Low-Cost, Modular, Quick-Change Fiber Spool
Background:
My team’s existing fiber winding spool is nothing more than a small diameter U-groove pulley fixed to a threaded rod, which leaves a lot to be desired. The small diameter creates a slow initial takeup rate, which grows rapidly as the fibers stack and increase the effective diameter. Plus, the “spool” wobbles, which makes the takeup rate variable over the course of one revolution. Takeup rate is an important factor of fiber formation and off-the-shelf solutions didn’t meet our criteria, so I set out to design and build a better spool.
What:
A better spool would:
Rotate about one axis with minimal runout
Remove from its driveshaft easily so that test samples can be switched out regularly and quickly
Quickly adapt to different spool diameters, so the takeup rate range (motor speed limited) can be varied
Cost as little as possible; I’d like to be able to store the fibers on the spool after spinning, so we’ll need many spools if we want to store many samples
Design Choices:
To satisfy criteria #4, I chose to make the cylindrical portion of the spool out of cardboard tube. We get kraft shipping tubes for a variety of projects in our lab so they’re plentiful, and they come in many diameters so we can make a step change in takeup rate easily. Criteria #3 is thus satisfied as well.
To mount the spool to the driveshaft I designed custom end caps that were made by FFF (aka FDM) on UVA’s Stratasys machines. The design includes axial ribs that grip the cardboard tube during rotation, but allow the tube to slide off the end cap for easy removal (criteria #2). Furthermore, the end cap design can be changed easily to accommodate different diameter spools, then printed anew.
Finally, I found flanged shaft mounts that I fastened to the end caps to attach the spool to a precision shaft. In this way, the end caps can remain concentric along the driveshaft and thus reduce runout of the spool (criteria #1). This doesn’t eliminate all runout because the concentricity of the Kraft tubes can’t be controlled and the tolerances at the flange mount-end cap interface are large to accommodate the likely wide tolerance of the cheap mount flanges I purchased.
Design Opportunities
A few aspects of the design, other than buying better hardware, stand out to me as opportunities for improvement in future iterations:
Threaded inserts could be installed in the end caps for fastening the flange shaft mount rather than using a through bolt and locknut. This would reduce rotating mass by reducing the length of the fasteners (qty: 4) and replacing a steel nut with a small brass insert. Plus, fastening the flange shaft mount can then be done with one tool from one side of the part. I chose not to do this because we don’t have the tools for heat-setting inserts and I didn’t want to risk trashing an end cap; I don’t have the time or budget for that.
The end cap could be designed to be built without support material by removing the inset for the flange mount. In my case a late stage design change necessitated the step to maximize the length of the spool. The shaft length was set in stone because I purchased it before adding a second pillowblock bearing, so the insets recovered 0.25” of spool length.
The cap could be designed with spokes to further reduce the part mass. I chose to keep the design simple to utilize a sparse infill as much as possible and reduce design and printing complexity, but it may actually cost less to design it like a wheel with spokes. We have 6” I.D. cardboard tube in the lab and if I make a spool from those then I’ll certainly implement the spokes.
How:
Building this spool was almost as easy as pressing submit; I sent the end caps off to the mechanical and aerospace engineering department’s 3D printing lab and they were done in a couple days. The lab charges $15/cubic ft (including support material) so the prints came out to approximately $27 per end cap. I ordered the flange mounts from Amazon, and used cardboard Kraft tubing that we had around the office to make the body of the spool. The Lacy Hall Student Experiential Center on Grounds has a horizontal bandsaw, so four feet of tube quickly became ten spools. Assembly was a breeze; all it took was fastening the flange mount to the end cap with M4 socket head cap screws and nylon locking nuts.
Like sandblasting a soupcracker… chopping this 3” ID kraft tube into 4” long sections was a breeze with this industrial bandsaw.
Results:
The new spool has significantly reduced runout and wobble compared to our original winder. The end caps grip the cardboard tube so the tube can’t spin relative to the end cap, but they can be removed easily so the cardboard tube can be exchanged for a new one. I was very excited to get the axial ribs right on the first try! I won’t be quantifying the effect of the new spool on fiber diameter consistency, because I have more significant aspects to design and test, but at least it’s a clear visual improvement.
The completed spool mounted to the winder module on the spinline frame. My teammates had ordered the stepper motor and controller shown before I arrived, but eventually I will replace the controller with a bespoke Arduino solution that will control the winder and a fiber distributor module as well.
Acknowledgements:
This project was supported by the U.S. Department of Energy (DOE), Vehicle Technologies Office under the contract number of DE-EE0008195.