at GitHub<\/a>. The overall dimensions are 46.4 mm by 87 mm (not including the slightly protruding ribbing). Walls are generally 4 mm thick, although four small sections are 5 mm thick to provide more “bite” for tapping holes. The four screw ports are M6 at 32 mm \u00d7\u00a064 mm centers. The running surfaces are wide enough for both RM1 and RM2 steel V-groove bearings (although it’s not a good idea to run steel wheels\u00a0on it unless it’s hard anodized). The standard MakerSlide V-wheels work, of course. With these, the wheel span is 104.6 mm centers, the same as for OpenRail on Misumi HFS5-4080 profile, or exactly 40 mm wider than for MakerSlide. The parallel running surfaces are centered exactly 40 mm apart.<\/p>\nFor extra strength, two MegaRail 80 profiles can be bolted together. The groove pattern on one side nests into that on the opposite side, for perfect alignment.<\/p>\n
The profile is extruded out of 6005A aluminium alloy (to be confirmed), and weighs about 3.2 kg per meter (MakerSlide is 0.9 kg per meter). \u00a0MegaRail 80 has area moments of inertia (a measure correlated with rigidity) about 18 times larger than MakerSlide in the wider direction, and\u00a025 times in the\u00a0narrower one. It is about three times more rigid in the wide direction than in the narrow one. I don’t have numbers for torsional rigidity, but I expect an even larger improvement, because of the unbroken outer wall.<\/p>\n
MegaRail Z<\/h2>\n
I have several candidate designs. I’m still pondering which is the best combination of features. MegaRail Z can be used, as the name suggests, as the Z axis of a gantry-style CNC milling machine, but also as the Y axis of a moving-bed machine. There are several different arrangements for the Z axis, each with advantages and disadvantages, and each favours different features (and dimensions) of the profile.<\/p>\n
Timeline<\/h2>\n
No idea yet. I am sending the MegaRail 80 drawing to the extruder\/fabricator tomorrow. They will give me an ETA, which I’ll take with a small boulder of salt.<\/p>\n
![\"Illustration](\"http:\/\/amberspyglass.co.uk\/blog\/wp-content\/uploads\/2015\/01\/MegaRail-A-300x284.png\")
members:<\/p>\n