Holding for cold bending

[paul]

I need to bend over about 1/2" on the long side of a 4" x 3" sheet of brass (0.7mm thickness). I've made a steel bending bar for the job but I can't get the bar and sheet in the right place in the vice - the sheet fouls the vice screw (the bar wouold need to be about 2" deep to work in that orientation).

Is it likely to be a total disaster if I turn it around and have a large upstand i.e. the 1/2" in the vice and 2.5" above? I've spent ages filing the sheet to size so I'd prefer not to trash it with a couple of whacks!

Also, is soft wood likely to work as well as aluminium betwixt hammer and sheet? I tried a bit of scrap using a steel er, 'blow-spreader' (what's the word, dolly or something?) and even that seemed to work ok.

[Steve M. W]

Paul

this is what you need

www.axminster.co.uk/product-Axminster-Adjustable-Vice-Jaw-Benders-20496.htm

Steve

[waggy]

Paul,

If you have a milling machine or some other sort of slotted table, you could clamp the metal on the table with a flat bar, the edge of the bar and the bend line in line with the edge of the table. A straight piece of steel or wood can then be used to press the free section up ( down ) to the desired angle. Don't forget to allow for the thickness of the material or the bend will be in the wrong place!
Personally Paul, I'd cheat! I'd cut the piece slightly oversize, bend it and finish to size! By oversize I mean a sixteenth or so, not a lot to throw away compared to scrapping the whole piece. The thicker the metal, the larger I go oversize.

Good luck,

Waggy.

[grahamo]

Can you hold it between 2 sqaure bars overlong, support one end of the bars in the vice and clamp the other ends together, beyond the sheet. the bars need to fairly sturdy. Try to keep the fold within the length of the bars.

I've never folded brass, my work was always steels, but avoiding direct hammer blows is a good idea to avoid stretching the metal, planishing flat will only stretch it more, and the main material will end up bowed. Wood - if used grain end on (like a mallet head) - tends to shrink the metal back and can save a bowed piece but better avoided.

wood won't give you the crisp corner it sounds like you want. Think about breaking the edge over with a mallet / wooden spreader then use another square bar or similar to spread the hammer blows close to the edge.

Any marks in the steel bar you use will mark the brass so polish them out. Use a spreader longer than the fold or round off the sharp corners as they will leave marks in the brass.

The inside of a fold shrinks and the outside stretches. The folds will have a small radius. In mild steel on pan folders I was taught the minimum inside radius should be the thickness of the material, so watch how sharp the corner of your bending bars are.

You develop a pattern based on the point in the metal that stays the same length (aprx 2/3rds down in mild steel)

In M/S this works out to be almost exactly the same as working to inside dimensions if fold is 90 degrees. When I was developing patterns in industry we almost always worked on inside dimensions.

hope this is of some use.

Graham

[paul]

As ever, all useful replies - many thanks

Graham, I just realised that clamping to one side of the vice is actually covered in Peter Wright's book (which I have) although he suggests supporting the free end using a dowel held in a vice on the floor. With the whacks I needed to give the test piece I don't feel that that would be very stable!

Seems like I need to figure out a means of clamping it flat and secure to the bench like Waggy's mill table suggestion. Thinking...

[jgb7573]

I would give a try to your suggestion of having a tall upstand. But I'd try with a bit of scrap first. I've used chunks cut out of catering size coffee tins in the past to get a feel of what is likely to happen.

[paul]

jgb7573 said:

I would give a try to your suggestion of having a tall upstand. But I'd try with a bit of scrap first. I've used chunks cut out of catering size coffee tins in the past to get a feel of what is likely to happen.

OK John... it can only go wrong!

[gilesengineer]

If wanting to put a crisp fold in metal sheet - and you're lacking equipment, try grinding up an old hacksaw blade to this sort of profile, and use it to cut a deep groove in the reverse side of the metal (using a steel rule or straight edge of course...). It should then fold easily and cleanly.
(don't cut all the way through, though....)

[paul]

Good idea
Gilesengineer