Cold Pull on U1?

U1 Toolchanger U1 Troubleshooting guides
1

What is the proper procedure to perform a cold pull on the U1?

When switching filament from PLA to TPU for any particular toolhead, I find I have some PLA contamination in the first few layers of TPU from some residual PLA left in the nozzle, etc.

With TPU this is undesirable because PLA contaminates the strength of the TPU, weakening it and certainly making Z layer strength bad! PLA makes a great interface layer for supports with TPU as PLA will not stick to TPU!

Obviously, the normal purge cycle when loading new filament into a toolhead was certainly not enough!

To solve this, I tried to perform a cold pull.

I performed these steps using the controls on the U1 printer control panel:

  • Unloaded the current filament from the toolhead
  • Removed the PTFE tube from the top of the toolhead
  • Heated the toolhead to 250 C.
  • Manually fed some white PLA into toolhead using the manual extractor feed control
  • Manually extracted a good amount of PLA until it looked clean (previous was a dark color)
  • Set the toolhead temperature to 100 C
  • Waited for the toolhead temperature to reach 100 C
  • Attempted to retract the PLA using the extruder controls ā† PROBLEM: Canā€™t retract, control disabled!

When attempting to retract the PLA at 100 C (typical cold pull temperature), the extruder would not allow retraction. The extruder controls were disabled!

I didnā€™t double check it, but it appears the extruder controls are disabled when the nozzle temperature is below (about) 170 C.

Is this the purpose of the yellow extruder gear lever? To disengage the extruder gear? Is this supposed to be used for a cold pull? What are the other uses for this lever?

I searched the Wiki for both Cold Pull instructions as well as the purpose of the yellow extruder gear disengage lever. I could not find either documented on the U1 Wiki!

I was able to manually slowly pull the PLA out of the toolhead and could hear and feel the extruder gear turning.

What is the purpose of the yellow extruder gear disengage lever?
This is my first 3D printer that had this lever!

Additionally: To answer my root question, what is the proper procedure on the U1 to perform a cold pull to clean the nozzle from possible left over contaminates when changing drastically different and incompatible filaments (such as PLA and TPU)?

2

I wouldnā€™t expect to be able to do a cold pull at 100c in the first place. I do cold pulls at 180C. Let it cool to 100C and then set the temp to 180C. Start hitting the retract button as soon as it hits 170C ( or at least thatā€™s what I do).

3

I donā€™t know if 180 C or 170 C would be considered a ā€˜coldā€™ pull, but if it works for you, ok!

Bambu suggests using 70 C so perhaps even my 100 C was a bit too warm. Note: Iā€™m not saying that Bambu is the best source of how to perform a cold pull, but this is the procedure I have used on my other printer and it seems to work well:

But still, Iā€™d like to know what Snapmaker suggests?

It seems the firmware may need an override or a change to allow retracting below 170 C otherwise we canā€™t use the extruder to help with a cold pull.

And still:
What is the designed purpose of the Yellow Extruder disengage lever?

Perhaps I should ask support in a ticket? I would think this forum might be a better location than to fill their support ticket queue with minor questions? Plus, it would help others as they will see the answer here.

Perhaps the Snapmaker U1 Wiki needs this information added?

4

Please check the WIKI. It does say that you are requested to contact support for Info re cold pull. i e the subject is covered.

5

I didnā€™t find any information on the Wiki about a cold pull. But perhaps I missed it?

Edit to add: to the Wiki had instructions on how to clear a clog, to me this isnā€™t a cold pull.

However, have already sent a message to support, but havenā€™t had a reply yet.

6

You can always disconnect the feeder tube and do a manual cold pull using the orange lever.

However, before that, run this stuff through and see how you feel. Amazon.com: eSUN 1.75mm, Cleaning Filament, Prevent Nozzles and Extruders Clogging, 100g Spool 3D Printing Filament for 3D Printers, Natural : Industrial & Scientific

7

You like this stuff and have you had good luck with it?

I was looking at it previously, but saw many complaints about it being undersized, and therefore causing problems, so I was hesitant to try it.

8

I donā€™t understand that. If it is only a cleaning filament and not intended for a print, it should not matter if its diameter isnā€™t well regulated. The need for a close tolerance on filament diameter is to meter the volume of filament being extruded (the length of filament being pushed through the extruder motor is a proxy for volume). Being able to relax the tolerance specification makes it cheaper to produce.

9

You have to read the reviews. .

It seems that since itā€™s under sized, that the extruder gears would not properly engage it and it ended up jamming up and getting stuck in their extruder causing a massive jam in the nozzle that was difficult to remove.

Iā€™m only asking if others have direct experience with this particular cleaning filament and had good luck with it.

Previously I have used white PLA to do a cold pull on my Bambu printer which seemed to work properly. I could see remnants of old filament being removed by my nozzle.

If I previously printed using a white or filament, then I would choose a black PLA for the cold pull operation.

10

I received a reply from Snapmaker Support on how to properly perform a cold pull on the Snapmaker U1.

I asked how to best clean the nozzle when switching from printing PLA to TPU because I found that the first few layers of TPU can be contaminated by left over PLA in the nozzle.

I hope sharing this information will help others.

Here are the instructions (I applied some formatting and cleanup for clarity):

Snapmaker U1 Cold Pull Procedure

We recommend performing a cold pull cleaning on the hot end using PLA filament.

The detailed steps are as follows:

  • First, load PLA filament and heat the nozzle to 230Ā°C.
  • Extrude some material to ensure smooth flow.
  • Then lower the nozzle temperature to around 70Ā°C and perform the cold pull
    • During this process, please remove the 6 mm filament tube
    • Release the driven extruder gear assembly (the yellow lever on the toolhead),
    • Then slowly pull the filament out.
  • Check whether the tip of the extracted filament is clean.
    • If there is still residue, repeat the above steps as needed.
  • It is recommended to perform this same cleaning procedure on all toolheads to ensure overall optimal condition.