The quest for the ideal hobbed bolt just took a new turn. On Monday afternoon I rigged up a steel "bolt hobber" (a piece of steel with a hole in it clamped perpendicular to the M8 bolt, to guide the tap). My setup was flimsy, but showed promise, so I think I should be able to hob a bolt.
If that fails, the option of cutting grooves with the Dremel tool and sharpening the "teeth" with a needle grinding tip is always a fallback option.
However, Quentin (designer of the Morgan) just posted his solution to the problem of the Eckstruder battling with 1.75mm filament:
RepRap Morgan 1.75mm extruder on reprap.harleystudio.co.za
This latest option is a modified RepRapPro Mini Extruder, which does NOT use a hobbed bolt, but rather a hobbed drive "gear" which is tapped in the centre (see bottom photo in the article). Quentin made his from brass on a small lathe, which I do not have access to, so at first glance, it leaves me with no option but to order one ready-made if I opt for this solution.
I might decide to stick with the hobbed bolt extruder for the moment (and accept filament jams) until I can figure out a way to manufacture a drive gear as described.
I will be thinking about this in the coming week...
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