Are those 'Bronze' screws really bronze?

What kind, options, etc.

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Andy Garrett
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Location: Nampa, Idaho

Are those 'Bronze' screws really bronze?

Postby Andy Garrett » Sat Oct 11, 2014 4:28 pm

I was wanting to use some bronze in a knife fixture and went to ebay to find a bar or billet. There, I found: aluminum bronze, architectural bronze, and others. I decided that I needed to educate myself about bronze alloys in general.

From my reading I have learned that architectural bronze and silicon bronze (what my boat is screwed together with) are more accurately described as 'brass' alloys due to the fact that they contain more zinc (what you blend with copper to make brass) than tin (what you blend with copper to make bronze).

Somewhere, (maybe it was the Boatbuilding With Plywood book or maybe it was here on the forums) I read that brass screws were bad for boatbuilding.

I always thought those silicon bronze screws were a bit too shiny. Plus they were soft enough that I have a hole cup of stripped screws that I was going to melt down for a guard on my boat knife.

Thoughts?
Andy Garrett

Perhaps the slowest Zip build in Glen-L history...

bjfrater
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Joined: Sun May 04, 2014 9:13 pm
Location: Auckland, New Zealand

Re: Are those 'Bronze' screws really bronze?

Postby bjfrater » Sun Oct 12, 2014 1:08 pm

Hey Andy

I dont know the answer to your question but I do agree that those screws are super soft. They are horrible to work with and probably the worst screws I have ever had to use.
I actually bent one the other day just pressing into the drill while trying not to strip the head while screwing it in!
I think If I were to build another boat I would go with 316 stainless screws take a square head driver bit.

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galamb
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Re: Are those 'Bronze' screws really bronze?

Postby galamb » Sun Oct 12, 2014 2:23 pm

Andy, you have tripped over "modern terminology" :)

Real "modern" bronze is 88% copper and 12% tin

Classic bronze used for blades was 90% copper and 10% tin - this is what is known as Commercial Bronze (today).

Silicon Bronze (as in marine hardware) is most probably 651 Silicon Bronze which is:

96.5% copper
0.8% iron
0.7% manganese
0.05% lead
0.8 - 2% silicon
and up to 1.5% Zinc (depending on the silicon content)

Brass that is used for screws (fasteners) is generally "High Brass" and is composed of 65% copper and 35% zinc (but there are lots of formula for brass). These are somewhat "softer" than silicon bronze twisting off easier when trying to fasten them to "structural" rather than "decorative" torque levels.

And yes, the Silicon Bronze still will twist off, particularly if you don't pilot it, it is more suitable than even stainless, which will rust from the inside out, in marine applications.

If you are looking to make a knife related item out of bronze, you need to look for the "commercial" variety (90%/10% - copper/tin).
Graham

Yes, Plywood is "real" wood :)

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it :)


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