Stir plate flask/dj

[beerboy]

I am going to make a stir plate and was wondering if anyone has use a one gallon glass demi-john on one?
Would it work with a 51mm 8mm thick stir-bar?

 

[Aleman]

It can work really well . . . some DJ's are better than others though . . . If you get a couple of good magnets then you have to put a spacer between the demijohn and the stir plate.

 

[beerboy]

Aleman - theres a lot on the web about building stir-plates, would you recommend a particular way of making it? Is the big steel washer beneficial?

 

[Aleman]

If you get hold of the really strong neodymium magnets then it is possible to actually stop the fan turning with a big stirrer on a thin bottomed flasks. . . . Hence the reason for some way of increasing / decreasing the height of the flask above the fan/motor.

The problem with Demi johns is that the base is domed in the majority of cases, but with decent magnets positioned the width of the stir bar apart then it should work . . . If you are interested I have a long Triangular stir bar I can't use with my stir plate that I'm willing to part with for a fiver. It's too long (80mm IIRC) and the magnets in the bar don't match up with those on the sir plate, and it flies around the flask like a mad thing . . . with a home made stir plate you can stick the magnets the right distance apart

 

[prolix]

get one of these puppies I got one they are great
big flask

 

[Aleman]

I got a 5L one . . . . :lol:

 

[beerboy]

get one of these puppies I got one they are great
big flask

He he ordered one of those last night!

some way of increasing / decreasing the height of the flask above the fan/motor.

Can I do this just by shimming the flask ie. putting some layers of perspex or cardboard under it?

If you are interested I have a long Triangular stir bar

I could be interested in that, I'll see how the 51mm one works in the 3L flask 1st.
Cheers
Ian
ps looking forward to brewing the Bohemian pilsner tomorrow, can do it outside too due to this glorious weather wahey!! :
Best look out for the flies though.... :hmm:

 

[evanvine]

There seems to be plenty of info on the "Stir Plate" but nothing on the "Stir Bar"!
What is its basic construction, I've never come across the idea before?

 

[prolix]

you have to buy the stirrer

 

[evanvine]

Oh silly me!
What size stir bar for a demijon?

 

[Aleman]

It depends on the distance between your magnets

I've got a 70mm bar that you would think was perfect for a demijohn . . . but because my magnets on the stir plate are closer together than this it bounces all over the place . . . my 50mm stir bar is fine.

Normally made by encapsulating a neodymium magnet (or two) in something like PTFE . . . certainly some sort of non-reactive plastic . . . I've seen someone make one by sealing a nail in a length of poly tube . . . but it is so much easier to buy a few of the flipping things.

 

[evanvine]

Many thanks Aleman, what is the simple relationship between magnet spacing and length of bar?
I assume from your post that the bar length should be less than the magnet spacing.
I like the nail idea (I'm never happier than when inventing some DIY project) I didn't know that the bar didn't have to be a magnet its self.

 

[Aleman]

Yeah, Stir Bar length less than or equal to the gap between the magnets on the stir plate.

You can always magnetise tyhe nail by stoking it across a powerful magnet . . . Stir plates work best with magnetised stir bars as the attraction is stronger.

The other issue with making your own is how you disinfect the bloomin' thing . . . with a PTFE encapsulated stir bar . . . you just boil it . . . and as I use pyrex conicals for my starters I do it during the starter production.

 

[evanvine]

Once again many thanks.
I know you probably wont agree, but I find "Domestos" works wonders!

 

[BarnsleyBrewer]

Would a 13mm stirring bar be o.k to stir a 1000ml conical? :hmm: