Building a Coolerbox Mashtun with a Copper Manifold
Sunday, June 25, 2017
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Building a Coolerbox Mashtun with a Copper Manifold

The manifoldThere are probably dozens of guides out there on the World Wide Web describing various ways to build a mash tun out of a cooler box and copper pipe. This is another one, but with as simple a combination of fittings as possible to build a cost effective mash tun as good as, if not better than, ones you might buy from a homebrew shop.

All of the pieces used here are readily available from most DIY stores. Have a look, use what you like, adapt what you don't, and above all, have fun making your own brewing equipment.

You will need the following materials:

  • A picnic cooler (in this case a Thermos 30 litre rectangular cooler)
  • 1m of ½ inch copper pipe (13mm external diameter in metric, but you can also use ¾ inch once you get the right joints and tubing to fit)All the bits
  • 4 copper elbow joints for 13mm pipe
  • 3 copper T-joints for 13mm pipe
  • A ball-valve tap
  • A hose connector
  • An adaptor nut with an inner thread fitting the tap and the outer thread fitting the hose connector
  • A metal washer with a hole that fits the diameter of the thread on the tap
  • A rubber washer with a hole that fits the diameter of the thread on the tap
  • A length of ½ inch reinforced PVC tubing

Click on the names to see what I mean.

The following tools are recommended, but use whatever you have!

  • A drill
  • A small drill bit
  • A hole saw or large drill bit that matches the diameter of the thread on the tap
  • A hole saw or large drill bit that is larger than the flange above the thread on the tap
  • A Dremel tool or hacksaw (if using a Dremel, get the reinforced disks for cutting metal)
  • A wrench or spanner that fits the adaptor nut
  • A file or deburring tool

Warning: when drilling or cutting metal with a power tool, make sure you wear eye protection. Small bits of copper can fly off and, in the case of a Dremel, cutting disks can suddenly disintegrate if you are not careful, sending shrapnel across the room. Safety first!

Building the manifold

The first thing to do is plan the lengths of the copper you need to cut. As my grandfather apparently said, measure twice, cut once (that applies to software engineering as well as carpentry!). Measure the smallest enclosed rectangular area of the bottom of your mash tun. In this case, the bottom was measured to be 270mm x 190mm. Following some of the suggestions in John Palmer's guide (roughly I might add), I wanted to leave a gap of 20mm between the manifold and the sides of the tun, with extra space where the outlet was to be, as I wasn't sure at the time how much room I'd need to get the tubing from the manifold to the tap. As a result, I planned on the manifold to measure 250 x 150mm.

As this was the maximum extent I wanted, I had to then take into account the dimenstions of the elbow and T-joints and how much of the piping would be in the joint sockets to be sure I cut the pipe to the right lengths. The elbow joints measured 30mm square, and the T-joints measured 40mm by 30mm. The socket in each took in 12mm of copper pipe. Using that, I was able to work out exactly how much each joint contributes to the dimensions of the manifold itself. See the box below for the maths.

The length or width added by an elbow piece is the Length of the elbow minus the depth of the socket in the joint into which the pipe is inserted. In the case of half-inch pipes, an elbow joint measures about 30mm square. The socket is about 12mm deep, so an elbow joint will contribute 18mm to the length.

Similarly, a T-joint measures 40mm by 30mm. Given the same socket depths, it will contribute 16mm along the long axis (40mm minus two sockets) and can be treated as equal to the elbox joint in terms of the width, or short axis.

So, the contributions to the dimensions (not the actual joint dimensions) look like this:

Elbow Length: 18mm; T Length: 16mm; T Width: 18mm

For the long sides we need two pieces of copper with a T in between and an elbow at each end. So

length of segments = (Required Manifold Length – (Elbow Length) – (Elbow Length) – (T Length)) / 2

(250 – 18 – 18 – 16) / 2 = 99mm

So, for each long side I needed two pieces 99mm long, so four of these in total.

For the segment where the tube was to connect to the outlet tap

length of segments = (Required Manifold Width – T Width – T Width – T Length) / 2

(150 – 18 – 18 – 16) / 2 = 49mm

For the end pieces it's simpler as there's no intervening T-joint, just the two elbows to add a bit of length.

length of segment = Required Manifold Width – Elbow Length – Elbow Length

150 – 18 – 18 = 114mm

So, two of these.


Using the above formulae, the cutting list looks as follows:

  • 4 x 99mm
  • 2 x 114mm
  • 2 x 49mm

The cut piecesUsing a fine hacksaw or a Dremel with a reinforced cutting wheel, cut the copper pipe into these lengths, keeping the cuts as straight as possible. Once you cut the first length in a sequence you can use it as a template to mark the remaining segments of that length to be sure they are all of the same length.

Once the pieces are cut you can do a first assembly of the manifold. This is a good time to mark where you want the slots to be positioned with a pencil, say every 10mm. Marking the pieces in advance makes it easier to put the segment into a vice or something for cutting, but be careful not to squash it. Then, using either your fine hacksaw or Dremel, cut the slots in the marked positions to about half way through the copper pipe. Once finished, use a file or grinding bit to take away the rough edges; deburring. You may also want to push something through the pipe to loosen small burrs on the inside.

This manifold is not going to use any soldering or brazing to keep it together. Using a pliars with something to stop it making gouges in the soft copper, slightly crimp the ends of each segment so they are no longer perfectly round. This needs very little pressure! Do it gently and slightly. Just enough so that when you insert the segment into the socket of the joint piece it gets a grip. It's surprising how well this works, and it means the manifold will stay together but also be easy to disassemble for cleaning.

Preparing the coolerbox

DrillingNow that the manifold is ready, you need to drill the holes to take the tap. The important thing about the position is to have it as low as you can while leaving enough room on the inside for you to tighten the hose adaptor onto the adaptor nut for the final assembly. Present the hose adaptor against the inside with the small grip nodes vertical so you know you'll have enough room to turn it completely. Mark the position using a pencil through the hose adaptor itself so you are marking the centrepoint. Then, use your small drill bit to drill a hole as horizontally as you can through the entire wall from the inside. This means you have the centrepoint marked inside and outside.

Use your hole saw attachment or large drill bit to gently drill through the outer layer of the cooler, and through the polystyrene between the layers, being very careful not to damage the inner white layer. Once drilled out use the drill bit that matches the diameter of the tap threads to drill through the inner layer. Use a fine file or sandpaper to smooth the edges of the inner layer so no stray bits of plastic can interfere with the seal later on.

Fitting the tap

Adaptor nutDepending on the diameter of your metal washer and the hole you drilled in the outer layer, you may need to take the cooler box apart to get the rubber seal and metal washer against the outer face of the inner layer. I had to do this, but the inner section came out very easily by just pressing against a couple of clips along the rim. Have the rubber washer against the outer face of the inner layer and the metal washer outside that again. In effect, you are sealing it from the outside. This is the safest option if you have a regular rubber seal. You could seal it in the inside if you were sure you had a food-grade seal, or even make one yourself using a silicone baking sheet and cutting out gaskets of the right size.

Once the seal and washer are in place you can fit the tap by pushing the threads through the hole and tightening it in place using the adaptor nut as shown. Your tap is ready to go.


Connecting the manifold

So, the manifold is ready and the tap is ready. Time to connect them. The easiest way to secure the interconnecting tube to the tap is to just use a regular hose adaptor as described earlier. The tube will fit tightly onto it and it can be screwed on and off the tap adaptor nut easily for removal. It will not come loose accidentally during a mash.

The tube endConnecting the tube to the manifold can be more problematic however. The tubing is also ½ inch so it fits snugly inside the socket of the T-joint, but not so snugly that it couldn't be easily knocked out during a mash. Not wanting to invest in more complex fittings, the easiest thing is to widen the the end of the tube that is meant to fit into this socket. In this case I used a short length of 10mm copper tubing I had left over from building a wort chiller. It fits tightly into the PVC tube and expands it enough that it make it a tight fit with the T-joint.

You have a choice as to where to position the T-joint for the tubing, either at one end of the manifold, right under the tap with a short length of tubing, or in the middle segment. I chose to use the middle segment (initially I had designed it to be at the end) as it ensured that the manifold lay flat on the base of the tun. Positioning it at the end with fairly inflexible tubing and a hose adaptor that sticks out a fair bit tended to lift it slightly, so I think the middle is a better choice.

All that's left to do is to screw the hose connector on and then test that it is holding water.

Fitted manifold

Done. Happy Mashing!

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