How to Build a Workhorse Grain Mill
Hello again. I will assume that, barring any unrelated catastrophes, those of you who paid due heed to my admonitions of caution in Part Two of this project series actually do still have the same number of fingers as you had before we started. If you don't but intend to continue anyway, I hope your knuckle dexterity isn't impeded by your knuckle head! But I digress. This time around we will build the bearing assemblies for the rollers, and then we will go about the tedious task of achieving rotational alignment. I will apologize in advance for what may be perceived as a significant decrease in the acerbic comments to which the reader may have become accustomed or even, perhaps, enamored. You see, to give our publisher some much needed relief from undeserved verbal assaults by hypocritical types who would disparage freedom of speech even while exercising that right as a means to deny it to others, we will dispense with any drama or the use of big words that might too easily pierce the thin-skinned or upset the delicate sensibilities of those so bereft of objectivity that they will deny the truth even when the Emperor is clearly unclothed. It might be less entertaining, but, what the hey, it's a humanitarian gesture.
The materials list for this segment is as follows:
Now to work. Get the 2" X 4" construction lumber and cut four 3-3/4" long pieces, making sure each end of each piece is perfectly square with the sides of the piece. Use a straight edge to draw diagonal lines from corner to corner across one face of each cut piece of wood. Drill a 3/32” diameter pilot hole through each piece at the point where the diagonal lines cross (the center point of the block). Make sure the pilot hole is perfectly perpendicular to the face of the block. Measure the outside diameter of the 3/4” ID black iron pipe. Select a spade drill bit that is about 1/32” to 1/16” smaller than the pipe diameter and drill a hole through each block using the pilot hole as a guide. Do not drill all the way through the block in one pass. Instead, drill a little more than half way from each side - the result will be a cleaner hole and the drill bit won't bind in the work piece. Again, the hole must be perfectly perpendicular to the face of the block. Use sandpaper to remove any rough edges or irregularities inside the hole and to slightly bevel the opening on each face of the block.
Set a block up on one of its narrow sides, with the long grain of the wood parallel to the work table. The end-grain of the wood must not be facing up! Find and mark the center point of the top side, then drill a 1/4” hole through to the large hole previously drilled. Use sandpaper to remove any rough edges on each end of the 1/4” hole. Repeat this process for each block.
Next, measure the thickness of each block. Standard 2” construction lumber will have an actual thickness of about 1-1/2” to 1-5/8”. Use this measurement to mark the 3/4” black iron pipe and cut four pieces, one for each block. Use a file to dress off any burrs or sharp edges on the ends of each pipe section. Now test-fit one of the pieces of 3/4” pipe onto the end of one of the 1/2” pipe sections on the rollers. Don't expect it to go on just yet, just get an idea of how much bigger the inside diameter of the 3/4” pipe must be made so as to slip snugly onto the 1/2” pipe without binding. Now the fun begins - using a medium half-round file, carefully remove material uniformly around the inside of the 3/4” pipe until it fits properly onto the 1/2” pipe. Work from both ends of the 3/4” pipe so you don't file the inside to a conical shape.
When the sections of 3/4” pipe have all been fitted to the roller axles, use a file or bench grinder to put a 1/16” bevel on one end of each 3/4” pipe section. If you have a large bench vise, use it to press a 3/4” pipe section, beveled end forward, into the hole in one of the wood blocks. Otherwise, use a hammer and a piece of scrap wood to tap the 3/4” pipe section into place. If you measured and cut correctly, both ends of the 3/4” pipe section should be flush with the surfaces of the wood block. If the piece is too long, this is not acceptable, so dress off the protruding end with a file or grinder until it is flush with the block. It is okay if the pipe is a little short, so long as the unbeveled end is flush with the block. Repeat this process until each 3/4” pipe section has been mounted in a wood block.
Set a block and pipe assembly on one of its narrow sides, with the 1/4” hole facing up. Center on the 1/4” hole and drill a 1/8” diameter hole through to the inside of the pipe - do not drill through the opposite side. Use a 1/4” drill bit to dress-off any burrs on the outside of the pipe - do not drill into the pipe! Use a file to carefully dress-off any burrs on the inside of the pipe. Get the small piece of 1/4” metal tubing and hand-press it into the 1/4” hole until it stops up against the pipe. Mark the tubing at the surface of the block, then remove and cut it at the mark. Dress-off any burrs on each end of the tube, then reinsert it into the 1/4” hole until it stops up against the pipe. The outer end of the tubing should be flush with or slightly below the surface of the wood block. If not, use a file or a rotary grinding tool to remove any protruding material. Repeat this procedure for each of the block and pipe assemblies. In case you haven't guessed, the small holes and tubing are the lubrication ducts for the bearings. The finished units are now the bearing assemblies.
You can set the bearings aside for now, and we'll get started with rotational alignment. The first step will be to make sure the axles are parallel with the surface of the roller. Set a roller on a flat work surface with one of the flange mounting bolts at the six o'clock position and use a square rule to measure the distance from the bottom of an axle to the work surface at both the outer (free) and inner (flange) ends of the axle. The measurement should be the same at each end of the axle within 1/64 of an inch, but probably will not be because the threaded hole in the flange is usually not perfectly perpendicular to the flange face. Make a chart with columns for Measurement Number, Inner Measurement and Outer Measurement, and mark this first set of measurements on the chart. Mark the flange at its six o'clock position with a #1. Rotate the roller 45 degrees and take a new set of measurements, this time marking the flange at its six o'clock position with a #2. Repeat this process for measurements #3 through #8. Usually, there will be four sets of measurements in which the outside measurement is equal to or greater than the inside measurement, and four sets with the opposite relationship. We will be looking for the sets where the inside measurement is the greater.
Review the data on the chart and select the measurement set where the inside measurement is greater by the largest amount. This measurement point on the flange will have to shimmed. Shimming will be most easily done with the roller assembly set up on the spare piece of 3-1/2” OD pipe, with the end to be shimmed facing up. With the roller set up on the holder, loosen the nuts on the four flange mounting bolts. Now get a 1/2” wide strip of aluminum foil and fold it lengthwise in 1/2” to 3/4” long layers until it is approximately as thick as the difference between the inner and outer measurements at the selected measurement point. Tear off any unneeded foil. Insert the aluminum foil shim under the edge of the flange at the selected measurement point, pushing it in about 1/4”. Now retighten the nuts on the flange mounting bolts. Repeat the measurement process. If the inside measurement at the shimmed point is less than the outside measurement, the shim is too thick and must be reduced. If the inside measurement at the shimmed point is still greater than the outside measurement, the shim is too thin and must be increased. If all of the inside measurements are equal to their companion outside measurements, no further shimming is necessary for that axle. If any of the measurement pairs do not match, repeat the shimming process at the point of greatest difference. It may take shimming at as many as four points to achieve parallel alignment for the axle. Repeat the entire process until all four axles are aligned parallel.
With parallel alignment achieved, we must now achieve radial alignment. Repeat the outside measurement process for any axle. All of the outside measurements should be the same, plus or minus 1/64th of an inch. If not, determine the opposing sets of measurements with the greatest difference and set the roller up on the holder pipe. Carefully loosen the nuts on the flange mounting bolts, then very carefully move the flange in the direction of the larger measurement, by a distance of one half the difference between the larger and smaller measurements. Make sure you do not displace any shims that were installed to achieve parallel alignment. Re-tighten the nuts on the flange mounting bolts and repeat the measurement process. If all of the outside measurements are equal within 1/64th of an inch, radial alignment is achieved for the axle. If not, repeat the radial alignment process until proper alignment is achieved. Complete this step for all four axles.
As a final overall alignment test, we will mount the bearings on the rollers and check for true rotation. First, we will need to make a pair of riser blocks to set the bearings up on so the rollers can turn freely. Find a short (6” or so) piece of 2 X 4 that is straight and true (check it with a square rule) and cut it into two equal pieces. Set the riser blocks down on a flat, level work surface. Now mount a bearing on each end of a roller, with the unbeveled ends of the bearing pipes facing the flanges, and set the bearings up on the riser blocks with the lube holes on the bearings facing up. If the bottom of either bearing block does not rest flat on the riser block, the bearing pipe is probably not mounted straight and true in the bearing block. If the gap is small (less than 1/8”) you may be able to correct by sanding off some material until the block rests flat. Otherwise, you should remake the bearing assembly. If both bearing blocks are resting flat on the risers, position the roller so that the #1 measurement point of one axle is pointing straight down towards the work surface. Measure the distance between the surface of the roller and the work surface at both ends of the roller body (3-1/2” OD pipe), and mark the measurements on a chart. Repeat for each of the remaining seven measurement points. If the measurements are all within 1/64th of an inch, congratulations, your workmanship is superb and you now have a properly aligned roller and bearing set. If not, you will need to analyze the data on the chart to determine the cause and appropriate corrective action.
If a given end of the roller is consistently lower than the opposite end, and the difference does not vary by more than 1/64th of an inch over a complete revolution, then the problem is almost certainly that one or both of the bearing pipes is a little off-center in its mounting block. This can be resolved by building up layers of 1-1/2” X 3” aluminum foil shims under the low bearing until the measurements at both ends of the roller are all equal within 1/64th of an inch.
If the measurements at one end of the roller are consistent, while the measurements at the opposite end are not, it is likely that the axle at the varying end is not properly aligned. Repeat the parallel and radial alignment procedures for the axle in question, then repeat this bearing alignment step. When you have successfully completed alignment for one roller, repeat the entire process for the second roller.
Continue to Part 4
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