Prusa i3 Rework Gregstruder - Inconsistent Flow

Hello RepRap community!

I've been working on a Prusa i3 Rework and have ran into problems with my extruder. The flow of PLA through the hot end is inconsistent. For several seconds the filament will flow properly, but soon after I can tell that the idler's bearing is not spinning (which indicates to me that the hobbed bolt is grinding). Finally the flow returns to its appropriate amount and continues the process.

Here is an image of my extruder:


Idler:


Hobbed Bolt:


I am using Ramps 1.4 with Marlin firmware. I have calibrated the extruder by removing the Jhead and measuring the real amount extruded vs my current steps value until the extruder would extrude the amount of filament it is expected to (measured using a caliper). Here are my current values for steps, acceleration, feedrate and jerk:

***********************************************************************************************
#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,4000, 812}
#define DEFAULT_MAX_FEEDRATE {500, 500, 2, 45} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {4000,4000,100,800} // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for Skeinforge 40+, for older versions raise them a lot.

#define DEFAULT_ACCELERATION 2000 // X, Y, Z and E max acceleration in mm/s^2 for printing moves
#define DEFAULT_RETRACT_ACCELERATION 800 // X, Y, Z and E max acceleration in mm/s^2 for retracts
***********************************************************************************************

I have read many forum posts regarding inconsistent flow and have checked the following common issues:
-Voltage to the nema 17
-loose nut on the large gear
-clogged jhead (I checked by feeding a 0.4mm guitar string through my 0.4mm nozzle)
-damp filament (I have tested many filaments)
-dirty hobbed bolt (I have cleaned out the ridges on the bolt)
-hot end temperature (I have tested extrusion any where from 175C to 240C with no change in behavior)

My current worries are that:
-The fan pointing at my cold end is not cooling enough (since the cold end is quite hot to touch when the hot end is heated).

-A potential parameter in pronterface/splicer/marlin (such as extruder acceleration/feedrate/retraction speed) that is off.
-faulty hobbed bolt
-bad calibration? I calibrated without the jhead attached until the value expected in pronterface was accurate (measured via a caliper)

Here are some prints to show how this issue effects the end results (all of these prints were printed with hotend temp of 200C, heated bed temp of 65C, using black PLA):

Die:


Top of the same die:


Rework gear:


Whistle:


Top of same whistle:


Thank you for your help in advance!

Edited 1 time(s). Last edit at 01/10/2015 02:24PM by bergerab.

Do you always run just 1 hold down on the extruder door? If so that may cause your issue. Make sure they are applying a good amount of pressure on the filament. It could also be bad filament, do you have more then one roll?

Yes I've always used one screw just because long M3 screws are hard to find around me. I'll order some online, but for now I just added a zip-tie keeping the other side tight.



With the screw I do have on the idler, I keep it very tight to make sure there is enough tension.

I have 8 rolls of 3mm filament that I have been using, all of them have the same results.

Thanks for your response!

Quote
bergerab
Yes I've always used one screw just because long M3 screws are hard to find around me. I'll order some online, but for now I just added a zip-tie keeping the other side tight.

Look at your local hardware store for "drywall butterfly screws"
Almost same size as an m3 but 4" long and imperial thread.
I just break the butterflys off and use the nut, though you could find a bigger/better nut in imperial size.

Steve

---

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

Thanks for the tip Steve! I'll check that out this weekend. By the way I love your instructable on how to build a prusa i3. It helped me build this printer! I do a lot of project sharing on instructables too, its cool to run into people who do the same.

Do you think you could take a look at my acceleration/jerk/feedrates and judge if they are a little too high/low? I couldn't find any good guides to fine tune those values in the firmware.

Quote
bergerab

Do you think you could take a look at my acceleration/jerk/feedrates and judge if they are a little too high/low? I couldn't find any good guides to fine tune those values in the firmware.

I use:

#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,4000,473}
#define DEFAULT_MAX_FEEDRATE {500, 500, 1, 25}
#define DEFAULT_MAX_ACCELERATION {9000,9000,100,10000}
#define DEFAULT_ACCELERATION 1000
#define DEFAULT_RETRACT_ACCELERATION 3000

#define DEFAULT_XYJERK 5.0
#define DEFAULT_ZJERK 0.4
#define DEFAULT_EJERK 5.0

Thanks for the positive feedback on the Instructable too!
I have started one on calibration, but not too far into it yet.

Steve

---

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

Thanks for sharing your calibration values! I just started printing another die with your exact values (besides your steps_per_unit of course) and I can already see that this print is going to be better. I think the main factor was slowing down the XY jerk, and changing my extruder acceleration from 800 to 10000. I'm still experiencing a little bit of the inconsistent flow problem, but I'll pick up that idler screw you suggested and see if that improves anything. Thanks again for all your help!

Just as an update, I've ordered all new hardware for my Rework extruder. I should get it by Wednesday. I'll update this post once I test with the new hardware to see if this resolved my issue.

E3d v6 hot end im running the same set up . Had a heat break problem minute but real. The aluminum heat sink and thinwall heat break will fix expansion problems unseen at the heat break and heat sink on the hot end

Matter hackers is where I got mine. Expensive but you get what you pay for have a look you will not be disappointed. I use mine daily no mmisprints on acount of plugging

Quote
bergerab
Just as an update, I've ordered all new hardware for my Rework extruder. I should get it by Wednesday. I'll update this post once I test with the new hardware to see if this resolved my issue.

What did you order?

Steve

---

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

I bought from this eBay listing: [www.ebay.com]
I chose that listing because it included not only the screws, springs and nuts but also a hobbed bolt. I'm a little skeptical about my hobbed bolt since I rebuilt this printer as an old Prusa i3 that was pretty damaged and I don't know what kind of damage could have been done that could possibly lessen the grip of the hobbed bolt. The $17 is kind of pricey for less than a handful of screws... but its very convenient. I've ordered screws from that seller before and the idler screws he sells are M3 60mm long flathead screws which are perfect.

Ok so after digging around I found a screw that was just long enough to work as a second idler screw.



After having the extruder run about 50mm of PLA at 200C I found that I'm having the same problem as before. I double checked the voltage going to the extruder motor, and that all the gears were moving consistently, and they are.
When I watched the extruder, I saw the bearing right below the screws spins consistently then suddenly stops for a second then continues which was followed by less PLA coming out the hotend.
My only other thoughts of why this is happening are that maybe:
-My hotend is poorly constructed
-My hobbed bolt is damaged

Does anyone else have any input?

Edited 1 time(s). Last edit at 01/13/2015 12:44PM by bergerab.

could also be bad wiring / loose connection to the E motor. the only other thing that comes to mind is a flat spot on the hobbed bolt, if poorly made. I just did that when cutting a new one last weekend, you would be able to feel it when turn the extruder by hand.

Thanks for the suggestion. I'll solder up a new bipolar stepper wire, then I'll take out the hobbed bolt and check for any flat areas. I'm a little curious.. how do you make your hobbed bolts? Is it as easy as using a dremel tool? Or does it require a special tool? I've just been ordering them online and I'm wondering if making them yourself is a better way than buying pre-made bolts. Thanks!

I just soldered a new stepper wire and it didn't change the behavior of the extruder. So then I disassembled the extruder to get to the hobbed bolt and I found a small (about 3mm) area where the screw was a bit beaten up. There were also some other areas that the ridges on the screw seemed a bit flat. Is there anyway I can "re-hob" this bolt? Or should I just rely on the one I bought from eBay? Thanks again for your help

cat.farmer thanks for the idea to check out that hobbed bolt. I just did some touch ups to the hobbed bolt and re-aligning with some washers, and the problem totally went away. Thanks everyone here for your help!

Glad to hear you got it working well.

Steve

cool, Glad I could help you out.
There are a few videos on youtube about making hobbed bolts as well as some things on the WIKI. It is fairly easy to do, and just as easy to screw up.