Auto rewind reel recommendation  

RE: Auto rewind reel recommendation

Hi

I've just added this which is dead simple and doesn't have the tug-back issue some (all?) rewinders users have reported.

https://www.thingiverse.com/thing:3690758

Best

Graham

RE: Auto rewind reel recommendation

Thanks!

RE: Auto rewind reel recommendation

I've been using https://www.thingiverse.com/thing:3338467

• I don't use the PTFE holder arm as it flopped around too much and bound up the filament.
• I have the filament come out beneath the spool.
• Getting the tension right seems to be an art and it changes as the spool is used up. Too loose and you get filament everywhere. Too tight and it fights the MMU and you get tool change failures.

I have read reports of the springs failing, but so far so good. I don't think these will be a long term solution for me, but they got me up and running. Currently I'm in the process of building a 2020 frame to hold the spools over my printer and I've made saddles to hold these spool holders without their frames.

I can not recommend NOT wasting your time with https://www.thingiverse.com/thing:3228827 enough. The path coming out the bottom of the buffer is at a weird angle that causes a lot of friction. Tight tolerances made it difficult to assemble and caused additional friction issues. Requires supports on some parts.

So far in my experience any stand alone spool holder needs to be attached to something or heavily weighted. The MMU will pull them around otherwise and that can cause you problems.

RE: Auto rewind reel recommendation

I just posted a new auto-rewind solution on thingiverse.

https://www.thingiverse.com/thing:3691892

Justification for doing something different than the previous designs from VincentGroenhuis and MartinHoffmann (both of which worked very well for me) is in the description.

RE: Auto rewind reel recommendation

Thanks everyone for your feedback and suggestions... studying all of it. Again, THANKS!

Assembling the printer is a lot of fun 🙂

RE: Auto rewind reel recommendation

I was struggling to build an auto rewind spool holder.

Then I read several posts, and what come out was that they are NOT a good solution.

Prusa is trying to get the reliability as high as possible (otherwise they could not think to have a farm of 3D printers and produce with them) and this is why they did not adopt them in the MMU2 / i3MK3 concept.

What I understood is that:

• Almost all the auto rewind spools use "plastic" springs, and believe or not after a while they stop to be reliable. Springs can't be done in plastic. Time wasted.
• Some design use "gravity weight" as a form of spring.  However the diameter of the spool is not always the same, and vary based on the consumption level (long at the beginning, short at the end), and based on the object design, it may be tricky to set up.
• Very important, several posts blames the inverse pressure. Basically they assume that to roll the spool back it may need as example 20gr force. That force is always present, and will sum to the one of the PFTE long tube friction + MMU2 mechanics, so that the extruder motor will have to constantly apply a huge power in order to be able to move the filament, and this cold make it hotter or even give irregular movement and extrusion.

I wondered why Prusa used the "black trays", and why they use still a modified version of the filament holder included standard on the MK3 on the new MMU2 Ikea Enclosure. After thinking a while, I though that the reason is: because they are simple and reliable.

On my other RigidBot printer the spool is maintained by a 100% balanced axial roll, where the spool is free to move without any effort.

And guess what ? Now and then, the force of the filament suddenly make the spool auto rolling, unwinding a lot of filament like, acting like a circular spring, making a big mess around: NOT GOOD.

Then I though to the black tray of the MMU2. The roll can be moved with a very low effort, but it never ever unrolls itself making mess: A GOOD SOLUTION.

I though also to the original i3MK3S spool holder. It never auto roll itself dropping meters of filament on the printer. Again A GOOD SOLUTION.

After all those consideration also I definitely do not recommend the usage of an auto rewind spool holder.

What I have also seen is that other more expansive MMU solutions on the market, still use exactly the same buffer concept, and normal spool holder.  So those may be the reasons... 😎 

Regards

RE: Auto rewind reel recommendation

I absolutely agree with you 'antimix' with one caveat...  If you want to tinker and enjoy the challenge then why not.

But there are certain things that are really difficult to overcome and at best will make re winders intrinsically 'fickle'.

When a spool is full it will have high inertia but needs to turn little as it circumference is large.  When near empty it is the reverse. 

To compensate for this the circumference of the filament will need to be monitored or spool weight and the clutch or weight or spring or combinations auto adjusted .  Or you need to manually tweak the re winder settings as it empties.   There are some pretty cool (but complex & large) prints out there to solve the rewind challenge without addressing this & I look forward to admiring the next generation that trys too.

These things will get more and more complex and are printing tour de force to be admired but unless you get a kick out of it Id go simple.   (as per my post above).

Personally I've got so many other things I want to design and print without wrestling the tool any more than I need to.

Best

Graham

RE: Auto rewind reel recommendation

Anyone can obtain reliable results from a MMU2S using only 10 short (75-100mm) segments of PTFE tubing. They need a segment after the filament comes off the spool and another right before it enters the MMU. The filament in between is fine in open air. But, for this to work, the spools must be 4-5 extraction lengths behind the printer.

All buffers are just an optimization to reclaim some of that space.

I've seen pics where some ingenious people have used empty spools to wind the open air filament a few times and significantly reduce their footprint. There are dozens of wallet style buffers out there, including the one Prusa ships with the MMU2S. Every one of these solutions is a huge improvement over the first solution described. But, each still requires its own real estate.

A rewinder is just a further optimization which reclaims virtually all of the wasted space.

I can imagine (and may one day try to design) an electronic rewinder. It is easy to envision several potential implementations involving: mechanical sensor to detect when the filament reverses, motor with clutch to rewind the spool, perhaps even a cheap VL6180x laser time of flight sensor to measure the remaining filament radius, etc. But, such a thing would be complex and expensive relative to today's mechanical alternatives.

It is easy to store some energy by lifting a weight or winding a spring while the filament is feeding into the MMU. The additional load on the MMU's steppers is very small as these motors produce tremendous torque. The real risk is the filament getting ground down due to pulling resistance, which I have not encountered.

The stored energy has to be enough to overcome the inertia of a full roll. The overall solution has to produce enough rewinds to handle an ejection when the roll is empty and the circumference is low. Once those requirements are met, it is an exercise in: size, complexity, print time, etc.

I have had significant with 4 different rewinder implementations. The only problem I have ever encountered is achieving 100% reliable empty spool rewind with some earlier versions.

I would not encourage anyone to build a rewinder until their MMU had produced several successful prints and done thousands of tool changes.

But, after that, I would encourage anyone to do so if their printer is in a space constrained environment.

RE: Auto rewind reel recommendation

Posted by: gandboss

Hi

I've just added this which is dead simple and doesn't have the tug-back issue some (all?) rewinders users have reported.

https://www.thingiverse.com/thing:3690758

Best

Graham

Graham,

I had not looked at the thing you posted prior to making my previous post and did not realize you were one of the guys using empty spools as a buffer.

That is a really simple design and well done. I'm envious of the vertical clearance you have above you printer and now understand why you would not bother with a rewinder....

RE: Auto rewind reel recommendation

Posted by: greg.h8.

I would not encourage anyone to build a rewinder until their MMU had produced several successful prints and done thousands of tool changes.

But, after that, I would encourage anyone to do so if their printer is in a space constrained environment.

From my experience, this is backwards. I agree that the auto rewinders aren't ideal for all the reasons you laid out, but they do offer a workable solution for those constrained on space. 

For example my space was such that with my spools against the wall I had 6" between the spools and the rear of the printer with the LCD box hanging off the front of the desk. There was simply no where to put a buffer and loose filament was likely to get tangled and caught by the bed. 

So for the space challenged, the auto rewinders can be the difference between giving up on the whole thing or getting a couple thousand tool changes. 

I've never looked at these as a final solution, just enough to get the printer working and make sure I wanted to continue with it before investing more money into it. 

Now I've invested in building a frame to hold them above the printer. From here I'll continue tweaking to find what works best. 

RE: Auto rewind reel recommendation

gnat,

your point is well made. If you only have one location option for the printer without even room for a buffer of some sort, rewinders might be the only way to get reliable prints.

I have an understanding wife who let me disrupt the household and spread things out while trying to debug my MMU2. The rewinders were what enabled me to move the printer to its long-term home and find peace with the spouse again.

RE: Auto rewind reel recommendation

Why thanks.   I got a bit lucky.   I had no space to dedicate to the printer when I ordered it so what you see here is a special micro extension to our summer house that is dedicated to be my electronics workshop.   It is the size of a small wardrobe floor to ceiling with its top made of upvc sheet like you get on conservatories plus a strip light.   It gave me good height though I initially wanted to use that lower rail for filament stock so having to dedicate it mostly for buffer spools is a shame but it does that job very well.  Hence me making skinny reels.  The top spools have a fixed towel over them to protect from UV.

With a bit of simple woodwork I'm sure a frame could be built with printer on the base to mimic this arrangement especially if backed on to a wall.

Cheer

Graham

RE: Auto rewind reel recommendation

I think this is a great combination.  Holds 5 Spools (on modified Tush Holders) & dries your spools as you print.  No issues with buffering.  Total cost is about US$100 + some PTFE Tubes inserted in 2mm holes I drilled.  Priceless!  

https://jmone.org/jmonenextcloud/index.php/s/DGBqcCEag4kax6J

RE: Auto rewind reel recommendation

Posted by: jmone

I think this is a great combination.  Holds 5 Spools (on modified Tush Holders) & dries your spools as you print.  No issues with buffering.  Total cost is about US$100 + some PTFE Tubes inserted in 2mm holes I drilled.  Priceless!  

https://jmone.org/jmonenextcloud/index.php/s/DGBqcCEag4kax6J

 

Hi,

Can you give more information about this? What is the product name/link?

Thanks

RE: Auto rewind reel recommendation

It's a Sunbeam DT6000 Dehydrator (Australian Model) but I'm sure there will be similar machines in other countries.  I got rid of all the plastic trays and got a sample tile (for $1 from the HW store) that I cut to fit the floor.  Nice and solid.  With some modified Tush holders (glued together in the middle) it will hold 4 x Spools side by side and 1 x Spool in the front.  Just drill a bunch of 2mm Holes in the top and insert some PTFE tubes and you are good to go.  I also stuck on top an Temp table for each filament type.  Best cheap upgrade ever, nothing beats fresh filament 🙂 

RE: Auto rewind reel recommendation

....and it takes up no more space than 5 x spools!

RE: Auto rewind reel recommendation

Posted by: greg.h8

I just posted a new auto-rewind solution on thingiverse.

https://www.thingiverse.com/thing:3691892

Justification for doing something different than the previous designs from VincentGroenhuis and MartinHoffmann (both of which worked very well for me) is in the description.

I am using the Rubbermaid 21-cup version of this and it simply rocks.  Once the MMU2s is fully tweaked, I am going to be using Verbatim BVOH for support intersections and it simply cannot be in the open air.  The more I used different wallets, the more I found they just added too much friction.

This rewinder solves the spring problem by using gravity based potential energy for the rewind.  Easy to load and unload the filament.  You can find it in my collection:

https://www.thingiverse.com/cybrsage/collections/mmu2-mods