On Fri, 14 Oct 2011 16:00:54 -0700 (PDT), TrailRat
wrote:

OK, now I know what I'm looking for I have a question about strength.

I am in the process of making a pair of manacles for a friend for a
halloween costume. The manacles are meant to look steampunk and are of
a steamed curved hardwood with brass fittings. The hinge will be brass
and I plan on replacing the hinge pin with a d-ring. This is for a
small length of brass chain (3-4 links). Despite these being a costume
piece, I am more then sure that they will see use and I am more then
sure that some bright spark will try to "break free" by tugging on
links. You know how that goes, I'm sure you've seen that in the
movies! Anyway, to save face I have decided to spot weld shut the gap
in the d-links so it doesn't separate under tension.

Will that work?

No. Spot Welding won't work without spending a few grand on special
tooling, and I doubt you want to do that.

When they manufacture welded chains for sale they have to use special
cupped jaws on a industrial-duty spot welder to clamp the two ends
together and transfer the power to the chain link ring on the gap
side. And it takes a LOT of power to weld chain links, because part
of the power is wasted going the other way around in the chain link
rather than across the gap. They usually use a 600-Amp class
industrial arc welder for welding chain links, not your little 100-Amp
hand-held spot welder - it's made for thin sheet-metal, period.

You'll have to Braze the links and D-rings shut. Oxy-Acetylene torch,
brazing rod, brazing flux. You can close up brass chain and make it a
lot stronger, and look hand-made.

Silver Braze is a lot easier to work with, but it's more expensive
per stick (though you don't use that much) and the color is going to
be slightly different from the brass chain. But that's the stuff they
use for connecting air-conditioning refrigerant lines.

The D-Rings might be Brass Plated Steel wire, don't be surprised.
Check with a magnet. It'll braze the same - but the steel in the core
won't melt on you, it'll just fuse the joint. The entire brass chain
link will melt on you if you get it too hot.

I'd like to see the design where you can replace the hinge pin and
braze the ends shut, though - you need to spread the D-ring and then
bend it closed into the hinge to replace the pin - then the ends will
be hidden inside.

You would have to bend the tabs of the hinge leaves OVER the
brazed-shut D-Ring to make that work.

* * * * * * * * * *

You can buy a small Oxy-Acetylene Welding and Brazing Torch Kit for a
couple hundred at Lowe's, Home Depot, Harbor Freight, Northern Tool,
etc. and you can keep and use it for many little jobs around the house
and garage for many decades. Tank exchanges (empty for full) will be
$20 to $40 depending on local market rates.

The little "Porta-Tote" style torches with the plastic bottle carrier,
20 cubic foot size Oxygen and 10 cubic foot 'MC' size Acetylene are
between $200 and $300, shop around. The small cylinders will be
enough for this project, but a little *too* small for working on cars
and home repairs.

Air Conditioning guys buy the Porta-Torch rigs solely because they
can be hauled up on the roof or under a house easily... If you go
this route, consider buying a second set of cylinders so you have more
gas when {not if...} they run dry on you in the middle of a job. About
$200 for a filled set.

For doing bigger things like car body repairs and gate hinges, you
want to step up to the 50CF Oxygen and 25CF 'B' Acetylene size welding
rig - a little more investment up front (about $400 for the torch, 25'
hose, regulators with a cart and a set of cylinders, and about $220
for a filled set of spare bottles) but they are big enough to actually
DO something.

-- Bruce --

(PS: Set your word wrap, guy. )