Terry and the Group
First the best of seasons greeting to all of you and yours.
Yes, aluminum can be and is spot welded as a general practice. Where I
work, Freightliner, the the large truck builders, many of the parts
used in the cab are spot welded together to form assemblies.
When I joined the company, almost 30 years ago, I apprenticed in the
sheet metal shop and spent about 10 years in that trade. We do build
boxes that resemble a normal chassis. If you take a chassis and
flatten it out you will see that where the corners are formed, quite
a bit of notching will need to be done. In a home work shop this can
be done with a small notching shear or a band saw. In the
manufacturing world this is done with a blanking die in a punch press.
I have seen others built by making a "U" shaped chassis and spot
welding 2 end pieces in to it. With this method there is less waist
of material, but still requires some notching. In your original
question you did not say what type of break you have. There are three
basic designs. The first two are basically a hinge and a lock bar to
hold the material, you move the hinge with with a lever and the metal
is held in place with the lock bar.
1. Pan, this has a one piece lock bar and it is not really suitable
for making chassis by the first method above, but will make them by
the second method.
2. Box, This has different width fingers that make the the lock bar.
These can do the first and second styles with ease if you have a good
selection of fingers.
3. Press, This type of break has a bottom die that is a "V" and a top
die that is a blade it is fixed to a ram that pushes the metal into
the "V" thus bending the material. The top die for box work must be
some what shorter than the length of the material being bent. To do
box work again you will need a good selection of top dies, In our shop
we buy top dies in long lengths and then have the tool and die
department cut them down to our needs. We will have a set with the
smallest about 3/8 and up. These can be but into the top Ram in
combinations of as many as needed. Top dies come in different radius
this allows one to make sharp square or rounded breaks. I will not go
in to that now except to say that you should not use a radius smaller
than the material thickness you are breaking This will tend to crack
the material.
About 18 years ago the company asked me if I would like to move to
the machine shop and go through a apprenticeship there. Well, I took
them up on there offer and now I am a foreman in the machine shop and
make my chassis a different way. What I do know is to make the
4 sides out of 3/16 or 1/4 inch thick stock and the top and bottoms
out of what ever thickness that I need to hold what is mounted on the
chassis anything from .050 to 1/4 inch. First I mill top, bottom
and ends the 4 sides to the height and width needed then drill and tap
these edges for machine screws that go through the top and bottom
plates. The corners are made in a similar way. Normally drill and tap
the ends of the short ends and use machine screws through the long
ones. If I need air tight or really want a very solid chassis I will
run a small bead of weld down the inside of corner after bolting it
together for the last time. Don't weld until your sure that any
holes that go through will not need to be counter bored. I have not
found a sorce of 1/4 inch pannel bushings that will go in a 1/4 inch
chassis with a 1/8 inch front panel. So I counter bore the inside of
the chassis or make my own bushings.
I would suggest that you go to your local library and find a book
on sheet metal working. You will need to have the formula for bend
allowance to figure out your flat patterns. BEND ALLOWANCE is the
amount of material that is subtracted from the flat pattern to make
the finished dimension that you want. The formula takes in to
account the material thickness and radius of the break and if you
are going to hold an inside or outside demising. I.E. if you
want a part that is 2 inches high OUTSIDE with a 1/2 inch lip
INSIDE on both sides you don't start with a 3 inch piece of material.
Also paste board is much cheaper than aluminum, stop by the craft
store and get some to practice on.
One of these days I will put up a web page with all this information
and some on basic machine shop practices. Like the project I just
finished. Pick up a couple of vacuum capacitors with out the pullers.
I machined the bells and the pullers with thrust bearings in about
3 hours.
Have a good holiday
Art
KB7WW
> Terry Gaiser wrote:
>
> Hey Group ... Best Of Holiday Wishes To All,
>
> After many years of wanting to put together a metal shop of some
> sort I am finally doing so. I now have a foot sheer to go along with
> my brake. Now I am trying to decide what the next tools should be
> ...
>
> One of my goals is too be able to make a chassis of any size and
> shape I may need. It looks like on commercially made chassis the
> corners have the flaps "spot" welded together. Who can tell me how
> this is done on aluminum? I remember the spot welders from metal
> shop in jr. high school and spot welding tin together ... is this
> all that is needed to put aluminum together? Another possibility is
> to weld the corners of the chassis together but I fear the needed
> equipment to do this would be very expensive?
>
> Any suggestions or help would be appreciated. If I can become
> equipped and able to turn out a nice chassis I have considered
> making them available to fellow homebrewers.
>
> Thank You,
>
> Terry W6RU
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