hey there today I thought I'd talk about
some stuff maybe let's stick around
today's episode is brought to you by the
letter beep and sponsored in part
through the generosity of the metric
system since 1792 the system trusted by
1516 so last night the missus and I were
in Los Angeles for the world premiere of
weld cart part 3 on the ride home she
said this old Tony I loved it but he
didn't really get much into the actual
bending my jaw dropped it must have fell
on the gas or got behind the brake pedal
cuz I don't remember much after that a
few days later after we came to in the
ER she turned to me looked me straight
in the eyes and said you really should
make a follow-up video as our monitors
beep tin that empty room I realized she
was right
this might upset a lot of tin knockers
but there isn't too much - bending in
theory anyway if you've ever tried it
yourself tried to get good accurate
bends well there's more to it than meets
the eye
bending can mean a lot of things to a
lot of people in fact it's got 19
entries on dictionary.com could mean
anything from this or this all the way
to this now I wouldn't go so far as to
say what we'll be doing here is
precision bending this is still the guy
in his garage I mean I can't do NASA
level stuff out here but I'll try to put
some thought into what we're doing just
like anything else you make if you're
making just one of something dimensions
are usually relative part a needs to fit
Part B with some level of acceptable
tolerance that keeps the thing
functional objective dimensions might
not be super important
kind of like the drawer I made in the
last video finished size wasn't that
critical as long as all the parts worked
together satisfactorily for me anyway
speaking of which yes I did cap the
holes in the welding cart sometimes you
make me wonder what channel you think
you're watching here Stefan got the
other end of that spectrum is making
parts for other people there you don't
have control over where that part you
need to make will go or how it interacts
with other parts in that case objective
dimensions are law you make it to spec
or it's trash no two ways about it
anyway let's make a couple of bent parts
work through the layout and see what we
get shall we
actually before we get into this just a
word if I may I'll try to keep what
you're about to see to an absolute
minimum here but we're going to be
getting into some math you want to bend
stuff you got to do some math you tell
me is it a contrived coincidence that
reorganizing the letters in sheet metal
spells mathletes but don't fret just
addition and subtraction I promise if
you're a little rusty please pause the
video and brush up just like all good
rulers throughout history I try to
provide both inch and metric dimensions
in my videos my channel is international
the numbers will be thrown around
working in both systems will get a
little sloppy I'm gonna do this whole
video in metric I know this is a
controversial topic but since you
brought it up let's talk about
measurement systems take this block as
an example in this universe's reference
frame it has some width to it it has
dimensions the block doesn't care if you
call it 2 inches or 50 millimeters it's
always whatever width it happens to be
so let's not get caught up in labels
shall we so 1980s would it be more
convenient and cause less confusion if
we all adopted the same system yeah
maybe personally and I recommend you
strive to do the same I have transcended
labels when I look at a measuring device
I see this which I'll grant you makes
taking measurements a little hard
sometimes now what was I even talking
about and for my flagship phone here and
see how it goes nothing fancy just
something for out here in the garage
since we're make pretend professionals
we should probably start off with at
least some attempt at a reasonable
drawing so this phone is fifty point
seven millimeters wide there's some
curvature some kind of rounded champers
but we'll call that fourteen point four
make that about eleven it's about 70 up
to the bottom of that camera bezel there
two megapixel they make a quick drawing
something like that is what I had in
mind
though to be honest i already forgot the
dimensions though he took I think I said
this return will be 11 phone is about
ten point four make it ten point five so
it actually fits in there seventy of the
back and I don't know seventy on the
return
sort of for the kickstand let's do a
quick flat pattern so that's 11 10 and
1/2 70 and 70 140 150 160 160 1.5
overall length let's do a chamfer to
chamfer so it looks nice
45 should do it I've already checked and
this is the squarest corner of this cut
off my half I need a line at 11 then an
additional 10 and 1/2 takes me to 21 and
1/2 it has a vernier scale on both sides
if I add 72 that it takes me to 91 and a
half and we said the overall length was
161 and a half okay I don't know if you
could see those scribe lines but I'm
ready to cut this happens to be one
millimeter thick mild steel I haven't
weighed my new phone but I think one
millimeter should withstand the
crippling forces we're dealing with okay
hold the train had a little brain fart
as I was scribing that sheet metal out
this ten-and-a-half
really bothered me this is essentially
the thickness of the phone because it's
not ten and a half it's essentially 15
it's 14 and a half plus some clearance
15 I mean come on I don't even think
Samsung can get it down to 10
millimeters let alone an LG I'm just
kidding that was a joke
don't start setting me lg8 male so that
ten and a half is really 15 that's 26
and 140 takes us to 166 I've already
gone ahead and laid that out on the
backside of this piece so this should be
correct now when it comes to sheet metal
you've got some options each one is
worse than the last but you have some
options it could use your psychic powers
but then you'd be laid up in bed for a
couple of days and you'd have to wait to
finish the project ideally what you'd
have is a full-sized CNC hydraulic shear
in your garage it's like an artificially
intelligent giant paper cutter on
steroids but try to pitch that one to
your significant other
oh wait next down the wish list might be
a compact to mechanical shear that'd be
pretty nice I've always wanted one stick
the metal in stomp on the pedal perfect
cut most of the time anyway but unless
you've got a lot of space or maybe you
do this a lot even the compact shears
tend to take up quite a bit of space now
sure there's plasma and freakin lasers
and that sort of stuff but let's look at
some perhaps more traditional items
stuff you might expect and shears are
likely the first thing that come to mind
in this case with one millimeter stock
that's probably fine any more than that
and you'll be staring down the barrel of
a serious workout then there are power
shears this is a Makita it's pretty old
but I love this thing gets a lot of use
down here could stand to be sharpened
but we'll have a closer look at this in
a minute and then of course there's Old
Faithful the angle grinder with a
cut-off wheel I'm also showing cold
chisels technically they do cut sheet
metal I wouldn't use them for a project
like this but they do cut for the sake
of sharing I'll show you what a cold
chisel does and these aren't called cold
just because they're heartless they're
called that because they cut metal cold
as in cold working basically with both
this and the air chisel we'll see in a
minute there can openers cutting sheet
metal with one of these is akin to doing
surgery with la chisel I guess usually
not very pretty this might be more adapt
at cold cutting small bolts or splitting
rusted nuts that sort of thing this
one's actually seen better days but
let's give it a try not pretty actually
if the chisel were a little sharper and
I was using a smooth backer like not
these serrated vise jaws I bet that had
come out a lot cleaner in fact let's try
it that's just a block of cold-rolled
steel with I guess a sharper edge a more
continuous edge all right it's a lot
better
this here is a sheet metal trimmer it's
a very close cousin to the cold chisel
just on the end of an air hammer and it
does basically the same thing it'll do
two cuts and pull out a center strip I
haven't actually used this in a while I
hope it still cuts it's not really the
highest quality cheap metal trimmer
there is I think I just got it with the
set that came with the air hammer this
is the kind of thing I might use to cut
a like a 55-gallon drum in half
something you don't want hot sparks
getting into and you're not really that
concerned with the quality of the cut
I'm actually quite surprised
that's quite a clean cut I may have to
start using that a little more often
there is sort of the chip it just kind
of bulldozes ahead of itself despite me
not even trying that looks like it
actually went pretty straight too and
here's the electric version of what we
just saw
except here that's got a moveable jaw
that actually does the cutting it's more
like power shears than a cold chisel
this isn't really all that sharp so the
lines are blurred I think you can get
these as add-ons to like a cordless
drill or a corded drill this you can run
up against a straightedge should measure
the offset clamp down a straightedge and
get the nice clean cuts
of course you can also do this with a
cut-off wheel set up a straight edge cut
your way through this is probably the
lowest barrier to entry
not counting shears of course but it
does make a heck of a racket dust and
dirt and all that kind of stuff anyway
let me cut this out and we'll talk about
bending
hi Bigsby can you give me an to bend
this for me
I'm sorry Dave I'm afraid I can't do
that
so this is my sheet metal bender if
you're a usual you'll have seen this
before I use this for thin sheets it'll
do up to I think 36 inch bends that's
almost a meter not quite but of course
the longer the bend the harder it is to
do as you saw this bender is a bit of a
compromise
there's no built-in clamping there's no
back stops there's nothing I just make
do with cut-offs I have on hand block
the part up clamp it down and pull the
bend it does a fair amount reasonably
well without taking up a lot of precious
garage space I know someone's gonna ask
but unfortunately I don't have plans for
this thing if you want to make one
you'll have to do with me and every
other cheapskate has since the dawn of
time build five of them until you lose
the will to bend and just make do the
rest your life with the last one you
made I'm just kidding there's tons of
plans around of every shape style and
size what they usually come down to is
two pieces of heavy angle iron with a
hinge at each end make it as long as you
think you need as beefy as you think you
need cut out some material and weld in a
hinge one side would get some sort of a
base or a way to attach it to your bench
or garage floor and the other side gets
a handle and then once your material is
clamped down you just simply rotate it
around the two hinges here I've got long
handles on either end just to help give
me some leverage let's get back to our
little phone stand appears to work the
phone fits it's not falling over and
there's no creaking sound let's have a
closer look the phone is a little bit
loose in there again it works fine but I
was shooting for a little bit of a
snugger fit now we wanted marked off and
bent at 15 millimeters this is the front
edge that's the flat the phone sits in
that's the back and that's the kickstand
measure what we got that is almost 16
millimeters
same thing on the other side let me grab
a school
yeah the bends all look reasonably
square how curious where did that extra
millimeter come from if I bring you in
really tight you can see the bends
happen right on the scribe lines which
are 15 millimeters apart and we saw both
bends or square so why isn't this inside
pocket 15 millimeters this part if we
were making it for someone else would
now be trash it just failed inspection
now the reasons why this isn't a size
are staring us right in the face but
it's hard to see because this material
is so thin it'll be easier to talk
through on something bigger something
thicker I happen to have this block
that's 2 inches thick my bender can't
handle stock this thick but luckily it's
only mild steel the first thing you
might notice is that the bend isn't
sharp there's a bend radius state the
obvious the material is deforming all of
the material on the inside of our Bend
has compressed it's sort of bunched up
the material on the outside of the bend
has stretched for that to happen the
material needs some breathing room it
can't just turn on a dime
that breathing room becomes the bend
radius just like me if you don't give it
breathing room it'll snap usually US
hobby folks don't have the kind of
muscle around to see that happening
steel but maybe you've seen it happen in
aluminum it has a larger minimum Bend
radius if you've ever tried to force a
really tight Bend on aluminum you'll
know that it breaks for steel that
minimum safe Bend radius is usually
smaller than aluminum in fact it can be
quite small it depends on the thickness
of course the grade of material trying
to bend its heat treat how you're gonna
try to bend it etc you can look all that
info up in our case with one millimeter
sheet it's not very much but it still
needs accounting for in my particular
case with this scrappy bender here I
don't have too much control over Bend
radius or a minimum Bend radius that is
to say I can make larger radius bends if
I use a rounded top die like this tubing
for example it's got much bigger radii
that I can bend stock around but if I
use a sharp corner tool like this cold
rolled flat stock and try to force a
smaller Bend radius on the material one
of two things will happen either and
most likely my clamps will slip
see the amount of force can get very
high and the way this bender works it
just can't take the heat as I try to
pull the bend those forces will transfer
onto the clamp and if it slips the bend
radius will get larger basically the
clamps will slip until the forces are
equal and I can pull a Bend option
number two
I've got 55 clamps across 24 inches of
bender the clamps don't slip but either
the material would crack or my bender
would break so in a way this bender has
an auto minimum Bend radius feature if
you go back and watch the weld card
video where I'm bending the drawer and
that material was thicker I was getting
large Bend radii off of this bender and
had to do some cleanup on the hydraulic
press since the inside dimension here on
the phone holder is 16 and set a 15 that
we intended it's evident that we picked
up a half a millimeter Bend radius on
each side had we known that ahead of
time we could have scribe the lines 14
millimeters apart instead of 15 in order
to end up with a finished feature that
was 15 millimeters you have to account
for what will happen during the bending
when you're laying out the flat pattern
you have to think about it before you
cut your blank or you might scrap your
part the amount of material you need to
account for before making a bend is
called the bend allowance and just like
it says on the tin it's the allowance
you'll need to make for the bend you're
about to pull of course you'll also need
to be careful of where these dimensions
refer to where on the bend line or at
the bend allowance that 70 millimeters
in this case refers to also where this
Bend allowance goes with respect to your
Bend line sort of depends on the
equipment you're using like if it's a
press break or like a box or a pan break
and what the intention of your final
dimensions are is the important
dimension of that Bend the inside or the
outside including the sheet metal
thickness like if you were to clamp on
this line here all of your Bend
allowance would happen outside obviously
after that clamp if you were to clamp
here this whole Bend allowance would
shift up a bit
you can't allow to bend something that's
clamped down in a big machine bottom
line you look this stuff up it's usually
presented based on your material
thickness T so for a certain material
say mild steel in this case you google
it and it'll tell you that the Bend
allowance is going to be one or two or
three times the thickness of the metal
that you're working with add that to
your flat pattern before you develop the
overall size of the part
then cut it out but to give you the
30,000 foot view I'm going to throw some
definitions at you so if you do look it
up you might have a better understanding
of what you're reading let's go back to
that big block I bent for you earlier
Bend allowance is this material here all
of the material that went into making
the bend its length of that arc
basically but if you look closely the
material has thickness to it in this
case quite a bit of thickness so how
long is that Bend if we measure on the
inside of the bend we'll have a much
shorter been allowance than we would at
the outside right so what gives remember
earlier we said when you bend something
the inside will compress and the outside
will stretch well if that's true that
means somewhere in between those two
extremes the material is seeing no
stress right if one side is all in
compression and the other side is all in
tension there must be a place where that
changes from one to the other and that
place is usually about the center line
of your material thickness the inside of
the bend got shorter the outside of the
bend got longer but somewhere in the
middle here the length didn't change at
all
and fun fact that place is called the
neutral axis that arc the length of that
arc through the part of the metal that
didn't deform is the bend allowance
that's the number we need to account for
in our flat pattern before we cut the
sheet stock so easy enough right for a
90 degree Bend it's just a quarter of a
circle pi times the diameter is the
circumference divide that by four and
you have your Bend allowance but not so
fast there partner what is that diameter
if we assume the neutral axis is at half
the material thickness it's easy right
take the bend radius which is always
measured on the inside of the bend and
add half of the material thickness bingo
bango you can now calculate the been
deloused
but the neutral axis isn't always in the
middle in fact it's usually a bit closer
to the inside maybe 45 percent of the
way in instead of 50 might not sound
like a lot but if you're doing a lot of
bends you can bet it'll add up and it
won't add up to profit you can be sure
that the location of that neutral axis
is called the K factor well the K factor
tells you where that neutral axis really
is it's like the x factor but way cooler
if you do a lot of sheetmetal work in 3d
cad like fusion or SolidWorks or what
have you
you may recognize that term that K
factor every bend you do in CAD wants to
know what factor you want to use because
well frankly it's important now the
software will usually have a built in
database of what that should
but it's always smart to double-check
just before clicking that okay okay
whatever let's just get on with it
button alright anyway this rabbit hole
has gotten deep enough
bottom line for kids like us either look
up the k-factor and figure out the bend
allowance for the material you're
working with or do a few test bends and
keep a close eye on what you marked out
versus what you got and just figure that
into the part you need to make holy
smokes what a mouthful but just one more
thing well actually there are a lot one
more things when it comes to bending but
one last point for now and I'm done I
swear it's not really a point even I
just want to put what you just saw in a
different light a quick example of why
this is important let's say we're laying
out a simple part with 90 degree Bend
lines something like this the way a
well-adjusted person would likely
dimension that is by giving you the
length of the two sides maybe one inch
on one leg and two inch on the other
pretty straightforward right but how
would you bend this
you really can't lay this out on flat
sheet metal have a close look at how
it's dimension then you'll see it's
quite sinister the dimensions span from
a simple reference edge the one you cut
presumably to the outside of an already
bent corner it's just brushing over
everything that happens in that Bend
what we'd really like if we're the ones
making the part are the flat lengths the
dimensions just up to where the bend
will start or finish simply because
that's how we're going to bend it right
you'd maybe clamp this line here and the
break and pull the bend but the person
that made the drawing doesn't really
care they just want a part that's to
size and that's where all the math comes
in based on these dimensions you'd need
to calculate what they call the setback
in this case it's an outside setback
just looking at it for a 90 degree Bend
it's the bend radius plus the material
thickness that's where you'd clamp the
material and the bend allowance we saw
earlier tells you how much metal you
need to fill that bend in how much metal
you need to actually make that Bend if
you give it too little the leg on the
Left will end up short give it too much
and the leg will end up long okay well I
think that's all I got I mean what we
did changes a little with different
types of bends that you're making the
equipment you're using and there's stuff
like material spring back error
accumulation you have to watch out for
if you're making a big part with a lot
of consecutive bends but at the core of
it it's really not that complicated just
take a deep breath and thing
get through before you start actually
bending metal it really wasn't my
intention to make a mountain out of a
molehill you know what I'm saying right
Bigsby
[Music]
thanks for watching