Saturday, February 6, 2016

Model 600

I have been anxious to build a larger mill ever since the first one got going.  After finding an acceptable source for stones in Denmark, I wired out the money and did not have long to wait.  It turned out that air freight was the cheapest so in a week or so the millstones were waiting for me in a bonded warehouse.  I made purchase terms CPT (cost paid to) Mitchell Field, again to save money, and I also did the customs clearance myself.  It was pretty easy.  The hardest part was the stones themselves--shipping weight was 360 lbs!  I rolled the fixed stone into the house, this one is a little larger than the runner stone and I think it weighs around 200 lbs.  The working area is 600 mm in diameter, and overall it is a bit bigger (27" across the top).

Here is the frame going together.  I used 4 x 4 Douglas Fir legs, 2 x 8 stringers, and some high-quality plywood for the top.  The bridge tree is a solid piece of white oak, and the jack is 3/8" rod that I threaded to 16 tph.  The construction is a little weird since I want to be able to disassemble it next year and get it up the stairs, which are quite narrow.

Here you can see the thrust bearing and the adjustable housing I made for it.  The runner stone is basically sitting on this bearing, and the bridge tree can raise and lower the spindle shaft.  The bearing housing is adjustable so that I can "tram the spindle," ie, align the runner stone to the fixed stone.  The lower bearing is an ordinary farm bearing.  I could not find the thrust specs for it so I will just wait to see how it does.  The shaft is 1 1/2".  The 9.6:1 gearbox is a lucky find from craigslist, otherwise I was looking at a double reduction drive to get the speed I want.  This will drive the mill at around 160 rpm I think.

Here is the spindle coming through the mill table.  The tapered bushing was custom made for me at a local machine shop.  I welded up the other bushing to fit into a keyway in the runner stone and drive the stone. 

The spindle has two flats on it so it can tap on the damsel while running and keep the grain flowing smoothly.

Another shot of the lower thrust bearing.  Bearing and pillow block came from fleet farm, and I had to trim the corners of the pillow block to fit my adjustable housing.

Lowering the runner stone into place for the first time.

The runner stone wobbled on the tapered bushing, which was a surprise.  It thought it would lock on perfectly.  I ended up slotting the bushing so that the taper would lock it onto the shaft better, and I made this additional bushing to drive the millstone into the tapered bushing.  I also had to pick the stone up a couple of times and put some brass shim stock on the side of the taper in order to get the stone square to the spindle shaft.  The black bushing is a weld-type bushing that comes from Farm and Fleet.

Lowering the fixed stone into place.  These type of millstones are designed to have the lower stone moving, not the upper stone.  Having tried it both ways on the mini-mill, I really like the lower stone being the runner stone.  The eye never clogs up and a single grain kernel feeds instantly into the stones for grinding.

The upper stone needs to be suspended on something so I settled on making the housing out of staves.  I had to cut up at least 40 to get all the way around, using up a lot of nice wood in the workshop.

It was kind of exciting getting this thing glued up in a timely fashion.  The masking tape works wonders for gluing up staves.  Tape the outside, flip it so the inside seems open up, then brush the glue into the joints.  When the staves are put in place the tape does an amazing job of clamping everything together.  Cross fingers it cures up and makes a strong housing!

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