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Tensile Strength - Brass or Bronze?

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Neal Swarbrick22/04/2014 11:27:26
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Hi all,

I am just finishing up my Myford MF74 Lathe and am in the process of tooling up. Am going to use the RDG 8-piece 6mm HSS tool set to start with. But that's by-the-by.

I already have a friend asking if I can make summat for him.

What he wants are two pillion-rider foot-pegs for his Harley. He wants them in hexagonal Brass but I'm wondering whether that material would be up to the job? Even if I can find hex brass in, probably, 2" cross-section.

Would Bronze be a better bet? I'm aware that in certain conditions brass can lose it's tensile strength due to electrolytic corrosion . . .

Advice please . . .

Neal

Chris Gunn22/04/2014 12:16:45
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Why not make them in two parts, a steel core to take the load, and slip on a brass hexagonal sleeve for appearance, hold the sleeve on with a screw or pin on the underside or Loctite it.

Chris Gunn

Mick Dobson22/04/2014 12:21:19
21 forum posts
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Brass (70Cu/30Zn) has the higher tensile strength at 550MPa, compared to Bronze (90Cu/10Sn) at 260MPa.

Therefore would seem brass is the preferred option. Easier to polish up too, and cheaper no doubt.

John Stevenson22/04/2014 12:39:33
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Don't matter.

If it's for a Hardly Dangerous it won't get used, only polished............................

Ian S C22/04/2014 13:07:16
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If it's the strength you need it is not the tensile, but the shear strength your looking for. Ian S C

 

Shear strength:

Brass   215 - 315   (MPa)

Bronze 295 - 435   (MPa)

Edited By Ian S C on 22/04/2014 13:17:01

Edited By Ian S C on 22/04/2014 13:19:52

Jo22/04/2014 16:00:28
198 forum posts

Pillion pegs don't need to be that strong: unless they are intended on protecting the HD when it is dropped.

2" A/F Brass is going to take more than your averagepilion rider's weight as they attempt to mount the bike but how big is the mounting thread?

Jo

John Stevenson22/04/2014 16:11:10
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One point to bear in mind given the sizes is price.

I make some unions for British Rail out of 2" A/F brass and a bar costs me £420 plus VAT

Noggin ends quote £8.50 per inch so that make their bars £994 a pop.

Mick Dobson22/04/2014 18:03:26
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"If it's the strength you need it is not the tensile, but the shear strength your looking for"

Both tensile and shear really; with a load applied somewhere along the foot peg, there will be a shear force at the fixing point (bolt or stud in the end of the peg) plus a bending moment (couple) acting about that point. So the foot peg could bend along it's length and /or shear at the fixing. I expect the weakest point will be the fixing bolt, not the footpeg, unless it is made very thin walled.

As mentioned, price could be the limiting factor, not material strength!

Mick.

Neal Swarbrick22/04/2014 19:46:30
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Thanks for all the feedback. Much appreciated

The steel core with the brass 'wrap-around' might be an answer, tbh. I could take the original peg, machine it to size then wallop! Nice idea Chris.

I wasn't sure whether it would be tensile or shear actually. It's good to know there are people here that do know what they're talking about. But John S is prolly right about it only being there to be polished if I know my friend. It's his pride, joy, girl-friend, the lot!

Price wise, if I can get him to accept round bar, the College Engineering Supply looks best value at a smidgin under £40 for one piece of 2" x 7" round. Hex-wise they only go up to 1" but you can get 2' of that for the same price . . . .

John Stevenson22/04/2014 21:03:27
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If you want to do the wrap around jobbie then think about bronze.

Reason I say this is you can buy cored bronze at far less prices than brass. Incidentally brass is now dearer then bronze ??

Leeds Bronze have a website where they list solid on one page and cored on another, You will have to ring them for a price but I deal with these people and never found anyone close for pricing.

You only want 2" ? they will sell you 2" and not bat an eyelid. Last time I used them I wanted some 6" diameter, 4" cored hole but only wanted 3 pieces cut to 3/4" wide finished size. These were for slip rings on a big AC motor.

No problem and delivered to the door two days later.

RICHARD GREEN 223/04/2014 10:43:44
313 forum posts
183 photos

Getting back to the question of material strength, what is best for silver soldered boiler fittings, brass or PB1 bronze ?

Richard.

Jo23/04/2014 10:55:00
198 forum posts

Boiler fittings should always be made out of bronze.

Brass suffers from dezincification when it is in contact with the water in the boiler and will over time fail.

Jo

Ian S C23/04/2014 10:59:19
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7468 forum posts
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My brass suppler has ornamental brass tube, I think there is hex, some of it has flutes on the flats, that would fit nicely over a cheaper core. Ian S C

John Baguley23/04/2014 11:00:20
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467 forum posts
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Jo beat me to it. I've had several brass fittings snap off when I've tried to remove them from a boiler. One of them was an injector steam valve. That would have been nasty if it had happened when the boiler was in steam!

John

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