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Author Topic: Exposed prop shafts  (Read 2443 times)

Beagle1831

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Exposed prop shafts
« on: March 23, 2017, 02:43:22 pm »

Just sorting running gear out for my next project (RN O&P class destroyer), thinking about exposed prop shafts with A frame supports.


Came across this potential problem, does an exposed type design need a longer tube length inboard to support the shaft, in comparison to the more usual fully enclosed (non scale) design seen on models?


Trying to get the balance right as a longer drive system raises the height of the motors, affecting stability & potentially creates more vibration?


Interested to hear any thoughts on this!


James
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Bob K

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Re: Exposed prop shafts
« Reply #1 on: March 23, 2017, 03:09:00 pm »

James:  I have several period warships with externally exposed shafts.  It is always best to select a type of shaft that you can shorten the outer, rather than shaft bearings crimped in at both ends.  How much you need to shorten the outers depends on your model, but leave enough going through the hull to securely epoxy in place using your A frame as the prop end support.
Most shafts will need some sort of end length adjustment, either inner outer or both.
Only in rare cases where the internal length available cannot be accommodated may you have to consider taking the outers out and through the A frames.  Not as realistic, but occasionally a necessity.
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John W E

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Re: Exposed prop shafts
« Reply #2 on: March 23, 2017, 04:10:50 pm »

hi there

like ,Bob K  I have built many warship with exposed prop shafts; all of them I have purchased commercially available propshaft and tubes with the phosphor bronze bushes either end.    Normally, I cut the outer tube to length using a model maker's miniature tube cutter; then deburring the cut end of the tube with a round file.  Next process I knock out the bush from the tube length that I cut off and place that bush in the freezer in the kitchen to freeze it.  The other piece of tubing which has the brass bush in and which we use - I warm the unbushed end on the gas cooker ring - then I remove the bush from the freezer, place it the right way up on a wooden block and drive the warmed open end of the prop tube over the end of the bush.

This is how I produce the majority of my cut down prop tubes.   On certain ones, I also drill a small hole about an inch or so from the end and solder on a small diameter tube to form a greasing point - so we can fill the tubes with grease or oil.    Several links follow to give you an idea - these are of models I have made - to give you an idea.

Last but not least, the A frames, are made in a similar way but I use soft solder to attach the support legs.   A lot of folk stipulate using silver/harder solder to solder this joint.   My motto is, is everything is lined up properly there shouldn't be that much stress on the A frames.

http://www.modelboatmayhem.co.uk/forum/index.php/topic,33734.msg350818.html#msg350818

http://www.modelboatmayhem.co.uk/forum/index.php/topic,15073.msg146597.html#msg146597

http://www.modelboatmayhem.co.uk/forum/index.php/topic,3462.msg36261.html#msg36261

http://www.modelboatmayhem.co.uk/forum/index.php/topic,354.msg414922.html#msg414922

http://www.modelboatmayhem.co.uk/forum/index.php/topic,9758.msg90496.html#msg90496

john

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Bob K

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Re: Exposed prop shafts
« Reply #3 on: March 23, 2017, 07:45:09 pm »

Beautiful work Bluebird, as always   :-))

If I may suggest Raboesch propshafts of the following types, which have a removable end bearing designed so that you can more easily shorten both outer and inner shaft lengths to suit your requirements. 

Types:  300-00   300-01   300-03  and 300-04.
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Geoff

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Re: Exposed prop shafts
« Reply #4 on: March 24, 2017, 05:06:59 pm »

When you fit the A frame make sure your shaft is perfectly straight as otherwise you will experience tight spots. Many shafts are not exactly accurate but because they are supported each end by the outer shaft we don't experience any great problems. As soon as you move to an exposed shaft there can be issues.


I usually construct a drilled cone which takes the thrust on the outer prop shaft bearing so there is no direct loading on the A frame.


Cheers


Geoff
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Beagle1831

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Re: Exposed prop shafts
« Reply #5 on: March 25, 2017, 06:06:25 pm »

Thanks for all the very helpful replies! Some superb warship models John, interesting to read the whole threads, lots to pick up.


Will let you know how I get on! I need to find a drawing of the A frames & shaft positions too so may take a while yet, the plans and sections I have unfortunately do not show these. Admiralty plans as the last (expensive!) resort !?


James
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