Too much force required to pull the filament out of Filament Box  

RE: Too much force required to pull the filament out of Filament Box

What is the internal diameter of the PTFE tubing you are using? I have been using tubing with ID 3mm (OD 4mm) for feeding filament from my dryers to my printers, which are set up with reverse bowden to the top of the enclosure. I have compared (not measured) the pulling force for PTFE tubing with ID 2mm to tubing with ID 3mm and the force required with the smaller ID is much higher.

RE: Too much force required to pull the filament out of Filament Box

I live in a country that can be very hot and humid.

My printers are in a outside building.

I bought a couple of Sunlu dryers, the outer diameter of the filament spools run on 2 shafts fitted with roller bearings.

These dryers never let me down, effortless pressure needed for the extruder to pull the filament through.

https://www.amazon.es/Filamento-Impresoras-Filamentos-SUNLU-Impresi%C3%B3n/dp/B08C9LKS3Y/ref=asc_df_B08C9LKS3Y/?tag=googshopes-21&linkCode=df0&hvadid=699840556964&hvpos=&hvnetw=g&hvrand=2033166900455643284&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1005548&hvtargid=pla-963907013946&mcid=bbd32f7f72983008ae0d7622106466c0&gad_source=1&th=1

Hope this helps.

RE: Too much force required to pull the filament out of Filament Box

Posted by: @antimix

Hello, I think that there were very few discussions on this problem.

I have built several versions of Filament Boxes to keep the filament dry, using the cereal boxes,  and inside there is also the desiccant. Of course I have connected them via PTFE tubes directly to the MK3.5-MMU3 buffer and to the top of the MK4 (that has no MMU3 for now). Very nice concept .. 😉 

Unfortunately I discover that all this combinations add an incredible increase of the force required by the extruder motor to pull the filament, even messing up the MK4 bed probing. Until now I was not able to measure, but I have just purchased a digital dynamometer and now I got the measures, and..

WOW I got forces between 5.04N and 7.65N (around 500 gr-f and 765 gr-f) 😨 

Event if the box are almost the same build, I identify the following changing factors:

• probably the bearings friction is different in each box causing different values of friction
• PETG have much more friction on PTFE tubes than PLA (but is PTFE really PTFE ? Or it is a fake Chinese PTFE with high friction 😎 )
• Using long PTFE tubes increase the friction
• The filament memory has a drastic effect in PTFE tubes: nothing is straight, so when the filament "decides" that the arc will be in the opposite direction of the PFTE tube path arc, the friction become very very high. I call this is the OS effect: the filament spool (O) rotates counter-clock wise enter in a low part of a S shape PTFE tube to go up on the printer, but the memory of the filament "refuses" to flex to form the upper S arc, and twists itself until it almost gets stuck in the tube 😤 
• Spools that rest on bearings, like the PRUSA spool holder have high friction compared to spools that pivots on a bar in their centre; those last have an extreme low friction (but tends to unwind by themselves 🤬 due to the filament memory, messing the spool)
• PTFE internal diameter can also affect the friction. Theoretically larger is better ?

 

- So, have you ever measured the real force required to unspool your filament ?

- Should a force between 500 gr-f and 800 gr-f considered acceptable by the current 3D PRUSA printers and Nema motors ? 🤔 

Say your opinion.

Regards

 

It could depend on the quality of the bearings and the lubrication of the bearings, and the surface area,for why you are getting more friction with bearings.

When the spools inner ring (circular), sits on a spool holder(also circular), the contact patch is less, than when the spools outer rim sits on 4 bearing or it sitting on a rod that is supported by greased bearings.

To lessen the friction on bearings one would need a better quality bearing with the seals removed, grease removed and use of a high quality bearing oil or a high quality and a little grease. 

I used to be into rc cars. The bearings that come with them are either cheap bad quality bearings or decent Chinese bearings. Some racers would order Boca Ball bearings for their rc cars or ceramic bearing for them. For transmission bearings where the transmission was basically sealed some would remove the rubber seal, degrease the bearings and use a light oil and replace the seal or keep the seal off to decrease friction. Also on the wheel axle bearings the seals would be removed, degreased, oiled and or re-greased, depending on the race conditions and one seal was installed, usually facing the outside facing the elements. 

I guess if we could fit bearings in the center of the spool and have the spool fit on a shaft we could have very low friction similar to bearings on a rc cars front tire that once spun by hand, could keep spinning for minutes.

RE: Too much force required to pull the filament out of Filament Box

I have just seen a video on using bearings with 3D print mechanics, and they said that the grease inside is for heavy duty use, but if we need to do light things like moving spool, the bearings should be washed in WD40. I will try to see the results.

RE: Too much force required to pull the filament out of Filament Box

Check the entry of the tube. It should have well rounded edges and preferably point in the direction of the center of the spool fill. Also use wide tubes and let the tube run all the way to the Nextruder and end in a terminal fitted on the Nextruder. There's an M5 hole there for that purpose. That way the pull force for the filament reacts directly to the tube and it does not affect your leveling.

RE:

I measured the force to pull the filament out of the box at between 0.5N and 1.0N using a spring balance. I have 30" of PTFE tubing. ID 3mm, OD 4mm. The spools rotate on an Aluminum rod inside of the box. I don't have any issues with the spools unrolling on their own.

RE: Too much force required to pull the filament out of Filament Box

My 2 cents. 
I have a dryer box, with rollers on bearings, what looks very fancy. But in reality the spool  is just dragged over the roller (what do not turn at all). So the friction between spool and roller is much less then what is happening inside the roller 🙂
The PFTE is a bit wider, so the filament passes through very easyly (also TPU is no problem). 
So I guess, the friction is mostly from the tube and (not to forget) when the filament is pulled around corners, tiny rounds. what makes it important to to keep the filament in a smooth line. 

RE: Too much force required to pull the filament out of Filament Box

Hi  Antimix,

The increased force required to pull filament from your Filament Box is likely due to several factors: bearing friction variability, type of filament, length of PTFE tubes, filament memory, spool holder design, and PTFE tube diameter. Forces between 500 gr-f and 800 gr-f might be too high, potentially stressing the extruder motor and affecting print quality. You might need to optimize your setup by checking the PTFE quality, reducing tube length, and ensuring spools unwind smoothly.

RE: Too much force required to pull the filament out of Filament Box

In the DryBoxDesk I built to house filament for my XL5T, there is a lot of PTFE tube to pull through!
See pic: https://forum.prusa3d.com/forum/original-prusa-xl-tool-changer-user-mods-octoprint-enclosures-nozzles/custom-dry-box-work-bench/#post-714906
In the 2nd pic of the 1st post in the thread, you can see a real sitting on the bar + extrusion. I added PTFE tape to the both, and that helped reduce the friction of the real rotating quite a lot.

RE: Too much force required to pull the filament out of Filament Box

use some dryer and you will be ok then

RE: Too much force required to pull the filament out of Filament Box

Yesterday I dismounted all. There was too much friction, and with high variability. I measured even 2.05 Kg from extruder at a certain point !!!!

• A box alone is between 350 ~ 725 gr (pulling just from the box hole). This variability depends from the boxes that are too tight, and sometime the high spool part touches one border of the box, creating friction.
• The bearings do not roll well. There is too sticky grease inside. I have dropped them in WD40 and IPA and left washing for some days, hoping that they will be able to  slide well. If not, I will put them on the ultrasonic washer.
• The aluminium bars are too short (I recycled them from the old box) and sometime the spool slide down.
• The BUFFER rolls add another incredible amount of friction.
• If the filament torques while unspooling, it increase the friction, and that's why there is such a high variation.
• Pulling a piece of filament from a 50 cm tube just take 184 ~ 245 gr based on  how the tube is bended. The greater the tube deflection, the greater the friction.

Now I am re-engineering (= rebuilding) the boxes, and I have just purchased some boxes that I hope will be bigger. Unfortunately often what you receive is not what you saw on the picture. I sent back lots of them in the past.

Regards

RE: Too much force required to pull the filament out of Filament Box

Today I received two PolyDryer boxes. They have the PTFE tube bigger : they use a 3.9mm inside diameter and the tube external diameter is 6 mm

I measured the force and it was very low 🤩 only 60gr. I will re-assemble one with a new longer tube in a way to connect it to the MMU3 and to the MMU4.