3mm propshaft

[Dodgy Geezer 1Participant @dodgygeezer1]

Why can we have them? 3mm props, I mean. 3mm is a standard size for brushless motor shafts now, and it would just be so much easier to run at 3mm all the way to the prop…

[Dodgy Geezer 1Participant @dodgygeezer1]

[ashley needhamParticipant @ashleyneedham69188]

Geezer. I would agree that this seems to make sense.

But you would end up with very thin propshafts and a corresponding reduction in length before you would suffer shaft whip, especially with all these powerful 10kw brushless motors being touted.

The prop boss would also become much larger in relation to the propshaft with larger props suffering in this regard.

It would also be probably more difficult to get a good thread on this smaller size, especially in stainless.

ALSO given that you would buy a coupling anyway, then it doesnt make that much difference having a 3mm motor shaft and a 4mm propshaft.

Ashley (sorry)

[Dodgy Geezer 1Participant @dodgygeezer1]

But you would end up with very thin propshafts and a corresponding reduction in length before you would suffer shaft whip,

Yes. Funny how that never happened during the days of imperial measurements – when 1/8" was the standard propshaft size – which is near as dammit 3mm. I was very happy with that on a Sea Commander and a Merco 35 – worked fine. I suppose metric steel must be whippier…?

As it is, I have to use 2mm shafts for my EeZeBilts, unless I want to have a propshaft which weighs more than the motor. But 2mm props are all too small to get the best out of the little brushless motors I use.

3mm is the obvious and correct size for what I need – amongst other things, that's why the small brushless use 3mm shafts. I have just started ordering props with a dog connector to make up my own 3mm drive train – perhaps I should drill a 2mm and tap at 3mm…? Doing this I either have a choice of a prop boss being very thin or being gigantic…

And, as you can see, I make my own couplings. Those are just knurled cylinders tapped 2mm, 3mm or whatever, with a thick-wall silicone tube. The good point about this design is that all my motors are compatible with all my propshafts…

[Tony HadleyParticipant @tonyhadley]

DG,

The Prop Shop sell both shafts and propellers in M3. With some of the props it gives a default thread, but different threads can be specified when ordering.

**LINK**

[Dodgy Geezer 1Participant @dodgygeezer1]

Posted by Tony Hadley on 27/04/2015 20:49:24:

DG,

The Prop Shop sell both shafts and propellers in M3. With some of the props it gives a default thread, but different threads can be specified when ordering.

**LINK**

Indeed they do. I omitted to mention it, but my 'eezebilts' are expected to cost under £10 total. Prop, shaft and rudder should be between £0 to £2. This is what a £0 prop looks like:

**LINK**

[ashley needhamParticipant @ashleyneedham69188]

Geezer. I accept all and any points made in defence of 3mm shafts and plse note I am not against them, you wanted possible reasons and I gave a few as i thought fit, to use as a discussion point.

I suspect the reason we dont have 3mm shafts is purely commercial. Volume of sales. 4mm is ok for use in most vessels and so this is what is widely available.

I doubt that modern steel is more whippy that imperial stuff. Whip would depend on straightness of shaft, straightness of tube, concentricity of bearing holes, lengths of shaft exposed at the ends, length of bearings (plain),vibration of prop/motor, coupling imbalance. I am only saying it stands to reason that the longer the shaft is the more it will be susceptable to whip. Having a smaller diameter shaft will mean that the propensity to whip will be reached at a shorter length than a larger shaft. I am not casting doubts on the ability of a 3mm shaft not to whip.

I have recently built a large number of vessels with those cheap 2mm shaft/prop assemblies and they seem to work fine, and are very cheap. My 5 foot lander is propelled by THREE 2mm shafts/40mm props !

I have seen the eeze DIY prop method before and am impressed by the simplicity of it, as befits the EEZE part, building your eezies in the spirit of the originals is great stuff, good on yer.

Ashley

[Dodgy Geezer 1Participant @dodgygeezer1]

And in return I should apologise for my rather ponderous sarcasm – since I fear you are quite right – the decision is almost certainly a purely commercial one.

Typical shafts in the 1960s were 2 BA and 4 BA – around 0.14 and 0.19 in, which comes out to M4 and M5 if you round up each time. And that makes commercial sense, because the small/medium sized boat kits that introduced kids to the hobby are no longer made. We now have bigger boats, and much more powerful motors, so if you're going to drop something it will be the smaller items in the range. And you just keep the really small M2 for plastic conversions.

I suffer because I produce boats squarely in the 12"- 24" range where M3 would be ideal. But all is not completely lost. If you look closely at the well-known 'Radioactive' range of plastic props you will see that they offer a 40mm, for instance, in both M2 and M4, and they do this by moulding the same prop, but pushing a brass insert centre tapped either M2 or M4 into it.

The key word here is 'pushed'. The insert does not appear to be moulded in. It just stays in because it's knurled. So it should be possible to remove it and substitute an M3 one – enabling me to do what I wanted – run a straight-through shaft from the motor to the prop and cut out the cost/complexity/off-centredness of a coupling.

Incidentally, for the VERY small props – 1 cm or less – I suspect that the sheet tinplate technique is going to be the easiest way to get a prop, and more efficient than a commercial cut-down one might be. As an aside, I do need to counter whip on the M2 shafts of 9" or longer – I put a small low-friction nylon bead in the middle of the shaft which does not touch the prop-tube sides at slow speeds, and suppresses whip at high speeds…

 

 

 

 

Edited By Dodgy Geezer on 29/04/2015 20:36:49

Edited By Dodgy Geezer on 29/04/2015 20:37:46

[Andy CParticipant @andyc56856]

Hi Dodgy

Don't want to intrude, but need your help. I am currently building the trident to the original size. When it comes to the propshaft I have one that will work, don't know what size as I don't have a a way to measure it accurately, but seems quite small. It was a throw away , cheap, not free, from my local model shop. However, I need a rudder and the ones in the shop are really quite big. Even the smallest ones. How do you do it? do you make your own and if so is it difficult?

Regards

Andy

[ashley needhamParticipant @ashleyneedham69188]

Andy c. I suggest you open the link ppsted by the geezer regarding eze craft and there are insatructions to make a rudder I believe. Easy peasy.

geezer. No probs. Suspect for the size of boats you are taliking about, home made props would be more than adequate. As i said, the 2mm Radio-active shaft/props are quite alright and dead cheap.

Ashley

[Dodgy Geezer 1Participant @dodgygeezer1]

Don't want to intrude, but need your help.

 

No one talking to me about EeZeBilts is ever intruding – (unless they break into my bedroom at 3am for a chat)!

Are you building a Triton? And are you aiming for originality, or are you happy to modify things? And what sort of skill/toolset do you have….

The original kits used a 'standard' propeller/rudder set, which is illustrated, with dimensions. here:

**LINK**

and this is how to make it:

**LINK**

 

You will see that the prop is 7/8" diameter, the propshaft is 5 5/8" long and about 2mm diameter. How does that compare with your shop one? The sizes above ARE small – you could put a somewhat bigger prop on the Triton – one up to around 30mm would fit without too much modification.

The rudder on the Triton is the larger of the two illustrated in the reference above. You will see that it is a crude oval of tinplate, soldered onto a thin (around 2mm) brass rod, running in a somewhat larger outer brass tube.

All the fittings on EeZebilts are small and simple (that's what it was like in the 1950s!) and you will find that modern fittings are often far too large. As I indicated above, I now use purchased props for many of the larger 50+ series (especially if I'm using a fast brushless motor), but for the smaller 50+ series and all the original eezebilts I make my own. It's FAR cheaper! And I always make my own rudders – for example, see:

**LINK**

For joining metal to metal I prefer solder. Have you used this before? If not, it's quite easy. For the rudder, you don't even need a soldering iron.

1 – Cut out a rudder shape (thin brass is ideal, but a tin can lid will do.

2 – put it on some soft wood, lay your rudder shaft on top of it, and hammer the shaft a bit. This will make a groove in the rudder blade.

3 – clean the rudder blade and shaft, put a bit of of flux on it and a bit of solder, then put the shaft in the groove and hold it over a gas flame with a pair of pliers. The solder melts, and you have a rudder. If it doesn't work, more heat will disassemble it ready for another go.

If it REALLY doesn't work, you haven't lost much – just the cost of some solder and flux. And the burn cream. But you have gained a lot of experience….

I don't find this work difficult, but that's because I've done it a lot. Soldering metal is a useful skill for all boat builders, and the usual reasons things don't work is:

– surfaces not clean enough (plumbers acid flux cures that very quickly!)

– not enough heat (you can't heat up a pound of brass with a miniature electrical soldering iron.

Sort those things out, and you can solder anything!

 

Some photos of what you are doing would enable us to provide much more detailed help. Is the above helpful?

 

 

 

 

Edited By Dodgy Geezer on 30/04/2015 00:15:02

[Andy CParticipant @andyc56856]

Hi Dodgy

Sorry, it is the triton I am building, not the much debated missile system. I have not soldered anything except electrical wires since I was at school. A while ago now. I have some solder, but might not be the correct stuff, will check it out. I will also stop off in Ewell, on my way home and buy some brass sheet from my local model shop. I am actually looking forward to trying this. Outside the garage I think, my smoke detectors are a bit on the sensitive side. I have some photos of the build, so will start a new thread and post up what I have done so far.

Cheers

Andy

[ashley needhamParticipant @ashleyneedham69188]

Andy. you are within spitting distance of Bushy park.

Apols if you have been before and I have forgotten!

C U Sunday with your build…current and past. bring batteries.

Ashley

[Dodgy Geezer 1Participant @dodgygeezer1]

I have some solder, but might not be the correct stuff, will check it out.

There is a difference between 'what is the right stuff' and 'what you can get away with'.

Ideally, mechanical parts like rudder blades should be 'hard' or 'silver soldered' – using a high-temperature solder and a gas torch. But for small items on an eezebilt, standard electrical solder is fine.

I notice that I haven't specified the metal thickness! An original KK rudder for the eezebilts was around 0.013" – 29 gauge? – tinplate. Tin cans (not aluminium!) are usually a bit thinner. If you're buying brass sheet, get something around 0.35mm in thickness. It will be fairly easy to bend, and to cut with a stout pair of (old!) scissors)

I find that plumbers 'self-cleaning' acid flux makes soldering a doddle. Just smear a bit on and the solder sticks, even to a rather dirty bit of metal…

And once you get the hang of soldering, you'll never have to buy a rudder again!  Though you will probably need a Dremel multi-tool or similar for the bigger rudders, where you have to make a slot in the shaft to fit the blade into…

Edited By Dodgy Geezer on 30/04/2015 10:35:37

[Andy CParticipant @andyc56856]

Hi Ashley

I do aim to get down one weekend as I am dying to meet you and Trevor etc and see all your wonderful, if secret, projects.

Dodgy, I have now started a build log and have put up some piccies to see where I am at. I will try out the rudder this evening when I have some more time.

Cheers

Andy

[Trevor HollowayParticipant @trevorholloway99134]

if you give us the heads up we can dust off some of the "unusual craft".

[Author]

Posts