Mk7 on ToM loses tension on filament half way through build

Mk7 on ToM loses tension on filament half way through build

Thaed 30 Aug 2012 23:49

Hi guys, it has been a while.

I upgraded my 1st ToM with the MK7 and it reminds me of how long it took to get decent prints when I first started with an MK5. Well, maybe it is not that bad. The design is very simple and that's good, but I have no idea how to fix this problem. There is a chance the problem isn't even what I think it is. The filament has stopped extruding on the last two builds at random points. Everything else continues on merrily, but no plastic comes out. The temps are all normal and there are no errors. If it were an MK6, I would manually increase the tension, but that is not an option on the MK7. Any ideas? Thanks.

Re: Mk7 on ToM loses tension on filament half way through build

Eric Lindow 31 Aug 2012 17:42

One possibility is that the area above the heat block is getting too hot, which can happen if the fan in front of the motor isn't functioning properly. This can make the plastic too soft to be gripped by the drive gear. A symptom of this is that you don't hear any grinding or 'misfiring' noises from the stepper motor, which you would if the nozzle was jammed.

You could check this by trying to force feed the plastic when it stops. If you can feed it this way that's an indication that the drive gear isn't gripping. Don't force it too much, as the soft plastic can 'ball up' under the gear which will require you to take the top of the extruder apart (don't ask me how I know this:)

If you do open the extruder you can check the drive gear for built up plastic. I need to clean/clear my gears every so often (I'm talking months here); the need for this becomes apparent when plastic stops feeding in the manner you describe. That problem is obviously unlikely in your case as you are starting from scratch.

Hope this helps.

Re: Mk7 on ToM loses tension on filament half way through build

Thaed 02 Sep 2012 02:42

Thanks. I have had the ball up problem before too. I cleaned it out but it still quit. I also saw the tell-tale half-moon on the plastic when I reversed it out. I'm going to try to loosen the plunger next.

Re: Mk7 on ToM loses tension on filament half way through build

dnewman 01 Sep 2012 02:52

With a new Mk7, many folks have found they need to start with only two of the three brass washers on the plunger or otherwise slightly decrease the tightness of that delrin plunger. After a while, when the face of the plunger gets worn down a tad, you can add the washer back.

What's this solving: if the plunger is a tad too tight and it hits a section of filament which is a tad wider than it should be, then feeding may stop as the filament simply cannot get past the tight plunger.

A lot of folks have also had very good success with http://www.thingiverse.com/thing:15718 .

OTOH, if you are using PLA then this is a typical symptom of the extruder being a bit too hot and you need to try a lower temp (185C rather than 190C, for example).

Dan

Re: Mk7 on ToM loses tension on filament half way through build

Thaed 02 Sep 2012 02:42

I'm going to try this next as the plunger is quite tight. Thanks.

Re: Mk7 on ToM loses tension on filament half way through build

Thaed 06 Sep 2012 12:59

I made this one on my ToM that still has an MK6 extruder. It fixed the problem with my other ToM's MK7 enough for me to print a better one on that. But I still have the dreaded half-moon problem: the extruder gear chews up the filament and it makes a nice half moon in the plastic and loses tension. Based on some input you folks, I think it is a temperature problem. I want to run little air hose to cool the plastic right at the extruder gear. We'll see if I can throw something like that together with an old aquarium pump or something.

Re: Mk7 on ToM loses tension on filament half way through build

rajendran1 05 Sep 2012 15:37

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