Rudder bushes

bert49uk

bert49uk

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I’ve had made and fitted new composite bushes to my rudder but they are a bit tight looking to borrow/hire a reamer but so far no luck, have looked on E-bay and Goggled it with out luck. I’m looking for 2’’ (50mm) reamer preferably an adjustable one, can anyone help
 
The amount of clearance is quite important to get right, the manufacturer of the composite you've used should be able to give you a clearance figure, this will or should allow for moisture swell and to a greater degree thermal expansion, assuming you are fitting it at current temperatures. In UK waters you can expect a rudder bearing to be operating at 20C-25C in the summer if immersed or possibly 30-35C if dry and in the winter down to near zero at the extreme, normally 7-8. Too big or small by 0.5mm will have an impact on wear rates or friction.
 
bert49uk said:
I’ve had made and fitted new composite bushes to my rudder but they are a bit tight looking to borrow/hire a reamer but so far no luck, have looked on E-bay and Goggled it with out luck. I’m looking for 2’’ (50mm) reamer preferably an adjustable one, can anyone help
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Good luck with the 2'' reamer, what is the composite you are referring to as this may assist in a solution for you.
 
I'm not being silly offering this as a solution, I've found Agricultural engineers/mechanics/fabricators a good and knowledgeable resource. My local one made me some Delrin bushes a few years ago, appears they are used in farm machinery a bit
 
That's not strictly a composite its a thermoplastic polyoxymethylene. Just that we supply composite bushes which are fibre and resin with lubricants.
Delrin has a moisture swell of around 0.25% and a thermal expansion of 10-13 x 10e-5 mm/DegC (check with your supplier)
Some composites are less than 0.1% moisture and around 2-3 x 10e-5 mm/DegC
I run through these calculations all day (using a spreadsheet)
I hope that helps, it's good to do a few sums and get it right. You'll end up with bearings that last longer and less movement in the shaft.
 
I also use composite materials commercially. On carbon filled ptfe we can get a change of 1mm in length on a 150 mm long bar with a change in temperature of less than 20 C
The point is to perhaps try warming the area including the bush to see if the dimension changes a lot
 
Halo said:
I also use composite materials commercially. On carbon filled ptfe we can get a change of 1mm in length on a 150 mm long bar with a change in temperature of less than 20 C
The point is to perhaps try warming the area including the bush to see if the dimension changes a lot
Click to expand...
Would that be Vespel?
 
bert49uk said:
i think its Delrin
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I would try an engine builders who do reboring of car motors, they will have a "hone" that they use for "busting " the glaze on engine cylinders before fitting new rings, this is a spring loaded type of reamer that is fitted with abrasive blocks instead of cutting flutes and can be reciprocated in the bush until you reach the desired clearance, a flap wheel is a good substitute.
 
REAMER

Hi Bert, I have what you need. Please send me a pm. I made some new rudder bearings from nylon
filled with molybdenum disulphide lubricant. However when I fitted them they were too tight. I got
a friend in the workshop ( I was working for a uni ) to make me a 2inch reamer. (Strange for a French boat-
rudder stock is 2inch stainless not 50mm)
 
Trouble is with MoS2 filled nylon is you will have to allow for around 8.5% moisture swell at saturation (that's for Ensinger Tecamid). Which means running big clearances if some parts are wet and others dry, it will also soften with heat/fiction and warm waters. I don't think this is the best choice for a marine environment where the bearing will see moisture.
 
Halo said:
We buy it as 25% carbon filled ptfe from Gappi in Rotherham
Apparently world production of this stuff is confined to 2 factories in Northern Italy
Hope this helps
Martin
Click to expand...
Gapi supply Torlon, Vespel is the Dupont carbon filled ptfe equivelant, there are many others. It's interesting as we have been replacing these types of material with MoS2 and graphite filled phenolic, that have better creep resistance.
 
I'm just about to go down the same road! Last weekend I discovered the rudder bearing skin fitting was loose and the white metal bearing was badly worn. I am looking at running the white metal out and replacing it with a "plastic" pushed in sleeve that will then be bored to size (2").

The question is what material does the experts recomend and also what tolerance for the ID? Whilst the boat is currently in the UK being refitted we do intend (eventually) to spend time in a lot warmer waters.

And why cant I get the spelll check to work!
 
I don't know of any other materials but Aquarius-50 can be used as a direct replacement for white metal bushes/bearings still lubricated with oil/grease.
This material is a variant of Maritex Aquarius (ideal for water or dry) with higher thermal conduction as grease/oil is less effective at conducting heat than water.

If you change the lubricant you have a wider choice of materials as many say they are OK in water.

Clearance will depend on the material and also the wall thickness so you will need to tell me the bearing carrier ID, and each plastic/composite has it's own thermal and moisture expansion rate so each material will pretty much have a unique running clearance when new. When fitting a new bearing getting this right dramatically improves wear rates as any bush that is over sized wears faster and under sized you'll have friction/stick/seized issues as the temperature or load changes.

As an example (this will be greater for thicker walled bearings)
Maritex Aquarius sea water lubricated 50.80OD shaft 70.00ID carrier
Min radial displacement 0.20mm
This takes account of Moisture bore closure 0.06mm
Bore closure from thermal change 0.09mm

To accurately calculate new clearance you can also take into account the bearing carrier and shaft material as these will have different thermal expansion rates.but generally sea water lubricated are assumed to run between 10 - 25C in UK or EU waters.
 
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