Finally finished the custom hot end and have tested it to a speed of 700mm/min @ 240ºc before the extruders hobbed bolt striped the filament. It has a 24vdc 40w heater, 0.4mm nozzle, copper heat block and a fan cooled aluminium body. I must say however that I had to tweak my design quite a bit as getting the hot end to feed without clogging was not easy and I was really a bit over confident with my initial design. Three try’s at different internals and success, or should i say relief. Thanks for looking
Here’s a thought. Why don’t we drive multiple hobbed bolts off the same large gear? It would increase the grip. Or was that stripping purely due to lack of heat reserve to melt the filament?
Interesting idea Mark. My gut feeling is once I hit 700mm/min the abs could not melt fast enough. I should try increasing the temp to 260 and see what happens. I forgot to watch the temperature monitor in Pronterface to see if the temp dropped when pushing hard.
To melt the filament you rob the heating block of energy. So a larger block that holds more would help with changes in rate, more resisters to input more heat energy would help maintain high feed rate printing.
Watching my KM print part of an e-nable hand this morning I was surprised just how much the heat fluctuates. Maybe Marlin isn’t doing checks often enough.
Copper heat block is must have
Definately Maxim, copper has the advantage of transfering heat fast but releases it slowly so maintains a more constant temperature compared to aluminium. It is strange stuff to machine however. Glad to finally find a use for the meter long 25mm diameter bar of the stuff I have had for a few years.
@Brad_Smith Next step should be the long heat block 
The filament needs more time to melt, and this is only possible in long block without overheating of the block. My heat block is 25 mm long XD
Good idea Maxim, mine is 12mm at present.
Nice work Brad! I hate machining copper!