Extruder Not Extruding Filament?

Hello,

This is my first 3d printer. I built the Prusa v2 from a makerfarm kit (excellent kit by the way). It uses greg's extruder. I am having some problems, where the hobbed bolt starts slipping, and begins to grind down on the filament until it breaks it off. I believe the hobbed bolt is of good quality after comparing it to other hobbed bolts I searched on the forums.

I tried playing with the tension of the extruder, but it does not matter how tight tension is, the bolt still begins to slip after about a minute of printing and breaks the filament

I borrowed a temp gun, and was checking the temperature of the hot end. I am using prontrface, and have the hot end temp set to 230C. Using the temp gun, I get a reading of 190C right next to the thermistor. I suspect this is my problem? I'm guessing the temp is too low, so the pressure required to extrude the filament through the hot end is too great, causing slippage?

Is the next step to remove the resistor and check the resistance value? Or check the thermistor? Or check the power to the board? What does the collective wisdom of the group suggest? I have attached some pictures for clarity. Let me know if you need any more info/pics, and thanks in advance!

Tim

If it's one of the cheap IR thermometers, they can't get an accurate reading from a Hotend, the sample area is too large.
Get a meter with a thermocouple and measure the temperature on the inside of the Hotend.

Assuming you are using ABS, take all the tension of the extruder and if the temperature is correct and the Hotend isn't blocked then you should be able to push the filament though by hand and watch it extrude.
Once you know the issue isn't related to the Hotend then you can start looking at the rest of the extruder, but if it's chewing up filament the issue is most likely the Hotend.

The same is true for PLA, except that PLA has a tendency to mushroom inside the Hotend and jam it if the thermal break is inadequate, which IME for most hotends means doesn't have a fan glowing across it,

I am in the same boat, with the same kit.
Have you found a solution?

I was able to get the prusa to extrude a little bit, maybe 10-15mm worth pulled into the hot end. Then the Hobbed bolt seams to eat away at the ABS. I haven't played to much with the tension, but I did open up the hinge on the Greg's and still had trouble trying to manually feed it. Could it be an issue with the hotend not being hot enough? I upped the temp to 250 and it extruded a bit more, but then it stopped and ate into the bolt.

Maybe the issue is with the temp sensor thinking the hot end is hotter than it really is. I don't have a laser thermometer (yet) to see what the temp is to check this theory...

Sure hope it is something symple.

I had this problem too with a different hot-end (self made). Hobbed bolt grinds into the PLA filament.
The actual problem was that the PLA filament inside the PTFE gets hot and expands. It gets stuck before reaching the hot metal, causing back pressure and grinding of the filament by the Hobbed bolt.

Polygonhell is accurate with his diagnosis.

Take the hot-end out and test it by feeding it the filament manually.
If it works, you have either a filament or hobbed bolt problem.
Else, your filament is stuck in PTFE tube due to high temperature. A fan running cool air on PTFE tube is a possible solution.

Edited 1 time(s). Last edit at 10/09/2012 09:56AM by peddiparth.

Hey Guys,

I do not know what a hobbed bolt is, but I had this problem and solved it! As with the recently designed heater bed, it suffers from very long, thin screws with springs that are too weak. TIGHTEN IT all the way. Also bear in mind, this may (will?) change your filament extrusion multiplier a few percent. However, that didn't work so reliably for me long term so I hacked the screws out, and tapped the holes with 1/4-20. I then replaced it with 2 lb force springs that are only 3/4" long. MCMASTER 1986K78 1 Pack Type 302 Stainless Steel Compression Spring, .750" Length, .300" Od, .022" Wire Diameter. This was used with a 1/4" machine screw (about 1.25" long) and again, I tapped the plastic instead of using nuts, as with my bed modifications posted here: Armani Creations and [forums.reprap.org].

Also, it is very important that you feed the filament in properly. Filament is curved. You want to feed in with the plane of the filament curve intersecting the horizontal axis, i.e., feed it so the when it goes in it is straight, not to the left or right.

IMO, this is not a heating issue (I've exceeded 250 C before) and used weird polymer mixtures too.

Edited 3 time(s). Last edit at 10/11/2012 10:19AM by Simba.

Simba not to sound disrespectful, but really? You don’t know what a hobbed bolt is? Hobbed bolt example

I don’t think we are having an issue relating to the heated bed in this issue, and if we are I can’t make the connection.

 

As to feeding the filament properly, how do you mean the filament is curved? As in it is round? As is when it passes through the grove on the hobbed bolt and the bearing it needs to go straight into the hot end? If so this is what it is doing. It then extrudes a little bit and then stops and the stepper will start to make clicking noise like the gear is being held fast (and it is).

 

 

I played with the extruding last night, when I disconnect the hot end and ran the filament through fine with no binding of the gears. I also put a piece of filament in the hot end and was able to push out a small amount of filament, but then it became to tuff to push by hand.  I reassembled the extruder and was able to extrude out a fair amount when I increased the tension of the bearing on the hobbed bolt. Then the filament stopped moving and the gears started struggling, when I gave the large gear a bit of help it would extrude some more.  After a while though this stopped working and the hobbed bolt started to chew into the filament again.

Is it:

An issue of not enough or too much tension?

The hot end being too hot (had it about 250, 230 gives similar results)?

The hot end being too cold?

The gears not lining up right?

The filament not being of quality (bought the ABS from amazon)?

Speed not being right?

Gremlins were fed shortly after midnight after bringing them inside after hosing them down?

Something else I am not seeing?

bringjustn Wrote:
-------------------------------------------------------
> Simba not to sound disrespectful, but really? You
> don’t know what a hobbed bolt is? Hobbed bolt
> example

Hah nothing of the kind. I'm just honest when I don't know something so I can learn, rather than trying to act smart at the expense of remaining clueless. Actually, in my decade of mechanical engineering, working in machine shops, reprapping, etc., I never came across a hobbed bolt. Where else did you see one besides these printers?

The filament is curved with a diameter roughly a bit larger than the filament roll it was on. In fact you can't straight it full ever, so this causes it to get stuck and not enter the hot end.

IMO, it is still lacking in tension, or conversely it is getting resistance by friction against the walls of the feeder tube/hotend, or some combination. In my printer, I really had to turn up the tension.

Simba Wrote:
-------------------------------------------------------
> bringjustn Wrote:
> --------------------------------------------------
> -----
> > Simba not to sound disrespectful, but really?
> You
> > don’t know what a hobbed bolt is? Hobbed bolt
> > example
>
> Hah nothing of the kind. I'm just honest when I
> don't know something so I can learn, rather than
> trying to act smart at the expense of remaining
> clueless. Actually, in my decade of mechanical
> engineering, working in machine shops, reprapping,
> etc., I never came across a hobbed bolt. Where
> else did you see one besides these printers?
>
> The filament is curved with a diameter roughly a
> bit larger than the filament roll it was on. In
> fact you can't straight it full ever, so this
> causes it to get stuck and not enter the hot end.
>
> IMO, it is still lacking in tension, or conversely
> it is getting resistance by friction against the
> walls of the feeder tube/hotend, or some
> combination. In my printer, I really had to turn
> up the tension.


Good to be honest, it makes it easier to learn for sure. While I have never heard of a hobbed bolt per say until I got interested in building a printer, the concept of hobbing gears, sprockets, and splines I have known about for about 5 years when I was a machinist at a company that put splines on input shafts for big vehicles (think tanks adn simi trucks). Now as an engineer I never seem them in my drawings. Wiki has a nice write up on the hobbing process if you are bored enough to read it.

I have increased the tension a fair amount and it works for a while, but still the same problem, though the idea of it rubbing the edge as it enters the hot end might be giving it just enough friction to stop it, and would explain why I can help the big gear along without much force. I'll toss the calipers on a few sections of the filament when I get home to see my tolerance, and measure the hole in the extruder body.

About how much tension would you say you have on the filament? Enough where the teeth on the hobbed bolt are digging into the filament?

I've occationally had the same problem. When my extruder starts clicking or 'bucking' I know that I need to adjust it quickly or it will dig into the filament and I'll have a whole new set of problems.

For me it was with PLA and the temp was too low, usually dialing it up a bit did the trick (4-5 deg. C).

Have you taken measurements of the cross-section of your filament over 8-10 places (at different angles) and averaged all but the largest and smallest sizes to enter that number as the filament diameter of your slicing program? That and the diameter of your hotend are how the slicing program determines how fast to crank the extruder (once you've entered a ball-park rate based on the number of steps and gear sizes and stuff).

Calibrating the extruder is an art of it's own that took me a while to get right.

Check out my blog for a list of the (many) issues I've tackled thanks to this forum and a few links I found online about calibration.

Hey!

I'm having exactly the same issue... I tried tightening up the screws, but was still unsuccessful... I think the issue might be when it retracts a little bit of filament during the printing process. It seems to really pull back hard and fast. What setting parameter changes how fast it pulls the filament back in (opposite of extruding).

Thanks!

I have been printing for a week with same issue but fixed mine my hotend came from maker farm as well and as long as u have the correct thermister selected in your firmware and is wired up properly your problem is not in your hot end. Here is what u do set your hot end to 230 let it warm up with your spring screws out where u can see your hobbed bolt make sure u have your bolt 100% clean of any left over chewed up filament if its in the grooves of the hobbed bolt its not going to work properly regardless so do that first.

Next make sure the alignment is 100% spot on the hole and the center of the bolt. Push your filament into the filament should be able to be pushed straight into the hole and extrude material without major force but do it slow and evenly if this works obviously it's your mechanical setup and not ur electronics. In regards to filament being straight u don't want your filament to be going into the extruder at an angle u want it going in as straight as possible so as the bolt is biting into the filament and pulling the force is as 100% vertical as possible and not from a side angle.

Close yo filament locked in place and make absolutely sure it is perfectly lined up in the absolute middle of the hobbed bolt or u will get a flase sense of proper tension on the filament. If its lined up and perfectly centered in between the bolt and the bearing and entering the extruded perfectly tighten the bolts as tight as u can get them with your fingers as you tighten both bolts do a little each so even pressure is applied on both sides of hobbed bolt if springs are weak and slinky feeling go ahead and replace with stronger springs or tighten down till the springs are fully compressed.

You want to also make sure your filament isn't binding on anything as the hobber pulls the filament into the hot end the less tension it has the better and less work it has to do.

As you extrude your filament get a flashlight to look down into it if u can't see it well and watch how it feeds

See what the gear does to the filament make sure bearing is spinning properly.

Another thing I done was put a series of dots on the outer 608 bearings so I can see it moving when the filament is between the hobbed bolt and bearing.

You should have no problems if u do all this.

My hobbed bolt has gave me no trouble since I figured this out best of luck

I ran I to this problem once myself, newb here (only 3 days), and my problem was too much tension. The easy was as someone else suggested is push the filament through by hand, if that works your either too tight or loose. Another way to tell if your too tight is look at your filament where the hobbed bolt is, if worn out then too tight.

Couple things to check (things I just learned last couple weeks). May not completely apply to your problem though.

Too much pressure / tension can create problem: it makes the filament deform and is bigger (where the pressure is) and can get stuck in the PFTE tube.

When I first played with the extruder, I also create problem: I retract filament too much and the hot filament became oval shape where the pressure is and won't go down any more.

Usually just take the extruder apart, and you should see why it gets stuck.

I also had problem like this: plastic coming out of the extruder inconsistently. And if I give some help pushing the filament into the extruder it would come out. The problem was caused by: the hobed bolt teeth were too fine, and the small filament dust just collected between the teeth. After some couple days, it couldn't push out filament any more. I made different hobed bolt with M5 tap (instead of M3), and it worked much better, no stuck yet, knock on wood.

Another source for inconsistent extruder flow is the temperature. I was using a PID temperature controller with dry contact relay. This set up was faulty and it give a large variation in temperature, and I would see my plastic flow is much thinner and won't stick to the previous layers. I replaced the dry contact relay with a solid state relay and it seems working more reliably now.

I made my own hot end and did have some problem at first, but lately it's run smooth for me. I'm using ABS at 230*C. My longest continuous print has only been about 2 hours though, but I've been using it every night for the last week.

-thanh