We have spent many months designing, developing, assembling and testing our custom-built, high precision dual 4 axis CNC machine. The machine has its four main axes (X, Y, Z, A) computer-controlled through CAM control software. It uses anti-backlash lead screws and ball screws, high precision/high torque stepper motors and high voltage drivers. The machine was extensively trammed and tested, the custom backlash systems further tweaked, and then certified using precision dial test indicators. We periodically re-tram it to ensure its continued accuracy.
We managed to get a repeatable 0.0025mm accuracy out of our X and Y movements over 10mm, and near-zero backlash out of a custom dual Z-axis movement. It uses gas struts with motor-driven rack and pinion, or we can swap to motor drive ball screws with cantilever suspension. We have both options available on the Z-axis, which allows a level of precision, repeatability and flexibility to choose the best Z motion method for the task at hand.
Typical machine shops have a general tolerance of +/- 0.10, with a fine tolerance of +/-0.05. By designing our machine to only focus on small parts no larger than 150x150x400mm (perfect for nearly every classic camera lens), we were able to improve accuracies by not having to worry about maintaining tolerance drifts as the distance of movement increases over half a meter. Thus, our machine is more accurate than many much larger CNC machines in typical machine shops due to its custom backlash and movement systems which focus on precise movements within a controlled footprint. We even have the option for flood coolant, mist or pressured air if we need. Lastly, a well trammed high torque 4th axis allows our A movement to rotate parts very precisely by interpolating points between steps and holding those locations under heavy load. Aluminium, brass, stainless steel and acetal can all be milled accurately from NC code programmed off our 3D models.
In addition to the computer-controlled 4th Axis, we have a secondary manually controlled 4th Axis, which provides B movements. The B-axis is used to appropriate, sub-divide and accurately space and position parts, for repeated operations that need to occur around the circumference of an object. From 6-bit coding of LM bayonets to cutting unique 11-position start helicoid threads that might advance 14.20mm per rotation, thus allowing an optical block to focus 0.7m to infinity with merely a 90-degree turn, our B-axis provides the missing pieces to allow us to have an all-in-one machine for bespoke lens mechanics design and fabrication.
The turning of parts down to partly finished components, before our CNC machine takes over, is done by our lathe. Our lathe has the capacity to create nearly any turned part that may be used in a standard mechanical camera lens, with maybe the exception of 800mm telephoto lenses! We utilise precise Mitutoyo callipers and Mitutoyo dial indicators to help ensure our parts are at the accuracy and tolerances needed to work on high precision assemblies like rangefinder lenses.
In the rare case, when a custom part needs making for a lens that is outside our fabrication abilities, we have a few different machine shop sub-contractors, that can do the areas of work we aren’t yet able to. These include sheet metal-based lens parts like brass fork sliders (used to prevent the front part of the lens from spinning when focusing) and aperture blades that require either punching or laser cutting.
We also have a Prosumer 3D printer, that again has been upgraded and modified to print carbon fibre and nylon. We can use this to prototype parts also to ensure fit, form and function, before moving onto to machining the final design.