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[dave parker]

Hi all
 
Go gentle, new starter here....
 
I am starting to accrue components to start my very first foray into model boat building but have come across an issue I am not sure if is normal or not.
 
I have got a 10" JP Accesories Prop Shaft, M4 threads both ends, 6mm Diameter tube etc etc, and also a plastic 3 bladed M4 threaded propeller.
 
When I screw the propeller on to the end of the shaft it tightens but there is still 5-8mm of thread left showing.
 
I have just been into my local model shop and been told that i need to cut back the threaded end of the shaft so that the prop tightens onto the nut and washer next to the bearing, something about not transferring the loads through the motor?
 
He walso went on to say that the other end that connects to the coupling isnt as important and is fine to have some threads on show providing it has a good connection to the coupling.
 
Is this correct?
 
Can someone maybe go through thte basics of Prop - Shaft - Tube - Coupling - Motor connections with me?
 
Many thanks in advance
 
Dave
 
 

[sailorboy61]

I think you'll find the idea of the nut and washer on the prop end is a lock nut. Obviously you tighten it one way, and in an ideal world this would be the ahead direction of the propellor so it naturally 'tightens' onto the shaft for what in most cases is the majority of the running time. Now conversley when you go astern, that would mean unscrewing the prop from the shaft, but the idea then is the locking nut is tight against the prop so it cant move. I would also use some threadlock - it comes in several strengths, go for the minimum!

[dave parker]

Thanks Sailerboy61
 
I am confused as to whether the nut and washer should tight up to th bearing then the prop tight uo to that, or do i tighten the prop as far as it will then loosen the nut back till its tight to the prop and not the bearing??
 
CONFUSED?!?!?!?

[sailorboy61]

Tight to the prop. If its tight against the bearing will cause friction and that will overload the motor, drain battery and other bad things......................

[black magic racing]

tighten the nut to the prop you want a little bit of movement,i would not put it tight to the bearing    kurt  black magic racing

[dave parker]

Hmmmmm

Forgive me for sounding dim but that would mean that there is 5-8mm of propshaft thread between the nut and the bearing and so the shaft can move up and down in the tube by this amount?

Where should the washer be?

Does that make sense?

[Martin (Admin)]

Hi Dave,

Welcome to the Mayhem!

Give me a ring, PM sent.

  Martin

[sailorboy61]

5-8mm is probably a little excessive, 2-3mm would be acceptable to me, so perhaps you could trim a tiny bit from the shaft without damaging the thread. There is probably allowance for thread to take into account different size props and depth of thread. The shaft shouldnt really move around in the tube too much if the coupling is well aligned - it is held at both ends of the tube by bearings.
The washer should go between nut and prop in my book at least.

[dave parker]

So am I right in thinking when running the prop pushes the shaft which then pushes on the coupling and into the motor which is fixed to the boat?

[sailorboy61]

              
 
 

So am I right in thinking when running the prop pushes the shaft which then pushes on the coupling and into the motor which is fixed to the boat?

[Netleyned]

             

And ruins the motor bearings 


Ned

[dave parker]

So is that not right then Ned?

[Netleyned]

The washer at the prop end should be between the locknut on the prop and the tube with no more than about a millimetre of play.
It then acts as a thrust washer transmitting the thrust from the prop to the hull via the stern tube.
If all the thrust is on the motor bearings they are not going to last very long.


Ned

[sailorboy61]

Already reduced the gap in an earlier post...................

[Netleyned]

Already reduced the gap in an earlier post...................

But not enough


Ned

[Martin (Admin)]

Threaded section should end just before the washers.
Threaded end can / should be cut down to suit internal length of prop.
 ( use a 'Dremel' & a cut off wheel - NOT a vice and hacksaw! )

Should be no more than 1mm-ish 'slop / play' lengthwise.

Some propshaft can be longer than the stuffing tube and a collar used inboard to hold the shaft in place.

[Den W]

In a word, the unthreaded part of the prop shaft should be about 1/8" or 3.25mm longer than the prop tube .thus giving you enough space to incorporate a teflon washer at each end .as per Martins diagram..

[scoop]

In a word, the unthreaded part of the prop shaft should be about 1/8" or 3.25mm longer than the prop tube .thus giving you enough space to incorporate a teflon washer at each end .as per Martins diagram..

And don't forget to fill the stuffing tube with grease to stop water coming back up the stuffing tube and flooding the hull when going astern, if using teflon washers don't use teflon grease use a petrol based one such as Castol LM
 
Cheers
Scoop

[essex2visuvesi]

In a word, the unthreaded part of the prop shaft should be about 1/8" or 3.25mm longer than the prop tube .thus giving you enough space to incorporate a teflon washer at each end .as per Martins diagram..

Where is a good place to get teflon washers? need some 4mm id x 6mm od

[Den W]

Hi, if you have access to a lathe ,you could try -- Gilbert Curry Industrial Plastics Co Ltd 

   16 Bayton Road Exhall,  Coventry, West Midlands CV7 9EJ

..they will supply you with any size (within reason)  solid teflon bar, and you can turn it down to what ever size you require at a fraction of the high street cost...hope this helps

[scoop]

Where is a good place to get teflon washers? need some 4mm id x 6mm od

Try astec models .....www.astecmodels.co.uk, type in teflon washers in the search and you will find 4 x 7 x 1 mm 8 for £3.90 and pretty close to the size you are looking for, saves firing up the lathe 
 
Cheers
Scoop

[tmbc]

hi m8

why buy a piece of teflon bar when you can buy them from prestwich just contact dave there used on fast electrics 4mm id 10 for 2.95 i think i should become a marketing guru finding these cheaper prices  !!

[essex2visuvesi]

http://www.ebay.co.uk/itm/Traxxas-Part-1549-Teflon-washers-4x6x0-5mm-9Pcs-/130627863468?pt=UK_ToysGames_RadioControlled_JN&hash=item1e6a0703ac&_uhb=1


I had already found these but he didn't post to Finland

[scoop]

hi m8

why buy a piece of teflon bar when you can buy them from prestwich just contact dave there used on fast electrics 4mm id 10 for 2.95 i think i should become a marketing guru finding these cheaper prices  !!

Nice spot  'Guru' I forgot all about Dave's FE pages on his website !
 
Essex.....www.prestwich.ndirect.co.uk/ or he trades on ebay under winninisall   

[Den W]

THE SELF SATISFACTION YOU GET FROM MAKING YOUR OWN BITS AND PIECES FAR OUTWEIGH ANY COST OF READY MADE (you never know what your going to get)...THIS IS  M-H-O and I,m not trying to out-do anyone else....  ..ps If you PM me I will gladly make you some when I get back from hols..  FREE  including postage  "simples"