The majority of frames we have built to this point incorporate a 44mm headtube to allow the customer to have a wide range of choices on how they want to build up their bike. While we have been using straight gauge headtubes, we wanted to include an additional ring of material at the top and the bottom of the headtube to increase the strength at both ends and to create a smoother visual transition between the headtube OD and the headset cup. To do so, we first needed a prototype.
Our process for developing new products is to build a prototype sample first to test the process or idea and evaluate it to improve the final product we offer to customers. Since we have the capability and desire to have control over the entire product, we chose to start from raw tubing stock and machine an extra headtube and ring to test the manufacturing process.
For the headtube ring itself, we chose to machine the profile in a few unique ways to help in the brazing process. First, we removed some material at the upper edge of the ring to reduce weight and to have less mass that needs to be heated to temp when brazing. We also chamfered the inside edge of the headtube ring to help promote the formation of a fillet and get material to pool at the top of the ring in a “well” before it is drawn down between the two pieces to form a solid bond.
Because of the internal diameter of the ring of material, we also needed to bore out the ID to make it a slip fit over the headtube stock. We chose to make this a tight slip fit which, as we will later discuss, would end up being a less-than-ideal choice.
With the headtube piece and headtube ring machined, we then cleaned the parts, slipped them into place, and brazed them together. The process went well and we were able to get the brass to drawn down between the two pieces fairly well without dramatically overheating the tube. Additionally, we were also able to get a fillet around the top edge of the headtube ring that would require little to no finishing after brazing.
All that remained was to review our work and decide whether or not it is worth the extra time to incorporate into our designs. To be thorough in our evaluation of the prototype, we needed to take a cross section of the brazed piece to see how well the two pieces were brazed together. We chose to cut the part in two places: one section where we knew there was good wetting out of the brass and another section where we suspected that we didn’t do quite as good of a job getting the brass pulled down between the parts.
In the image above, we can see that the brass has formed a nice fillet at the top end of the head tube ring and there is a faint line all the way to the very bottom of the headtube. This is a great example of what you would want a properly brazed joint to look like.
The second image shows the same nice fillet at the top of the ring and decent wetting out of the joint except for the last 10-15% of the overlap. Here, the brass does not penetrate as well throughout the joint. This will still result in a strong joint but could lead to issues with finishing and isn’t up to our build standards. We suspect that this happened as a result of a very tight interface between the two parts as well as incomplete heating of the lower edge of the reinforcing ring.
Fortunately, because we were still able to get a complete joint between the two parts, we have proven the concept and know that we will only need to make a few alterations to the design to make it ready for production. The version we will incorporate will include the following changes;
- Expand the ID of the reinforcing ring to help the brass wet out between the components
- File axial grooves to further promote wetting out of the joint
- Heat the bottom of the headtube ring and add material from the bottom instead of only from the top
By making these changes, we feel we can incorporate this new element into our designs to improve the function and the aesthetics of the final product. Look to see more of our frames adding these kinds of components in the future.
Ride Fast. Ride Far.