THE NORTHSHORE FLOATING POOL THERMOMETER

SKILLS INVOLVED
3D printing, sanding, painting, drilling (cleanup of printed holes), gluing, small electric wire cutting and stripping, soldering.

DESIGN NOTES
I am a retired architect, now working as a lifeguard and swim instructor at my local YMCA.  This project came about as a way to replace numerous thermometers we have tried that seemed to give conflicting readings over the past few years, and thus I developed the Northshore Floating Pool Thermometer.

The case was designed around a readily acquired and reasonably priced digital thermometer that I procured through ebay.  There are many available (search LCD thermometer external probe), though most appear the same.  The one I have been using has reading in Fahrenheit and is powered by two coin cells.  The case measures 45mm x 25.5mm and is a snap fit into the Thermometer Platform.  Currently I have made 4 of these over the past 6 months, and only one has had the initial batteries die, so it seems to be reasonably efficient even though the display is constantly on.  I paint the outside of the case to ensure that any possible voids in the prints are filled; I have noted no water infiltration.

This is the second iteration of the case design, and is working quite well.  We do not keep the thermometer floating continuously, but only put it in when doing our chemical readings, 4 or 5 times a day.  The module samples every 10 seconds, and usually settles its reading within 20 seconds or less.

The case was designed in Vectorworks, which is my CAD platform of choice from my design days.  It is assembled from 14 3D printed parts, the thermometer module, a small piece of acrylic for the view screen, a commonly-available silicone canning jar gasket and numerous stainless steel 3mm and 4mm screw assemblies  a BOM is listed below.  I do all my printing in PLA, .2mm layer height, 30% fill and 4 perimeters; no supports should be required.

PRINTING AND ASSEMBLY
The Case Top and Bottom pieces were recently redesigned to eliminate the need for printing with supports and the resulting finishing issues; the case top should be the only piece that will require some attention (there are many videos available online showing various ways of cleaning up prints).  I use multiple light coats of auto body spot putty with sanding in-between to smooth out the rougher areas (this is noxious stuff!), then paint the exterior surfaces with 2 or more coats of spray sanding filler and do my final sanding with 400-grit wet-or-dry paper.

The Platform Base is assembled from 8 parts that are joined by glue.  I designed all the pieces to have a tight enough fit so they can be snapped together in their alignment, but I recommend that the 6 Base Extension Pieces be clamped until the glue sets to ensure a good, strong bond.  The Platform assembly can be attached to the Case Bottom either before or after painting (if they are to be joined afterwards, the bottom surface of the case bottom should be masked before painting).

The final finish is 2 or more coats of spray paint applied to all outside areas, being careful to avoid paint on the bottom surface of the Case Top and the corresponding surface of the Case Bottom where the gasket will be located.

The Case Top Window is cut from a piece of acrylic, 52mm diameter.  It should fit snugly under the Case Top, and is initially glued in place to the raised rim using a strong waterproof glue  superglue would work well here, but be careful to have a continuous, light bead on the raised rim.  Additional sealing is achieved with silicone caulk applied to the Sealing Ring, which is then installed on the outside edge of the acrylic window, followed by a continuous bead of silicone caulk around the outside of the Sealing Ring  see the pictures.

The Thermometer Module comes with a probe wire that is approximately 1 meter long, too much to fit into the case.  I desolder the two wires from the circuit board, shorten to 6-8 inches (150-200mm) and resolder.  Disassembly and reassembly of the case is quite simple.

The probe is inserted into the hole in the bottom of the Case Bottom and sealed with a healthy application of silicone caulk.

The case is designed for a silicone gasket used to seal canning jars, measuring 2.9 (73.6mm) ID and 0.09 (2.3mm) thick (OD is not critical).  I drilled the holes for the screws by sandwiching the gasket between the Top and Bottom Cases, marking the hole locations with a pencil and then drilling the holes with a piece of brass tubing into which I had filed a few teeth, chucked into my drill press.  The result is nice, clean holes.

When tightening the bolts, be careful to not over-tighten to avoid warping the cases or cracking the plastic; a moderate, even compression should suffice.

The Case Top has an attachment point for a cord to keep it from wandering.  I use parachute cord.  My current anchor of choice is a galvanized 5/8 nut.  At some point I will make something a little more elegant.

BILL OF MATERIALS
-   Digital thermometer module with external probe
-   PLA filament
-   6 case screw assemblies, each 4mm x 20mm cap screw with 2 washers and 4mm nut
-   2 platform attachment screws, each 3mm x 10mm machine screw with washer
-   Clear waterproof glue, super glue or other
-   Silicone caulk sealant
-   Finishing supplies -- sandpaper, auto body spot filler
-   Spray paint

3D PRINTED PARTS
1a  Case Top - Upper
1b  Case Top  Base
1d  Sealing Ring
2 - Thermometer Module Platform
3a  Case Bottom  Base
3b  Case Bottom  Lower
4a  Platform Base
4b  Thermometer Probe Support
4c  Base Extensions (print 6)

