(slow rock music)
- It's part three of our How to Build a Bike Frame series,
and the GCN hand-built frame is nearing completion.
With considerable help from our teachers
here at the Bicycle Academy, like Andrew.
Now, believe it or not,
there are just two processes left to go
before our bike is ready to roll.
If you missed parts one and two of the series,
then the links to those videos are in the description,
but for now Andrew,
it's time to do some brazing, right?
- That's right.
Okay.
- What are all these bits and bobs that we've got
plugged into the frame, first off all?
- So what we've got here in the head tube
is some big lumps of brass.
These are heat sinks. - Okay.
- They're gonna draw some of the heat out of the tubes
when we're brazing.
They basically protect the tubes,
stop them from overheating,
and it helps maintain their shape.
- Okay.
Now what's the difference between brazing
and the tacking that we've already done?
- So the tacking is little spots of braze.
- [Simon] Yeah.
- So fundamentally it's the same thing.
But basically, there's not enough there to do the job.
So you could probably build this up,
try and ride it, and it will fall apart.
So we're gonna put some more braze on
and then it will be nice and strong.
- [Simon] Okay.
Let's do it.
- So it's not good enough to just lay down the braze
anywhere on the frame. - Okay.
- Because if we do it in the wrong place, at the wrong time,
then the frame will end up all twisted.
So-- - Right.
- If you think about the head tube here,
we don't want to braise on the sides
before we braise on the top and the bottom.
- Okay.
- If we braise on the bottom here first,
before we do anything else,
then that's probably gonna steepen up
the head tube and we don't want to do that.
- Right.
- So I'm gonna start off by laying down some braze
in this mid-section here and here.
- Yep. - And then working my way
around until we filled up the whole fillet.
- Okay.
(slow rock music)
Right, you can see that the whole bike has been brazed up,
but Andrew is being kind enough to let me loose
on the most important part, the left rear dropout.
So, this is gonna be my first experience
with proper brazing.
We've done tacking but I'm assuming
there's a very different technique here, right?
- Yeah, that's right.
So we're gonna put a bit of preheat into the area,
'cause the dropouts quite a lot thicker-
- Yeah. - Than the seat stand here.
Then, you're going to start off by effectively
creating another tack, then we're gonna add more material,
and we're gonna flow that around the joint,
so we can build up a nice fillet.
- [Simon] Okay, and where am I gonna start?
I mean it might be a stupid question, but--
- So we wanna make sure that we don't introduce
any kind of misalignment into the frame.
So, we're gonna start along the centre plane of the bike.
- Yeah. - Then we're gonna ding dong
each side of the joint until we've built up the full fillet.
- Okay, so it's a case of start at the front,
then go to the back, and then each side?
- That's right. - Okay.
So, now kind of like working your way around this.
- No, we don't want to do that.
If we did that over the whole frame,
then it would all be a little bit wonky.
- [Simon] Right, okay, yeah we don't want that.
- Right there.
(slow rock music)
Good job, excellent.
- Yeah? - Yeah.
- Right one, raised up frame.
Look at that.
Can we keep it like that.
- Yeah, pretty much.
We've got to do a few other bits and pieces.
We've got to put some braze on this,
we've got to do some finishing.
So, the first stop is we need to ream and face.
The head cheap and we need to cut the thread in the BV
before we put it onto the alignment table.
- Right, that's our final stage, right?
The finishing?
- Pretty much- - Reaming and facing.
- We're gonna put it on the alignment table,
and then once we've done that,
then we're going to start shaping the fillets.
- Now Andrew I'd like to say
I know exactly what I'm looking at here, but obviously,
for the sake of the viewers,
well, perhaps you better explain.
- Okay, cool.
So we've got the frame that we just made
on the alignment table. - Yeah.
- We've put the frame on the table
to see how straight it is.
- Okay.
- So, the process of putting this much heat into the frame
to create the brazes, or indeed, if you were welding,
means that there's always going to be
a little bit of movement. - Yeah.
- But as we can see here,
everything lines up really really well.
So, that means that straight after the brazing,
it's really straight.
So then what we're gonna do
is check everything in real detail,
and if there's anything that we need to tweak a little bit,
then we'll tweak it.
- Okay, and by tweaking, does that mean bending?
- Yeah, effectively, all though not,
it will be measurably with the table,
but not to the naked eye.
So, we'll quite carefully put a little bit
of force into the frame,
or sometimes we'll use a little bit of heat
to create a little bit of movement.
- Okay.
So, it's been reamed, it's been aligned,
and now, the final stage in the finishing process,
is to actually give it those classic flowing lines
that you know and love from a fillet brazed frame.
Jake here is about to do the honours.
But, what is the process?
- So basically we've got enough braze
to make it really strong.
- Yeah. - We want to make it
super smooth so that we can't see the transition
between the tubes under the paint.
- Uh huh. - So Jake
is going to take a file,
and he's going to start smoothing that out right now.
Then he's going to follow up with some emery.
- Okay, and how much can we actually get rid of here,
because you don't clearly want to lose any strength,
but, you know, when do you stop filing?
- So, there's all sorts of calculations that you can do,
but fundamentally we want to leave
as much as we can on there. - Okay.
- And just make sure that we've got a nice,
gentle, arc between the two. - Okay.
So that the braze is giving its strength.
- [Andrew] Absolutely.
- That is a thing of absolute beauty,
but it's a pretty labour intensive process,
this last bit, isn't it?
- The most labour intensive bit of the frame?
- Yeah, I mean when you leave,
Jake's going to keep going, he's not going to bed.
- Oh, thanks Jake. - Yep.
- It's going to take about two days,
and then it'll be really nice and smooth,
and it'll be ready for paint.
- Wow, that is absolutely fantastic.
Right, well, when you next see this frame,
it is going to look very different.
And in fact, when I next see this frame,
it's going to look very different.
There is going to be a full video on that,
so make sure that you subscribe to GCN,
in order that you don't miss it.
And then if you want to, of course,
see parts one and parts two
of this How to Build a Bike Frame series,
to see how this has all come together,
click down here and down here.
- Can we have those back?
- Sure, you sure you can't spare them?