CHUMBA Select Steel Tubing
Each frame starts as a bin of tubes that matches our build of materials. Our chosen blend of 4130 Cro-moly allow our bikes to be a unique blend of the toughest, lightest, and best made materials in the industry. Tube sets are chosen per model to achieve the perfect ride quality. We always use a few guiding prinicples though:
- Bent double-butted down tube to strengthen the steering junction by supporting the head tube from impacts on the trail more horizontally then a straight tube would while keeping the main triangle light.
- Oversized chainstays to ensure everything you put into the bike gets transferred into the trail and is stable loaded down. Bends and profiles are chosen per model, but they are all oversized.
- Oversized main triangle tubes to miter stronger around one another and provide predictable tracking through technical terrain.
- Stainless steel dropouts dramatically increase frame strength at the dropout and will remain rust free.
After tubes have been passed for quality our frame builders measure and prepare to cut each miter. Every tube is mitered according to our frame drawing specifications. Tried and true our Bridgeport vertical and Hardinge horizontal mills are our workhorses. USA made fixtures from Anvil Bikeworks hold each tube as they are mitered. Our goal is to miter and weld the frames so well that when they reach the alignment table they need little to no adjustment. Tight miters yield the strongest frames and the cleanest welds.
After tube mitering, frames are assembled in an Anvil frame jig set to measurements that precisely match our drawings. The frame is then tack welded to ensure a perfect fit at each miter. Next, the frame is moved to a welding stand where our frame builders can move the frame 360° in all directions. Care is taken to lay accurate and consistent welds. The rear triangle alignment is checked throughout the welding process to ensure accuracy. Once complete the frame builder does a 1st frame builder check of the frame and then moves to the alignment table for final adjustments.
We have a beautiful steel top alignment table. The table has a perfectly level surface allowing the frame builder and production manager to inspect every frame tolerance. At the alignment table each tube and dropout is checked with with precision measuring tools to ensure the frame is true. Careful adjustments are made to place the bike in alignment from front to back.
Once the frame is ready the frame builder certifies the alignment and passes the frame to the production manager for final inspection. At this stage we have a completely assembled frame with no paint on it. Each weld and tube is visually inspected and probed for any possible inconsistencies. Frames at this stage can be sent back for revision or they can be passed or failed. If a frame is sent back for example: for a less then perfect weld or a burr a 2nd frame builder and 2nd production manager check is preformed once the revision is made. Attention to detail and production checks are critical to our quality assurance, when your frame arrives we want you to be proud to own it, ride it and have the bike for years to come.
After approval our frames are cleaned of metal dust and prepared for powder coating. Our powder coater is also mtb rider and frame builder and we have built a trusted partnership overseeing the entire powder coating process and handling of the bikes. After painting is completed our powder coater does a first check, if the frame is passed it is then inspected a second time by the production manager.