Find or getting appropriate sized bolts made up

Cardo

Cardo

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In a plastic tub!
www.yacht-tinkerbell.co.uk
I'm in the process of sorting out the seriously bodged job done on the rudders on Tinkerbell. As with many other bits on the boat, the theory is good, but the implementation is painful.

The twin rudders hang on brackets using M12 x 90mm bolts. This works, but the problem is there is play between the bolts and the brackets, allowing the rudders to move ever so slightly. This causes a "knock knock knocking" that can be quite irritating in the rear cabin when there's a bit of a swell. I had hoped to improve this by using nylon top hats. I bought some 12 ID x 14 OD hats, and drilled the brackets out to 14mm. The hats fit snugly in the brackets, but unfortunately it seems M12 bolts have an outer diameter that's slightly smaller than 12mm, probably close to 11.5mm ish, maybe less (I need to buy some callipers!). So we still have play, although now it's SS on nylon, instead of SS on SS, so hopefully it's slightly improved.

Question is:
Is there a supplier that will have SS bolts that have an OD of just shy of 12mm? Or is it possible to get them made up at a reasonable cost?
 
A 12mm bolt is 12mm on the crests of the threads but you could reduce this by having a bit machined off , say to 11.5 or so.
Would not compromise the strength of the bolt
 
I like the plastic bush solution - after all, very many boats have rudder posts rotating in plastic bearings. I have not done the same job on rudder pintles but I have on my gooseneck, stainless steel pin in an aluminium casting. I reamed out the aluminium and inserted bushes made from plastic water pipe. The OD of the pipe was too big for the bore of the new holes but slitting the plastic and removing a short piece of the perimeter fixed it. I made several up as spares but several years later there seems to be no wear.
 
You might find it easier getting bushes machined from Delrin to suit the bolts you have. Delrin is better for that application than nylon as it does not swell and wears less.
 
Tranona said:
You might find it easier getting bushes machined from Delrin to suit the bolts you have. Delrin is better for that application than nylon as it does not swell and wears less.
Click to expand...

Hmm, good idea.

I think I'll leave on what I have now and see if the nylon bushes do swell up a bit and make a more snug fit. If they don't swell enough, I'll look into these Delrin jobbies.
 
Get the 1/2"bolts and one of your washers. Stand at the vice and start filing with a nice flat file. I've taken loads more than that off steel bar to make it fit into steel tube when internally sleeving the steering shaft on my trials car. You can get a very snug fit.
 
I had the same problem, and solved it by machining some delrin bushes to fit. I was able to make the four bushes to fit each location tightly, all with slightly different OD's. I made a stepped plug gauge out of delrin to find the size that would fit tightly. the variation was only about 0.3mm between the different bushes.
 
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If you get stuck I could machine up a matched set of Acetal/Delrin and stainless bolts, something like the boom bush & pin, http://ffsystems.co.uk/boat_parts.html but with bushes in Acetal/Delrin and the pin being a bolt

Nylon will swell more than acetal/delrin so may tighten in time

If you use bolts with just the minimum essential length threaded, i.e. just the short bit stuck out the end of the bush, then you should get a better fit with none of the threaded part inside the bushes. Rolled thread bolts may well have the threaded section very slightly wider than the non threaded section and with the non-threaded section just less than 12mm, as you have found, but thread cut will be the other way around with the smooth part of the bolt a tad wider than the threaded part as you start with a 12mm bar and cut threads into it rather than start with an undersize bar and roll the threads onto it.

Apologies if teaching to suck eggs etc...
 
I suspect that the bolt is 12mm but the thread is less. If you used a longer bolt such that the solid part was long enough to project through the fitting you could then add a sleeve to enable the threaded part to apply pressure once the bolt was tightened
Or turn the bolt round & have the nut the other end so that the round part, rather than the thread, goes through the nylon
 
DinghyMan said:
If you get stuck I could machine up a matched set of Acetal/Delrin and stainless bolts, something like the boom bush & pin, http://ffsystems.co.uk/boat_parts.html but with bushes in Acetal/Delrin and the pin being a bolt

Nylon will swell more than acetal/delrin so may tighten in time

If you use bolts with just the minimum essential length threaded, i.e. just the short bit stuck out the end of the bush, then you should get a better fit with none of the threaded part inside the bushes. Rolled thread bolts may well have the threaded section very slightly wider than the non threaded section and with the non-threaded section just less than 12mm, as you have found, but thread cut will be the other way around with the smooth part of the bolt a tad wider than the threaded part as you start with a 12mm bar and cut threads into it rather than start with an undersize bar and roll the threads onto it.

Apologies if teaching to suck eggs etc...
Click to expand...
I may take you up on the offer of machining up some Delrin bushes. It sounds like it may just be the ticket.

Daydream believer said:
I suspect that the bolt is 12mm but the thread is less. If you used a longer bolt such that the solid part was long enough to project through the fitting you could then add a sleeve to enable the threaded part to apply pressure once the bolt was tightened
Or turn the bolt round & have the nut the other end so that the round part, rather than the thread, goes through the nylon
Click to expand...

The bolts I'm using only have a thread at the very end. The bit that is in "contact" with the bush is solid. I need to get myself some callipers so I can measure the bolt and establish precisely what sizes I need.
 
I'm not sure if I'm visualising the problem properly, so this may not be relevant.
When I owned and Impala, the rudder clonked at anchor.
It consisted of gudgeons with through hole on the rudder, U-section brackets that went top around each gudgeon and a long pin through the lot.
IT was all over ten years old and a bit slack.
There was movement both between the pin and the rudder, and the hull and the pin.
I sorted it by opening the 3/8 holes in the rudder to 10mm, as well as the upper hole in each bracket.
The lower hole in each bracket, I tapped M10.
Replacing the pin with two M10 bolts which were solid in the brackets (nut on the bottom) meant the bolt was not moving in the brackets, and reaming the holes in the rudder gudgeons to fit the bolts closely gave very little slack. 5 years later it was still OK as it was only wearing over the large area of the gudgeons, and there was only one point of movement instead of two.

I'd want to know the side load was spread over a large area of the plastic bush or it will wear fairly quickly, but they're easy to change.
 
I'm just wondering if a temporary fix can be sorted here until you have more time and easier access to rudder brackets.
If instead of trying to align the brackets directly inline with each other (which makes good sense for a nice smooth operation), could you you rotate them to take up any play? I can't remember if you have 2 or 3 brackets per rudder, but if it's only 3 you could just twist the middle one.
 
I have grabbed a pic from your blog (and turned it the right way up) to make things more clear.

Is it the bolt I have arrowed?

rudders-e1381824278351.jpg
 
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