Monday, February 15, 2016

Putting it together

So after a little more than two weeks of work the Model 600 is up and running!  Here is how it looks in it's new home, hooked up to the bolting cabinet.

Gluing the top onto the tun (casing).  The staves actually did not stay true and the entire housing is kind of squashed, although you can't see it without a measuring tape.  I made the tun to be one-piece, meaning that the upper millstone has to slide out the bottom.  I managed a nice fit but perhaps a little too tight.  I'm not sure if the stone would come out in the middle of summer when the wood is swollen with moisture.  The upper millstone has 3 large thread inserts around the circumference, and at least 6 smaller ones on the top, in no particular pattern.  I am using bolts in all of them.

So here is what it looks like without the tun.  The game is that the upper millstone has to be perfectly supported in space so that the lower millstone can be raised up to just barely touch it, in perfect alignment.

This hopper is a bit small but I had already made it for another project so it will do for the time being.  The shoe is so-so and when I get around to building a larger hopper I will try to make a better shoe.

Belt slippage became an issue on the second run of the mill.  The runner stone would start slowing down if the grain was fed too fast.  I built the mill with two-belt pulleys because my free two hp motor came with one already on the shaft, and it seemed about right.  But running with two A-sized belts I am getting slippage.  I looked online and determined that in this circumstance a single belt can only be expected to transfer about .7 hp.  Keep in mind the rpm coming out of the gearbox is 180 rpm.  The driver pulley has an A pitch diameter of 4.4 and a B pitch diameter of 4.8.  The pulley on the spindle is a 5/5.4.  I might do a little better with B belts, but I think a more drastic solution is required.  So for now I just tightened the belt as much as I dared.

I don't want to tighten the belt too much because it starts messing with the stone alignment and pulling on the upper bearing, which needs to allow the spindle to slide through when the runner stone is raised and lowered.  So my long-term solution was to order some three-belts pulleys.  This was easier said than done because sheaves of this type can get expensive.  The ones I finally found were only about $40 with the bushings, but then belt size became a problem.  The new sheaves take a 5V belt, and those don't usually come in sizes less than 50" (my ideal is a 41" belt in this space).  Anyway, I finally found some 45" 5V belts online and I think there is just enough room underneath to slide the power unit over and tighten the belts.  

There is a lot of hemming and hawing in this area.  Large sheaves can get expensive--several hundred dollars is quite common.  The next mill I build will probably not have a gearbox, so reduction will have to be by belt.  The European mills using a 600 mm stone run the stones at 480 rpm, which would take a more than 3:1 reduction with the belt drive.  Furthermore, to get enough torque at that rpm requires a serious motor, in the 10-15 hp range.  5 hp is about the max you can expect to run off of single phase 220 v electricity, so things start to get messy and expensive.  I wanted to stay on single phase 220, and the 2 hp motor I source was really nice because it only draw 13 amps at full load.  I can use No 12 wire and a 20 amp light switch to control it, but any bigger and I will need a special motor start switch.  I wanted to keep this project sane and simple.  

I'm really glad I took the time to weld up a good adjustable bearing base for the lower bearing.  I can really tune up the alignment quickly and accurately and get the stones singing, like they should.

Note the 3/8" rods clamping the tunning down to the table.  The lower stone will be pushing up into the fixed stone, and that stone needs to be able to counteract that force.  This is where this style of mill departs from most stone mills built prior to the 20th Century, where it was normal for the top stone to turn and the bottom to remain stationary.  In the old style, the pressure is limited to the weight of the runner stone, whereas in this style the pressure is created by the bridge tree pushing the runner stone up to the bedstone. 

I never did a budget but I think this cost me around $1500 to build.  The millstones were $1000 shipped to the airport, the gearbox $85, and I spent $75 at the machine shop.  The motor was free and a lot of the wood was also free.  There were bearings and a shaft to purchase, and two bushings that I used to make fittings with.

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