I like your idea for building-up worn or slightly under sized shaft bearings using soft solder Roy.

This is not a technique that I have ever tried, but it sounds good and is well worth a try,

Next time I have a worn shaft in a model that I don’t have time to remove and replace, I will give this idea a try 👍

My experience with using tubing is mixed.

For very small motors and shafts (10 years.

My experience with Zippkits' coupling, which is made of Tygon type tubing is that it slips or deforms (twists) eve with the ends clamped. Changed to the Dumas "dogbones" on all of my Springers. These work great and will handle some misalignment like champs.

Lew

When buying or making couplings to fit between the motor shaft and the propeller shaft, I aways bought or made each end with any appropriate screw thread to fit the propeller shaft or the crankshaft if they were threaded.

I now realise that using a screw thread at either end of a coupling may not give as good an alignment as a plain accurate bored hole would do.

To get the absolute best alignment I machine a solid bar to the exact length of the coupling to be used when making and fixing my motor mounts to make sure that the motor and shaft are in perfect alignment.

Once all adhesives/resins etc are set and the motor mount is secured the solid alignment bar can be removed and replaced by the coupling.

If the coupling adaptors are bored to fit the motor shaft and the prop shaft they can be secured with a grub screw to the shaft rather than being screwed onto a thread at either end.

A flat can be filed onto the motor shaft and or the prop shaft under the grub screw position to secure it and prevent the shaft slipping inside the coupling.

Your mention of using tubing on the HUCO type coupling adaptors has prompted me to mention my use of the “rubber” gas tubing that is used on outdoor heaters and barbecues etc.
Whether they burn Propane or Butane they all use the same (usually) orange coloured fabric reinforced tube.
This exceptionally strong but slightly flexible tubing (when used in short lengths) is perfect for making couplings from.
Once cut to length and with the chosen adapters pushed in to each end, they can be drilled though and pinned to make a very strong and durable coupling that can handle quite a lot of power.
If a lathe is available it is very easy to make your own adaptors from whatever scrap bar stock comes to hand.

I have also been making and modifying prop shafts since I was at school in the 1960’s.
The propellers were generally 4BA or 2BA back then, but unlike other threads of the day such as Whitworth and BSF etc, the BA threads are actually metric !
When the propeller sizes changed to 4mm and 5 mm I found that they could still be used on the old BA prop shafts using the 5mm props on the 2BA shafts and the 4mm props on the 4BA shafts.
All these years later, I still have some old BA size propellers and never hesitate to use them on any metric sized prop shafts if they are a size I could use.

Hi all I was a bit off piste on another thread but thought this might be better under a new subject.
Some time ago now when I had easy access to a lathe I would make my own up from steel shafts brass tubes and bronze rod, if I could find any. I have to buy like most others now, or cut and fit from my accumulated others.

When you have a selection of prop tubes etc, you will find that they are not always interchangeable as the industry standards for a 4mm shaft vary so that some will not fit into another tubes bearings. If you need to use bearings from one tube in another you can use the shaft to knock out the end bearings and they may well fit into the tube you want use.

It is best to have an electric read out caliper, you have a choice of Imperial or Metric measurement. You will then find that very few shafts are actually 4mm, but usually a few thou under. Many of us older modellers have propellors that were 4BA thread rather than M4 size. Quite often interchangeable, which is OK for the propeller but not if you are screwing on a Huco or the like coupling at the other end. As the slightest angle that they tighten up to will cause vibration.

So what to do? The first thing is to make sure the bearings fit the shaft, if not the bearing can be gently opened with a fine tapered file, I do mean gently. If the shaft will ease in but tightly, then use an abrasive cleaner like Sif to lubricate and turn the shaft until it feels free. When assembled run the shaft give each bearing a tap with a small hammer while spinning and it should get into a final free alignment.

Should the bearing be a loose fit in the tube then apply a film of solder to the bearing allow to cool and insert into a drill and spin up and apply a file to reduce the surface until the required increase in diameter is reached.

It is best to fit a thin washer on to the shaft at the prop end then a 'thin' nut and then the prop. Screw in the nut until it rests against the washer it should be square with the shaft and then screw the prop up to and lock with a spanner. It is best if the washer hole will slide over the thread but not up the shaft.

If there is a rudder in the way and you can get away with a sideways shift of the rudder, then I do this as well to enable the shaft to be withdrawn without releasing the rudder. At the other end same procedure with a washer first this helps to square up the locking nut on the thread and then the coupling part.

Lately I have used the Huco brass parts with some 2mm wall thick tubing as the coupling. It is good to get the coupling end of the tube above the waterline but not essential. Before final fitting of the prop shaft I use a mix of lubricant / seal made up of a third of each of the following. Vaseline, 3 in 1 oil and WD40. Mix it up and you should be able to suck it up into a syringe, then insert end of syringe up the shaft and squeeze in the mixture.

When you have done this then push the prop shaft in but keep your finger on the open end to stop the mixture from coming out and then it will distribute back around the shaft. This mixture idea comes from Ron Dean of Deans Marine. It looks thick but has almost zero drag on the shaft and keeps the water out.

The silicon tubing works for drive motors go up to about 40 watts, I often glue the motors in place using clear bathroom sealant. It is quite strong enough and will absorb any small vibration there may be. It can be peeled off at a later date without problem.

As an aside, on a vintage open frame motor I had, I decided to give the motor some bearings as the frame was just very thin ally. I used some interlocking brass tubing for the bearings, and soldered them together about 3 tubes altogether with a suitable washer as a stop.

I cut brass tubing with a Stanley knife just rolling it as the knife cuts in, but remember to run a wire inside the tubing so the small piece does not fly off. The ally on the motor was opened up to receive the 'bearing', and same at the other end and it all worked very well.

I think next time I need a bearing for a prop shaft I will use the interlocking brass tubes as it is so easy make and replace.
Roy