Making rudder bushes measurements

Rhylsailer99

Rhylsailer99

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I'm about to make some rudder bushes , any ideas on how much excess bore should be. Ie if the bar is 25.4mm should I make the hole 26mm to allow easy movement. I don't want to make the hole to big to aLlow excess play though. Is there a standard size of oversizing the bore.
 
I've worked with Acetal/Delrin and would suggest the smallest clearance compatible with free movement, 0.1-0.2mm. Delrin comes in lots of grades and will wear anyway. Bear in mind that there might be wear in the area where it's in contact with the bush so check measurements all the way from the top of the rudder shaft. Unless the two bushes are dead in line the rudder will potentially bind.
 
I might go with 1mm oversize diameter as I have to get the boat lifted to get the rudder in place and once its fitted , ideally I need to get it right 1st time.
 
Rhylsailer99 said:
I might go with 1mm oversize diameter as I have to get the boat lifted to get the rudder in place and once its fitted , ideally I need to get it right 1st time.
Click to expand...


In my view 1 mm oversize is far too much. I would be looking at a max of 0.1 mm or even less.

Looking at my one Zeus a average running fit would be about .001 to .002 inch for a 1 " shaft.
 
Rogershaw said:
In my view 1 mm oversize is far too much. I would be looking at a max of 0.1 mm or even less.

Looking at my one Zeus a average running fit would be about .001 to .002 inch for a 1 " shaft.
Click to expand...
OK ill make them slide them on and see how they feel , im just worried of the rudder becoming stiff once on the boat if I make it too small a tolerance.
 
Rhylsailer99 said:
OK ill make them slide them on and see how they feel , im just worried of the rudder becoming stiff once on the boat if I make it too small a tolerance.
Click to expand...


Also if the bush is a press fit in the boat you will need to compensate for the reduction in the bore diameter dur to the press fit. If the bush is glued in as some are than this compensation will not be required.

Also f the bust is too tight after fitting it can be eased out with a small fine grit flap wheel in a drill or die grinder.
 
Rogershaw said:
Also if the bush is a press fit in the boat you will need to compensate for the reduction in the bore diameter dur to the press fit. If the bush is glued in as some are than this compensation will not be required.
Click to expand...
Yes thats a point i make bait pumps with bushes and I make a press fit and I need a 9mm hole to allow an 8mm bar to slide free. The hole shrinks a lot when its pushed in tight.
 
Doesn't nylon expand in seawater ?
I used the blocks they use as pile guides on pontoons. 20 times more slippery than ptfe and hard wearing plus very easy to cut and drill.
It's uhmwpe.
 
Rappey said:
Doesn't nylon expand in seawater ?
I used the blocks they use as pile guides on pontoons. 20 times more slippery than ptfe and hard wearing plus very easy to cut and drill.
It's uhmwpe.
Click to expand...
I've found uhmwpe is one of the best for wearing with sliding movements and does not take on any moisture but its a bit chewy to machine and hard to get a tight tolerance. Try putting a file to uhwmpe and it just slides off and doesn't even touch the surface
 
I did my lower rudder bush between tides so was in a bit of a rush. Took the lower bracket off , went to my shed, cut it to size with chop saw , if the rudder stock was 46mm then I bored a 46 mm hole and it fitted nicely. Put it back together and job done!
A sander worked well for taking sharp edges off.
 
Rappey said:
Doesn't nylon expand in seawater ?
I used the blocks they use as pile guides on pontoons. 20 times more slippery than ptfe and hard wearing plus very easy to cut and drill.
It's uhmwpe.
Click to expand...


Nyon does absorb water and does expand.

I use vesconite for both rubber and prop shaft bushes as its designed to run in water and very little expansion.

uhmwpe is a good material but machining can be tricky.
 
I am going through the motions of getting some new bushes having just spent three weeks digging a hole to drop our ,rudder out. I had hoped the rudder would literally drop out as there was some play in the bottom bush.

It turned out that the aluminium rudder shaft had worn rather than the bottom bush. This allowed the rudder to drop about 50mm then jam solid.

Getting the rudder shaft out took some time using a long timber G clamped to the rudder , washing up liquid as a lubricant and loading the rudder with weight.

I hung a bucket full of 10 high density concrete bricks to help gravity and then had to work the rudder to eventually get the shaft to drop.

Putting the same design of bush back in will be pointless. I will have to increase the length of the bush by at least 25mm to ensure it is bearing on unworn shaft.

I have also been advised to use vesconite with a clearance fit of 0.1 to 0.2 mm.

I think the bottom bush should ideally be a minimum of twice the diameter of the rudder shaft in length.

The idea of compensation of the internal diameter as a result of a push fit into a rudder tube doesn't make sense. Modern adhesives will hold the bush in place with no problem. With this in mind I would consider a slight step in the outer inserted diameter in the top half of the bush to allow a reasonable thickness of adhesive. The lower part will I hope still compress slightly onto the worn part of the shaft as a result of a push fit tolerance to the rudder tube.

I am now missing the access I used to have to a lathe. Anybody in North Wales able to do a bit of turning?
Steve.
 
I turned the bore a little undersize and used an expanding reamer once I had fitted them. You can pick up a second hand one on ebay and sell it when you are finished.
 
Last edited:
Savage Seadog mentioned acetyl of which Delrin is a good example, that would be my choice - a good stable engineering plastic, which machines well (unlike uhmwpe). His advice on clearance is also good, if they are a press fit -002" would give some room for the squeeze.

Don't go near nylon for bushes that get wet - people replacing steering bushes on the cheap with nylon have already caused enough rudders to seize.

Peter
 
I also used acetal on my new rudder bushes. Great material for the job and available in rod form - an engineering outfit may have some off cuts.
 
Also keep in mind that tubes to fit the bushing to may not be round which may change the press fit.
I'd also stay away from "modern adhesives" in this matter.
 
Rhylsailer99 said:
I'm about to make some rudder bushes , any ideas on how much excess bore should be. Ie if the bar is 25.4mm should I make the hole 26mm to allow easy movement. I don't want to make the hole to big to aLlow excess play though. Is there a standard size of oversizing the bore.
Click to expand...
I have sent existing bushes to suppliers to make to exact replacements. Otherwise allow some overage on the order and be prepared to pare away material after offering up. Acetal etc can be filed or ground out with care IME. If this relates to bushes on a Bav I can offer further assistance. BTDI.

PWG
 
TSB240 said:
I am going through the motions of getting some new bushes having just spent three weeks digging a hole to drop our ,rudder out. I had hoped the rudder would literally drop out as there was some play in the bottom bush.

It turned out that the aluminium rudder shaft had worn rather than the bottom bush. This allowed the rudder to drop about 50mm then jam solid.

Getting the rudder shaft out took some time using a long timber G clamped to the rudder , washing up liquid as a lubricant and loading the rudder with weight.

I hung a bucket full of 10 high density concrete bricks to help gravity and then had to work the rudder to eventually get the shaft to drop.

Putting the same design of bush back in will be pointless. I will have to increase the length of the bush by at least 25mm to ensure it is bearing on unworn shaft.

I have also been advised to use vesconite with a clearance fit of 0.1 to 0.2 mm.

I think the bottom bush should ideally be a minimum of twice the diameter of the rudder shaft in length.

The idea of compensation of the internal diameter as a result of a push fit into a rudder tube doesn't make sense. Modern adhesives will hold the bush in place with no problem. With this in mind I would consider a slight step in the outer inserted diameter in the top half of the bush to allow a reasonable thickness of adhesive. The lower part will I hope still compress slightly onto the worn part of the shaft as a result of a push fit tolerance to the rudder tube.

I am now missing the access I used to have to a lathe. Anybody in North Wales able to do a bit of turning?
Steve.
Click to expand...
I can help you out i have a myford lathe in Rhyl and will be ordering some 60mm delrin to make uses.
 
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