Why did Leica switch back to a brass top-plate for the M7?

[gl5]

Why did Leica switch back to a brass top-plate for the M7? What

was it previously?

 

In my experience working in a machine shop when I was

younger, I seem to remember that brass is not necessarily that

durable, although it is very machinable (easy to machine).

[roberto_watson_garc_a]

zinc was before on M6 and late M4P´s, it returnrd to brass on M7, I don´t know why, but each has it´s goods and bads, zinc is very strong and hard to bend, but prone to rust if scratched, wile brass may softer but not rustable, stil very strong just take a look on M3´s and on, hope an expert can tell us more.

[charles barcellona www.bl]

The original tops in the M3, M2... all the way up to the beginning of hte M4-P line were stamped brass. The later M4-P up to the M6-TTL are cast zinc.

 

Brass stampings that are complex take many ?dies? and punches, to both form the cover, and to make all the holes in it. The viewfinder windows, top holes for winding, accessory shoe, shutter speed, etc were all punched, not machined. The smaller holes, those used for screws, may have been machined. Any countersunk screw openings were certainly machined rather than stamped. Brass ?work hardens? so, there may have been an annealing process (softening the metal via heat and quenching, just the opposite of steel).

 

Zinc can be cast at relatively low tempertures using gravity or rotary molding. I would imagine that Leica uses rotary molding, as is the custom with high precision parts. Zinc can also be cast using a reusable metal mold, or a disposable ceramic mold. Either would work in this case, and I'm not sure which Leica uses by looking a tthe parts. Zinc can also be sort of die molded/stamped which used a two piece die, and molten zinc that is sort of squeezed into shape. They may use that process too. Someone looking at the inside of a top plate might be able to tell which process they used.

The advantage to a cast plate, is that its inexpensive compared to an extensively worked top plate. The cast one will require some slight amount clean up but this can usually be done with a hand grainder and or simple handtools like a file or deburring blade. All openings would be cast into the part. Cleanup might consist of removing ?flashing? and cleaning up square corners. Depending on the process, a parting line or rotary mark might need to be lightly sanded off the exterior for aesthetic appeal.

 

Zinc and brass can both be chrome plated directly without intermediate plating required, but I think there are some chemical passivation steps required for zinc that are not needed for brass.

[andrew n.bra hrefhttp]

The main reason is that since they are now using CNC mills,

they went back to using brass because they <U>could</U>!<P>

 

In the past, using all the different dies to manf. with brass was a

super-expensive PITA - not so now. So they use brass. They

could just as easily use a 6000 series aluminium alloy, or Ti

alloy or whatever.<P>

 

Brass is strong and malleable and easy-to-machine and plates

very well. You can also paint it if you want (eg. the black-paint

LHSA, Millenium models).<P>

 

See also <A HREF="http://nemeng.com/leica/042b.shtml">the

topic on this</A> in the FAQ I maintain.

[gl5]

fascinating!

 

thanks everyone for the info.

[charles barcellona www.bl]

Andrew, being somewhat associated with precision machining, I'd like to point out that the top plates are not machined, except maybe for a few of the smaller holes which would be made on some sort of jig, not CNC milled.

 

To mill the top plate or bottom plate from solid would be very costly and most difficult to do! Difficult because as the brass gets thin, it becomes very hard to machine. Also, consider the square holes in the top plate. These could be machined, as the corners are slightly radiused, but it would be far far easier to stamp them in.

 

If CNC machines had anything to do with fabrication of the top and bottom plates, it is to BUILD the tooling required to stamp them accurately. Dies and fixtures on a punch press will wear with a fair amount of use. Keeping the tooling in good enough shape to hold tolorance is a job, and most manufacturers have in house tool departments just to keep the production machinery going.

[andy_piper2]

Charles, if you're interested in M7 construction, fine machining etc. you might enjoy the following link regarding a tour of the M7 parts manufacturing facility in Portugal.

 

http://www.imx.nl/photosite/leica/mseries/m7.html

 

Mr. Puts does NOT specifically say the top plates are CNC-machined - he does say they are 'machined out of one piece of brass".

 

Under the stress of, say, dropping a camera body, zinc will crack where brass will dent/bend. I think. (?) I don't know if this has any bearing on the return to brass. It may just be that Leica-lovers have always mourned the departure of the brass top plate and Leica is only satisfying the customers.

[klkx]

Well... the term 'machined' can be many things to many people, and brass plate is solid! To the somewhat uninitiated, machined could be just about any machine process. I think in terms of cutting, turning, bending, grinding, pressing, punching etc. All of which are pretty much some form of machining, but I tend to align with milling and turning as machining.

 

I think the visual there is a hunk of brass about the size of the top of the camera, that is somehow transformed into a top plate. I cant see that happening.

 

On the other hand, 'CNC' describes Computer Numeric Control equipment, and this could in fact be sheet metal working equipment. I was in Logan Utah about 10 years ago and saw some outrageous sheet metal working machinery at Campbell Scientific. One machine took a 4x8x.050 sheet of stainless, and punched and bent and drilled it into a nice neat little metallic cabinet, all without the intervention of human hands. This was a slope front affair, with numerous square openings for keys on a keypad, and LCD display. Was a nice intricate process, which included spot welding the corners. I have no doubt even more intricate parts could be made with such a system, and such a system is in fact CNC type equipment.

 

Now I have the hots to get to the Leica factory, just to see what they're really doin!

[andrew n.bra hrefhttp]

Yeah well, of course I'm just assuming they are using CNC!<P>

 

But I don't think it's an outrageous assumption. (1) I v.strongly

doubt they have gone back to using the different dies and

presses they abandoned after the M4-P. (2) I have personally

seen CNC machines spit out entire bicycle gear wheels (made

from a 7000 series Al alloy) with a far more intricate design than

a Leica top-plate (eg the lots of precisely cut gear teeth and the

wheel itself full of holes to cut down the weight).<P>

 

So CNC here would make sense to me. Mind you, I don't think

it's worth dying in a ditch over, right? :?)

[charles barcellona www.bl]

I think the forum users ought to make donations to raise enough money to send ME to Solms to get the answer straight once and for all !!!

 

No seriously, it matters naught how, as long as it is so.

 

BTW, the devil in the detail of the top plate is the thickness of the metal. Once it gets to a certain point, its just a real chore to hold (in order to use a cutting tool on it) without crushing it in the process.

[michael_kastner]

Brass is soft and won't rust, but zinc won't rust either (sorry, Roberto). As as matter of fact, zinc has the special metallurgical quality that it can easily be applied as a coating on other metals (which <i>do</i> rust, like iron) and at the same time prevent any rusting (thereunder), even if it <i>is</i> severely scratched. But that's not any real answer to your question, Tristan.

[al_kaplan1]

No, zink doesn't "rust" in the sense that reddish brown crud forms on it like the rust on steel and iron. It does oxidize though, forming a white powdery form of "rust".

[andrew n.bra hrefhttp]

Zn alloy also has a different density to that of brass - so it

transmits sound differently. Just guessing, but maybe it's also a

reason for going back to brass. My Zn M6TTL sounds much

"brighter" than my brass M4-P whenever I take a photo, although

the differences could also be due to different shutter

lubrication/adjustment etc.<P>

 

BTW, on the CNC point - the outer casing of Tom

Abrahamsson's

<A HREF="http://www.rapidwinder.com">RapidWinder</A>

<U>is</U> CNC machined from a solid slug of what he calls

"aerospace alloy". This isn't speculation as I have emailed with

Tom about this a few months ago (for background info on the

RapidWinder FAQ topic).

[roberto_watson_garc_a]

I meant the white powder rust Michael, I have seen it on a M6 classic, of course it can be cleaned up and nothing seems to happen, but eventualy it comes back, I have seen it under rewind crank.

 

Do you think rapid winder housing be more expensive to make than wich ever M top plate? now that you mention it Andrew

[Rob F.]

"No, zink doesn't "rust" in the sense that reddish brown crud forms on it like the rust on steel and iron. It does oxidize though, forming a white powdery form of "rust".

 

---Especially in Miami, eh, Al? I ought to know; I was born there. Salt air corrosion city.

 

Quite some time ago, one of our members ventured the viewpoint that Zinc is a harder material than brass, and thus less likely to dent. Now Andy clues us in that zinc cracks, while brass only dents.

 

I guess I'd rather have a dent than a crack. Maybe that's why they switched back. Though I've never read a complaint here about a cracked top plate. Guess we're a careful lot.

 

Bob Fleischman

[andy_piper2]

"Zn alloy also has a different density to that of brass - so it transmits sound differently...My Zn M6TTL sounds much "brighter" than my brass M4-P whenever I take a photo."

 

I definitely noticed that when I've tried most (but not all) M6 bodies, the ratcheted backstroke of the wind lever makes a more distinct "clink-clink-clink" sound than my brass M4/M4dash variants, which just sort of whisper. I finally decided privately that it was a function of either the zinc or the extra 2mm of 'attic space' on the TTLs acting as an echo chamber. I haven't had enough opportunities with M7s to test the theory with a 'new' brass top.

[oliver_s.]

OK, I'll go and check how the M7 top plates are made. But where shall I go? Leica has confirmed that they outsourced the top plate production. AFAICR it's a small company that specialises in production of precision metal parts in the proximity of Solms. (It is <i>not</i> Leica Microsystems, the by-now-independent subsidiary which a number of Leica engineers have transferred to recently.)

[timothy_swan]

I had 2 m6's and an R4s that all had bad corrosion of the zinc top plate. It

would appear first as small blisters, which would grow over time. It didn't affect

usability at all, but it was really ugly. Yes, I live around saltwater, but I have

many other cameras, including an M3, that never had this problem. I for one

applaud the return of brass.