Hot-end/extruder issues: 1. filament slipping, 2. delayed filament extrusion

Hi all. Am just wondering if anyone has advice regarding two issues I've encountered with my GregFrost's Hinged Wade's Extruder and a self-made hot-end.

Hobbed bolt and filament slipping

Firstly. The PLA filament (1.75mm) I'm using is slipping to the side (i.e. left or right) away from the hobbed part of the bolt - and consequently not being forced into the hot-end at all. Has anyone else encountered this? It might be due to uneven forces in the springs I'm using on the hinge bolts, but I haven't figured out a way to measure this properly yet. Also, sometimes it slips to the left, and other times it slips to the right - i.e. it seems random. Might I have the filament force too high? (I've read that about 55N is about right for filament drive force - i.e. about 27 N on each spring - but haven't measured this yet).

Also, I bought the hobbed bolt online. Maybe the groove isn't deep enough?

Lag in filament extrusion

Secondly, there is a significant delay between issuing an extrude command and the filament actually exiting the hot-end nozzle. E.g. I hit 'Extrude' (5mm) in pronterface - but the PLA isn't actually extruded until a given delay afterwards. I haven't measured this exactly, but it seems to be almost a second. I suppose a certain amount of lag is acceptable - but this seems way too large. As far as I can tell this lag could seriously mess up my prints, no (especially when printing at higher feed-rates)?

I think it's partly down to my hot-end design. I have a PTFE barrel with 2mm internal diameter running almost to the end of the brazz nozzle - but it stops about 4mm short (don't ask why - the design was partly ad-hoc). So there's a small "reservoir" where melted filament must accumulate before being pushed through the nozzle hole. I guess this might be the problem? Might having the PTFE barrel running all the way to the nozzle tip solve this?

Is the delay due to communications between Pronterface and the Reprap motherboard?

Edited 2 time(s). Last edit at 04/18/2012 10:57AM by dslc.

Have you tried a filiament guide? I find it works much better.

[www.thingiverse.com]

Jim K.

The most likely cause for the delay is all the plastic oozing out of the melt chamber during warm up and having to be replaced. You need to prime it before the build so the extruder is full. You then shouldn't get more than a few tens of milliseconds delay when you start extruding.

---

[www.hydraraptor.blogspot.com]

I've ordered two different hobbed bolts (one from a seller on ebay and another from ultimachine) and they were completely different. Both worked, but the bolts were different lengths, the hobbing was in a different spot, and the shape and depth of the grooves was completely different. So ordering another hobbed bolt or two from different suppliers might solve your problem.

I've also tried and failed to get 1.75mm PLA working with Greg's extruder and a makergear hot end. After a few attempts I managed to get the smaller filament guide hole set up correctly (it wasn't as simple as just changing the filament diameter variable in the OpenSCAD file), but then the extruder would jam constantly. I'm sure there is a way to get it to work properly, but I've had much better luck with this: [www.thingiverse.com] and the makergear wooden adapter on top of the hot end.

As far as the extruder lag goes, in addition to nophead's sage advice, I've also observed a lag between when you click the pronterface button and when the extruder motor moves. If this is what you are experiencing, it hasn't caused me any issues during a real print.

dslc Wrote:
-------------------------------------------------------
> Hi all. Am just wondering if anyone has advice
> regarding two issues I've encountered with my
> GregFrost's Hinged Wade's Extruder and a self-made
> hot-end.
>
> Hobbed bolt and filament slipping
>
> Firstly. The PLA filament (1.75mm) I'm using is
> slipping to the side (i.e. left or right) away
> from the hobbed part of the bolt - and
> consequently not being forced into the hot-end at
> all. Has anyone else encountered this? It might be
> due to uneven forces in the springs I'm using on
> the hinge bolts, but I haven't figured out a way
> to measure this properly yet. Also, sometimes it
> slips to the left, and other times it slips to the
> right - i.e. it seems random. Might I have the
> filament force too high? (I've read that about 55N
> is about right for filament drive force - i.e.
> about 27 N on each spring - but haven't measured
> this yet).
>
> Also, I bought the hobbed bolt online. Maybe the
> groove isn't deep enough?
>
> Lag in filament extrusion
>
> Secondly, there is a significant delay between
> issuing an extrude command and the filament
> actually exiting the hot-end nozzle. E.g. I hit
> 'Extrude' (5mm) in pronterface - but the PLA isn't
> actually extruded until a given delay afterwards.
> I haven't measured this exactly, but it seems to
> be almost a second. I suppose a certain amount of
> lag is acceptable - but this seems way too large.
> As far as I can tell this lag could seriously mess
> up my prints, no (especially when printing at
> higher feed-rates)?
>
> I think it's partly down to my hot-end design. I
> have a PTFE barrel with 2mm internal diameter
> running almost to the end of the brazz nozzle -
> but it stops about 4mm short (don't ask why - the
> design was partly ad-hoc). So there's a small
> "reservoir" where melted filament must accumulate
> before being pushed through the nozzle hole. I
> guess this might be the problem? Might having the
> PTFE barrel running all the way to the nozzle tip
> solve this?
>
> Is the delay due to communications between
> Pronterface and the Reprap motherboard?

Thanks for the advice all. Just a quick follow up ...

Quote
Jim K.
Have you tried a filiament guide? I find it works much better.

After reading your suggestion I put together a makeshift guide using a small wood block (approx. 8mm x 7mm) with a small groove on one edge for the filament. And it just got me through my first proper print (the 20mm box from spacexula's calibration set)! So, tentatively, I will say that this seems to have solved the filament slip problem (for the time being at least). Spot on!

Quote
nophead
The most likely cause for the delay is all the plastic oozing out of the melt chamber during warm up and having to be replaced. You need to prime it before the build so the extruder is full. You then shouldn't get more than a few tens of milliseconds delay when you start extruding.

That makes perfect sense. I haven't had a chance to measure this more carefully and am printing at very low speeds at the moment at which delays aren't likely to be a factor - but that's good to know. (I still have one or two concerns about my hot-end design - e.g. I haven't factored in the issues that people seem to have with PLA sticking to their PTFE liner, etc., but that's a separate issue).

Quote
Wraithnot
I've ordered two different hobbed bolts (one from a seller on ebay and another from ultimachine) and they were completely different. Both worked, but the bolts were different lengths, the hobbing was in a different spot, and the shape and depth of the grooves was completely different. So ordering another hobbed bolt or two from different suppliers might solve your problem.

Well, hopefully I won't have to as Jim's suggestion to use a filament guide seems to have resolved that issue.

Quote
Wraithnot
As far as the extruder lag goes, in addition to nophead's sage advice, I've also observed a lag between when you click the pronterface button and when the extruder motor moves. If this is what you are experiencing, it hasn't caused me any issues during a real print.

I'm relieved to hear that. Thanks for the info.

Thanks for the info on the makergear hot end also. I've been thinking about buying one but will probably wait a while longer to see if my current one lasts.

Edited 1 time(s). Last edit at 04/18/2012 05:15PM by dslc.

Hi everyone

I guess I'm the only one with overheating problems. I'm such a newbie. My hot end goes up to 350c everytime I switch it on. To the point where the PEEK is melting down onto the brass threads.

Where should I be editing on the config file to get it right? Or could it be a hardware fix that I need? It is still extruding but it refuses to print anything(it waits). Just extrudes.

Tried to print the bed-leveling stl from thingiverse once, but it moves the Y axis straight crashing to the front of the motor area. Tried to edit the config file to limit the maximum length of Y axis(default of 200 to 170) but it makes the carriage run erratically and violently!

Using Sprinter with Pronterface.

I'm using a J-Head MkIII-B with 100k thermistor. Prusa(bought from MixShop) running on RAMPS 1.4 with heatbed.

In pronterface there is a window to the left bottom that displays heater and bed temp.

I would unplug the hotend until you adjust this. 350 will melt eveything.

In my version of pronterface, you can chose abs pre set at 230 and pla set at 185 or type in what ever temp you want.

Your Y axis problem sounds like your electronics are not picking up your endstops. If you are using micro switches, Test these by trying to home your x or y and manually pressing these micro switches before the bed gets near them.