Model Boat Mayhem
Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: Hagar on August 27, 2008, 08:39:25 pm
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Ok hopefully a simple question. DIY or scratch built propshafts. brass bar in a brass tube, fine no problem thus far. How does on a) hold things together? b) bearings, where can you by them? how do you fix them?
I kind of need a rather long propshaft- approx 55cm!! That is the shaft needs to be about 55cm, the tube only needs to be about 25 - 30cm.
Any suggestions?
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Westbournes do a shaft that has a 260mm outer tube. All you would need to do is make a 4mm shaft and thread one end.
Simple if you say it quick. ;)
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Hagar,
Avoid using brass tube to support the shaft. What you need is a bearing or bush at each end of the brass tube to run the shaft in and a 'P' bracket or similar at the prop end of the shaft.
Ian
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Hagar i built mine from steel tube and bar with industrial chain links for the bearings fixed in the ends with areldite
(http://i168.photobucket.com/albums/u176/darran77/how%202/P1000442.jpg)
(http://i168.photobucket.com/albums/u176/darran77/how%202/P1000443.jpg)
(http://i168.photobucket.com/albums/u176/darran77/how%202/P1000444.jpg)
(http://i168.photobucket.com/albums/u176/darran77/how%202/P1000445.jpg)
(http://i168.photobucket.com/albums/u176/darran77/how%202/P1000446.jpg)
daz
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I use brass tube and phos bronze bearings, oil filler pipe at the engine end and they last forever (well nearly)
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SHG used to sell bearings (oilite?) for prop tubes. Not sure if they still do.
Barrie
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Ok hopefully a simple question. DIY or scratch built propshafts. brass bar in a brass tube, fine no problem thus far. How does on a) hold things together? b) bearings, where can you by them? how do you fix them?
I kind of need a rather long propshaft- approx 55cm!! That is the shaft needs to be about 55cm, the tube only needs to be about 25 - 30cm.
Any suggestions?
Bearings
Bearing material http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=3257136 (http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=3257136)
Mail order but,to use the trade counters, you need to get a D.P.C. number first.
There's bronze in the metal stock section.
Check out the their other plastics & small ungeared dc motors too.
Push fit like Graupner and loco engineers.
Don't use 2 ballraces per propshaft!!!
The rest is common sense.
stern tubes
Avoid flex and use 3/8 dia. minimum at 55cm.The brass ones in shop are that diameter for a good reason.
You can get 55 cm long ones.If you come up blank,look in the Hobbys catalogue or JRPerkins.
Regards
Barry Park
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Hi there Hagar
the following is an extract from the Whaleback build on this forum, which I am doing.
The propshafts are made from commercially available propshafts and I have made many of these type of propshafts and I have not had one fail yet. There are 3 of these type prop shafts in the MTB, which should be classed as a low-flying missile :D .
Here is a scribble to explain the method/possible method of constructing the cut-down prop shaft and the P bracket support - this is a method I have used several times, when we didnt have the facility of a lathe to manufacture the parts.
We commence by obtaining a 'shop purchased' prop shaft of the correct length that we require for our prop shaft. We remove the prop shaft from the tube; mark off on our tube the required length for our new prop tube - and, then cut it at our mark.
I normally cut the tubes in half with a small modellers pipe cutter - this does give a nice clean cut. I then remove all the burrs and dress the prop tube up.
The next stage is to remove the bush from our redundant piece of prop tube - what I normally use to remove the bush is a tube which fits pretty neatly inside our prop tube, or, I have used a discarded knitting needle (from the Mrs) and I tapped the bush out from the inside.
The next procedure is to warm up gently, normally on the cooker top, the end of the tube where the bush is going to fit. Prior to doing this, I normally put the bush into the freezer compartment of the frige and I divvent mean a bush from the back garden so while the bush is being frozen and contracting, the tube is going to be expanded with the heat. This makes it a lot easier to fit the bush back into our new section of tube. Let it cool down naturally, out of harms way......... yes I have tried to pick the tubing up when its still been RED HOT and yes, it does bring tears to the eyes.
The next stage, as you will see by the drawing, is to make the support bracket - this is basically 3 pieces of tubing. The inner tube must be the correct diameter to fit over your prop shaft and it must be not too tight of a fit, you must be able to spin the shaft in the tube.
Then, its a case of two pieces of tube which will fit over the tube over your first piece of tube. These are all cut to length slightly longer than one another - inner tube being the longest and these are then soldered - just with normal soft solder - then I make a mandrel up and shape as has been mentioned previously in this build - with a file and emery cloth and then I add the support leg.
I do hope this makes it a little clearer - and - I will add further scribbles as we go along - but, just as a side note - the rudder and rudder tubes are made up basically the same way as we make the P bracket up - and I will add a drawing to explain later on.
Now....just going back to fit the deck.
aye
john e
bluebird
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Thanks Bluebird, but you are to late. I have already read all of your master classes and I might say they are great.
I have today bought a meter of 4mm steel for a new shaft and a rabosch (?) 290mm propsaft. So all I've got to do now is make a shaft holder as in you feature. Just happen to hav a few phosferbronze bushes laying around to!
Thanks for all the feed back. Now I'm off to find an other problem for you all to solv! ::)
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The hole in my bushes are to small! attempts at drilling them out failed misserably!
Where can I buy more? 4mm shaft so I guess a 4.5mm hole?
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Hagar, you really need to ream out the bushes. 4.5mm will be too loose and ultimately end up with excessive wear and subsequently need replacing.
Probably best if you know someone with a lathe to knock out some for you.
Ian
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You should be able to find ardinary modeller's brass tube with 4mm bore. A bearing does not have to have thick walls of the bearing metal so just glue it into say a block of aluminium for support. The fit won't be as good as a hole reamed to size but you can save that for mark 2 when you have more time and tools.