3mm ABS filament feed speed slow

I'm tearing my hair out here.

I've just built a prusa i3 and I'm using a wades style extruder with a j-head 0.4mm hotend trying to print 0.2 mm layers I've got the temp set to 230 and so far I'm having to set my max feed speed to 1mm/s or I'm getting skipping ... if I loosen off the idler then I can increase the feed rate but the hobbed bolt just cheese grates the filament.

I'm wondering if the hobbed bolt could be contributing ... there is very little in the way of a groove for the filament to sit in if you know what I mean ... it is very flat with quite small teeth cut into it ... the teeth are very even though and are certainly efficient at grating up the filament

I know that the feed rates are not going to be very high with 3mm filament but I'd have thought I should at least be able to get into double figures ... Not sure what I'm doing wrong or how I can go about fixing it.

The hobbed bolt is indeed a major factor in filament transport, the short answer would be a straight yes. First, check if the teeth in the hobbed bolt are exactly aligned with the hole in your extruder. If the filament gets a little on the side of the teeth, it will chew much more into the filament.

If the teeth are too small it will slip, if they are too big, it will 'eat' your filament, especially when doing retractions very quickly.

You can also get a buildup of ground-up filament that causes the space between the teeth to get filled with filament which in turn also causes slippage.

Good you start looking into the bolt, most people overlook this part when just starting out with their first printer.

Thanks ... it seemed sensible the motor is a 68oz-inch holding torque so it seems daft that it should have trouble stepping unless the filament is being held too tightly but if the pressure is released the filament just gets stripped.

Another thing crossed my mind is about the line up between the top of the J-Head and the hole in the Wades ... when I feed in the filament I have to have sharpened it or get it at the right angle or it gets caught on something ... I wondered if due to what is obviously a slight misalignment there is extra drag on it causing problems.

You need a groove in the hobbed bolt to make sure the filament is held against the hobbing. Without the groove, it could shift from side to side and compromise the grip.

You might try a grooved bearing here but you'd have to be certain that the bearing is centered on the hobbing.

I know a grooved bearing is mostly for extruders with a guide, but does anyone know if a grooved bearing will help in any way if the extruder is already running fine? I want to get into designing my own extruder and I want to try and make a groove in a bearing with my dremel tool.

I realize now this is actually in the wrong place ... but just to put closure on this I got a replacement hobbed bolt with a much more pronounced groove and teeth that are more grid like rather than just lines across the bolt and things are much improved.

Edited 1 time(s). Last edit at 01/16/2014 07:30AM by BarneyG.