HOW I BUILDING A FRAME[待续]

刘影

I started this blog with the intent to show my readers how I fabricate frames and forks. The blog has morphed a bit to become a place to update customers on progress. I will keep the progress reports coming, but I want to get back to my original plan. I have taken a lot of photos of the build process of Nathan's bike, and I will lay them out in installments. This first installment shows the first steps of machining the tubes and prepping some of the castings.

First step is to give the new frame an identity. And not just some cold number, but a name to go with it.




Here are the materials all laid out. Tubing from left are seat stays, chain stays, down tube, seat tube, top tube, head tube. Note the markings on the main tubes. Those indicate the butt transitions where the tubes go from thick on the ends to thin in the middle. The rear dropouts and seat stay bridge are shown on the left. The lugs and BB are on the right.


I begin with rough cutting the chainstays to length.
The chain stays are then set up in our tube mitering fixture.



The next tube to be worked is the seat tube. This tube has a double cut. The first cut gives the shape of the inside of the BB shell.


The next cut makes room for where the down tube and seat tube overlap. This cut is at 90 degrees to the first cut and approximately 60 degrees to the down tube. The rotory table sets the ST/DT angle and the upright peg sets the tube perpendicular to the first cut.


The next tube is the top tube. The first cut is made at approximately 73 degrees.


Next, the cut length is set on the fixture. You can see here that the tube needs to be rough cut to length.

The cut length is set on the leading edge of the block. This is a 58.1 cm top tube.

This precision turned dowel is set on the fixture and the tube is butted against it. This dowel is parallel to the cutter. This keeps the miters in perfect plane with each other and helps create a straight frame.

刘影

Next is the down tube. There are 3 cuts on the down tube. One where the tube butts against the head tube, one to give it the shape of the inside of the BB shell, and a third where the seat tube and down tube overlap. What's that you say? Didn't we take care of that with the second cut on the seat tube? Yes, but I hate looking into the shell and seeing a piece of tubing just hanging there not doing anything. So I cut it off. And then when you look into the BB shell, all you see is a nice, clean interior.The first cut is the BB end of the down tube. A simple 90 degree cut.

The down tube cut length is set and the peg sets the tube perpendicular to the first cut.



Next is the third cut. A pivoting dowel is again used that is parallel to the cutter.


And then the third cut is made.


Here is the completed main triangle and chain stays. The rest of the braze-ons are also laid out.
In the next installment, we will mock the frame up in the jig and maybe do some tacking.

刘影

Yikes, It's been awhile. We left off in the last installment with all of the tubes coped and mocked up in the fixture. There is still some work to do before we tack the frame though. One thing I try to do before tacking the frame is braze on as many..errr...braze-ons as possible. Why? Well, when you heat things, they expand. Now, picture a nicely made frame. It's all aligned and happy. Then, you go in with a torch and heat up small, localized sections of the tubes with abandon. Things will get squirely on you. If you add the braze-ons beforehand, the tubes have done their thing and you can move on to tacking and brazing the frame straight without worry of undoing all of your hard work later. That was a run on sentence, wasn't it?

First up are the brake bosses. The frame is in the jig and my handy Henry James jig has an integrate bridge and boss jig. The bosses have been machined to fit the stay very tightly.

Next, the parts are cleaned and placed back in the jig. Flux is then added (the grey stuff). Flux is an acid that becomes reactive at around 900 degrees F. It gobbles up all of the oxides on the surface of the steel and promotes the silver to "wet out" on the surface of the steel. This is a special flux I get from Fred Parr. It resists burning very well and is very easy to rinse off after the joint has cooled.


The joint is heated, the water in the flux boils off and the flux becomes powdery. Hotter yet and the flux liquifies and begins to work its magic. At about 1150F, the silver filler rod is added to the joint. If all goes well, you will be left with a joint that appears to be covered in ice. Good heat control = no burnt flux.

Next come the two cable guides on the seat stays. This is a cross bike with top tube cable routing, so the rear deraileur cable runs along the right seat stay.
Fluxed...

Brazed...


The front derailleur cable is run down the backside of the seat tube, around a pulley and back up to the derailleur. This is the boss for the pulley.

Fluxed...


Brazed...

Next up are the triple stops on the top tube. A witness line is used to be sure the stops are on the top dead center of the top tube.

Fluxed...
Well, you get the idea...





So, if all has gone well in your brazing and you haven't gurnt your flux, a quick dunk in hot water is all that is needed to remove the flux.

Notice the areas of clean steel where the flux was and the discolored areas just outside. If the flux had not been there, the silver would not have adheared to the steel.





Next up, final tube prep and tacking...

刘影

这是一个手工钢架作坊，大家可以观赏他的BOLG

希望他的产品越做越好

http://bikesbyzank.blogspot.com/

arena55

个人觉得 国外的爱好者 动手能力很强

刘影

那是靠这个赚钱的

老胡

人家是个厂……

蓝魔之泪

天呐
好PL

蓝魔之泪

开始还以为LZ是个老外呢

lambert

引用第8楼蓝魔之泪于2008-06-26 13:55发表的:
开始还以为LZ是个老外呢

lz是圆圆