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dannyk

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Posts: 21
Reply with quote  #1 
I would appreciate any advice on tools to accurately bend the sheet metal. We use a vice and hammer and it is surprisingly not very precise. Seems like a metal brake would be good but I can't figure whether it would work for this or which model is good.
Thanks
Danny
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jgraber

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Reply with quote  #2 
Yet another long answer to a short question. 

I assume you mean the 0.093" think Aluminum sheet 12"x24".
  Otherwise, Which sheet metal do you mean?"  0.093" thick Aluminum sheet, paint grid, metal soup can, Vex Motor Mounts.
A picture of "not very precise" and more details of what you expected would be helpful.

Q: "whether it would work for this (what 'this' do you mean?) or which model is good.
A1  I have not found much precision success with the sub-$70 Harbor Freight sheet metal brakes, or by extension, any brake that lists "use your own C clamp".  
A2  Yes metal brakes will work for bending sheet metal.  Heavy models costing ~ $400 or more will probably do a good job.  But unless a team is working in a school metal shop with equipment from the vo-tech 1960's era, most teams will get by with some tool or method they make themselves (which also looks good in the Engr Notebook).

Here are some other tips that may help with any method.
* Precision requires practice to position correctly for the bend line,  a firm clamp, a firm flat stiff bending plate, with enough leverage to make the bend.
- Practice comes from making several small demo models.  Draw a line where you clamped it, bend, and see where the bend is in comparison.
- A vise with a smooth top edge, or with hardwood jaws with a small radius will make a smoother line.   A vice is usually a firm clamp if it is as wide as the bend line.
- Don't expect a square angle,  there will always be some radius,  so allow for that.
- A hammer is not a flat stiff bending plate!  At least use a flat piece of wood as a pad, so that the hammer force is applied to the entire bend line, not just one place.  I have seen a hammer, board, $20 carpenter's vice from HF work ok on motor mounts.
- For precision, consider the wiki picture of backgauge on https://en.wikipedia.org/wiki/Bending_(metalworking)
- You could try making a precise fixture and good clamp by drill/tapping a couple holes in a piece of 1/2" Aluminum bar (hub material) and screwing down the metal to be bent, then clamping that in a vice and bending with board and hammer over the edge of the Aluminum bar.  Then practice to see how far from the bend you should drill the mounting holes in the bent piece to get the bend in the right place.

- Vex motor mounts have oval cut outs at the bend line to make the metal want to bend there, rather than elsewhere, so you can drill a line of holes on the bend line to do the same thing.

Please post what you tried, to pay it forward to the forum.

 

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EvansPhysics

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Posts: 36
Reply with quote  #3 
Our kids have started using the inexpensive harbor freight brake and they usually get better results than their old way of bending in a vise.  

With that said... the brake can be very accurate IF the width of the bend is not too large.  Up to 3" or so and it works very smoothly.  6-8" requires more care (and clamps) but works fairly well too.  Once you get over that length, the bends are very imprecise and difficult to make.  

2 years ago, the kids bent a 16"x1" strip into a 16" long L.  It was a very difficult process that used a clamp about every 2 inches.  The brake deflected so much that someone else had to use a hammer to assist and only the edges were bent to a full 90 degrees.  They finished it by clamping it in a vise and hammering down the middle... it wasn't the best looking part, but it was functional.

So... if you have the budget, the cheaper brake is a nice tool to have, but you can survive without it too.  If you get one, you need to know its limitations and temper the kids' expectations.  I wish the thing was only 8-12" wide.  It would be cheaper, take up less space, and not mislead you to its capabilities.

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dannyk

Junior Member
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Posts: 21
Reply with quote  #4 
Follow up, the team has not had a need to bend the sheet metal but did locate an old sheet metal box brake in the school's metal shop that looks like it will do the trick if needed. Thank you for the help.
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