Many thanks for the tips, DoN. Here's some more details:
Solid Edge quotes the following bend formula:
PZL = pi * (BR + (NF * THK)) * BA / 180
where PZL = "Plastic Zone Length" (que?) BR = Bend radius NF = Neutral Factor (they suggest 0.33 for this) THK = Thickness BA = Bend angle
I have drawn a pair of simple U-brackets, which should nest inside each other. I'll make them up tomorrow, & report results.
Both are in 1.5mm aluminium. They *should* fit in each other, with the side holes in line. Bend radius was set equal to thickness, ie 1.5mm.
No 1: Outside width = 50mm 1 hole in each leg, centre 12.5mm above outside bottom plane.
No 2: Inside width = 50mm 1 hole in each leg, centre 11.0mm above outside bottom plane.
Solid Edge drew flattened images, imported into AutoCAD. They show:
No 1: Distance between bend lines = 47.13mm Distance from bend line to centre of hole = 11.07mm
No 2: Distance between bend lines = 50.13mm Distance from bend line to centre of hole = 9.57mm
The brake is Australian made (I don't have the name to hand). Its adjustment of the wing distance will have the same effect as your adjustment of the clamp position. In both cases, its the distance from clamp edge to the vertical plane of the raised wing that matters. There is no stop for the wing angle - that's left to the user's skill :)
In the above case, I make the clamp - wing distance should be 1.5 * thickness, ie 2.25mm, to get a bend radius (measured in a plane in the middle of the sheet thickness) equal to the thickness.
firstname.lastname@example.org (DoN. Nichols) wrote:
:In article , :David R Brooks wrote: :>My project involves folding 1.5mm and 2mm aluminium sheet (think tube :>amplifieers :) :>
:>CAD packages such as Solid Edge will compute sheetmetal bending :>allowance, etc., for a specified "bend radius". This of course works :>fine if you are bending in a press, with V-dies formed to the radius :>in question. :>
:>I am bending using a brake (the machine with a hinged "wing" that :>swings up to make the bend.) The only adjustments I have are: :>1. Set the scribed bend-line forward of the edge of the clamping bar. :>2. Set the "wing" to swing a little in front of that bend line. : : Who made the brake you have? My DiAcro finger brake has two :settings -- but different from your description of yours: : :1) Adjustment for thickness of metal to be clamped -- moves the : "fingers" up and down so the clamping is just over-center for : maximum grip. :2) At the back -- an adjustment to move the edge of the fingers : back relative to the joint between the "wing" (apron is more : what I would have called it) and the stationary part. : :3) Actually -- there is also a third setting -- the stop pins : which determine just how far you can bend before the apron comes : to a stop. These pins can be moved to various holes appropriate : for different desired angles. : :>Is there a convenient rule for converting thickness & bend-radius into :>those settings? The design has 2 U-folded pieces fitting within each :>other (simplifying somewhat): I want them to fit with minimal :>clearance (obviously, not negative clearance!), so my bending needs to :>be accurate. : : I would consider the bend radius to be a function of how far :back the edge of the fingers is behind the line joining the apron and :the base. I think that you will have to try with some scrap of the same :type and thickness of metal to get it really right. : : But -- for the most simple state -- when the fingers are exactly :one metal thickness behind the join line between the apron and the base, :you will get a zero radius at the inside of the bend, and a radius equal :to the metal thickness at the outside of the bend. (But if it is too :hard an alloy, you will also get a crack along the bend.) : : If you are measuring the bend radius at the inside of the bend, :I think that a reasonable approximation would be the setback of the :fingers minus the thickness of the metal. : : There are three reasonable places to make the radius measurement :-- the inside of the bend, the outside of the bend, and the center line :between those -- and I don't know which is the standard one to which :your software is working. I just set up with some scrap to get the feel :of the settings -- but I also don't use a CAD program for doing the :layout. : : Perhaps someone else will respond with more experience in this :field. But at the moment, I see no other followups. : : Good Luck, : DoN.