DIY Stir Plate

9 Jun

As some of you may know I am an avid DIYer.  I just love building and tinkering with things so I am actually surprised that I haven’t had a DIY project on here yet. If you don’t usually “do it yourself” a stir plate is an easy way to start, since its fairly uncomplicated and pretty rewarding. First off, what made me build a stir plate instead of just buying one?  Well, cost for one. A common homebrew stir plate can run anywhere from $40 to $100(higher for laboratory quality). I built mine for about $20 but I did have some supplies handy that would have cost me an extra $15 or so. The second reason for this stir plate is in my search to purchase a stir plate I found a lot of unhappy reviews and ill designed/cheaply made products.  In my opinion, no company has stood out to make a quality home brew stir plate at a reasonable price. So I set out to build one, and if you look around on the internet this is a fairly common practice with tons of online resources and information.

Through my research, this is what I came up with.

It is a USB powered computer fan that came with its own speed knob which I fitted with a magnet and protective plexiglass covering. This thing runs like a dream, powerful enough for 2l and infinitely adjustable speed with the awesome knob/potentiometer that the fan came with.

Want to build one now? I thought you might, here is what your gonna need.

1- A 120mm computer Fan. Any will work for a variation of this project but you want the one with the integrated potentiometer. This fan is made by Thermaltake and can be found HERE on amazon.

2- A magnet. Not any magnet, a VERY strong magnet. You can purchase neodymium magnets online that will do the job but I got mine out of an old computer hard drive. These magnets are strong and most importantly the stirbars center properly on them.

3- A pack of small washers and one tiny nut and bolt.  The washers I got came in a pack at hardware store, they are a little less than 1/2in in diameter with about 1/8in hole. These washers don’t fit perfectly but they don’t really need to, so anything close will work. You also need one tiny nut and bolt approx 1/8 in by 1/2in long to attach the knob to the plexiglass top. I used a small self threading screw I had, but i wouldn’t recommend it because unless you are very careful you can break the plexiglass.

6- Plexiglass and spraymount. If you don’t have any laying around, my suggestion would be to go to a framing store. Ask the framer if he has any scrap pieces of plexiglass. (They usually do, since plexiglass is used for framing large artwork and is cut to size) You can offer to buy it off them for a couple bucks but they will usually just give it to you. I got my piece which was about 20″ x 36″ for free, since they were just going to throw it in the trash. If you go to a chain like Micheals or Aaron Brothers they will also have spray mount. Buy the smallest one you can find. I had repositionable spraymount at my house so this is what I used and in my opinion permanent strength is not needed.

5- Stirplate supplies. You want to make yeast when your done right? Well your gonna want a flask, DME, and most importantly a stirbar all are easy to find online or at you local homebrew store. You NEED the stirbar to properly place your magnet, so just get all your goodies at once. I found that the bars 1″ through 1.25″ work best. You want your bar to be about a long as your magnet, this will ensure the bar is centered and spins true.

6- A USB charger.  Chances are you already have one, (my fiance did!) or you can source one online or at a local thrift store. If you cant find a USB charger you can use any ac-dc converter with about 5v and ~1000 miliamps.  My charger is 2amps (2000 miliamps) but this fan does not draw that much power and is rated for 5v at .3 amps for a max of 3.6 watts. You might have to do some testing if you chose power supply rated for a different amperage or even volts, but if you go higher on the volts you have to use less amps to not fry the fan. If you are changing the power supply please do  yourself a favor and do the appropriate research. ALSO you should know enough about electricity to be safe, and use good judgement even though these are low voltage systems.(I am not responsible if you electrocute yourself.)

7- Tools. You will need a screwdriver(Phillips#2) a drill with a decent bit set, a metal ruler/straightedge a utility knife and a pen.

Sound complicated yet? Its really not. You can do it, I know you can!

Here is how the fan comes.

This fan is more expensive than a normal pc fan, but this one is SOLID and has a built in potentiometer for speed control. It also comes with a retractable USB cord that hooks right up to the fan. Take your screwdriver and take off the protective shielding and speed control knob. Keep the little bolts that hold these on and we will reuse them to attach the plexiglass.

Then get your plexiglass, ruler/straight edge a pen and utility knife, we are going to cut this sucker to size.

For those of you who haven’t worked with plexiglass, its not all that hard but keep in mind it is slightly brittle so be careful with it. If you score properly the plexiglass will easily snap with clean lines. First measure out a 6.5″ section and make a line with your pen on the protective outer plastic(keep this on). When you have that, properly place your straight edge and score along it. I used a cutting mat under my plexi so I didn’t mar up the kitchen table but anything even cardboard will work.I like to do the first passes light, then once I have a groove I try to put more and more pressure on it. I did mine easily with 3 light passes and 3 hard passes from edge to edge.

Once your satisfied with your scoring place your plexiglass on the edge of the table like so, with the ruler on top.(scoring facing up)

Hold the ruler tight to the face of the plexi and in one quick motion push down on the outside piece of plexiglass. It should just snap right off giving you a nice clean break. Repeat this process until you have a nice square 6.5×6.5 inch piece of plexiglass for the top of your stir plate.

Now we need to drill the mounting holes into your new plexiglass top. Mark your holes where you need to drill. I did mine with a leftover plastic fan shield from a past stir plate project but you can use the metal fan shield that came with the fan just as easily. Center it and tape it to the plexiglass then just drill the holes out. You can use the bolts that came with the fan to check you holes and see how they will sit when assembled.

Note that drilling plexiglass can be hard, you can easily  crack it if not careful. I like to start with a very small bit and gradually move up to the size I want, I usually use 3-4 different drill bits. This is a good time to drill your hole appropriate for your knob, it should be 1/4″ in from top left corner.  Congratulations you now have a slick stir plate top that is easy to clean and protects you stir plate from the threat of exploding starter krausen.

Now we are going to place your magnet. First we apply the spray mount. Do this outside and on top of something because this stuff can be nasty. Give your magnet a light coat of spray mount from opposite directions. Less is more with spraymount, you don’t want it to run or be too goopy. Let it dry. Yea you heard me right, let it dry. This stuff will stay sticky and will coat the magnet and not come off, making your life much easier.

What you see on the magnet isn’t spray mount, its residual glue from the hard drive. It wasn’t going to interfere so i didn’t worry about it. You should barely be able to tell by looking at your magnet that you sprayed it, but it will be sticky.

Then place your magnet on the appropriate side of your fan as close to centered as you can.

This is the hardest and most critical part of the project. If the magnet is not properly centered your stir bar will spin uneven and get thrown off the magnet. This is why we have repostionable spray mount, you should be able to move your magnet just by pushing on it or peeling it up and replacing it. You will need your stir bar and you flask with water to test that its centered properly.

If you can’t tell, I taped two washers to the bottom of my plexiglass so I could test, reposition the magnet and test some more. This magnet gave me a hard time because the bar is attracted to one side more than the other. My bar kept getting thrown and I couldn’t figure out why until I looked down at the bar and where it sat on the magnet. Remember we aren’t necessarily centering the magnet just the stir bar to the spinning of the fan. After that my stir plate worked perfectly and the bar spun true at all speeds. I marked around my magnet when I found that perfect spot, so if for any reason it moved or I wanted to take it off i can.

After that all that is left to do is assemble and finish up. Make sure you put your washers on to keep the magnet from hitting the bottom of the plexiglass. Bolt your knob down using another washer on the bottom side and make sure all your connectors are on tight. That’s it! You now have a stir plate that in my opinion looks better than most on the market, is just as functional, and cost a fraction of the price. Plug it in and start propagating yeast!

Stop shaking that starter home brewers! A stir plate is grows twice as much healthy yeast as a normal starter so get to it and make yourself one of these.


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