6" Mill Jars
Entry posted by marks265
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I've had or made about 4 different versions of ball mills in my day. When things got serious and I moved up to a large ball mill the one thing that never changed was the mill jar that I use. This style has been an "old faithful" for me so I'll share what I have done. The material I use is schedule 40 PVC plumbing pipe and parts. There is a lighter duty PVC pipe known as Drain, Waste, and Vent (DWV). I've lived through a couple of dropped jars in my day and I would like to give the rigid schedule 40 pipe a little bit of credit for at least not making a mess. If I remember correctly I don't believe the two are interchangeable, schedule 40 parts won't fit DWV and visa versa. The joints still hold well and do not leak.
I went with a 6" pipe because it is large enough for me to mill powder. Four inch pipe is too small for me to get done the amounts I like to produce and 8 inch would be too heavy and too expensive to make. The next consideration is the cement to glue the parts together. There is a heavy duty PVC cement that I like to use. Every little bit helps as far as I'm concerned and these jars rattling around for hundreds of hours may be a testament to the heavy duty glue. These jars may be a little pricey when done but they have been well worth the cost and have been maintenance free. Now lets go shopping!
I checked out a few different big box stores and some or most do not carry 6" PVC supplies. Below is a recent price list of the parts used.
6" X 4" reducing bushing $14.86
6" Coupling $14.33
6" Cap $12.99
6" Pipe X $37.26 (your call) I went with a 10 footer myself.
4" Pipe X 5 feet $8.99
4" Kwik cap $3.49 shown above which is a rubber cap with hose clamp to seal mouth of the jar.
8 oz of heavy duty cement $7.99
4 oz cleaner $3.49
So a trip to the store will cost about $110 unless you want to build more than one.
Now that you have all the parts it is time to cut and assemble. I cut my 6" pipe to about 16 to 18" long. You are going to want two pieces of pipe because the second one will be used to cut strips about a 1/2" wide for "lift bars". The second piece of pipe can be a 1/2" shorter than the first so that the lift bars will fit end to end easily enough. These strips are cemented in to keep the contents from staying as one mass of material and help to keep the mill media and your powder constantly mixing and working to mill more efficiently. I cut these strips with a circular saw but you can use other tools. Just watch your fingers please!
This is what it looks like when I had clamped my cemented lift bars in place:
Once the lift bars are set the rest of the jar can be assembled. If you have never worked with this material before please see the instructions of the cement. Usually you want to clean or prime both PVC mating parts then add cement to both parts and twist them together. Any excess cement that collects at the joint after assembly is spread around the joint to fill the crack. The cement sets up pretty quick so take care when assembling the parts.
The next picture below is a shot looking down the inside when the reducing bushing and lift bars are assembled. I like this arrangement because the reducing bushing makes the jar more compact in regard to length. The reducing bushing also keeps the powder more in the jar and not in the mouth of the jar if a reducing coupler was used.
And here is the completed jar without the rubber cap. Take a moment to notice that the 4" pipe is just long enough to bottom out in the reducing bushing and then sticks out just far enough to accept the rubber cap. This again helps with trying to keep the milling material in the jar, reduces weight and jar length is kept to a minimum.
The jar can be used within an hour or less. I let it sit for a day just to be sure.
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