Of course Doug concave is even better, sorry if I didn't notice.
The important thing is that it is not convex because it slips away.
I only flattened it because all I needed was a file, to make the hollow in the grub screw I would have had to have a column drill. I didn't have the patience to wait and have a friend do it for me.
Of course I should have done like you, it's better.

Alessandro,
Re "the point of contact with the grub screw is flat".
Actually if you look closely you will probably find that the end is concave.
Some have conical ends, i.e. pointed for locking into softer materials.
Doug😎

All's well that ends well Chris🤞
But I think a thread sealer like Loctite (probably the best known type) would be better than Araldite. That just sits on top and could crack off. A thin thread sealer creeps into the thread (like capillary action) and locks it.
If you really won't have any access to the tiller in future you should consider Ross' 'belt and braces' solution of drilling the rudder stock and fitting a bolt and lock nut. WITH Loctite😉
Looking forward to seeing the finished vessel (?) in action.
All the best, Doug😎

Hi ChrisG.

Your problem allowed me to see other very interesting solutions.
Thanks for sharing.
I used the system, which Doug tackles in an absolutely professional manner, for the engine shaft.
In fact the point of contact with the grub screw is flat.
However, reading you makes me wonder whether I would have been better off using thread locking glue (loctite).

Hello Alessandro
Your understanding of my problem is excellent as is your ability to understand mine and other problems posted on this website. Your ability through translation to comprehend our ramblings and confused chatter is to be congratulated.
Whilst I agree that it is good to be able to access all moving parts and electrical components in our builds it is not always possible, I try to build every part that will be difficult to access after completion with as much strength and longevity as is possible and an element of 🤞fingers crossed.
With help from other friends on MBW I am now happy with the steering on my build but will continue to look forward to yours and others help and suggestion as my build progresses.
Thanks and best regards ChrisG

Hi ChrisG.
With the advice of ColinH and Doug I finally understood your problem.
Doug's last sentences especially made me focus on the issue.
At first I thought something was preventing your movement (a disastrous translation).
In my opinion Colin and Doug's advice is perfect.
I'll tell you my opinion on this but, as often happens to me, it's just to make you aware of another solution and tell you how I did it.
I myself doubt many of my choices, so I tell you this only to broaden the possibilities available to you.
First of all, in my opinion, in an RC model, every part (element that can break or deteriorate) must be able to be reached. Maybe you can't do anything about it anymore. In this case, patience and let's get to the problem of the arm.
Now I understand that you are afraid that the kinetic chain between the servomechanism and the rudder will be interrupted (due to the loosening of the screws) so you were looking for the best solution to tighten the arm.
To overcome this problem some time ago I used a single piece of harmonic steel that was inserted into the holes in the rudder and in those of the servo.
The steel rod never comes off if properly shaped, it has no grains that loosen and absorbs small impacts quite well.

Thank you all for the help. I have filed a flat in the rudder post, scrapped the grub screw for something man enough for a screwdriver, put it all back together and save for a few minor finishing bits I now have a robust steering system that I will be confident with after putting the lid on the hull.
All the best ChrisG

Thank you Lew,
The servo and the connecting parts are Futaba and I believe the grub screw to be 2mm, the allen key I keep dropping into the bilges is definitely 2mm. I am awaiting the delivery of the grub screws, various, before attempting anything more radical.
Your recommendations are gratefully received and if not used now will be remembered for the future and I thank you for them.
I cannot remember any time in the past having trouble sorting the steering it is usually the one of the more straightforward parts of the build. This is probably due to me straying so far from the original kit hull.
It is very good though to know that you are not alone and have so many knowledgeable friends on line prepared to help and advise and I thank you all.
Best regards ChrisG

ChrisG,

I'm not sure if the UK is 100% metric. Here in the US I bought "set" screws in imperial sizes from Amazon as it seems the majority of these accessories is that. I don't know what you are using as the control arm (bell crank), so I can't recommend a specific screw.

Often you don't need a set/grub screw as a regular head screw will work. In fact I use a regular (round/pan) head screw if the control are is in a difficult place and need a long shaft screwdriver to tighten in screw.

As for the mechanism between the servo much of these parts are the same as used in RC planes and some vehicles.

Some tips:
►If your control wire is too long and flexible you can stiffen it.
►If your control arm slips you can get it as close as possible and file a small flat where the screw aligns to the rudder shaft.
►Lube the rudder post and shaft like your stuffing box. (I use petroleum jelly).

And finally, you are not wasting anyone's time here! Ask away.

Lew
Florida 💡, USA

Very impressive workshop Doug, I am an envious fellow modeller. Thanks for the advice regards ChrisG