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Magnesium Alloy

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Steve Withnell27/08/2016 09:29:15
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848 forum posts
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I bought an old Bell & Howell 16mm movie projector a while back for a bit of fun. It's an amazing piece of engineering produced around 1962. Just to add to the fun, the audio amplifier uses EL84's

Anyway, the retaining screws that hold the case to the frame were a right mixed bag of threads shapes and sizes, but my best guess was they should have been 6-32 slotted panheads (but bigger heads than normal).

I decided to drill and tap 4mm all the holes and use flange head screws.

Reading the service manual I spotted a warning that the frame is a magnesium alloy casting and proper workshop practice must be followed.

What is the appropriate "workshop practice" for drilling and tapping this material? I'm assuming there is a fire risk when machining the alloy. The first one drilled and tapped just fine

Steve

I.M. OUTAHERE27/08/2016 10:17:46
1468 forum posts
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Tweaked my interest this one as i know nothing about working with magnesium alloys so Wikipedia to the rescue !

I didn't see anything other than a mention that these alloys are highly inflammable in dust or small chip form and to keep the temperature below 470 C .

I don't think you will achieve this drilling and tapping a few holes .

I'm sure some one with more experience will come along shortly !

Ian.

DMB27/08/2016 10:19:13
1350 forum posts
1 photos
Steve,
When job finished have a good clean up to get rid of all mag ali swarf as its a very real fire hazard.
BR used to use a mix of iron and magnesium filings to do onsite welding of rails. Stuff used to burn like hell white hot.
Somewhere on this forum a long time ago there were comments about the potential dangers and I think at least one shed man had a fire.
Take care!
John

Edited By DMB on 27/08/2016 10:20:03

Edited By DMB on 27/08/2016 10:20:44

Edited By DMB on 27/08/2016 10:22:07

Edited By DMB on 27/08/2016 10:23:09

Andrew Johnston27/08/2016 10:21:02
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I don't think it's an issue with the metal working techniques per se. I recently cut up some magnesium sheet on my guillotine as a favour to a client, and it was no different to aluminium. Possible problems are due to the combustion of magnesium. In the form of fine swarf or thin ribbons it can spontaneously ignite. Once burning you either need a class D fire extinguisher or a bucket of dry sand to put it out. The same problem occurs with some other metals, notably titanium. Having looked at the cost of a class D extinguisher I turned down a job machining titanium for the same client. In practise I suspect there is unlikely to be an issue. But since my garage/workshop is integral to the house I didn't fancy explaining to the household insurers how I'd managed to burn the lot down.

Andrew

Brian Wood27/08/2016 10:27:07
2578 forum posts
39 photos

Steve,

​Finely divided magnesium and its alloys are a fire hazard, but I hardly think you will run the risk of any kind of conflagration drilling and tapping a few holes. I would though take the precaution of drilling wet, by wet I mean with paraffin or WD 40 dripped in the hole.

Then gather the swarf and burn it

Regards Brian

SillyOldDuffer27/08/2016 11:13:58
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8863 forum posts
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Posted by Brian Wood on 27/08/2016 10:27:07:

Steve,

...

Then gather the swarf and burn it

But be aware that trying to put out a magnesium fire with water will cause an explosion. Burning magnesium + water = burning magnesium + steam + hydrogen + air = whoosh bang!

If I was going to work magnesium on any scale I'd research how to do it first, including what to do with the scrap.

Dave

roy entwistle27/08/2016 11:24:36
1551 forum posts

Brian A fire hazard and using paraffin ? I wouldn't have thought so

mechman4827/08/2016 11:44:53
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Would any of the above apply to 'ZAMAK' ... Zinc Alloy; also known as Mazak

'ZAMAK is an acronym for Zinc Aluminium Magnesium and "Kopper".

**LINK**)

Has any one machined Zamak / Mazak as they both contain elements of Magnesium ?... Just curious thinking

George.

Andrew Johnston27/08/2016 11:51:07
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A small amount, not a problem. The percentage of magnesium is very small, the alloys are mainly zinc.

Andrew

Geoff Theasby27/08/2016 11:54:06
613 forum posts
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Drilling and tapping Mg shouldn't be a problem, since any heat will be conducted rapidly away. Consequently, the metal in the mass never gets hot enough to ignite. Dust and swarf, though, Beware! As it is light and insubstantial, heat rapidly builds up.

Geoff

Brian Wood27/08/2016 11:57:04
2578 forum posts
39 photos

Roy,

The stuff will burn under water too. I was suggested a tried and tested cutting fluid to take away the chance of rubbing and heating while drilling. I would never suggest working that way with magnesium swarf in any quantity. I have seen the effects of a zirconium swarf fire, it needed a torch to get it going, but once started----

Steve is talking about opening out a few holes to a new tapping diameter, the swarf generated will be barely enough to hide a very small stamp.

I think the reality of a fire is vanishingly small, somewhere along the lines of a sparkler in a birthday cake, but would having a bag of dry sand ready to dump on it appease you?

Brian

roy entwistle27/08/2016 12:22:31
1551 forum posts

Yes I once had a small quantity of very fine aluminium swarf ( like spider web ) go up on the lathe, not something to relish

Circlip27/08/2016 12:42:21
1524 forum posts

Yonks ago I bought a speedboat with a 65Horse Mercury outboard hung on it. The whole rig was cheap because the motor "Didn't work". Hardly surprising with a broken con rod poking through a hole in the crankcase. Top and bottom (front and back cos the engine crank is vertical) crankcase halves, like a VW is line bored to clamp the main bearings and checking with supplier would have meant a new crankcase complete. Coupled with the fact the cylinder head is part of the "Top" casing, deferably an expensive replacement.

What about welding the hole closed, filling a 25mm x 15mm piece of missing case?

"No, it's a Magnesium Aluminium casting" was the agents retort.

"Yes, but is it Magnesium Aluminium or Aluminium Magnesium"

Attacking a broken piece with a blowlamp confirmed the latter so a local welder with Tig welding Aluminium experience costing £30 (35 years ago) was a considerable saving. A bit of internal scraping cleaned it up and on reassembly ran like a dream.

Depends which is the major element when thinking of repairs and safety precautions.

Regards Ian.

John Stevenson27/08/2016 12:44:16
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Gordon Bennett it's 3 or 4 tapped holes not a bloody space shuttle.

You stand more chance setting fire to your moleskin trousers trying to cut the welds to get you out your armchair.

Andrew Johnston27/08/2016 13:19:57
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Posted by John Stevenson on 27/08/2016 12:44:16:

Gordon Bennett it's 3 or 4 tapped holes not a bloody space shuttle.

...........but look what happened to the space shuttle!

John Stevenson27/08/2016 13:46:59
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Don't think a Myford has that horsepower !!

mark smith 2027/08/2016 14:00:44
681 forum posts
337 photos
Posted by DMB on 27/08/2016 10:19:13:
Steve,
When job finished have a good clean up to get rid of all mag ali swarf as its a very real fire hazard.
BR used to use a mix of iron and magnesium filings to do onsite welding of rails. Stuff used to burn like hell white hot.
Somewhere on this forum a long time ago there were comments about the potential dangers and I think at least one shed man had a fire.
Take care!
John

Edited By DMB on 27/08/2016 10:20:03

Edited By DMB on 27/08/2016 10:20:44

Edited By DMB on 27/08/2016 10:22:07

Edited By DMB on 27/08/2016 10:23:09

Hi, You sure it wasn`t aluminium BR were using, though they often use a magnesium ribbon fuse to set the reaction off. Thermite reaction.

Andrew Tinsley27/08/2016 15:17:50
1611 forum posts

You don't need to worry about doing drilling and tapping on a magnesium casting, unless your drill is totally blunt and ignites the stuff.

It depends a lot on the exact composition of the alloy. Magnesium with just 2% iron is non flammable,or maybe it was silicon, I can't remember right now and I don't have my notes here. It seems to be very difficult to get hold of. At least I cannot source it.

If you think you have a problem, I am casting the stuff! You should see the remote control set up that I have. If the argon atmosphere fails then I have somewhat bigger problems than you might have!

Before the engineering community comes down on me with much wrath. I might say that my casting setup is highly professional and is operated remotely. If anything did go wrong, then I am in a remote area free from housing or for that matter the melt is remote from myself! At least two people are present during a casting operation. So safety is absolutely paramount.

I would not recommend trying this for yourself, I still have not got a clean casting and I have put a lot of work into the set up. So much so that I can't give up now!

Andrew.

steamdave27/08/2016 15:39:33
521 forum posts
45 photos

When I was a lad, we used to buy strips of magnesium in the local chemist shop, about 1/8" wide and 12" long from memory. 'Twas great fun to set fire to it with a match.

Dave
The Emerald Isle

Steve Withnell27/08/2016 15:55:31
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848 forum posts
215 photos

Sounds like the only risk is the dust and chips dropping into that nice valve amplifier.

Thanks!

Steve

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