cover is in place I see no need for bigger set screws.
|06-02-2008 03:18 PM|
There is no problem (yet) getting the steering head off the rudder post. It is loose on there at present as it rotates a little before the key stops it and so it's able to turn the rudder post. If it were jammed on there I would see no play.
The problem I forsee is trying to get a new key to fit such that there is no circumferential play in there, or very little. Things are going to be worn on the shaft and on the rudder head, methinks.
What I cannot figure is why the designer thought that it would not fret on there? If it is a sliding fit to start with, it must have had a clearance, and even with bigger lock studs, it would fret and so the clearances build with time?
|06-02-2008 12:58 PM|
Originally Posted by Freesail99 View Post
|06-02-2008 12:08 PM|
I am fairly confident that the rudder head flange will come off. I was more concerned about getting it back on there so that it does not fret again. You can see the steering head at the top of the rudder post here....
Image of WK Union 36 worm-gear steering - Photobucket - Video and Image Hosting
This fretting is an old (albeit high-speed) problem on motorcycle shaft drives, and it is not easy to stop it wearing worse without constant re-greasing.
It puzzles me, as on the prop shaft of the ship, there is no way that flange is going to fret on there... it is rock solid with a big lock bolt on it.
I guess this is the penalty paid for the steering head flange going on there easily in situ at time of assembly... it never is quite locked in service, as there must be assembly clearances, and fretting breeds more fretting, it seems.
It is getting slowly worse, and it eats at your confidence.
I really cannot lose steering on that ship, as I will not be able to hold her without that rudder, and there is no aux steering facility...
Image of Crinan Canal Summer 2007 - Photobucket - Video and Image Hosting
|06-02-2008 10:22 AM|
|Freesail99||While I can offer no help to your problem, I feel your pain. I spent 4 hours trying to remove the nut on the rudder shaft. I even put a pipe on the wrench handle and bent the pipe. Nut is still on.....|
|06-02-2008 10:11 AM|
steering head keyway play...
The steering on my ship... a Union 36... is a worm gear design.
On the top of the long rudderr post is a big flange... we have called it the "steering head" A circumferential (rotation angle) play has developed between the head and the rudder post.
The steering head is bronze, and uncorroded.
The steering head is keyed to the shaft with what appears to be a bronze key... it is not easy to see.
There are also two very small grub screws... very small indeed... that seem to help hold the steering head to the rudder post, a little.
I am hoping that the key is worn, and not too much the shaft, though I am ready for disappointment.
I cannot get the rudder shaft out of there without a sanity check.
Has anyone faced this situation?
I have spoken to two very helpful boaties, and they recommend a new key, at least. One of them is confident that he can machine a slightly wider key, after I furnish him with the dimensions. He plans also to beef up the wee locking screws to something a bit more substantial, in stainless.
I plan to measure with a Vernier, and to take a paper rubbing of the key with oily hands... that one works sometimes.
Next task is to strip the steering head off there. The compartment is very cramped. I will crick my backbone out of joint, I am sure, again.
The vast majority of the steering play is at that interface, so I hope I can improve it somewhat. The ship has no reserve steering position. Maybe I will fit a below deck tiller arm on there too, while I am below.