Bronze Alloy

Under "workshop techniques" section, I put a question relating to my proposed rope cutter. I was pleased to see a couple of suggestions regarding the plastic bushes but more importantly it was pointed out that I was proposing to use gauge plate whereas I needed to use stainless steel grade 316. It was also suggested " leaded"

So to look into this, I contacted the Stainless Steel Assn... I received a very prompt reply. The chap said that i should look to use a " Standard Duplex grade ss"Not sure what that is - Anyone used it before??

The chap then went on to say that perhaps I would do better using a Bronze Alloy. He pointed out that my propeller was made of the same stuff. Sure enough research shows that there are several grades of this & some are salt water resistant & excellent for this purpose ( rope cutters)

I do not have a price yet, but am asking if anyone has experience of machining this material. A bit more in cost may be better than buying a steel that my light mill cannot handle & I just wear out milling cutters by rubbing & vibration & not cutting due to lack of force etc

Any comments gratefully received

thanks

Edited By Sam Longley 1 on 30/01/2018 18:14:24

Have a look at Keith Fenner vids? He machines quite a lot of boat stuff

Duplex stainless steels have a different alloy structure,and have better corrosion resistance. Personally, I don’t think this is all that important for a marine application - the difference might be apparent in high temperature applications or with food or brewing equipment, but 316 is perfectly adequate for marine work.

One of the bronze alloys might work as well, maybe silicone bronze for example, but would be more expensive and more difficult to source. 316 is very close to bronze and brass alloys on the electrolytic scale, so electrolytic corrosion is no reason to avoid stainless.

The only real problem with stainless in marine applications is crevice corrosion - caused by a lack of oxygen. It won’t be a problem with something like your rope stripper which is surrounded by a free flow of water. It is sometimes a problem with prop shafts, particularly on the taper where the prop is fitted, and manifests as what appear to be burrows or worm-holes. But even this is not enough to persuade boat builders and engine installers to use anything other than 316 for prop shafts - yes, some older boats have bronze shafts, but I bet 95% of boats have stainless shafts fitted.

Steve

Thanks, but what i am really worried about is machinability with a milling machine. That would be worth some extra cost. & yes i did have a bronze propshaft years ago now you remind me !!!

Bronze as you know is used for bearings. It is kind of 'slippery' so needs a sharp tool to cut it and tends to grab and break small drills. It is actually a very strong material and takes a fine edge which is what allowed the Bronze Age to happen and persist in use into the Iron Age. The Roman's famous short swords were short because their iron was crap but cheaper than bronze.

All the bronzes I’ve machined have been fine - some are surprisingly tough, all of them need very sharp cutters but rarely any problems (except sometimes when I’ve ignored my own advice and used a blunt twist drill on a very deep hole). I would say that 316 stainless is tougher to machine than any bronze I have experienced.

To be honest, since most of the machining I have done on marine work has been repairs and modifications to existing components, it is difficult to know exactly what type of bronzes that I’ve dealt with. I think silicone bronze is one of the tougher variants, and is used for machine screws, bolts and other fixings - I have machined lots of that with no problem. Some so-called bronzes are actually brass (copper/zinc alloy) - to be avoided at all costs because of dezincification (there are some exceptions to this, but not many).