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Author Topic: Hardware Preference 2mm Vs 4mm Propshafts  (Read 915 times)

plastic

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Hardware Preference 2mm Vs 4mm Propshafts
« on: March 09, 2019, 03:49:27 PM »

Hi All
Brain picking time again...

I need to fit a couple of 12" propshafts into a 1/96 Destroyer - do I go for 2mm or 4mm? What do people recommend?  I'm using a pair of 355 motors and I usually run at scale-ish speeds - about 12"/sec.

I like 2mm propshafts with rubber couplings because they run nice & quiet and they look more correctly sized.
I like 4mm propshafts because they are beefier and longer lasting.

Do you think that propshaft choice would affect the eventual sale price when it goes on ebay?  Opinions?  Any bad experiences with 2mm shafts?  Too easy to bend?
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derekwarner

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #1 on: March 09, 2019, 09:56:08 PM »

Just thinking backwards from outside the box  %)


A 4mm diameter propeller shaft in 1:96 is about 384 mm diameter in real life


A 100,000 tonne bulk carrier in real life may have a tubular prop shaft of 400 diameter


This comparison makes the smaller 2 mm diameter shaft look the better option  O0


Derek




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Derek Warner

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Colin Bishop

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #2 on: March 09, 2019, 10:22:04 PM »

To be reasonably accurate the shaft should be exposed where it exits the hull and the end supported on an A bracket just in front of the propeller. This would require a collett where the shaft exits the hull to take the thrust.

Are you intending to replicate that?

Colin
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gingyer

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #3 on: March 09, 2019, 11:29:40 PM »

what type of model is it?

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derekwarner

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #4 on: March 10, 2019, 12:42:17 AM »

Just thinking a little more  %) ......


That M2 diameter may be a little small ....or may be one of the elements that does not lend itself to being accurately scaled


What is the Series of the motor & diameter of the motor shaft?, and what is the diameter of the propeller/s?...and finally, what is the diameter of propeller drive thread form?


Derek
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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #5 on: March 10, 2019, 03:07:36 AM »

personally, if it was a short shaft ie 6".them M2, you can still go with M2 at 12", but personally again,  i would want a vearing halfway down the shaft, this woulld help stop vibration. you coul go with M3, but it will be custom made. M4 is the other option, again I would still consider a bearing halfway down. props are freely available from propshop or sitek etc
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plastic

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #6 on: March 10, 2019, 07:21:09 AM »

To be reasonably accurate the shaft should be exposed where it exits the hull and the end supported on an A bracket just in front of the propeller. This would require a collett where the shaft exits the hull to take the thrust.

Are you intending to replicate that?

Colin
No, I was just going for simplicity with a standard shaft supported by the end bracket - that's why I was thinking of using 2mm shafts because the O/D of the outer tube is small enough to look scale-ish.   

I'll be using 30mm 3-blade propellers.
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plastic

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #7 on: March 10, 2019, 07:32:14 AM »

personally, if it was a short shaft ie 6".them M2, you can still go with M2 at 12", but personally again,  i would want a vearing halfway down the shaft, this woulld help stop vibration. you coul go with M3, but it will be custom made. M4 is the other option, again I would still consider a bearing halfway down. props are freely available from propshop or sitek etc
That's one of the issues I was worried about - the shaft flapping about inside the tube.  If the shaft is not 100% perfectly straight, how can you thread the shaft back into the tube?   Surely it will bump into the last bearing and you'll never get it in?   An M4 shaft will be less likely to whip around inside the tube so could live with just end-bearings.   The problem is the O/D of the tube is about 8mm, really chunky!  Almost 3' diameter at full size!
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Tug Fanatic

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #8 on: March 10, 2019, 08:28:03 AM »

I agree about a 12in 2mm shaft being rather flexible etc
How about having the inner shaft long & the outer tube shorter? You could always use a collet as the thrust bearing. That would halve your problem.
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Andyn

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #9 on: March 10, 2019, 08:33:01 AM »

As previously said, depends on what prop you're turning and how much is unsupported. Going back to your original question, no I don't think it'd affect a selling price, and 4mm shafts will still be silent if using a rubber coupling, in fact if a direct drive electric boat is making drivetrain noise you've got something wrong somewhere.


Personally I'd never use a 2mm shaft above 6". As to the outer diameter of the shaft tubes, have a look a look at the Caldercraft fineline shafts, they're 6mm outer. I don't think you'd need a center bearing on something powered by a 385 doing low speeds
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Colin Bishop

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #10 on: March 10, 2019, 09:29:04 AM »

Quote
How about having the inner shaft long & the outer tube shorter? You could always use a collet as the thrust bearing. That would halve your problem.

That was what I suggested earlier. It is more accurate to scale and effectively gives you an intermediate bearing. The downside is that you will need to make up and fit the end bearing yourself although its not particularly difficult. The thrust load to the hull is taken on the collett. Example below. One of the smaller personal manufacturers will make you up a suitable shaft and tube combination plus an end bearing too.

Colin
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Colin Bishop

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #11 on: March 10, 2019, 09:53:14 AM »

Further to my post above. If you want to keep it simple then have a look at the M2 shaft assemblies from SHG Model supplies on page 21 of their catalogue.
http://www.shgmodels.com/acatalog/

The outside diameter is only 4mm and they are well made. I have a couple of long ones in my liner build and they run true. On a destroyer you will still need to add a support between the prop end of the tube and the hull to steady it from prop vibration.

The lengths quoted by SHG are for the tube, there is about 10mm of shaft exposed at each end. One end is plain the other threaded M2.

Colin
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raflaunches

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #12 on: March 10, 2019, 07:46:09 PM »

Just to throw another penny in to the lake... what about going in between? You could go for a M3 shaft, unfortunately there may be slightly less choice but Dean's Marine provide them


http://deansmarine.co.uk/shop/product_info.php/cPath/35_46/products_id/2234


And I'm sure Prop Shop can make M3 props. It occured to me that if you want a slightly smaller scale diameter but want something closer the 4mm diameter strength then M3 might be another option.


I tend to use M2 for destroyers in 1/96, and then M4 for heavy cruisers and battleships for scale appearance. But I do ensure if I have M2 dia shafts I don't have a shaft any longer than 8 inches just incase of bendiness and whiplashing.
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Tug Fanatic

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #13 on: March 11, 2019, 07:39:16 AM »

Further to my post above. If you want to keep it simple then have a look at the M2 shaft assemblies from SHG Model supplies on page 21 of their catalogue.
http://www.shgmodels.com/acatalog/

The outside diameter is only 4mm and they are well made. I have a couple of long ones in my liner build and they run true. On a destroyer you will still need to add a support between the prop end of the tube and the hull to steady it from prop vibration.

The lengths quoted by SHG are for the tube, there is about 10mm of shaft exposed at each end. One end is plain the other threaded M2.

Colin
I think that Glynn Guest has used these in quite a few of his designs.
Is it possible/easy to remove the end bearing so that the tube can be shortened or is it crimped in a way that makes this difficult?
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John W E

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #14 on: March 11, 2019, 09:10:25 AM »

hi there, if you really want to be close to scale at 1:96 for your propshafts on the destroyer, 4mm is slightly small in scale terms.   Prop shafts in the real boats are normally in the region of 2 ft diameter - so I have always opted for 4mm or 1/8 for 1:96 scale models.  As far as putting thrust bearings on - on open shafts - they don't have to be on the outside.  The destroyer I built a while ago I incorporated the thrust blocks internally.   I am putting a photograph on, but, its not so clear.   The other photograph I will attach is of a destroyer and take a look at the diameter of the propshaft - if you enlarge the pic you will see workmen working below the shaft - to give you an idea of the size.
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Colin Bishop

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #15 on: March 11, 2019, 09:25:11 AM »

Quote
Is it possible/easy to remove the end bearing so that the tube can be shortened or is it crimped in a way that makes this difficult?

I don't know but I suspect that in trying to drive out the bearing you run the risk of distorting the tube itself. In any event, from what John says above, the diameter of the 4mm tube itself will look pretty much like a scale shaft and it will be much easer to fabricate an A bracket at the prop end as you won't have to make another bearing.

You could even add a short sleeve over the tube where it comes out of the hull to simulate the scale tube size. All very much easier and a robust solution.

Colin
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GG

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #16 on: March 11, 2019, 10:18:57 AM »

I've used the "Radio Active" brand of shaft/tube and 3 blade propeller assemblies in a few models.  Just measured one and the shaft diameter is 1.7 mm and the thin walled brass tube 5.5 mm in diameter.  They can be shortened quite easily by rolling the tube on a flat hard surface using the sharp blade of heavy duty craft knife.  Once this has made a continuous notch around the tube it can usually be snapped by gentle bending of the tube.  I find this makes a neater job than trying to cut the tube with a saw.  The down side is you have probably taken the sharp cutting edge off the blade but it's still sharp enough to cut things (including you!).


The plastic bearings are only a push fit into the tubes and so can easily be pressed out using a dowel or similar and refitted into the cut end of the tube.  I usually save the piece of tubing cut away for making things like rudder shaft tubes.


These assemblies are perfectly adequate for modest powers such as the RE 360 or 385 motors with 6-7.2 Volt batteries.  There are however two potential problems, firstly the small shaft diameter can make a secure connection to the motor shaft difficult.  Sometimes I've used a short length of "rubber" tubing successfully but now tend to use homemade couplings using suitable collets.  The second problem is the propeller which just screws onto the shaft.  This is not the most secure method and there is a propeller somewhere at the bottom of our garden pond to prove it!  I did find some small nuts in my "junk boxes"  that would screw onto the shafts and so act as lock nuts (or Jam nuts as our colonial cousins are want to say).  Alternatively, or perhaps as well as a lock nut, a dab of thread locking compound is a good idea..?


Glynn Guest
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plastic

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Re: Hardware Preference 2mm Vs 4mm Propshafts
« Reply #17 on: March 11, 2019, 10:27:24 AM »

On M2 shafts, I always use a dab of threadlock for the propeller with a nut locked against the prop and an M2 washer between the nut and the prop tube as a thrust washer.
At the motor end, I use a washer bewteeen the tube and a locking collar so the shaft is positively retained with minimal end-float.  I usually use the Graupner heavy rubber tube couplings to link the shaft to the motor - cut down in length so there's less slop.
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