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Crumbling Monkey Metal

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Neil Wyatt20/01/2019 11:35:12
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I'm fitting a new body to a guitar I 'made' in 1993. It's got a Floyd Rose (or more likely a copy) bridge that dates back to about ten years earlier so it must be about thirty five years old.

It was hard to tune and when I removed it from the guitar the reason appeared obvious - the three fixing screws for the part inside the guitar was loose.

This does get a fair bit of stress taking the whole string tension, balanced by three springs. Especially when it was on my brother's strat in the days before I got it!

However, it seems the damage is not as simple as just stress cracks as the whole part is riddled with cracks that make it look like the whole part is swelling from the inside. My guess is it started to gradually swell and split due to tinworm and this then led to the actual breaking of the parts the screws fit into.

It's a pressure casting but I'm going to machine a replacement from 6062 aluminium alloy.

Neil

bridge (1).jpg

bridge (2).jpg

Tim Stevens20/01/2019 11:49:45
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993 forum posts

A common problem with old diecast alloys - whether zinc based or aluminium based. From memory, it can be caused by a lack of purity in one or more of the alloying elements.

And you are right - the answer is to start again - fortunately in this case it seems a straightforward part to machine. Or do I mean straight forward, then back again, then sideways, and then endways ...

Regards, Tim

Edited By Tim Stevens on 20/01/2019 11:51:02

Chris Trice20/01/2019 11:58:54
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What Tim says. A lot of old die cast cars from some specific manufacturers have the same problem usually around rivets.

Gray20/01/2019 12:07:18
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Doesn't look right for an original Floyd Rose, almost certainly one of the far eastern copies that were around at that time. IF your making a new block, I would recommend brass over any aluminium alloy. The block helps with sustain on a floating trem. I used to make these and most customers wanted a bigger block so they were made almost double the thickness of a standard sustain block. Floyd Rose now sell them as a replacement part. Is yours fitted with fine tuners and the double locking type?

Brian H20/01/2019 12:50:52
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1047 forum posts
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As Tim says, a common problem with old diecasts. Austin seven carbs are notorious!

Brian

Howard Lewis20/01/2019 12:59:02
1798 forum posts
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Some old diecasting just seem to turn to powder. Have an old Rivarossi loco that I dare not look at too hard for just that reason.

(Last week, a recent alloy Toilet Handle broke. The fracture was so full of blow holes that it looked like a silver painted Aero chocolate bar!)

No doubt, your shop made replacement will be far better than the original when new, and have an infinitely greater life expectancy.

Howard

Georgineer20/01/2019 13:05:22
219 forum posts
12 photos

It has the delightful name zincpest.

George

Martin Hamilton 120/01/2019 13:54:17
70 forum posts

Some of the castings on old Emco machines can suffer with diecast corrosion problems after a number of years where they start to burst open. I looked at a 1979 Emco compact 8 recently & the leadscrew bearing blocks at either ends of the leadscrew were bursting & splitting open purely with age.

Nicholas Farr20/01/2019 14:01:03
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Hi, it could have been an inspiration for Neil Diamond's song "Cracklin' Rosie". teeth 2

I'll get me coat.

Regards Nick.

not done it yet20/01/2019 14:07:20
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It’s a reaction with water. Damp storage or just cold with a fair fair humidity will cause expansion of the cheap MAZAK. I’ve encountered this with north american autoknitter sock knitting machines. Probably why English made versions were fitted with cast iron cylinders and steel parts.

Bazyle20/01/2019 14:10:02
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My search to find out what you were talking about led me to a site advertising 'build your own bridge'. Massive disappointment on finding it was the modern kids version of build something ie select the colour and trivial stuff.

Well at least my knowledge of stuff I will never ever need to know about has increased. If you machine your own at least you can boast 'machined from billet' when meeting cheapskates who only have a diecast one. laugh

vintage engineer20/01/2019 15:00:41
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It's caused by hydrogen embrittlement. A naughty trick foundries do on aluminium castings is to add zinc to bulk out the aluminium. This comes to light when you try to weld the crap!

Ed Duffner20/01/2019 15:02:26
713 forum posts
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Neil, a preferred metal is 1018 cold rolled steel for trem blocks. I'm not sure what the equivalent of 1018 is here in the UK.

Ed.

Neil Wyatt20/01/2019 15:37:43
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Posted by Gray on 20/01/2019 12:07:18:

Doesn't look right for an original Floyd Rose, almost certainly one of the far eastern copies that were around at that time. IF your making a new block, I would recommend brass over any aluminium alloy. The block helps with sustain on a floating trem. I used to make these and most customers wanted a bigger block so they were made almost double the thickness of a standard sustain block. Floyd Rose now sell them as a replacement part. Is yours fitted with fine tuners and the double locking type?

I'm pretty sure it's a copy, with fine tuners but old enough not to be double locking.

The guitar is a bit of a hack I just want to be pretty, I have plenty of rock solid guitars so one with feeble sustain might actually be a nice change - plus brass is expensive and I have the ally

I could get a brand new licensed one (as used on cheap Chinese guitars) with locking (and much simpler construction) for £11, but I like the challenge of making the part.

Neil

Neil Wyatt20/01/2019 15:45:06
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Posted by Ed Duffner on 20/01/2019 15:02:26:

Neil, a preferred metal is 1018 cold rolled steel for trem blocks. I'm not sure what the equivalent of 1018 is here in the UK.

Ed.

Hmm could use steel. EN32 is probably close, but I'm sure EN1a would be fine.

Will need some sort of rustproofing.

Hmm will need an M10 x 1mm tap. I can make one that will do the job in aluminium but might struggle in steel. This was meant to be a cheap project but I've already had to buy a jack socket, a bottle of blue ink, three cans of polyurethane varnish, scratchplate material and the new body...

img_20190117_084332662_hdr.jpg

Edited By Neil Wyatt on 20/01/2019 15:45:36

Neil Wyatt20/01/2019 15:48:37
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Posted by vintage engineer on 20/01/2019 15:00:41:

It's caused by hydrogen embrittlement. A naughty trick foundries do on aluminium castings is to add zinc to bulk out the aluminium. This comes to light when you try to weld the crap!

But where does the hydrogen come from?

Nigel Bennett20/01/2019 15:54:39
276 forum posts
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Mazak (Zamak if you're in the US) as used for a lot of zinc die-castings were very prone to crumbling away (Old Hornby Dublo stuff and many pre-war toys sometimes suffered). This was due to minute amounts of lead in the alloy causing grain growth. If the lead is below a certain concentration, there's usually no problem.

SillyOldDuffer20/01/2019 16:35:29
3978 forum posts
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Not a new problem. To read all about it see Zinc Pest

Dave

daveb20/01/2019 17:35:53
601 forum posts
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Reminded me of an engineering firm who made motor scooters in the late 50s. The handlebar bracket was a Mazak casting, the handlebars tended to fall off.

Neil Wyatt20/01/2019 17:36:05
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Agreed, it's zinc pest, not tinworm

Neil

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