Framebuilding process at 18Bikes
There are quite a few steps to building a frame so these are only the more major ones. Once the drawing is complete the first task is to Prepare the bottom bracket shell by facing it to width using the lathe.
Next the headtube is prepared, in the case of our eccentrically machined headtube this means a rough cut to length, reaming and facing then mounting in our fixture on the lathe and turning to remove material from the front.
The rest of the tubes for the frame are inspected for defects and the butt profile of each tube is checked and marked.
A few of tools we use including dummy axles, disc tab fixtures and our headtube machining fixture
The jig is set up according to the drawing
The seat tube forms the backbone of the bike, the mitre to the bottom bracket needs to be exactly 90degrees to ensure everything else will line up. The seat clamp slot and any bottle boss holes are also drilled.
The downtube and toptube are mitred making sure the extra DZB butt is at the headtube.
The chainstays are bent and mitred to the bottom bracket and dropouts.
One of the controls on our Harrison L5A
Vent holes are drilled to allow the argon gas that flows through the frame jig to get to the back of the welds. This prevents oxidisation, distortion and makes a stronger joint. This also prevents pressure build up inside the tubes as they are welded shut.
Any small braze-ons such as cable guides and water bottle bosses are added before the tubes are welded into the frame to make clean-up easier.
An accurate mitre
Before welding the tubes everything has to be spottlessly clean. Any mill scale is removed with abrasives both inside and outside of the tube and everything is cleaned, first with hot soapy water, then using acetone to make sure no oils or greases are left behind.
Now we're ready to weld the bits we've got so far. TIG welding is fairly fast but the sequence of passes around each joint has to be carefully monitered to ensure correct alignment once the frame is removed from the jig.
The seatstays are cut from a length of 4130, filled with sand and bent to the appropriate shape using oak formers. They are then mitred to fit the frame.
The seatstays are cleaned in the same way as the rest of the tubes and welded into palce.
The frames alignments is checked, the seat tube reamed, headtube reamed and faced and the bottom bracket tapped and faced. This frame is ready for powdercoat!
To ensure we build the best frame we possibly can we have invested in the best tools for the job. As you've read, the process of building a frame is quite complicated with lots of steps. Having the right tool for each step is very important to us.
We use an Anvil
frame jig and various small fixtures to keep the frame and other small bits aligned.
To weld the frame together we use a Miller Dynasty 200DX
welder. We use a weldcraft torch, a miller footpedal and stainless filler wire on all our welds
A 1950's Harrison horizontal milling machine
The biggest items in the workshop are an old Harrison Lathe
and Milling machine
, these allow us to make our own fixtures and jigs as well as mitring the tubes more accurately.
One of our oak tubing blocks
Along with all of these machines and specific tools and fixtures we have a vast amount of hand tools
and could not be without our oak tubing blocks
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