How to Carve a Shrink Cup

The principle of a shrink cup are, the cup are cut from a fresh log and you put in a bottom made from dry wood. When the cup drys it will shrink and make a tight fit around the bottom. If your skilled enough you can make a cup that are watertight.

This is a easy and quickly made project. I'm using simple tools that most of you already have. My cup is made from birch but you can make it from any wood. It just needs to be fresh cut.

Most will already have all the tools needed to make a cup. If you want to go very simple you can make it with only a saw, a knife and a hand drill.
But the marking gauge and the power drill makes it easier.
The ax, the froe and spookshave are used to make the bottom.

If you don't have a suitable knife look at my instructable showing how to make the perfect carving knife

https://www.instructables.com/id/How-to-design-and-make-a-perfect-carving-knife/

I went into the forest and found a place with a lot of small birch trees. I have asked the owner and have got a permission to cut a small tree. From one tree you will get enough wood to make a lot of cups.

Drill the holes before you cut it. That way it is easier to hold the wood, and you don't need a holding device.

The making of the bottom takes some patients and some skills. If you want to make a tight fit the ledge in the cup and the bottom needs to be very accurate. If you are skilled enough the cup will be watertight.

While you make the bottom store the cup in a plasticbag so it won't dry out while your working on the bottom. You can all so store it in a bucket of water. Just don't let it dry. If you want to wait to finish the cup you can store it in the freezer until you have the time to make the bottom.

With the froe I split the dry firewood into thin pieces of wood. Thy need to be 3-5 mm thick.

Remember to always split the wood in the middle. That way you will get two straight pieces.

If you like you can skip this part and use a piece of plywood or a thick piece of veiner.

The carving of the bottom are very simple but it takes patience to make it as accurate as it has to be.

The is the exciting moment, will the bottom fit...

Here you can see more of the cups I made the day I took the pictures for this instructable. As you can see the cups can vary in size and shape, with are with out bark etc.

''Making it watertight.''
If the bottom are accurate enough the cup will be tight. After 1-2 weeks you can test the tightens by pressing the cup to you mouth and try to blow through it. If no air gets through you will be able to use the cup for drinking.
Before I use the cup for drinking I immerse it in linseed-oil, leave it in the oil a day or two. Take the cup out of the oil, dry the excess oil of and leave the cup to dry. I like to let it dry 2-3 months, that way I'm sure that the oil are hardened all the way through.
I only use the cups with out bark for drinking. They are better when you need to clean the cup. I only use the cup for cold drink, mostly mead. I don't leave the liquid in the cup for a long time, if you do that the cup will leak at some point.

The same technique can be used to make a funny shrinking bracelet. First you have put it on you will not be able to take it of again.