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[NoNuFink]

I seek enlightenment.
For a model boat - say up to about 3ft long and not intended for racing but maybe scale(ish) speed for a fast launch or an MTB & electric power, what is the best material for the bearings? I suspect that Stainless ball races is overkill and plastic of some sort is underkill (Is that a word?). Phosphor bronze? Gunmetal?

Suggestions and reasons appreciated.

NNF

[morley bill 1]

Hi I allways use brass Bill.......

[Andyn]

PTFE is perfect, goes nicely with PTFE grease, too.

[Martin (Admin)]

Oo! Good question NNF!

What size shaft will you be using? M4?

I seek enlightenment.
For a model boat - say up to about 3ft long and not intended for racing but maybe scale(ish) speed for a fast launch or an MTB & electric power, what is the best material for the bearings? I suspect that Stainless ball races is overkill and plastic of some sort is underkill (Is that a word?). Phosphor bronze? Gunmetal?

Suggestions and reasons appreciated.

NNF

[Peter Fitness]

I have used brass but I also acquired a small bronze rod of the right diameter, so I use that too. Both work well for me. I make my own prop tube assemblies, and turn the brass or bronze in my lathe so it's a tight fit inside the tube.


Peter.

[NoNuFink]

@Hairy Andy
Don't I remember that PTFE is a bit dodgy when it comes to machining?

@Martin
Yes probably M4

@ Peter Fitness
Do you use any method to retain the bearing or is it only a tight fit?

Cheers all  NNF

[PICKETBOAT]

NNF


For scale models spinning props up to reasonably fast speeds (think MTB), bronze is best.


Here is something to think about.
With very basic models (think simple hull with little deck detail) it is possible to flip the model over on the bench and using a metal rod, hammer out worn, leaking and noisy bearings and replace them. This is not possible if the scale model has a mass of delicate deck detail. For this reason I aim to fit one stern tube and bearings to last the life of the model.
If you build models and sail them once before relegating them to the mantle piece, stern tube lubrication is not a big issue. If you intend on clocking up a lot of nautical miles then it is essential. The bearings soon wear oval and start letting in water. Packing the stern tube full of grease is not a good move. Bridging the space between the shaft and the inside of the tube causes drag and wastes engine power. Grease also has a tendency to dry up if the model is not used for some time and eventually has to be cleaned out .
Fit some sort of stern tube lubrication and use oil as a lubricant. Try replacing the washers at the ends of the shaft with the hard red fibre type. These absorb oil, "bed in" and form a good low friction seal avoiding a big oil slick astern.


Good question by the way and something I never thought about when I built my first model.         

[Martin (Admin)]

 
Why do Nylon bearings wear less than the steel shaft it bears?

[TailUK]

Nylon falls into the group of plastics that are known as "self lubricating" this makes it perfect for gears and bearings.  It also remains stable at high temperature.  It something that happens on a molecular level.

[Jerry Hill]

Nylon absorbs water and swells, so fine if there's a clearance to start with, Delrin is better for me. I use leaded bronze and waterproof grease on high load or high speed stuff with a biodegradable oil lube on a total loss system. Just alternatives for thought really.

[Guy Bagley]

I HAVE USED ACETAL WITH NOPROBLEMS

[TailUK]

Delrin is DuPont's trade name for Acetal or Acetal Homopolymer resin to give it it's proper name.

Nylon does swell when wet but by a predictable rate which means it can be allowed for when tolerencing parts.  Acetal works better but a denser material would be preferable Phos Bronze or even Australian Iron Wood or Central American Lignum Vitae which were both used for full shaft bearings.

[PICKETBOAT]

I used to know an old model boater, building models on a tight budget (ie a state pension). He always used the little flip tops off the Fairy Liquid washing up bottles. He hammered them into the ends of the brass tube and carefully reamed them out to take the shaft. Worked fine and non of his models sank, I think?   

[TailUK]

I used to know an old model boater, building models on a tight budget (ie a state pension). He always used the little flip tops off the Fairy Liquid washing up bottles. He hammered them into the ends of the brass tube and carefully reamed them out to take the shaft. Worked fine and non of his models sank, I think?

That's a good one.  They would be some kind of polyethylene or polypropylene and would work very well. Could be very good with smaller shafts like 2mm or Krishna's favourite, bicycle spokes.   I'm going to give that one a try!

[ballastanksian]

Hm, Tinking of replacing my cheap loose plastic bearings with brass ones now. Those red fibre washers, they are thrust washers I assume Steve?

[boatmadman]

I have always used Colphos bushes. It is a high lead content bronze with good self lubricating properties.
I turn them to size and finish with a reamer, they are 10mm long and secured in thick walled brass tube using locktite.
I have never yet had to replace a bush.
Ian

[Peter Fitness]

NNF, I sometimes solder the bearings in the ends of the tube for security, especially if my machining was not too accurate and the fit is not really firm. I always silver solder a lubrication tube into the prop tube so I can fill it with waterproof grease, in my case, outboard motor grease which is water resistant. The subject of tube lubrication usually starts a discussion between those who believe it places an unwanted load on the motor, and those who don't. In my case, I have never found it to be a problem, but that may be because all my boats are relatively slow moving, tugs, pleasure cruisers etc, whereas high performance boats may suffer if grease is used. The photo shows one of my home made prop tube assembles complete with slide on grease cap which helps to push the grease into the tube. - and keep it there


Peter.

[PICKETBOAT]

Hi all


I agree that on models with big hefty stern tubes and slow turning big props internal drag on the shaft caused by grease is less of a problem. Common sense really. On smaller models it can be an issue.


The red washer trick is a good one. Yes they do act as internal and external thrust bearings and work well. They do need a little adjustment to take up any play after they have "bedded in". You will find the wear surface polishes up with use. They do eventually wear out (over very extended use) but replacement cost is small.   

[NoNuFink]

Thanks for all the info guys. - Looks like my hunch that Stainless ballraces would be overkill was correct.
I'm not certain about these red fibre washers - exactly what type are we talking about?  Anyone have a link? 

On an associated tack - I assume that everyone is using stainless steel shafts?

NNF

[red181]

to simplify matters for you, get on to shg marine, and buy a few acetate plastic bearings, couple of quid a pair. They are water lubricated and push fit into the stuffing tube, tell them its for M4. No soldering etc, and when they need replacing (virtually never) they can be pushed out. You can adjust endfloat using m4 stainless (so they don't rust) washers.

I use a variety of bearings, acetate, ballraces closed and open, glacier water cooled, it all depends on what you are doing, they will be fine for your application

 

[Jerry Hill]

Delrin is DuPont's trade name for Acetal or Acetal Homopolymer resin to give it it's proper name.

It is, but to be sure it's not the same as Acetal wholly. Delrin is tougher, stronger, machines better, and wears better than Acetals from others. As such it should be noted as being a superior Acetal variant for the purpose of shaft bearings.

[Peter Fitness]

Where would you be likely to buy Delrin of a suitable size?


Peter.

[Jerry Hill]

Where would you be likely to buy Delrin of a suitable size?


Peter.

http://www.directplasticsonline.co.uk/Delrin_Rod.html

[Peter Fitness]

Thanks Jerry


Peter.