Re: Press brake auto back stops - DRO / Accuracy

Bill, typically what I do is some test samples of different mat'l.
There are listings on the web and in books of what the bend center
line should be, however it is also dependant on how tight a radius
and how much pressure your delivering at the brake [stretch in the
mat'l]. On new mat'l I would typically do several test coupon's ,
say take a pc that is 10" lng x 1" w and break a lip on either end
at 2" then measure it up w/ a caliper to see how close it is, if its
not what you calculated it to be, then you go through your numbers
backward and figure out where its different. Once you've done that
you can usually hit it right off the bat every time. I've had
experiances where they changed the mat'l hardness on a project [
w/out telling me] and the parts just didn't fit. Of course on the
shop floor everything is the draftsman's fault so.. when they came
to me w/ it and we figured out what the issue was.. it was still my
fault.. I should have known that THEY changed the mat'l :-) Ahh
welll..

Solidworks has 'sheet metal' built right into the program. You just
bring up your sheet metal tool bar place it on the desk top and
roll. I've got to really liking it for doing this stuff.. auto
relief's and all the little nick-nak's it has, are really great. Esp
lofted sheet metal parts. I do lots of transitions, sqr to round,
offset sqr to round, truncinated sqr to round.. they all take the
same amount of time.. not more than 10 minutes to lay out vs's 6-10
hrs in AutoCad. Its a great tool.

Hope that helps.

Jarrett

> Hi Jerry And All:
> Quick Question. What materials bend on the center line of

the

> stock thickness? Most sheet metal forms closer to the inside bend
> side on the one-third of stock thickness line from my experience.

i

> just looked in my Engineers Black Book (2nd ed by Pat Rapp) and it
> shows a "Q" correction factor for bends but does not show the bent
> center line. It shows that a softer material can have a smaller
> inside radius then harder material but not the bend centerline. I

am

> going by past experience and my diemaker design books. Another
> fact not mentioned yet is to use two drive motors on two parrall
> threaded rods (a known distance between centerlines) and then you

can

> set the backstop at an angle. This would be like is those used on
> foot shears. I have one and the scales work great when you have

good

> light but it does take a bit of cranking to go from a short piece

to

> a long piece.
> Also, I just though, do you you a third party software for
> Solidworks to do your s/m layout and folding or can you do it
> directly in Solid works. Awaiting your reply which will be very

much

> appreciated.
> GOD'S BLESSINGS
> Bill
>
> Actually calculating setback's and bend radi is not an issue. It's
> been done manaully for years and w/ a simple CAD system or some
> simple math it can be done very quickly. I recommend doing a

sample

> break on a pc of scrap mat'l [ if your going for 0.01" accuracy]

but

> otherwise these formula's will get you VERY close.
> Check out http://www.thefabricator.com/Bending/Bending_Article.cfm?
> ID=356 or search on google about how to set out bend radi. The
> basic's of it is knowing what thickness your mat'l is. Most metals
> and alum will form around the centerline of the mat'l. You also

need

> to know the form radius [ the inside rad of the corner after

formed]

> then calculate your part length of your part [after its formed]
> using your lip sizes and your radius. The total part length will

be

> the length of the centerline of the mat'l of the formed part.
> Simple. The break location is the center of the formed corner

rad.

> Which can also be easily calculated. Or if you want to spend money
> on programing, buy SolidWorks, its what I use and its dead

accurate

> and fast, and programable for mat'ls which don't form on the
> centerline of the mat'l.
>
> Jarrett Johnson
>