New User - Twisted the Auger Pipe and Stripped a Gear (Resolved) (Page 1 of 2)

Has anyone tried a 1/2 inch hole for the pellet port into the auger pipe?  As you can see in the attached image, the 1/2 inch hole is much smaller than the one that comes with the kit.  Is it necessary to have a long hole?

Working this troubleshooting out with the customer via email as they emailed as well. I agree that the smaller hold will probably cause some inconsistent feeding issues.

Here is a history leading up to the failure:

1) I successfully extruded the 1 pound bag of ABS pellets that came with the Filastruder
    a.  While extruding I ran the SESTOS PID autotuning and let it go for 1-2 hours.
    b.  But I didn't check if autotuning completed before shutting off the power
2) Purged the ABS pellets until no ABS extrusion came out.
3) Raised the temperature to 220 C to prepare for the PETG pellets.
   a. Waited 10 minutes after reaching 220 C
   b. Then poured in PETG pellets.
   c. The extruded PETG diameter was 1.4 mm
   d. Lowered temperature to 190 C and lowered table height.
   e. Extruded filament diameter was now about 1.7 mm
   f.  But the filament coiled in a 4 inch circle - difficult to wind onto reel by hand!
   g. Shut down machine for the day.
4) Heated up Filastruder to 190 C and waited 10 - 20 minutes to stabilize temperature.
5)  Turned on motor
    a.  PETG filament started coming out.
    b.  Temperature dropped from 187 - 190 C to about 165 C in about 2 seconds.
    c.  Auger pipe turned 90 degrees clockwise (with auger rotation)
    d.  Auger stopped and gear box started knocking.

Notes:
I'm not sure if I correctly set the CC adjustment on the stall protection board.  I didn't hear the "soft click" the first time so I just turned it counter-clockwise enough that it should have been 0 and then turned it clockwise 7 turns.  After the catastrophe I realized that turning counter-clockwise past the "soft click" puts it back up to maximum current (I think).  I didn't know how to check if the CC adjustment was set correctly at the time.  If I understand correctly, now, hooking up the heater to the stall protection output terminals and turning the CC adjustment clockwise until you get 1.4-16 amps is a way to know positively that the stall protection is set for sure.  Somebody correct me if I am wrong here.

Also, I think the temperature drop to 165 C just before the catastrophe was because cooler PETG from the auger entered the chamber.  I think the PETG has a higher melt flow temperature than ABS and I may have needed to wait for a definite 30 minutes after thermocouple first reached 190 to ensure enough length of flowing PETG before turning on the motor.

I will use the forum to communicate then - I think this will benefit new users.   

Tim,  in a previous post (Help with Stall Protection Board - 2015-02-04 18:09:13) you wrote:

"
Oh, with a multimeter this is simple!
With the gearmotor unloaded and set to full voltage, you should see around 5.5RPM. One thing - because PWM is used to control motor voltage, it will always appear as ~12v to the multimeter.

Next, go full CCW on CV until you hear the click, disconnect the motor, connect the terminals for the multimeter. Set the meter to the 10A setting. Connect the meter terminals where the motor was. This will apply a short on the output of the motor. You can then adjust CV in the CW direction until you see 1.5 amps - this should be about 6 turns past the “0” point."

QUESTION:  Does this still apply?  So you use the CV to dial in the 1.5 amps?  Or was that meant to say CC?

Here is the link:  http://www.soliforum.com/topic/9692/hel … ion-board/

Tim,

I now have a solid 1.5 amp (or whatever I want to dial in with CC adjustment) on the output of the stall protection board.  I confirmed it with both the heater hooked up to the stall protection board output terminals via graphical readout and also using the multimeter hooked up to the output terminals.   I think the fluctuations I was getting were because of two things: 1) I had the stall protection board resting on the aluminum chassis while I was testing it and/or 2) the wiring was messy so I fixed it up.   

I want to order the gears now and an auger tube+flange and a piece of Kapton tape so I can get this machine running again ASAP.  How do I order the auger tube+flange and tape if it doesn't show up on the order site?

I just got my new gears and auger barrel.  Question:  does the metal spacer shown on the finger slide onto the shaft of gear 5 with the smaller diameter side touching gear 5?

Anyway,  I went ahead and put the bushing on the bottom of gear 5 and closed up the gearbox and reassembled the filastruder with the new auger barrel.   I have the CC set to 1.6 amps and CV set to 12 V and am extruding the Eastman PETG material. 

My Input Settings:
Temperature=220C
nozzle diameter = 1.75 but is probably actually 1.6 mm?
Table height = 2.5 feet
Exit fan is fully extended and extruded filament drapes over the PTFE tube

My Output:
Temperature reads 198 C
Current reads 1.6 amp all the time.
Extruded filament diameter = a very consistent 1.6 mm
Extrusion rate = 4 inch / minutes (shaft barely turning) then jumps to 24-30 inches / minute for 10 - 20 seconds then back to 6 inch / minute.

Questions:
1) Why won't the temperature rise above 198 C?
2) Is it ok for shaft to turn so slow while motor constantly at 1.6 amp?
3) Can I increase the amps?
4) Should I increase the nozzle diameter (drill it out)
5) Can anyone see anything wrong with my setup from the picture below?

I moved the insulation to shroud the nozzle, moved the the center of the fan under the nozzle exit, raised the filistruder nozzle exit height to 4 feet as you suggested above.  Additionally I drilled out the nozzle hole to 2 mm angled the filastruder with nozzle downward by about 30 degrees and set the temperature to 220 C.  So now it extrudes pretty good and the temperature stays near 220 C even though the stall board reads 1.6 amp pretty much all the time.  The Eastman PET filament diameter is 1.4 to 1.5 mm which is too thin.  I am going to follow the Eastman PET filament material review link and increase the nozzle diameter and temperature. 

NOW THE SCARY - so I noticed that the current jumped to 2.6 amp.  It was extruding fine but I shut it off quick.  I turned it on ant it was 2.3 amp but then the stall kicked in and current went down back down to 1.6 amp.  Is this normal?  Does the current sometimes go above the CC set current if nothing is stalling the motor?  Does the CV adjustment somehow allow the current to overshoot?

Turning 15deg isn't a big deal, it just means the barrel wasn't tightened enough when you installed the new one.

The value of the stall protection board limit shouldn't jump around. It sounds like something might be up with your stall protection board. It might have been damaged from back when it was set on a metal surface while powered. It might be good to pick up a new one, order from the store and reply to the order notification with a link to this thread and I'll refund the cost of the board as a courtesy.

When it hit 2.6 amps was the barrel fully heated? I would expect an empty, fully heated barrel to be a half amp or so of motor load.

Yes.

Also, a couple other things. I suspect the FEA analysis you performed isn't quite right as I've experimentally loaded barrels higher without yielding (though I don't suggest this). It is rather challenging to get an FEA analysis to match real life, especially without knowing the alloy of steel being used. An FEA analysis is only as good as its input data.

It doesn't matter if the barrel is able to move or not, 2.5 amps worth of torque is 2.5 amps of torque. The barrel being able to rotate doesn't impact the stress experienced by the material, as the torque needed to accelerate the barrel is negligible.

Another possibility is incorrect assembly of the gearmotor, resulting in less than nominal torque for a given current. Though that wouldn't cause the current to jump around, it would explain why the 220C extrusion was causing the motor to reach overload. I'll check on that bushing placement tomorrow.

I agree that physical experiment is better than FEA but at least FEA can give some insight.  And I also agree with you that I don't have the steel properties of the steel pipe (especially the yield stress which several sources indicate can be much higher - like 400 MPa instead of the 170 MPa I assumed).  But, for what it is worth, here are the initial FEA results based on these inputs:

Young's Modulus = 200 GPa
Poisson's ratio = 0.29
Yield Stress = 170 MPa
Tangent Modulus = 20 GPa (which is 10% of YM)
Torque = 12 Newton-Meter

The maximum stress with a 12 Newton-Meter torque at the end of the auger barrel is 174 MPa at the location in the image.  But this is just a localized stress and the average stress in the cutout region is more like 70 MPa which is well under the assumed 170 MPa yield stress. 

The full torque is 'felt' by the pipe regardless of whether it is rotating or not. For a given shaft, torque at one end of the shaft is equal to torque at the other end of the shaft, assuming the shaft's angular acceleration term is negligible (which it is in this case).

Torque_in = Torque_out + alpha * I

Where Torque_in is the torque on one end of the shaft, Torque out is the torque at the other end, alpha is angular acceleration, and I is the moment of inertia. So in this case  if there's 10N-m applied at one end, the entire barrel is subjected to 10N-m whether it is rotating or not.

it is possible though that the motor hadn't reached its limit while the barrel was rotating. That would cause a lower torque than the limit to be applied to the barrel.

As for the gearmotor assembly, here's a fresh gearmotor:

http://imgur.com/a/2hP6c