BCN3D Sigma bowden tube retention fitting

thingiverse

8 July 2016 EDIT: I've created a new edit with a metal shim that performs better, but may be challenging to construct without suitable tools. Due to this complication, I've also created a 3D printable shim here: http://www.thingiverse.com/thing:1664774. It works better than the threaded version, but I've left the threaded version in place, perhaps to assist someone else with a similar need, but not precisely this application. A remix of sorts, although not by much. I took the concept from StikDesign and "streamlined" it a bit, removing material and reducing the amount of support (and time) necessary to accomplish the same result. Credit goes to StikDesign for coming up with the threaded tube concept, an elegantly simple solution for a nuisance of sorts. The BCN3D Sigma dual extruder printer is a work of technological art. The prints are beautiful, even at 300 micron layer height. I understand that a few machines suffer from bowden tube creep and release, as did mine. This fitting, properly created, processed, and installed, solves the tube creep. Another EDIT! I wasn't happy with the weakening of the bowden tube, nor with the need to recalibrate after each bowden tube removal. With a suggestion from MatterHackers, I came up with the added item to this post. It's a conventional feeler gauge from the auto parts store. This one is 0.88 mm thick, which appears to be nearly perfect to apply gentle but firm lifting force to the underside of the gripper release ring. I used a series of drills, ending with 8.5 mm. Unfortunately, the feeler gauge is made of seriously strong grade steel and I pretty much destroyed the cheap bits from, well, where does one buy cheap stuff today? With help from an abrasive cutting wheel, I chopped open one end, tapered the "fingers" and cleaned up the burrs. Using the TLAR method, a mid-point cut and two ninety-degree bends, the result is superior to my printed fitting. Print Settings: Printer: BCN3D Sigma Rafts: No Supports: Yes Resolution: 0.300 mm Infill: 25% to 50% - not critical Post-Printing: Some work remains After the print is removed from the print bed, clear away the supports from the main underside counterbore, to provide clearance for the gripper ring in the hot-end. Drill out the end holes with the 3.2mm bit and replace the M3x5 cap screws with M3x10. Cut the center hole's threads with a sharp M6-1.0 tap. Dull taps will not work well. Using a sharp M7-1.0 die, cut threads on the bowden tube, approximately 40 mm from the end. Use the above noted 3.2mm bit to reinforce the bowden tube, preventing crushing and enabling the use of pliers to prevent the bowden tube from twisting under the force of the die. Follow up the M7 die with an M6-1.0 die and cut to the same distance. It's challenging to get it started, but once going, it moves smoothly. Remove the existing filament (already done, if you've cut threads on the bowden tube!) and the two cap screws. Thread on the fitting and check for appropriate depth of insertion on the hot-end. Adjust as necessary, tighten in place with the M3x10 cap screws. Because the hot-ends have effectively been removed and replaced, it will be necessary to perform a calibration after reloading the filament. How I Designed This OpenSCAD the hard way Well, not really the hard way. I'm not a programmer, but it's fun to see what can be accomplished on the simple side. All the parameters are listed at the start of the included code. The great thing about this program is that it's free and you don't have to be a CAD genius to download it, this code, and start changing things to meet your requirements. Custom Section Many tools needed for the newer version Have a 3.2 mm drill bit or precisely measured rod available to reinforce the tubing while cutting threads. A pair of pliers will be used to hold the tube from twisting. The standard hex-key set that came with the Sigma, to remove the cap screws. Something to clear away the minimal supports (pliers?). A drill press, vise, under-part support, a set of quality drill bits able to cut tool steel, a high-speed rotary tool, often called a Dremel tool, an abrasive cut-off wheel for the rotary tool. Patience.