Sunday, November 19, 2017

Tangle-Free 3D Printer Spool Holder

One of the common problems in 3D printing is filament tangling on spools.  It is primarily a user problem because the filament comes from the manufacturer in an untangled state.  Improper handling of filament spools is the main cause of tangles.  Whether it should be possible to cause tangles through mishandling at all is a subject for another blog post.

Proper handling means keeping the free end of the filament under control at all times when loading and unloading a spool on the printer.  When you take a spool off, you must thread the free end of the filament through one of the holes in the flanges, or secure it some other way.

There is also a mechanical aspect to the problem.  Specifically, stiff filaments like PLA like to uncoil from the spools and will do so any chance they get, especially when they are fresh and the spool is full.  Most spool holder designs will allow the filament to spring over the flanges which easily results in filament tangling and failed prints.

A few months ago I designed a spool holder that prevents the filament from springing over the flanges by pressing rollers against the flanges.  The spool rests on two bottom rollers and a third roller, at the top of the spool, moves down and locks in place with the twist of a nut.  The rollers turn on F608zz bearings that I had left over from the UMMD build.  The rollers are tapered to keep the spool centered in the holder.

Filament spool holder for 3D printer from Mark Rehorst on Vimeo.

I printed and assembled two of the spool holders, one for use on UMMD and one for use on SoM at the makerspace.  After using them for a while I discovered two problems.  First, filament spool flanges aren't always perfectly round (and neither are 3D printed rollers).  I found that adding a couple rubber bands to pull the top roller down against the spool did a better job of keeping the flanges in contact with the rollers and keeping the spool centered.

Rubber bands were added to both sides to ensure that the top roller stays in contact with the spool flanges.


The other thing I found was that as simple as it is, my spool holder design was too complicated for some people.  I have found the spool holder at the makerspace taken apart on more than one occasion, and a couple times I found a spool mounted on the top roller!

I decided to try to fix that problem.  I redesigned the spool holder based on a design I saw on Thingiverse or Youmagine - I can't find the original as there are literally hundreds of design for spool holders on both sites.  It has 4 rollers instead of 3 and they're mounted on levers so that the weight of the spool causes all four rollers to press against the flanges, thus preventing the dreaded spring-off and resulting tangles.

The new design uses bearings salvaged from hard disk drives- the same type I used in the 3D printed Van de Graaff generator.

Typical HDD head lever bearing.


The rollers were printed using single wall vase mode in Slic3r so there would be no seam or little bumps at layer starts/stops.  The printer nozzle was 0.6 mm in diameter and the walls are 0.75 mm thick.  I printed a test piece to get the right size to be a tight, press-fit on the bearings.

Test block used to get the hole sizes to press fit on the bearings.  Holes vary by 0.1 mm in diameter.


One of the rollers in Slic3r.  It used single walled vase mode with inner and outer brims to help keep the part stuck to the bed.  Each roller took about an hour to print.


The lever arms are printed ABS and the roller bearings screw into the plastic.  The pivot bearings press into the levers.



The base was printed using PLA with  10% infill, 2 perimeters, and 3 top and bottom layers.

Here's the base printing.  It used almost the full width of the bed.

And now, here's what you've been waiting to see...





Fits 200 mm spools...
Tapered rollers keep the spool centered.


Fits 160 mm spools, too...

Tapered rollers keep the spool centered.
If you have a printer with a large enough bed, you can print this spool holder.  Here are the design files.

Using a Laptop as a Desktop Computer

My 9 year old desktop PC has been having trouble keeping up with my CAD and 3D modeling work.  It was a pretty hot machine in its day, but that day has long passed.  Recently the graphics card has been crashing and only sort-of recovering, and I've been getting BSODs from Win 7.

I started looking for a replacement that would have a CPU with at least 4 cores (even though most software uses only one core, I use a couple programs that can take advantage of multiple cores), lots of RAM, and a graphics card with at least a couple GB of dedicated RAM.  USB 3 would be nice as would bluetooth, and dual band wireless networking.

I started pricing out components for a new build and quickly got up to about $800-1000 range.  Ouch!

Then, before I could start ordering parts, someone at the makerspace informed me that he had a couple 4 year old laptops he recently picked up at an auction, for sale at the very reasonable price of $100 each.  The machines are Lenovo W530 with a quad core 2.7 GHz i7 CPU, 8 GB of RAM supporting up to 32 GB in 4 slots, an Nvidia K1000m 2GB graphics card, bluetooth, dual band wifi, USB 3.0, lighted keyboard, full HD antireflective/antiglare display, SD card slot, fingerprint reader, 720p webcam, DVD burner, etc.

I was hesitant at first, but after looking up the machine and its specs, I started to change my mind about it.  The CPU would run rings around the CPU in my desktop machine, likewise the graphics card.  $100 got me the laptop with a battery in unknown condition, no power brick, no HDD and no OS.  A quick scan of ebay turned up plenty of cheap parts and accessories for these machines which were corporate work-horse type computers.  There's also plenty of documentation and software support on Lenovo's web site.

What I had:
Win 7 install disks
500GB HDD
240 GB SSD
keyboard and mouse
3D mouse
32" BenQ display
USB hub

What I needed/wanted:
RAM- 32 GB DDR3 1600 SODIMM- $180 via ebay
HDD caddy to replace the DVD drive - $8 via ebay
170W power brick-  $30 via ebay
mini displayport to displayport cable - $8 via ebay

What are the advantages of using a laptop for a desktop?  Smaller, quieter, lower power use, and a built in UPS (the battery) that will prevent loss of work if AC power fails.  I can take it with me if I really need to.  What's wrong with it?  Some inconvenience powering up because it's a laptop.  Otherwise, it's all good.

When I got the laptop, the battery had just enough juice in it to power up the machine and run some diagnostics- all good.

The power brick was the first thing to arrive, so I installed the SSD and Windows 7 (will probably dual boot with Linux, later).  After charging the battery I found it was able to power the machine for 5-6 hours at a time, so the battery was in great shape.  After installing Win 7, someone else at the makerspace suggested that I try installing Win 10, so I gave it a shot and it turns out the machine had a corporate license associated with the CPU so Win 10 Pro installed itself and registered just fine!

I installed the 500 GB HDD in the optical drive slot, moved all the user files to that drive, and installed all my CAD and other programs to the SSD.  The machine boots fast and programs load very quickly.

The computer sits on a shelf above the display on my work table where it is within easy reach to disconnect things and move it if I need to take it with me somewhere.  I have a USB hub on the worktable to plug in things like my Yubikey, thumbdrives, phone, etc.



I adjusted the power settings to shut off the display after 10 minutes of disuse and never sleep.  When I am finished with the computer for the day I hit the sleep button on the keyboard.

It's cold in my basement, so I run an electric heater when I'm working down there.  A few days ago the heater blew the circuit breaker on the power strip that it and the computer were plugged into.  The display went dark and I was momentarily panicked, but then I realized that the computer has a battery and sure enough, when I flipped the circuit breaker, all my stuff was still there, ready to go.