Introduction
As homebrewers we use rubber stoppers for a variety of purposes. One common application is to connect airlocks and tubing to fermentation vessels like glass carboys. In some instances we need a stopper with more than one hole in it – for instance to fit an airlock and a thermowell or to use positive gas pressure to rack between vessels.
These stoppers are not easy to find but, if you search the internet, you can find vendors selling two or even three-holed stoppers. These tend to be expensive and the options for hole dimensions are limited. It would be much better if we could drill our own holes the way we want in rubber stoppers.
A quick test with a new (hole-less) stopper and an electric drill and a standard twist bit will quickly show that drilling holes in rubber is not easy. The drill may go through the rubber but not much of a hole will be drilled and the result will be practically useless. I’ve heard that freezing the stopper beforehand will help but I’m not convinced.
Another suggestion is to use a short length of copper tubing and file one end into a sharp cutting edge. When put into an electric drill, the tube can then slice its way through rubber. Copper is a fairly soft metal, so I don’t think it’s very suited for cutting purposes and there is a limited choice of tube diameters. However, the idea of slicing the rubber is appealing and so this approach was investigated further.
Hollow Hole Punches
As often happens to me, I start looking into some sort of new idea to fix an old problem and then find that the solution is already readily available. In this case, there are tools called hollow hole punches that purport to cut clean holes in a variety of materials including rubber. So, I suppose this article is more about how to use these punches on rubber stoppers and how well they work for this purpose. There are a variety of these hollow hole punch sets from various vendors but I went cheap and bought the set shown in the picture below from Harbor Freight for about $7 (with coupon). The set includes 6 punches with diameters covering 3/16 to ½” in 1/16” increments, so these cover most of the sizes we’ll need.
Close inspection of these punches shows that there is a sharp cutting edge at the end that should be able to slice its way through rubber – similar to the copper tube mentioned above. These punches are made from steel and should last much longer than copper and are ready to use.
Tools
- Spade or Forstner drill bit – see below for suggested sizes
- Hollow Punch Set – including 3/16″, 1/4″, 5/16″ and 3/8″
- Drill Press (recommended) or Hand-Held Electric Drill
- C-Clamp
Cutting Holes in Stoppers
Rather than writing copious words of wisdom, I thought I might try and put together a video of how to cut holes in stoppers. This is my first foray into the wonderful world of video tutorials and I think my video below is almost understandable.
I’ve put in a few following notes to cover things that weren’t very easy to include in this video.
Notes:
- The size of hole in the piece of wood to hold the stopper while cutting holes in it will obviously depend on the size of the stopper. The table below should give you guidance as to what size hole to drill in the wood for the stoppers commonly used with glass carboys. As usual, I’ve mixed up the dimensional units (what it is to live in America). At a push, a hole cut with 1-1/4 bit will probably work with any of these three stopper sizes. Obviously, stoppers can be used for other purposes than just for carboys, so cut the hole in the wood to suit the diameter and height of the stopper you want to use.
- Because rubber can stretch, it’s prudent to make the diameter of the hole you cut in the rubber stopper a bit smaller than the diameter of the thing you are going to stuff into it. For instance, for an airlock with a stem diameter of 3/8″, cut a 5/16″ hole in the stopper.
- It’s better to cut the smaller hole(s) in the stopper first as these will be less likely to allow the stopper to distort during cutting of subsequent holes.
- I used a cheap plastic dropper pipette to add the dishwasher liquid around the hollow punch prior to starting the motor. Some dishwashing liquids are packaged in squirty bottles – these would be ideal to add the liquid directly from the bottle. Use a spoon if you have to.
- Note that because the stopper is probably going to make contact with your beer, don’t use heavily scented products or any products that contain toxic or nasty tasting chemicals. Don’t use oil or water either.
- Make sure you thoroughly clean the drilled-out stoppers before use.
- I haven’t tried cutting holes in silicone stoppers this way. If you have, please give us some feedback.
- I erroneously called the drill press “table” a “stage” in the video. That’s what happens when you use microscopes.
Applications
There are many instances in homebrewing in which multi-holed stoppers might be useful. I’ve used them in two of the projects listed in the Projects section of this website:
- Installing a Thermowell in a Fermenter for Monitoring and Controlling Temperature
- Making a Positive Gas Pressure Device for Racking and Filling Bottles From a Glass Carboy