Extruder cutting divots in the filament

I had a very similar problem. I was able to extrude manually after brushing out the extruder, removing, trimming and reinserting the filament, but then it would grind out a divot every time I tried to print. It turned out it was a very small partial clog in the nozzle. I was able to remove it with some 28ga wire after a few attempts. Everything is running smoothly now. I'm certain I caused this clog by leaving the extruder on for too long while I waited for the bed to heat up.

I've seen you've been having quite a few problems with your extruder(s), and maybe it's best to limit your variables until you get things running smoothly. There are a lot of reports as I'm sure you know about black filaments causing problems. Try to avoid black and filaments from untested suppliers until you can get things working. I've been using the natural ABS from octave for pretty much everything because I usually have to sand and paint everything I make anyway. The natural seems to be a lot less prone to clogs.

I am VERY careful about not leaving the extruder heated without extruding plastic.  If the problem continues after reducing the tension on the spring, I will try what you suggest.

I just switched to an Octave white (or natural: hard to tell them apart), in part because of your recommendation.  We will see how things go.

Just turn up the extruder speed in the manual controls, above the extrusion distance.  Mine would run at the default of 300, but if I turned it much higher than that it would skip.  It seemed that long infill lines at something like 70mm/s required faster extrusion than that.  So you could try manual extrusion at slower speeds, or higher temperatures.  Sometimes it will extrude ok for the first few mm, but you can hear the motor start to strain a little as the nozzle begins to fill up, and then it begins skipping because the back pressure has gotten to high.

The longer the zone of melted plastic, the harder it is to push because that plastic can squish and try to go sideways.  The best results come from a short melt zone so you have rigid filament pushing against a small amount of melted plastic.  The Makergear style extruder is at a disadvantage because the heater is above the nozzle.  The melt zone is the length of the heat core + the length of the nozzle.  Something like the Jhead has the heat surrounding the nozzle so there is less melted plastic.

It is possible that the heat is traveling too far above the heat core and there isn't enough solid filament in the barrel to push  the melted plastic through.  So taping a fan to the front of the extruder so it can blow on the PEEK and the top of the brass barrel might help.

I'm waiting for the replacement hot ends from SD for Printer B, so I decided to try to reinstall the original hot end in that printer.  I printed a complete new set of jigsaw replacement parts, redesigned the tensioner, and assembled everything.  Switched from black and white filament to red (first time with the red).  The hot end dribbles, but I cannot get any filament into the top of the hot end, either with the hob gear, or by hand.  Same thing with cleanout wires.  The top of the visible part of the copper/brass threaded barrel is at 265 C (which may be "too hot" for the PEEK if I recall some other discussions), while the nozzle reads 212 (with the printer set to and reading 200).  I guess I'll have to wait for the SD replacements to arrive to get the 2nd printer going.

The first printer is doing very well, now that I backed off on the spring tensioner.  That may have been the cause of all of my erratic hot end/extruder behavior.

What are you measuring the temp with?   If the PEEK got to 265 it is probably toast.   If the ABS melted in there, it could easily have jammed up the PEEK, or the PEEK has changed enough to block the filament.   

Keep an eye on hotends.com.  He'll probably get 1.75 in stock no that the Holidays are over, if the new Solidoodle ones don't work out.   Definately verify the thermistor readings before you print with it.   I tend to be suspicious these days of a thermistor that isn't embedded.

There is really a great advantage to purchasing to the Solidoodle as it consolidates all the parts and generally the actual structural platform is great. It is certainly more of a solid piece of equipment than most of the other options out there. Additionally, the price really is very low. If you are wanting to build one from scratch, you could do a lot more, but it wouldn't necessarily be cheaper and the man hours you would put in would probably cost as much as the printer on its own. I would think instead, it would be really cool if we came up with an essential unboxing procedure and checklist that leads into essential and then suggested and then optional mods. This way one could purchase the printer and put as much extra money and time into it as they want. Based on the performance of my machine and experiences with others, (they are all unreliable to some extent without maintenance and mods) I am getting the SD 3 and using the 2 as an experimental machine to upgrade the 3 to my ultimate printer. I'm not saying their product is unbeatable or there hasn't been quite a few struggles with qc and shipping times, but I don't think any printers at this level have escaped these issues.