Bronze Bush

[Sailfishing]

Hello everyone,

This is my first post to the forum, however I have read many and gathered an awful lot of help from doing so, however in this case I am stuck...

I am the owner of Sailfish 18 fitted with a retractable keel. The keel is wound up and down on by a bronze bush mounted on the keel running on a stainless steel thread. The bush is badly worn and I am going to make a new one. My problem is what to make it out of? I have access to loads of brass but fear it may be too soft and ware very quickly. Ideally if anyone knows of the ideal material and a supplier that will sell a very small amount that would be ideal...

Any thoughts?

Many thanks in advance

Kev

 

[earlybird]

It sounds as if phosphor bronze might be a good material. This can be obtained from many metal stockists. try one for model engineering, eg Chronos, Metalsontheweb, Macc model engineering supplies, or possibly ebay.

 

[vyv_cox]

I agree with earlybird that phosphor bronze would often be specified for this duty. However, it should be remembered that the alloy is a modified brass that does not have great corrosion resistance. Its life will not be great, but may well be long enough.

True bronzes are copper-tin alloys, so if you can get hold of some of this it would be better for corrosion resistance and good for wear resistance. Gunmetal is a typical alloy that may perhaps be available from stock. It is sold in a leaded form, which would be ideal.

Alternatively aluminium bronzes have excellent corrosion resistance and reasonable wear resistance at low speeds, which presumably includes your keel! I happen to know that the bearings on the Thames barrier are made from this alloy.

A machine shop will normally carry stocks of these, but try these suppliers too.

 

[earlybird]

Vyv, I take your point re gunmetal etc for bushes. However, I read the OP as refering to the screw nut of the CB operating system, not the pivot bushes, hence I thought of PB on account of its toughness.

 

[Sailfishing]

Thanks for the prompt responses, what ever was there before has not really corroded at all, its just worn on the thread, would you surmise that its prob not PB then?

 

[earlybird]

[ QUOTE ]
would you surmise that its prob not PB then?

[/ QUOTE ]
For myself, I would be perfectly happy with PB, and would expect it to out-live me, but I'm an OAP. However, your existing nut might well be gunmetal, I'm sure either would do, and GM could be easier for machining a female thread. PB, esp. in its cold drawn form can be a tough cookie. Arising from Vyv's post I've done a bit of googling, it seems that the zinc content of PB can be between nil and 9%, that of Colphos 90, a leaded variant stocked by several model suppliers is 3% Zn. NB it's fairly dear stuff as metals go.

 

[vyv_cox]

Oops! /forums/images/graemlins/blush.gif You are correct and I stand corrected. Just shows you should check before you write, no matter how much you think you know.

Ignore what I said about PB further up the thread, it's rubbish. Phosphor bronze will be fine, especially if what you are requiring is a nut that runs on a screw. Leaded gunmetal would be fine if it was a parallel bush but perhaps not so good as a nut. Aluminium bronze is very good stuff but maybe not so available.

 

[Sailfishing]

So phosphor bronze or aluminium bronze would both be fine, PB more available so I'll try for that...

Anyone recommend a supplier? or is it just a session of googleing?? lol


Cheers,

Kev

 

[vyv_cox]

I posted a link in my previous post. That was OK, even if some of the other info wasn't.

My advice would be to find your machinist first, then worry about the material. Chances are he will have a small piece or will be able to source it.

 

[Sailfishing]

I can do the machining myself, its just that all we have access to is stainless... and small quantities of brass...

 

[Norman_E]

Just a thought, if you are making a new part and have the equipment to cut the thread, why not add a grease nipple to the side of the nut to deliver grease right to the threads? Lubricating a nut that way drives dirt and grit out of the nut, whereas smearing grease onto the threaded rod attracts dirt, which then gets into the nut.

 

[Sailfishing]

thats a good suggestion Norman, I may well follow that up. would be very minimal extra work...