Almost-Frictionless Filament Spool Holder for Replicator 2X by opwernby

Last crawled date: 3 years ago

Here is my Almost-Frictionless Filament Spool Holder for the MakerBot Replicator 2x (and anything else which mounts spools the same way). It gives your printer a continuous, smooth feed of filament with no snags, friction hold-ups or other problems - which is great considering how weak the Replicator extruders' feed motors are. Having built one of these (and reprinted several parts because it failed in the middle) I tested it by using it to build another - and I didn't have to reprint anything that time around.
The design is based around an aluminium central shaft on which sit two skateboard bearings: that big rotor you can see sits on those bearings and touches no other part of the device: it moves smoothly and effortlessly. It's also only one millimeter less in diameter than the hole in the center of a spool of MakerBot filament, so those spools won't wander around on the holder any more: they'll be stable and predictable instead.
Spools click onto and off the holder over a spring-loaded catch which keeps them mounted firmly on the rotor until you decide you need to remove it. Meanwhile, the base of the device fits into the Replicator's existing filament holder holes: it's got a little design in it to grip that opening fairly securely, so it doesn't get pulled about.
Requirements
To build one of these, you'll need the following other supplies:

Two skateboard bearings, size 608 (the standard size for skateboard bearings); these are super-cheap: look on Amazon. I got these: http://www.amazon.com/gp/product/B002BBGTK6


One 20mm and two 30mm M3 socket cap screws (you can use a 20mm shoulder bolt instead of the 20mm screw if one is available); the screws are available at any hardware store; you may need to order shoulder bolts online. I didn't bother, and mine works fine.


A spring capable of raising the catch. The one I use measures 20mm in length by 9½ in diameter; it has a wire diameter of 1mm and contains seven coils, counting the ends, and it came in a package of assorted springs from Home Depot. It's probably overkill, but it's what I had lying around. As long as your spring has a 9 to 10-mm diameter and can raise the catch easily, you'll be fine. Here's the pack of springs I got; the one I used for this is the center one in the top row in the product image; there are four in the package: http://www.homedepot.com/p/Everbilt-Spring-Assortment-Kit-84-Pack-15642/202045461

An aluminium rod at least 109 mm long, with an 8 mm diameter, to fit the skateboard bearings. If you haven't done precise cuts and drills on round metal rods before, order enough to make four units (you need one rod per unit), because you're going to waste at least one or two of them learning to cut the metal properly: it's about getting used to the actual material being used. I already know how to cut metal, and (to my everlasting embarrassment) I still managed to screw up three before I finally got it right. I used this - it's aircraft grade, dead straight and almost impossible to bend by mistake: they come in one-foot lengths, so one bar can make two Rods: http://www.mcmaster.com/#9403t54
Recommended Tools

A drill with bits sized at 1/8" and something substantially smaller such as 1/16"; optionally a 7/64" bit as well (see below);


A metal saw (easiest if it's a metal saw blade in an electric saw);


A file, or sandpaper, or something you can use to abrade plastic;


A 2.5 mm Allen/Hex Key (the one which comes with the Replicator will do fine);

A light hammer such as a framing hammer (or a big hammer and a light touch!).
Printable Parts
Included in the printable objects for this device are the following:

A Base: the end which attaches to the Replicator;


A Rotor: the rotating part, which even has bearing oiling tubes in it, should you ever decide you need such a thing (just use a can of WD40 with its optional tube attached to the spray nozzle);


A Cap: the other end of the device;


A Catch: the spring-loaded element which retains the spool of filament;


A Bearing Alignment Tool: this helps you install a Bearing into the Rotor;

A Rod Template: this helps you cut the aluminium Rod to length and to drill holes in the right places.
Instructions
Notes

Study the rendered picture above showing all the components in their correct relative positions (minus the Rotor, which appears above everything else, for clarity). A picture speaks a thousand words...


When printing, always use a raft; you must also use supports for everything except the Rod Template, which doesn't require them. Using a raft ensures that all pieces are produced with a predictable size independent of the alignment of any specific printer's head. All parts except for the tools should be printed in high quality with layers sized at 0.15 mm or less, and with four shells. Refer to the relevant images above for further information. The component with least tolerance is the Catch; this should be printed with four shells and at least 20% infill, although I would recommend printing it on its own, with 50% or more infill, if you can be bothered to do so. My recommendation is to print the components with the alignments shown in the images above: these alignments are designed to produce components optimized to handle stress in the vectors they are expected to receive it, and print at slow speeds so that the resulting parts' measurements come out more exact. But, by all means, experiment.


It should go without saying that every part, once printed, needs to be made scrupulously clear of build-time support material and rafts, and so on: in this project, cleaning the parts is vitally important: (a) friction is your enemy, and with design tolerances down to a millimeter in many areas, extra bits of plastic will cause friction; (b) extra support material in some areas of the device, such as the Bearing sockets, will induce wobble caused by misalignment of dependent components, which leads to more friction. Don't be shy with sandpaper, files and so on!


To test for friction in the assembly, spin the Rotor - if all is correct, you shouldn't encounter any friction. If you do, try to find out where it's coming from and file that part down a little. Minor friction can sometimes be corrected by rotating the Rotor manually for a while, to allow it to wear down obstructions inside the device.


If you detect a large amount of friction, or if the device fails to rotate, check all parts for warping and reprint any which aren't perfectly straight. Realize that the only point of connection between the Rotor and either end part (Cap or Base) should be through the Bearings, via the Rod - in other words, when assembled, the Cap/Base and the Rotor should never come into contact with one another at all. If all the parts have printed properly and are clear of extraneous material, the design provides for at least a 1mm gap between the Rotor and any other printed part throughout the device (internally, near the bearing, that gap increases).

The Rod is responsible for maintaining alignment between the parts: if you detect periodic friction in the rotation, this could be because the Rod is slightly bent, or because the Bearings are not both perfectly aligned in their sockets, the misalignment causing the Rod to be off-centre. To determine if this is the case, remove both Cap and Base, hold the assembly horizontally by the Rotor and spin the Rod. If it isn't spinning perfectly straight (i.e. you see wobble in either of its ends), then you've found the problem. To determine whether the problem lies with the Rod or Bearings, remove the Rod and roll it on a known flat surface, such as a stone kitchen counter. If the Rod does not roll perfectly flat, it is causing the problem; if it does, then the problem is in the Bearings: check the sockets to ensure that they're uniform and free of debris.
Printing and Assembly

Print the Tools.


Print the Rotor. I recommend using four shells with only 15% of infill: the lighter the rotor, the less inertia it has, and the less trouble the printer's extruder motor will have turning it. Less than 15%, though, and it can begin to lose shape to some extent, especially on the parts which print horizontally. Once it has printed printed, it's especially important to clear out all support material from the center of the Rotor, most especially in the small housings where the Bearings will sit. The device is designed to print as few extraneous supports as possible in that area, but pay close attention to it nonetheless. Assuming you're printing the Rotor standing on its thick end (which you should be), it'll be that end's bearing housing which merits special attention.


While the Rotor is printing, you have plenty of time to prepare the aluminium Rod. Do this slowly and patiently: this part is crucial, and it's not as easy as it sounds to drill a perfectly-aligned hole through a round, smooth piece of metal, even with the Template's help, if you rush the process.


First, test the Rod as described in Note 6, above: if it's not perfectly straight, discard it and try another. Then insert the verified, straight Rod into the Template so that it butts up against the Template's closed end. Wrap blue tape around the center of the assembly so that the Rod doesn't move. Note that the Template tells you which end of the Rod is going to be which: remember this by marking - say - the "Base" end of the Rod with a marker or a piece of tape which will still be there when you've removed the Rod from the Template.


With the Rod fully inserted into the Template, use a metal-saw blade to cut off the protruding part of the Rod to make it the same length as its guide channel in the Template, following along the end of the template to help keep the blade straight.


Drill the holes. The Template is designed to allow you to drill right through it, and to help guide the drill bit, so try to be careful not to abrade the sides of the Template's guide holes, since this will cause it to become inaccurate. Use a very small (1/16" or 5/64") drill bit to do this; insert the bit all the way into the guide holes before you start drilling, then use the guide holes to help you drill a straight hole right through the Rod: do this pressing only lightly at first, since too much pressure on the Rod before there's a hole will make the drill bit slip. If possible, after drilling the first hole, leave a similarly-size drill bit or other object in the hole, sticking right through the Template and the Rod, to prevent the Rod from moving in the Template while you're drilling the second hole.


If you mess up a hole and decide it can't be used, simply turn the rod 90 degrees in the Template and try drilling both holes again: the Filament Holder won't care if there's an extra hole in the Rod, just as long as you can insert screws through the right place.


Once you've drilled both holes, remove the Rod from the Template and drill right through the holes you've already made, this time with a 1/8" drill bit, to widen them enough to accept M3 screws (use a 7/64" drill bit instead if you want the screws to cut a thread into the Rod: this makes the entire assembly fractionally tighter, but it makes disassembly and reassembly more difficult). If you wish, you can do this with the rod still mounted in the template: the process will be marginally easier, but it will ruin the tool's guide holes by making them too large for the Template to be used for another Rod, and there's no real need, since the larger drill bit should find its own way through the existing holes with no need for a guide.


Finally, file the Rod around the openings of the holes and around the edges of both ends to remove swarf, and to ensure everything is smooth. Test the Rod again to ensure that it's still dead straight: if not, you're back to step 3a again...


Print the rest of the objects (the Base, the Cap and the Catch).


While those objects are printing, insert the bearings into the Rotor. Use the Bearing Alignment tool to help: the Bearings fit extremely snugly. Put a bearing onto the corrugated end of the tool - if the fit is too tight, file the tool a little to make it easier. Align it with the socket in the rotor (the tool's fins should help you center it in the Rotor) and tap the end of the tool gently with a hammer while the Bearing seats itself. You can also tap around the edge of the bearing with a hammer and a rod. Only tap the edges, though: the Bearing is delicate and you'll damage it if you hit it anywhere else.


Assemble the Cap to the Rod. Use the marking you made earlier to know which end of the Rod to put into the Cap. Be very careful not to damage the opening of the tube into which the Rod fits: this is the Cap's contact point with its Bearing. You can line up the bolt holes by looking through the upward-facing part of the Cap, where the Spring and Catch will sit. The Rod fits into the Cap extremely tightly, so insert a screw into the hole at the other end of the Rod to give yourself leverage, so that you can turn the Rod easily. Once you've got the Cap and the Rod lined up correctly, screw them together from the underside of the cap using a 30mm M3 socket cap screw.


Test that the Catch can move freely in the opening provided for it in the Cap, and that it can rotate properly on a 20mm M3 socket cap screw. If it can't move properly in the Cap, file or sand it and/or the Cap until it can; if it can't rotate properly on the Screw, drill through the hole in the Catch with a 1/8" drill bit.


Insert the Spring into the socket provided for it in the Catch, then mate that to the Cap and holding it together with one hand so that the bolt holes in both line up, and insert the 20mm M3 socket cap screw or elbow bolt into the assembly with the other hand.


After tightening the screw into place, ensure that the catch moves properly and freely: if it sticks, then either the screw is too tight and is compressing the mounting into the catch, grabbing it, or else there's some support material from the print process still attached to one of the objects. This completes the Cap assembly.


Insert the Rod into the Rotor's thin end, threading it through the Bearings you installed earlier, pushing the Rotor all the way up to the Cap. This may take patience: there's virtually zero tolerance between the Rod and the Bearings. If it proves impossible to insert the Rod into a Bearing, use a small amount of oil on the end of the rod to make the process easier; if this fails, file the end of the Rod very slightly so that it fits. Once you've completed this, you should have a Cap and Rotor sitting properly together, with the thin end of the Rotor pointing at the Cap and the thick end pointing away; there should be roughly a millimeter gap between the visible parts of the Cap and Rotor. Test for and correct any friction, as described in the Notes, above. If the Cap and Rotor touch, it means that something has printed incorrectly; rather than reprinting it, however, you may be able to get away with wearing away a bit of the Rotor's Cap-facing end using an orbital sander with a medium-grit paper (remember to remove any melted plastic residue afterwards).


Having ensured that the Rotor spins freely on the Cap, assemble the Base to the Rod. You can line this up easily by following a spine on the rotor between the screw holes on the Base and Cap, lining them up by eye. Before securing the Base, ensure that the Rotor still spins freely, and make corrections if necessary, as with the Cap. Then secure the Base to the Rod using another 30mm M3 socket cap screw. This completes the device assembly.

Test the movement of the device. There should be no detectable friction. Remember to test it by moving it slowly as well as by spinning it quickly: small obstructions will be undetectable at speed but very obvious at fractional RPM, which is how the device will operate in the real world.
Enjoy.