Drilling a Keg
Being a novice metalworker (geek by trade), I found drilling a tap hole in a keg a bit intimidating. I did plenty of reading on aussiehomebrewer and talked to a few people I knew in the metalworking game. This is how I did it:
Safety
First and foremost is safety. Wear safety glasses. Wear hearing protection. Keep your workplace tidy. Think about what you are doing before you do it. There is no reason to get hurt doing this.
Tools required
I used the following tools:
- Safety Glasses
- Ear Muffs
- Electric Drill
- Drill Bits (3/8", 1/2")
- Centre Punch
- Hammer
- Bastard cut rat-tail file
- Round chainsaw file
- Cutting Compound
Mounting the Keg
I needed a way to keep the keg stable whilst I was drilling and filing it. I used 2 saw horses and a couple of ratchet tie-downs as shown in the pic below. The pot is my HLT - it works just as well with kegs.
The tie-downs hold the three parts together as a whole, making it very stable.
Marking the hole
Mark the tap hole with a permanent marker. I placed it far enough off the bottom of boiler and mash tun to not interfere with doing up nuts on the tap assembly. The clearance to the bottom can be made up with a piece of bent copper pipe. I'll detail this later.
Punch the hole with a centre punch. This is very important from a safety perspective - it will stop your drill slipping off the smooth curved surface of the keg wall.
Making the hole
To fit my threaded tube I needed a 3/4" hole. My biggest drill bit is 1/2", and even if I had a bigger one, I doubt my drill would handle it. I decided to drill to 1/2", then file out the rest. Filing was surprisingly easy - it took about 30 minutes to drill and file a hole once I got the hang of it.
I read plenty of posts by people having success with a holesaw. I looked at at doing this, but I could either buy a really cheap job which I wasn't confident would work, or buy an expensive bi-metal holesaw. This would have set me back over $50 and probably would have been destroyed by this job. If you already have this sort of gear, this might be an option.
Stainless steel is very different to mild steel when drilling. SS quickly work-hardens when heat is applied, so it is necessary to drill at a slow speed. Reports I have read indicate 100-150 RPM is optimal. I initally tried using a battery drill as I could run it a lot slower than my corded drill. The battery drill is an 18V model, about middle of the range. It simply didn't have the power to cut the steel, even with a small bit. Move on to the corded drill.
I began by drilling a 3/8" hole then follow that with a 1/2" drill. Use plenty of cutting compound (or oil, kero, WD-40) and stop if you see smoke to let things cool off. If the steel work-hardens, you will just wear your bit out. Run the drill as slow as possible, and use a firm even pressure. Watch out as the drill bit pierces the steel as it tends to bite. This is a hazard with the larger bits - it bites hard and the drill will spin on you. Keep your face above the level of the drill handle to avoid getting smacked by it when it spins.
Once the 1/2" hole is finished, place your threaded tube or nipple over the hole and trace around it with a marker to get your final hole size.
Filing the hole
Next, get to work with the bastard file. Try to keep the hole as round as possible - it's hard to file out a file-shaped indentation in the side of the hole. Keep going with the bastard file until you've hit the marked lines.
Next, grab the threaded tube and place it over the hole. The hole won't be perfectly round, so you can see where you need to file next. Grab the fine file and use it from here. Keep going until the tube fits. Tidy up the hole with a piece of emery paper to get rid of the sharp edges.