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Author Topic: Propeller shaft Question  (Read 5193 times)

cosmic

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Propeller shaft Question
« on: March 14, 2010, 08:48:53 PM »

Greetings all. I'm scratch building Helene Euphane, a 1902 US Atlantic coast fisherman, in 1/38 scale. This is my first R/C after a shift in static builds, and I'm quite ignorant of the art in terms of hardware. Here's the first of (probably) many future questions to tax your patience. %)

The plans call for a !/8" shaft turning in a 3/16" tube. Standard brass tubes of these smaller sizes have a .014 wall. that means slop between the shaft & tube is .035. I don't know why they do that. It seems excessive clearance and the only justification for it that I can think of is it's possibly related to heat expansion of the shaft causing seizure.

I would rather use a 5/32' tube with the 1/8" shaft, which would give a clearance of .003, a nice slip fit. I intend to lubricate it with high vacuum grease. Question to you power boat R/Cers: can I do this without concern?
 
Thanks in advance.
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DickyD

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Re: Propeller shaft Question
« Reply #1 on: March 14, 2010, 08:53:14 PM »

You'll have to hang on a bit for an answer Cosmic as we dont use inches anymore on this side of the pond, we use millimeters {:-{ etc,
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Richard Solent Radio Controlled Model Boat Club http://www.srcmbc.org.uk

Shipmate60

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Re: Propeller shaft Question
« Reply #2 on: March 14, 2010, 08:57:11 PM »

cosmic,
It is usual to fit bearings or bushes at each end of the outer tube.
If it is a long tube then a centre bush can be fitted.
This has the advantage of leaving clearance for lubrication.

Bob
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cosmic

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Re: Propeller shaft Question
« Reply #3 on: March 14, 2010, 08:59:14 PM »

Sorry about that Richard 0.035 would be 0.89mm, 0.003 would be 0.08mm
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DickyD

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Re: Propeller shaft Question
« Reply #4 on: March 14, 2010, 09:03:25 PM »

I'll go with Bob and the bushes.

Can you not buy ready made shafts and tubes ?
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cosmic

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Re: Propeller shaft Question
« Reply #5 on: March 14, 2010, 09:07:51 PM »

I'll go with Bob and the bushes.

Can you not buy ready made shafts and tubes ?
I don't know. Can you give me an online source?
I'm at a loss as to how one may fit a bearing, or lubricated bushing, on the water end of the tube. Won't it rust or dry out?
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DickyD

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Re: Propeller shaft Question
« Reply #6 on: March 14, 2010, 09:16:12 PM »

I think about the nearest shaft size would be M4 which is an off the shelf size at all our suppliers over here, You really need to contact one of our members in the States for shafts over there.

Post a question on the forum and head it for someone in the US, would be the easiest.
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cosmic

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Re: Propeller shaft Question
« Reply #7 on: March 14, 2010, 09:35:41 PM »

Richard, I don't need a local source. Any online source will do.
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boatmadman

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Re: Propeller shaft Question
« Reply #8 on: March 14, 2010, 10:02:27 PM »

I don't know. Can you give me an online source?
I'm at a loss as to how one may fit a bearing, or lubricated bushing, on the water end of the tube. Won't it rust or dry out?

In my opinion the best materials to use are phosphor bronze or leaded bronze bushes, with stainless steel or bright drawn steel shaft. High quality ss will not rust, bright drawn may do in time.  Also, bronze, and in particular leaded bronze is to some extent, self lubricating in water.

I think some manufacturers use brass for bushes, its ok but not as good as bronze and will need a little lubrication.

If you are concerned about oil/grease getting into the water, mass produced bought in shafts do not have the tight tolerances that can be achieved with one offs, so, if you know someone with a lathe - thats the best way to go.

For your interest, I have used bronze bushes for years, never had to replace one and VERY occasionally add only a little light oil for lubricant .

Ian

PS. Others might not agree with my comments, but they work fine for me.
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Peter Fitness

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Re: Propeller shaft Question
« Reply #9 on: March 14, 2010, 10:29:15 PM »

Ian, it doesn't really matter if others agree with you or not, what matters is that it works for you.

I happen to make my own prop shaft assemblies, and I generally use bronze bearings, although I have also used brass, and so far I have had no problem with either material. By using a thrust washer and an O ring at the prop end, and filling the prop tube with waterproof grease, I have never had an instance of water ingress via the prop shaft. An example of a home made one below.

In answer to Cosmic's question, if he doesn't have the facilities to make his own, then he will have to go with ready made, and rely on information from closer to home as to where he can obtain one.

Peter.

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boatmadman

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Re: Propeller shaft Question
« Reply #10 on: March 14, 2010, 10:35:17 PM »

Shafts made for current project, Bourbon Orca.

Ian
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Re: Propeller shaft Question
« Reply #11 on: March 15, 2010, 09:50:53 AM »

The brass tubes supplied in the K&S Metal Center (It's an American product) series closely slide into each other, so you could "Build up" bearings in the ends of a suitable O/D tube. As the grade of brass used is a bit on the soft side for bearings (Bronze is better, and Acetal is worth a look) making your own from raw materials ain't much of a problem if you have a lathe. Not got a lathe?? One of your big box companies is selling a micro lathe at $72. Might seem a "lot"?? but the possibilities it opens up for not only prop tubes but other turned fittings. Just a suggestion.

  Had a look at Tower Hobbies or any of the other sites on your side of the pond Cosmic??

  Regards   Ian.

 
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cosmic

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Re: Propeller shaft Question
« Reply #12 on: March 15, 2010, 10:37:37 AM »

Ian, I looked at them "all".
I don't have a lathe, and I'm amazed that you found one for $72US. Did you mean $720? If $72 is right. please tell me where to find this gem!
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geoff p

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Re: Propeller shaft Question
« Reply #13 on: March 15, 2010, 04:12:30 PM »

Like you, Ian, I didn't have a lathe (until recently, anyway) and where I lived, in Taiwan, they hadn't even heard of model boats, let alone brass and stuff for making them.

The only tubing available was anodised aluminium intended for tail-rotor supports for helicopters.

I managed to drill-out one of the plastic end-plugs supplied, by putting the stern-tube - with plug - in one electric drill, and a 4mm bit in another drill and basically aiming one at the other.  Luck was with me and I could still count to ten.  But a repeat attempt for the other end was a total Failure.



This sketch shows what I did for the inboard end of the tube - a poor-man's version of lignum vitae, with whatever hardwood I happened to have.  The block was 'stuck' to the ali tube with Araldite.

The tube was stuffed with Vaseline and the block has happily withstood the sidethrust of a geared drive for a couple of years.

Geoff

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Circlip

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Re: Propeller shaft Question
« Reply #14 on: March 15, 2010, 08:22:43 PM »

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cosmic

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Re: Propeller shaft Question
« Reply #15 on: March 15, 2010, 10:29:23 PM »

Interesting yo note, Ian. I was just yesterday in my local Harbor Freight in Beaverton. Oregon. Never saw that. It's tiny, and no crossfeed, but what the hey! 78 bucks! I'll go for one. Thanks.
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seahawk 1

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Re: Propeller shaft Question
« Reply #16 on: March 15, 2010, 10:50:11 PM »

Greetings all. I'm scratch building Helene Euphane, a 1902 US Atlantic coast fisherman, in 1/38 scale. This is my first R/C after a shift in static builds, and I'm quite ignorant of the art in terms of hardware. Here's the first of (probably) many future questions to tax your patience. %)

The plans call for a !/8" shaft turning in a 3/16" tube. Standard brass tubes of these smaller sizes have a .014 wall. that means slop between the shaft & tube is .035. I don't know why they do that. It seems excessive clearance and the only justification for it that I can think of is it's possibly related to heat expansion of the shaft causing seizure.

I would rather use a 5/32' tube with the 1/8" shaft, which would give a clearance of .003, a nice slip fit. I intend to lubricate it with high vacuum grease. Question to you power boat R/Cers: can I do this without concern?
 
Thanks in advance.

I found, like most of us in the US, our 'inch' stuff just doesn't lend itself well to available props, etc.  Most props I have used on my tugs are M4 thread, which meant I had to use an M4 threaded prop shaft.  Harbor Models, or Loyalhanna Dockyard offer the best selections here in the USA.  If you want an 1/8" shaft/stuffing box, I have one as well as a 3/16" 10-32 thread shaft with oilite bushings in the stuffing tube.  PM me and I can help you out.  Looks like your in the same neighborhood!

Mike
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cosmic

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Re: Propeller shaft Question
« Reply #17 on: March 16, 2010, 03:16:08 AM »

Mike, those two sources are greatly appreciated. I never would have found them!
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