How to Build a Workhorse Grain Mill
Believe it or not, this time we are actually going to finish this project. I'd promise not to do any more seven part projects, but that could lead to something even more daunting - an entire issue of the Brewing News dedicated to the Thrifty Gadgeteer. Not that I would mind it one bit, but the rest of you might not be ready for that ever. Besides, that would mean I would have to take even more time out from battling the forces of Arrogant Incompetence, which would be dangerously irresponsible.
This time we will make the motor mounting Adapter Plate, install the motor, wire-in a switch, set up the mill, and go over a few operating instructions. Let's start on the motor mounting Adapter Plate. The instructions for this part are a bit less specific, because the Adapter Plate has to be matched to the bracket that came with the motor, and I have no way of knowing exactly what motor and bracket you were able to scrounge. Start by fully assembling the mill, including the drive pulley. Do not install the grain hopper or the catch bin. Next, lay the 6" X 10" piece of 1/16" to 3/32” thick Plate Steel flat on the work surface. Measure and draw center lines parallel to the 6” and 10” sides of the work piece. Place the motor, mounting bracket DOWN, on top of the work piece so that the bolt holes in the mounting bracket are aligned on the 10” center line on the work piece. Adjust the position of the mounting bracket so that ends of the bracket are equidistant from the ends of the Adapter Plate. Use a pencil to draw circles on the work piece through each of the bolt holes in the mounting bracket. Remove the motor and mounting bracket from the work piece, then by hand test-fit drill bits through the bolt holes in the mounting bracket until you find one that is closest to the size of the bolt holes. Mount this drill bit in your power drill. Find the center points of each of the circles you drew on the work piece, then draw lines across the work piece through the center of each circle and parallel to the 6” sides of the work piece.
On each of the lines drawn through the circles, measure 1-1/2” IN from each 10” side of the work piece and mark a drill point, then mark a second drill point on each line one drill bit (the one mounted in your drill) diameter closer to the center from each 10” side of the work piece. Now drill the holes (8 of them altogether) through each drill point using the drill bit previously mounted in your drill. Use a straight edge to draw lines parallel to the line on which the holes are drilled and tangent to the sides of each hole. Use a small file to break through the thin bit of material remaining between the two holes in any of the four pairs of holes, then repeat the process for each of the other pairs of holes. Mount a metal cutting blade in a saber saw and carefully cut along the lines running tangent to the holes until you have removed all of the material between the outermost holes at each end of the work piece. You should now have two approximately 3” long slots, one at each end of the work piece. Use a file to dress-off any burrs and sharp edges. Now bolt the motor and mounting bracket to the Adapter Plate using the original mounting bolts, nuts, washers and lock washers (or replacements of appropriate size).
The motor will have small pulleys at each end of the rotor shaft. Remove the larger of the two pulleys and save it for another project. (Hey, you never know!) The smaller pulley will have a series of small ridges and grooves between the inner and outer edges. These ridges and grooves must eventually be removed or else they will chew up the drive belt. Removing them will also reduce the diameter of the pulley slightly, increasing the size difference between the motor pulley and the roller pulley, resulting in greater mechanical advantage. We will have to wait until we have the motor mounted on the mill before we remove the ridges and grooves. But first, we need to determine the direction of rotation of the pulley. The easiest way to do this is to get an old power cord and temporarily wire it to the leads or terminals on the motor. Use a couple of wire nuts to secure the leads to the power wires or connect the power wires directly to the motor terminals, and secure the ground wire on the power cord to the outer housing of the motor by adding a nut at the end of one of the bolts that hold the motor together. Set the motor between a couple of heavy objects (concrete blocks will do nicely) so it can't move, then quickly insert the power cord plug into and then immediately remove it from an outlet. You should be able to observe the direction of rotation. The direction of rotation must be CLOCKWISE. If the direction of rotation is COUNTER-CLOCKWISE, the pulley must be removed and remounted on the opposite end of the rotor shaft. Once you are sure the direction of rotation is CLOCKWISE, we can continue building the motor mount.
Carefully set the FRONT of the mill on the floor. Facing the BACK of the mill, the roller drive pulley should be on the RIGHT. Pick up the motor and place it on the BACK of the mill so the pulley on the rotor shaft is approximately aligned with the roller drive pulley. Note that in order to achieve alignment, the Adapter Plate will overhang the side of the mill. Use a pencil to mark the Adapter Plate where it begins to overhang the side of the mill. Remove the motor from the mill, then remove the Adapter Plate from the motor. From the “overhang” mark, measure 1-1/2” IN toward the 6” center line bisecting the 10” length of the work piece and make another mark on the work piece. Through this mark, draw a line across the work piece parallel to the 6” sides of the work piece. We'll call this the Alignment Line. Now measure the distance between the Alignment Line and the bolt hole at the opposite end of the Adapter and subtract 3/4”. Use this dimension to determine the width of a 6” long piece of 2” (actual 1-1/2”) X construction lumber and cut to size. Place this piece of construction lumber (the Offset Block) on the BACK of the mill (which should still be laying face down) so that one 6” side is aligned parallel to and 1-1/2” IN from the RIGHT, and the top edge is parallel to and 8” DOWN from the TOP of the mill. Draw a line completely around the Offset Block onto the BACK of the mill so it will be easy to realign the Offset Block later.
Set the Offset Block on a flat surface and draw lines 1-1/4” IN from and parallel to the top and bottom edges of the Block. Mark on each line at 1-1/4” IN from each end and at the center point. Set drill points and drill a 7/32” diameter hole at each mark - make sure the holes are drilled perpendicular to the face of the work piece. Use a 3/8” diameter drill bit to counter-bevel each hole just enough to fully seat a #10 X 2-1/2” wood screw with the head of the screw flush to the face of the work piece. Place the Adapter Plate on the Offset Block so that the Alignment Line on the Adapter Plate is aligned with one 6” side of the Offset Block and the TOP and BOTTOM edges of the Adapter Plate are aligned with the TOP and BOTTOM edges of the Offset Block. Clamp the Adapter Plate to the Offset Block to maintain alignment. Flip the assembly over so the Offset Block is on top of the Adapter Plate, then use a #10 X 2-1/2” wood screw to scratch the surface of the Adapter Plate through each of the holes in the Offset Block. Also draw a line on the Adapter Plate where it overhangs the edge of the Offset Block. Remove the clamps and set the Adapter Plate on a flat surface with the marked side UP. Draw a line parallel to and 1/2” IN from the overhang line toward the center of the work piece.
Realign the Adapter Plate on the Offset Block and clamp in place. Drill a 1/8” diameter pilot hole into the Offset Block through the center of each of the 7/32” holes in the Adapter Plate - make sure the holes are drilled perpendicular to the face of the work piece. Remove the Adapter Plate from the Offset Block and realign the Offset Block on the BACK of the mill. Drill a 1/8” diameter pilot hole into the BACK of the mill through the center of each of the 7/32” holes in the Offset Block - make sure the holes are drilled perpendicular to the face of the work piece. Fasten the Offset block to the mill using #10 X 2-1/2” wood screws. Fasten the Adapter Plate to the Offset Block using #10 X 1-1/4" Steel Pan Head Slotted Wood Screws. Mount the motor onto the Adapter Plate with the mounting bolts positioned at the TOP ends of the slots. Return the mill to normal upright position. Plug the power cord in and use a half-round file to carefully remove the ridges and grooves on the rotor shaft pulley as it is rotating. You should end up with a single “U” shaped channel between the inner and outer edges of the pulley. Unplug the power cord. Now use a tape measure to measure the belt path around the rotor shaft and roller pulleys. I advise getting an automotive “V” belt that is just slightly smaller than the belt path measurement. Once you have the belt, install it onto the pulleys - put it on the rotor shaft pulley first, then thread it into the groove at the top of the roller pulley and rotate the roller pulley clockwise until the belt rolls into the groove all around the pulley. Now adjust the position of the motor on the Adapter Plate until the belt is very tight, and tighten the mounting bolts securely.
OK, now we need to build a simple switch so the mill can be turned on and off without having to mess with the power cord once it
Remove the temporary power cord from the motor and save it for another project. Cut the receptacle plug off of the extension cord, then feed the free end of the cord into the workbox through the wire hole closest to the FRONT of the mill at the BOTTOM of the workbox. Once about two feet of cord has been fed in, loop it over and start feeding the free end back out of the workbox through the wire hole closest to the BACK of the mill at the BOTTOM of the workbox. Feed through enough cord to reach around to the BACK of the mill to the terminals on the motor, plus about 6” of slack. Strip about 4” of the outer insulation from the free end of the cord to expose the three wires within, then strip about 1/2” insulation off the ends of the three wires. Connect the power wires to the motor terminals and connect the ground wire to the outer housing of the motor. Once the wires are connected to the motor, pull back on the section of cord between the motor and the workbox to take up the slack, leaving just enough slack so the motor position can be adjusted on the Adapter Plate without pulling the cord tight or causing it to come into contact with any moving parts.
Pull back on the plug section of the cord until the loop of power cord protruding from within the workbox just touches the top inside surface of the workbox. Now carefully remove the outer insulation from the loop, leaving about 1/2” of insulation inside the box where the cord sections pass through the bottom of the box. Cut the BLACK power wire at the top of the loop, then strip about 1/2” of insulation from each free end. Attach the free ends to the terminals on the power switch, then mount the switch in the workbox and install the cover plate. Congratulations! You have just finished building the mill! Now all that remains is to adjust the crush gap and you'll be ready to mill your grain. As a safety precaution, do not plug in the power cord until after you have the mill set-up and you are ready to crush grain. NEVER have the mill plugged-in unless the mill is fully assembled.
To adjust the crush gap, it will be necessary to remove drive belt, the dust shields and the bearing retainers. With the roller assemblies exposed, loosen the adjusting screws at the front of the mill and use the blade of a screwdriver to gently pry the front
Once the roller gap is observed to be constant, you can try a crush test. Keep in mind that different grains will require different crush gaps, depending on their size and hardness. So some experimentation will be necessary, and a chart should be made to guide you in setting the crush gap for each grain type. I recommend you start out with the base malt you most often use. Install the hopper and catch bin, start the mill, then slowly pour about 2 to 3 ounces of grain into the hopper. If the mill jams, shut it OFF immediately - the crush gap is probably too narrow - unplug the power, rotate the roller pulley COUNTER-CLOCKWISE by hand, remove the hopper and vacuum out the grain from between the rollers. If the mill operates smoothly, allow it to run until the change in sound indicates all of the grain has been crushed, then turn the mill OFF. Pull out the catch bin and retrieve a handful of crushed grain and look at it closely. The husks of the grain should be largely intact, and the kernel should be broken into several chunks. If the husks are shredded into small pieces and/or the kernel has been ground into powder, the gap is too narrow. If the grain has not been crushed, the gap is too wide. Adjust the gap one shim width at a time until the proper crush for the subject grain has been achieved, then record the gapping information on your chart. Repeat this procedure for the various grains you most commonly use.
OK, now for some DOs and DON'Ts:
Oh, and I almost forgot, DO enjoy using your mill - you deserve it, I'm pretty sure you worked your ass off building this project.
A final note - you high-volume brewers can make an extension for the hopper by cutting the bottom out of a One Gallon Plastic Fruit Juice Container. Just cram the narrow end into the top of the hopper and you've got a large funnel that makes it easier to pour in the grain and increase the capacity of the hopper at the same time. OK, I've had it. This project has worn me out. Don't ask me what I'm doing next, 'cause right now I don't know myself. It's a surprise. Yeah, that's it, a surprise, and you'll just have to tune in next time to find out what it will be. Rest assured, however, that, whatever it is, it'll be cheaper and better to make than to buy!
Yours in Frugal Fraternity,
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