Flange screws

[John Kasaian]

I'm concerned about using different metals together. I've seen Fiats self destruct because iron waterpumps were installed on aluminium engine blocks and I've heard of the historically notorious freezing of the (iron cannon)balls off the(brass)monkey which (you guessed it) brings us to the subject of lens flanges and the screws used to attach them to the lens board. My SOP is to use brass screws when mounting brass flanges and steel screws when mounting steel flanges but I just received an aluminium flange that fits a compound shutter, so the question is(since I can't find any aluminium wood screws) is whats best to use on aluminium, steel or brass? Or, am I overly concerned about the whole thing and it really dosen't matter as long as the screws are strong enough to keep the lens from falling off??

Thanks!

[Michael S. Briggs]

I think you are being overly concerned about disimilar metals. The serious problems occur when the two metals are in contact with water because an electrolytic reaction ensues. If you are still worried, use stainless steel screws.

[wfwhitaker]

Overly concerned.

The Fiats would have self-destructed anyway. They're Fiats.

[Jim Galli]

It doesn't matter because the brass lens barrel is going to freeze into the aluminum flange and you'll have to pry it out of the lensboard with a claw hammer. Use soft screws so the heads will pop off.

[Dan Fromm]

John, I've never used antiseize compound on a camera because I'm not sure what will vaporize out of it and condense where I don't want it, but the research needs to be done. Here's your chance to serve society, go to it!

Cheers,

Dan

[Stan. Laurenson-Batten]

I doubt if there is any problem as the material used would not be pure, but an alloy which is treated to prevent chemical or other deterioration when used in conjnction with other metals. Rest assured.

[d.s.]

John, From my sailboat experience... stainless and aluminum are one of the worst combinations. Moisture in the air is enough to start the reaction. Try Bronze if it's available. A search for fasteners on the web might lead you to a retailer that carries aluminum screws or bolts. (#6 or #8 machine screws should be fine). Maybe S K Grimes has some in stock.

[jantman]

Another boater's vote against mixing stainless and aluminum. In a saltwater environment (some spray) I've seen the aluminum corrode in THREE WEEKS.

If you want aluminum screws, try use-enco.com it's Enco machine supply, and they have no minimum quantity. If you're really worried, used plastic fasteners :)

[Stan. Laurenson-Batten]

I totally agree with the above advice, NEVER mix stainless steel, 365 marine grade, or otherwise, with aluminium in any form. If possible use mono metal which is a form of protected hardened aluminium. You will then be able to use your camera under the red sea! (EX.RN sea diver).

[Michael S. Briggs]

John isn't making a car water pump nor a sail boat, nor was he asking about sea diving. I don't expect that the metals he uses will be in constant contact with water, and I don't expect corrison to be a problem for his flange and screws.
If salt water got splashed on his lens, he probably should take it apart as much as possible and wipe it off with fresh water.





See http://www.corrosion-doctors.org/Aircraft/galvdefi.htm for information on "Galvanic corrision". If someone still wants to be careful, consult a table of a "Galvanic Series", such as http://www.corrosion-doctors.org/Aircraft/galvseri-compat.htm.
If you still want to consider this corrison issue, the table lists plain low allow steel as being galvanically close to various aluminum alloys and better than the stainless steel I suggested. However, probably most hardware store screws are zinc plated, which makes them more disimilar to aluminum.





I can't think of any old lens that I've looked that the showed extra corrision around the flange mounting screws. Any corrison is usually over the entire surface and isn't from the contact of dissimilar metals. This shows the results of decades of use and storage -- nor do I think that the old timers were using screws of exotic alloys.





I've never heard of "mono metal" and haven't found anything on the web or in a reference book that I have. Was "Monel metal" meant? However, Monel metal is a nickel alloy that is galvanically farther from aluminum than stainless steel.

[Michael S. Briggs]

Something I forget to say: while zinc has a greater galvanic difference from most aluminum alloys than steel, the galvanic order, starting with the most anodic, is zinc, aluminum, steel. Since the zinc is most anodic, in any pairing of these metals, the zinc will corrode faster, and the corrosion rate of the other metal will be reduced. So the zinc of common hardware store screws will protect the aluminum flange.





Another link: http://www.ocean.udel.edu/seagrant/publications/corrosion.html.

[Ralph Barker]

I would suggest, John, that you might want to replace that aluminum flange with a 14k gold one to avoid both galvanic action and oxidation, but someone might take me seriously.

Aside from cosmetic considerations of matching colors reasonably closely and such, I don't think you really have a great deal to worry about, considering the care that your mounted lens is likely to receive. Hidden oxidation of the aluminum threads might be an issue over time, but I'd think a bit of bee's was on a q-tip swirled around on the threads of the flange would solve that potential concern for your grandkids.

[John Kasaian]

Thanks for all the advise. Right now I've got the flange on with brass screws. Strangely enough, I might have some silicone bronze wood screws laying around(left over from a 23' Bear) and a bottle of mica based anti sieze compound (left over from flying a Super Cub around Alaska in '92) Not much gets thrown out around here! My manic obsessive thing about corrosion surfaced when I started messing with some older lenses in aluminium barrels. On many of the bezels I've found a lot of corrosion thats almost obliterated the make/model/focal length info. Some of it almost looks like it could be exfoliation, though I have no way of telling on such a small area with any certainty. Considering these were pretty expensive items in their day and would have been well taken care of, I wonder how this corrosion, if its not due to exfoliation, could have gotten started. Thanks!

[RichSBV]

Everything everyone said up there is true ;-)

Never use any type os steel next to any type of auminum... I've seen the results for decades in cars & trucks...

I can't speak for brass or bronze though?

My first three thought wre: nylon/plastic screws available at any hardware store. Not as strong as metal, but should certainly hold a lens. And you could always drill a few extra holes. I would go with a hole all the way through and use a nut on the back though...

Simply coat the aluminum and whatever metal screw you use. This should offer a few years worth of protection.

You could also try "blued" screws available anywhere gun parts can be obtained. The blueing is an oxidation process that prevents any further oxidation or interaction with other metals. Same thing for anodizing aluminum.

As for your 'exfoliation', it reminds me of a problem that came up 30 odd years ago with automotive aluminum wheels. There is supposed to be a fungus that happily eats aluminum. I've seen the results, but I can't say it's a fungus. Sure looks like it?

And after all this, wouldn't it just be easier to have another flange made?

Good luck any way you go, and let us know in 5 or 10 years whther or not it corroded ;-)

[John Kasaian]

Rich, Exfoliation is, to my understanding(and I could be wrong) caused by some defect in the aluminium as part of it's manufacture. The wing spars on old Beechcraft twins with the two little vertical stabilizers(looks kind of like a baby constellation) were noted for this problem. Exfoliation in steel might be due to something else---its been a long time since I read the book. I recall hearing the bacteria story too. It'll probably get recycled through the MSN home page one of these days= photo of distressed woman with caption:"Is bacteria eat your wheels?";-)

[Stan. Laurenson-Batten]

Michael. No, NOT Monel.

Mono was/is, the generic term used in the marine and aircraft trade for treatment of metals attributed to, I think, a French chemist by the name of Monod who was a NB prize winner.

Back to the thread. Materials used in instruments, which include cameras of repute,most likely have aluminimum in their structure, not pure but A1 combined with silicon and or magnesium. This not only improves the strenth of the metal but also the protection from errosion. As far as Monel is concerned, I find I am unable to agree with your assertion that the nickle and copper alloy has a tendency to corrosion. But,of course, nothing is perfect for every circumstance. I stand by my two previous posting on this tread.