Extruder Woes

Hello everyone. I've been banging my head against the wall trying to figure out a problem with my new printer. I just finished building a RepRap Wallace and everything so far works great, except for the extruder. The extruder is a Greg's Wades Reloaded extruder with a 1.75mm J-head and a .5 mm nozzle. I have a fan running across the PEEK on the J-Head because I am printing PLA. I've attached photos of the result. It typically prints fine until about 10-15 minutes in to the print then the voids begin. If I simply put a tiny bit of pressure on the filament as it goes into the extruder the issue corrects itself. While this is a fix, I'd like to not have to stand next to it and press filament to make it reliable. Here is a list of things I have tried:

1. Adjusting the tension on the guidler. Gone from barely touching to all the way shut.
2. Adjusting steps per mm for the extruder motor.
3. Temperature (gone down to 175c up to 210c).
4. Cleaned hobbed bolt.
5. Checked and double checked filament diameter. Measured in different places and took the average.
6. Changed placement of filament spool to make sure there was no binding going into the machine.
7. Tried different filaments (two different filaments from two different manufacturers)
8. Changed printing speed (typically kept it pretty slow)
9. Tried retraction on and off, no change.
10. Checked the actual temperature of the extruder versus what the thermister says. There is a difference but I have taken that into account.
11. Checked the connections to the hot end to ensure that they were not coming undone.

I've run out of things that I can think of to check. Anyone have any ideas??

Thanks!
Thaj

If you do not have enough current it might not be pushing enough on the filament, try turning up your current by turning the e0 (assuming you have a ramps 1.4 board) pololu potentiometer clockwise, if you go to far it will start clicking or making noise, usually less tan a quarter turn is necessary, there are how to guides out there to adjust your current with a volt meter as well. This is all I can think of, I had problems with this as well a while ago.

That was a stellar idea. Too bad it didn't work . I've got it right up to just before it starts to make noise and I am getting the same result.

12. Adjust voltage on extruder...

Are you positive it's a 1.75 nozzle and/or extruder and not a 3mm?

Steve

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My updated Instructable on our Prusa i3 Build
[www.instructables.com]

Looking at the J-Head with my calipers and I don't think you could get 3mm through it with the liner, so I'm assuming that it is 1.75 as advertised.

That photo actually looks like you are over extruding to me, if so then it may be jamming the nozzle since there is no place to go. You say you checked the size of the filament and I assume you then used that number in your slicer. Try adjusting the extrusion multiplier down a ways (normally set to 1 so try .85) and see if it looks any better.

Other thoughts. Have you looked at the filament when this jams an is the hobbed bolt chewing a gouge into it? If yes, then the problem is from the hotend down. If no, then the problem is in the extruder. Either the filament is not pinched tight enough or the motor is not turning. With the smaller 1.75 filament (compared to 3mm) I would think pinch pressure would be more critical.

Frustrating. 
If it works some of the time that eliminates a lot of the issues suggested.
One question; Is anything happening after 10/15 minutes? Is your extruder gear getting hot enough to lose bite?

Have you pushed filament through by hand? -Does it flow out straight down with no wiggle on it? 
It's possible for debris to linger in the nozzle. Sometimes it jams then it will clear itself for a while.
It doesn't take much muck to cause a problem.

Have you cleaned out your nozzle?
Try hand extruding a little, switch off the heat, and as it starts to stiffen, pull it out to form a long thin filament.  It may take a few attempts but it's possible to pull a nozzle shaped blob of plastic out.
(Described better elsewhere)
Make sure that your filament isn't picking up dust.  A wiper sponge may help.
Try some top quality filament from a reputable source to be sure.
I have some PLA that prints beautifully 99% of the time. 1% it does just what you describe and then I'll find a little grit in the nozzle.
 Happy hunting. 
-a