EdW.... Thanks for the input.. I use these in many places on my Helicopters for 'Thrust Relief'.. I am going give the Bronze loaded PTFE bushes a try, as I think they will work behind the prop underwater.. If they fail I'll try the ball type of thrust bearing on the 'dry' end of the tube!

EDIT..
I wondering now how any Bearing would manage in the muddy environment at the end of a Boat Propshaft. Maybe as EdW suggests any Thrust Bearing will have to be mounted inboard!

DG

@DGoss999 I have used thrust bearings like these before and found then to work well but I put them at the motor end of the prop shaft.

https://www.gearsandsprockets.co.uk/miniature-thrust-model-bearings/

I am planning on making a set of small Bronze loaded PTFE thrust bushes for the Prop end of the propshaft. One will be a tight fit on the propshaft, the other will be shouldered to fit pressed onto the end of the shaft outer tube. I'll follow up with how this work out!!

DG

Hi Rodc I do not think the post has wandered off as the side issues even in this case have all been a talking point We have a machinists 'how to' and several members have used things to hand like the many sizes of brass tubing available.

There were more than a few makers of steam engines back then (?!). Most drilled holes at 1/2 inch intervals, even Marklin (Germany) made the equivalent of Meccano and kept the same hole spacing so it was a small marketing point for a steam engine to be compatible with other associated toys.

Lucky you, to have your set of Meccano set incremented each year, my presents were a Meccano set (a guaranteed success with me) but the number of the set was random and mostly an A set!

I also belong to a Meccano club as I love to see and smell the models and they are frequently very complex. An old type No. 10 set is a starter set, I asked how much was in a Block setting crane with a 12 foot long jib. The answer was about £4000 ( yes four thousand) of Meccano.

If any of you saw the Paddington Bear film with the Meccano fairground rides in, they were made by a friend of mine in the club. He comes up with enormous model Fairground rides 5+ feet high with flashing lights and with many moving parts.

Having a Meccano set as a child must have produced many engineers later on.
Regards
Roy

Phosphor bronze is the best bearing material however brass is adequate for the amount of side pressure that is made with a shaft and a brass bearing of about .250" (6.35mm) in length x 2 (one at each end).
Silver Steel BS1407 Tolerance for diameters less than 1" are ± 0.00025" on nominal diameter.
So measure your stock bar and go for a clearance for a plain bearing fit of
Minimum 0.0010" = 0.0254mm
Maximum 0.0015" = 0.0381mm.

In terms of producing this "FIT" its best achieved by drilling 0.0010" smaller than required size and then reaming (without coolant)
Reamers can be made to produce plus or minus from their stated size but this is something only an experienced engineer would be able to do.
So If you are using only drills, first drill about 0.015" smaller and then with the finished size. If a test drilling produces a hole oversize then again a drill can be made to drill smaller by touching the outer points with an oilstone to slightly blunt the cutting edge, we are however talking a small amount say 0.0005" to 0.001".
Finally lubrication is essential so an oiling tube should be fitted of greased on a regular basis.

roycv i had the real Meccano back in the mid-1950s. I used to receive an "upgrade set" each Christmas. By 1965 i had the highest complexity grade+i had been gifted 2 clockwork motors. I never had an electric motor altho my parents did gift me a stationary steam engine whose bolt-hole pattern matched Meccano ( I dont recall the mfgr but it was NOT Mamod or Wilesco(?) ). Ran it dry & the boiler leaked afterwards so then i put a piece of aquarium hose between a propane torch pipe & the steampipe & ran it on propane vapour a few times until it finally seized up. But i digress. Sorry for hyjacking this thread😔

Rogal118: You asked a simple (but very good) question. I hope in all these words you are able to figure out how much clearance you need between your shaft and tube.

Lew
Florida 😮, USA

Hello Rod, Meccano is a bit of a generic name now. But I have a confession to make as I have a Meccano set still.

As I said the only similar open frame motor was with Trix. But after a working visit to the Nuremberg Toy Trade Show in the '90's I was amazed at how many different construction sets there were around the world.

The Meccano electric motors like the E20R are from very old designs I have the original design, my one from 1940, for the E20R which is called an E120 and after a little work it now works very nicely.

Regards
Roy

Reminds me of a meccano set

Hi again, the last bearing job was on an electric motor a few years ago. It is an old style type motor, but new, this one was part of an obscure Indian toy construction set.

In this case there were no bearings at all. The shaft spins in a plain ally side support for the motor. I made a bearing and found some brass tubing to fit and some more to fit over that and a light soldering holds them together. There was about an inch to make both bearings. I soldered a tight fitting washer to an end.

I used a tapered reemer to slowly open up the existing bare hole. The bearing was a tight fit and then cut to size. I made the other and fitted the 2nd. one. When all bolted together again and some power applied I knocked the 2 bearings to get them to settle, cleaned the area and applied some superglue.

The motors ( I have 2 ) are surprisingly powerful not like the Trix similar motors, this one is driving some Mamod 'toys' and is to entertain the young and not so young at our club exhibition.

You can see the multi-tube bearing with the brass washer showing.

The silver frame motor is as original but a friend fitted bearings for me. I have seen this same motor in an early (1947) GB model boat, so it's antecedents are a bit puzzling.

Regards
Roy

Hi Rogal and good morning everyone.

I was translating my message when I read Colin's.


Indeed, if there is the possibility of using bronze I would follow Colin's advice.
I know the characteristics of the two alloys: bronze and brass and I would be really tempted to try bronze in this circumstance.
I really like the characteristics of brass but I didn't consider bronze just for commercial reasons.
In fact, brass profiles and rods of various lengths and sizes can be found in many shops and are very easy to find.
Bronze is much less easy to find (at least in Italy), in fact I have never found it in the shops where I bought copper, steel, brass and aluminium.

Having said this, let's move on to Rogal's specific question.
I used various tricks.
In the model I'm working on now, I didn't use complete propeller shafts because the ones on the market weren't the right length.

If you want to see how I built it you can see this post:
I'll insert it last, otherwise it will cut the post.

To briefly summarize, I'll tell you that I used: a brass axis (rod) approximately 4 mm thick, three microbearings approximately 4 mm thick internally and approximately 8 mm externally.
Brass spacers with an external diameter of approximately 8 mm and an aluminum tube with an internal diameter of 8 mm and an external diameter of 10 mm.
I had to sand and file the pieces a little to fit them because the measurements are not very precise.

With three bearings inside the aluminum tube it is impossible for water to pass through. Especially if you consider that: axle, bearings and spacers are immersed in lubricating grease.

However, I was interested in ensuring that the water did not even reach the first bearing (i.e. the one closest to the axle exit hole) so as not to ruin it.
To prevent the water from reaching the bearing, entering the aluminum tube through the hole, I placed a plastic cap at the end of the tube glued to it and painted (also for aesthetic reasons).

This cap was pierced to allow the 4 mm diameter brass shaft (rod) of the propeller to pass through.
Sorry Rogal but I didn't take any measurements; the hole is made by eye using a 4 mm drill bit.
Even though it was done by eye, the hole was perfectly adherent but with very little friction. It doesn't slow down the rotation of the axis at all.
This is because I first created a very narrow hole and then gradually widened it in small steps.
Always testing how the axis rotated and never taking a measurement.

I really like the fact that you want to be so precise but, even when taking very precise measurements, the drill always overhangs a little more than expected and wanted.
I speak for myself as I have terrible tools and work at home (I don't have a laboratory dedicated to this hobby).
In short, even today I would recommend making a very narrow hole (a lot of friction) and, only then, widening it with abrasive paper or other methods until you obtain a minimum space between the axis and the hole with very little or almost no friction.


I usually also adopt this caution (in this case completely superfluous):
I put a little soap (or grease) on the brass axle near the hole (just outside the hole).
At that point I apply a little (very little, almost not visible) of silicone which, once dry, will not adhere to the brass axis due to the soap.
This trick will prevent water from entering but after some navigation it is better to remove the old silicone and put a new one back on.

I can suggest other methods that I just thought about but never implemented because the cap was more than enough.
I report them here just for information, maybe someone will want to try them to experiment. Mind you, I haven't used them.

1. A syringe (without needle) filled with grease can be attached at one end to the tube that introduces the grease into the axle case. If you ensure that the syringe plunger is always under pressure (for example by using simple rubber bands) the internal pressure of the grease will prevent the water from entering. The pressure will not be too much to cause the fat to come out.

2. For this other method a metal or alloy cap must be used.
The axle slides into the hole of the same diameter as the axle for a length of at least 1 cm.
In this centimeter the axis will be threaded but the hole will not.
At the beginning it will have to be a lot of friction; then you will have to turn it specifically to wear out the thread so that it adheres perfectly but almost without any friction.
The trick is in the direction of the thread.
To understand, think of the Archimedes screw that lets the water out of the hold.
I repeat, the tube in which the thread of the brass axle runs must not be threaded but rather smooth.
If it's not clear, tell me and I'll attach a drawing.
This method is very experimental; After thinking about it I was going to try it but then I gave up.
The drawback is that in the long run the metal or alloy tube in which the threaded axis rotates could widen too much.

But I repeat, if the hole is well adherent and greased, no water should enter. No water enters me.

https://model-boats.com/forum/128542#128947

I find using a reamer and then lapping in with a piece of the shaft material works best. That way you get a perfect seal between the bush and the shaft. I use stainless steel for the tube, bronze for the bushes and silver steel for the shaft.
Just remember to clean completely after lapping.😁

May I suggest that you carefully measure the 4mm shaft as it seems a bit variable, as does 1/8th shaft diameter.

I was trying to use existing bearings and move them to other prop tubes, which did not work. I also found that the prop tube wall thickness varies as well.

If you drill a slightly smaller hole and then open it up with an exact fit drill you may well get a different diameter hole than drilling with the latter size drill first.

I have 'cheated' a bit with other (motor) bearings and used brass interlocking tubing that fitted. Seems to take the wear with suitable lubrication and replacement bearing tube easy to replace, but none have worn yet.

However if you can make bearings on a lathe you might as well make the tube, shaft, plus or minus threading and bearings yourself.

If you do thread the shaft yourself make for a tight fit to the prop or U/J. You can always run it through the die again taking a tiny bit more off.

Good luck
Roy

Good morning, I wouldn't want to use brass, I would go for bronze as it is far better wearing. But when drilling I like a 5thou clearance. Cheers Colin.

What Lew said. That is the method I use and it works very well.
I might note that I use a syringe filled with grease to inject it into the filler tube.
Barry

Although it has been said "There isn't really a difference: a bushing is a type of bearing. In general, a “bearing” facilitates movement between two parts while reducing friction. Simple in design, the typical bearing has two surfaces that roll over each other, enabling two mating components to move friction-lessly."

So I like to use the word bushing indicating two close fit surfaces, usually one fixed and the other moving. As for bearing, I think of one moving surface and the other consisting of multiple parts as in ball, roller..., type bearings.

These definitions are not cast in stone but I use them for simplicity and clarity in getting points across. Just my preferences.

I use off the shelf tubing from K & S. Fortunately (perhaps one of the very few good reasons for Imperial measure) the tubing and solid diameters fit well into the next size "giving a slip fit".

So making my stuffing boxes with shafts is pretty easy and works great.

As for your issue I don't think you want a tight fit. Using a slip fit with sufficient sealing grease or whatever you use (I use petroleum jelly) will do the sealing job. The 4mm equates to .1575 inch. In checking my "inch" tubing I found the marking on the containers indicating the wall thickness of the tubing to be .014 inch. The incremental difference between the next size tubing is .015625 (1/64) inch. so that makes about .0016 inch difference around the outside of an inner tube and the inside of the outer tube.

Double this (.0016 inch X 2 = .0032 inch) for the difference you would need in clearance on the diameter. So a good answer is probably .0032 inch or .081mm. Without going through all sorts of calculations, this seems to work fine for me. Just make sure everything is straight.

Lew
Florida ☀️🚤, USA