An hourglass is an ancient and extremely simple time measuring device. We needed one to mark the 5-minute limit on the talks given at the Hack and Tell events at Technarium hackerspace, however, we could not find any hourglasses at the local DIY and construction stores. One of us looked at the kitchen gadget corner and thought of using two cone-shaped pepper shakers. The top cones were made out of very thin stainless steel that can be welded using a TIG welder. TIG welding is more difficult to master than MIG/MAG welding, however, it offers greater control of the process.
So far, the hourglass works fine and it is a great conversation piece. In addition, it is superior to the store-bought ones because the timing can be adjusted — you just have to screw the hourglass open and add or remove some sand! You can also customize the hourglass with custom paints, coloured sand, decals or LEDs.
Anyone who is looking for a small project to practice their TIG welding skills or would like to have a unique timepiece can make one. If you do not know how to use a TIG welder or do not have access to one, making a 3D printed or glued frame that keeps the holes in alignment might work as well.
Tools and materials
You will need:
- 2 identical salt or pepper shakers with metal tops and a single hole each. In our case the hole was 2mm wide. Take care when choosing the shakers — the tops should not be too flat as some sand will get stuck there.
- a TIG welder, suitable filler rods, a well-sharpened electrode, shielding gas, welding mask, gloves, and other protective equipment
- a vise
- a short metal rod that fits tightly into the salt shaker holes
- some cold water for cooling the welded piece in case it has some molded-on plastic parts that might melt
- fine sand or other material (we used quartz sand of 0.4mm grain size)
Step 1: Positioning the salt shakers
Unscrew the glass bodies and put the metal cones nose-to-nose.
Insert the short metal rod through the holes — it will keep the holes aligned.
Center and clamp them in a metal vise.
Step 2: Preparation for welding
Check and set up your equipment! We used argon shielding gas for welding, setting the gas flow at 8-10 l/min. The current was set to 10A DC. We picked 1mm thoriated tungsten electrodes and a number 6 TIG gas cup with gas lens.
An additional difficulty was caused by the fact that the plastic rings on the cones would have prevented the welded metal from contact with the welding ground. In order to achieve the proper grounding, a few turns of aluminum filler rod were wound up and then pulled over the wider part of the cone so that it clamped tight. Then the other end of the rod was led out to the ground clamp.
Check and put on your protective equipment: the welding mask, protective clothing, and gloves.
Step 3: Tack welding
An important step after positioning the salt shakers together and clamping them in a vise is tack welding. Tack welds are short intermittent welds that keep the welded items together and prevent them from moving or twisting due to stresses arising when the welded metal heats and cools.
After tack welding you can remove the filler rod that is used to position the salt shakers together.
Step 4: Welding
Clamp the item back into the vise and proceed to weld the two cones together by turning the piece in the vise.
Welding is a delicate process, as the metal is very thin and prone to burning through or twisting. To protect the molded plastic rings we found it necessary to periodically cool the item by dipping it into cold water. Try to keep the weld dry because any water interferes with welding. However, the high heat conductivity of metal means the piece cools down even if just a part of it is submerged.
Step 5: Assembly and calibration
Let the item cool down before touching it!
Dry the sand or other granular material you’ll be using as well. Take care to choose what you’ll use — a scientific study has shown that the granule-to-hole size ratio must to be larger than 1:12 but not greater than 1:2 — otherwise, the flow will be irregular due to a complex interplay between gravity, air pressure, transient granule structures, vibration, air currents and temperature (I. Peterson, “Trickling sand: how an hourglass ticks”. Science News, Vol. 144, No. 11, available at the free library).
Now it’s time to decide on the time interval the hourglass will be measuring. You will have to empirically determine how much sand you will need by flipping the hourglass several times and adding or removing sand.