Folding Sheet Metal

[GWRdriver]

I have a question for the experienced hands on the board concerning the bending of sheet metal, specifically 1/16" thick half-hard brass.

What I wish to do is make a 90 degree bend in 6.50" wide plates which will form the outside front and side sheets of loco side tanks. The bend needs to have perhaps a 3/32" inside radius resulting in a 5/16" or so radius outside. All other joints, horizontal and vertical, will be butted and assembled with internal angle.

I have no proper bending equipment, other than making clamps from what might be cobbled together from odd pieces around the workshop, but seeing as how these plates will be the front and outside surfaces naturally I'll want them to come out as crisp and flat as I can make them.

The last time I did such a job (radiused tank cormers) I took the cowardly way out and milled flats in a length of heavy brass tube which was then sliced into quarters (actually just over 1/4s) and the plates abutted and riveted to the milled flats. I'd prefer to bend this time and of course I know the sheet will need to be kept annealed at the bends.

Any experiences or advice on how to pull this off would be welcomed.

[greasemonkey]

Hi Harry
Clamp the sheets on your mill, put a small (i.e. 2 mmm or 1/16" dia) round nosed cutter in the spindle and machine a line on the inside at the bend point to approx half thickness. Remove sheet and bend. Finally run a fillet of solder along the inside edge. The deeper the score line the sharper the bend.

Andy

[Jo]

Bending metal: I have just done my Clayton water tank.

I suggest that what ever method you try that you get a bit of scrap and mark two lines on it that are the two expected sides of the bend. Then try bending it. In my experience, if you don't use Andys technique above, it never bends at the radius you expected or where you thought it would bend.

Bender: I ended up copying a set of cheap sheet metal benders, angle iron in the vice with another bit of bar clamped on works but getting exactly 90 degrees is troublesome.

Jo

[Shawki Shlemon]

There is a formula for bending allowance ,I have forgotten it , but one can make th part a little bigger and trim the extra later ( after the bend ) . To get the radius file the corner of a steel flat to 3/32 R and use it on the inside of the bent. You are going to paint the tank, can you use copper sheet for this side , it will be strong enough for the job . If you use brass most probably be OK if you achieve the bend in one operation but if crack occur , soft solder it .Have a try on small piece of scrap . Good luck .

[dscott]

Now the best tool to use is a fly press with a set of v tools, now as Jo says by using angle iron we have a set almost ready to use. Now the inner radius can be done by filing the inner piece of angle to 3/32" and the outer edges of the other angle to a good radius to save marking the tanks. covering these in masking tape helps. Garages are usually very helpfull especially the older ones who have a power press, everything gets layed out flat. Failing this get 2 strong G cramps put the bottom angle in your slightly open vice and carefully squeese the assembly together, it is supprising just how much pressure you can get from these.

David.

An avid collector of anything that clamps and holds metal!!!!

[GWRdriver]

Although more suggestions may be on the way, thanks very much for the ideas so far. Good food for thought.

Jo & David, the press crimp method has promise, I even have a chum with a good sized hydraulic press. By adding side guides to the female die one could probably improve the chances of getting the bend perpidicular to the sheet edge.

Andy, I like the milled score idea as that will allow me to make nice crisp 90 corners in a few areas and possibly eliminate some built-up (piecemeal sheet & brass angle) construction, but I don't see it as a solution for the larger radius corners. I have lots of uses for this though so if not now then certainly later, for instance in fabricating toolboxes and loco lamp bodies without having to juggle half a dozen little plates.

And yes of course, always try a piece of scrap first.