Sunday, September 07, 2014

I recently made the move to an iPhone based on a 1/2 price sale.  The biggest driver was the camera, and now I have a convenient way to document building activities.  Hopefully posts will now be more frequent.

I'm working on a cross bike at the moment.  The lugs are Newvex, meaning that they're probably silly ornate for cross bike.  Still, it'll look nice.

 All the curlicues require clean brazing.  They can't be cleaned up later.

From there, its on to fitting the DT to the BB.  Start by fitting on jig, and setting up pins.  Then I can take it off the jig, and registering the tube to the BB with the pins, scribe lines off the BB.

That's blue layout dye on the tube, but sometimes a black marker works just as well for a scribing medium.

Originally, I planned to use Reynolds 631 but the tube was too short.  That surprised me as the frame isn't that big at 57cm, but I grabbed a True Temper Versus tube and problem solved.

You can see the scribed line below.  Look closely and you'll see one of the holes for the pins.

For this joint, I trimmed with a hacksaw before breaking out the files.

Sometimes trimming first is faster.  Depending on shapes, the hacksaw might be replaced by a rotary tool with a cutoff disk.

OccasionallyI'll use a sanding drum on a bench-top drill press, although generally this is only something I do with carbon tubes.

Here's the trimmed tube:

Now comes my favorite tool: a Grobet USA 14" bastard cut half-round file.  

This is a file that fears no tube (although some take longer to due to being hardened).  

For today, its short work, followed by a little finishing with a 12" 2nd cut and an 8" bastard cut.

Here is a tube, coped to the scribed line.  That, however, isn't quite what we need.  Scribing often involves positions and angles that don't allow the scribe to get right into where we want it.

Now it's time for a test fit, and to determine what needs to be cut back.

The first image was too dark, even using the fancy phone.

Here's a try using an LED bike headlight.  It's better, but probably doesn't show you what I saw, so lets try another angle.

Below you can see that the bottom side of the tube is a bit long.

Small matter, just a few more strokes of the file before its done.  Note in the picture, the BB is again pinned to the tube to ensure proper registration.

So at this point, it was time to trial the seat tube.  The angle between it and the DT, as cast into the BB, was a bit off.  I could force things together, but don't like to build that kind of stress into a frame.

It's time to adjust the BB.  The BB is a pretty heft casting, it's not really going to adjust  very much.  Primarily, the ends of the sockets will move, and the inner socket will then allow some movement by the tubes, so all will be well.

Doing this requires some big heavy bars (I think mine came from Omar at Oasis Cycles).  

This pic should offer a sense of the scale of the bars.  They're solid, with copes built-into the ends so that they can fit together inside the BB or a lug.  

Prop one against the floor, and find a 200 pound weight to hang off the other, and shortly the adjustment is complete.


Often, though, adjustments are necessary to maintain a tight fit of the the socket around the tube.  Spare the hammer and spoil the BB.  It's what I say.

Mounting things into the jig now shows that everything fits together without springing any of the tubes.

And after removing from the jig, we can look at how the seat tube and down tube come together in the BB.

Mind, the seat tube hasn't been fitted for anything but its angle (which is steep on this frame).  

The cope on the bottom will come next, but for now, the square end makes is easier to see how well the tubes fit together.  And they look fine.

The next pic is fun because its hard to see what's going on.  Well, that's what I think.

All of the lugs suffer from oval openings.  In part, this has been corrected by squeezing the longer diameter to make the holes rounder.

This doesn't always work.  For example, the seat cluster is a fairly rigid casting, with the TT socket and seat bolt ears providing a bit of triangulation around the seat tube socket. 

These accouterments also make it impossible to find purchase in the vise for the required squeeze. 

At these times one just has to file away metal to achieve the necessary round bore.  Although it occurs to me now that an adjustable reamer might be worth a try in the future.

To file the backside of the ST bore, the lug was laid on its back, on top of the vise jaws, with the seat bolt ears firmly clamped in place.  

But, I'm no good at filing up side down, making it difficult to file the front side of the bore.  

Luckily, those rigid seat bolt ears can also be used to secure the lug under the vise jaws.  And yes, I could put my weight behind the file while opening up the front of the bore.  

Apart from opening bores on all the lugs, I drilled the vent holes in the head tube.  For those not familiar, a hole is placed behind the lug that provides an open path from the head tube into the down and top tubes.  

This helps the flux removal soak be more effective, and ensures air circulation for the life of the frame, that limits condensation and thus limit internal rust.

The holes are drilled using progressively larger drills until the required diameter is reached.  

In this case the required diameter is 1/2", because that's my largest bit.   

Below is a finished hole.

Some of you may recognize the tubing clamp as being from a Park stand.  I use a table mount Park bike stand as a quick clamp for tubing.  

A lot of drilling, sawing and filing occurs here.  It's much quicker than tubing blocks, albeit not quite as secure.  

When brute strength is employed, I generally revert to tubing blocks and a heavy bench vise.

By the end of the day the front triangle is test fit together with all joints coped and lugs in place.

The top tube lugs still need more pin holes set, and the vent hole in the ST is yet to be drilled.  However it feels like a productive five hours.

With this done, I'll focus on cable stops and the front derailleur hanger.

At that point, I can start brazing up the front triangle.

Meanwhile, you can see that work has started on fitting the chain stays.

Stay tuned. 

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