On a screw auger, one can replace broken fins, or flytes, as they are called, or the complete auger can be fabricated by the following method. It is relatively easy once an understanding is gained on how to proceed.

    The flytes will look like the detail to the left. These rings are what will form the flytes. After the measurements have been calculated, the rings are cut as shown.
     
     The edges will need to be finished depending on your use. Make allowances for grinding or machining. After being cut, they are pulled slightly apart, and the bottom edge of one ring will be welded the upper edge of the next ring, OR the reverse will be used to weld the rings together. That is, the top edge will be welded to the bottom edge. This is very important to remember.

     The direction of the screw will be changed when the flytes are joined together by using one method over another, and because of that, you must determine whether the screw will turn to the left, or turn to the right when in goes into service. This will allow you to determine what way to weld the rings together. If you are confused, cut two small rings out of paper and join them together by each method. You will see then what happens. Think of in terms of a left hand thread, and a right hand thread. Turning both in one direction will produce opposite reactions, and the same holds true for the screw.
     To begin the process of fabrication, the measurement between the flytes is needed. This is known as the pitch. In this case it is the measurement - (A) 6". Next, the bare shaft will be laid out. Place a centerline on the top of the shaft. The figure (A) 6" is measured onto the shaft along the centerline, and marked on the shaft.
     When you have done this, then take a fine wire and wrap it around the shaft to make one complete revolution from one point to another, as illustrated by (B). This is called the starting point and the finishing point. Make sure the wire is not twisted, and lies snugly onto the shaft. Mark the wire where it meets both points.  Only two points are actually needed for this. The large drawing shows four points only because it allows a better perspective without crowding things too much. Each of these 4 points shows the 6 "spacing of the flytes along the shaft, with more spacing continuing along the shaft as required.
     Take the wire off of the shaft and pull straight. Measure the distance between the two points that are now marked onto the wire. You now have the circumference of the shaft hole. For sake of clarity and example, a rough guess will be assigned here for the length - let's say 18". This figure will be used to calculate the proper diameter of the hole that is to be cut in the plates for the shaft.
     The formula is as follows: Circumference divided by 3.1428. So you would have the math look like this: 18" divided by 3.1428 = 5.727" dia. is the proper diameter of the shaft hole. To determine the outside diameter of the flytes, take the height the flyte needs to be from the shaft. In this example that figure is (C) 7.5", and multiply by 2 (for both sides). This gives the answer of 15". Add 15" to the diameter 5.727" which = 20.727". The outside diameter of the flytes  - (D) - is 20.727", and the formula is:   height x 2 + dia. = outside diameter.
     As stated before, a good way to see if things are what they should be is to take your answers and draw them out on heavy paper. This time however, draw the rings out full scale and be particular. Once they are cut out you will have a replica of the actual ring. Once the rings are all cut out and welded together, they can be installed onto the shaft. Each ring will make only about 2/3 of a turn around the shaft. You will need to allow for that when you cut the rings out to ensure that there are enough. Multiplying the number of flytes by 1.33 should give you the correct amount of rings. In the case of the drawing 5 flytes can be seen. If one multiplies only by 2/3, then 5 flytes would only go around the shaft 3.3 times. So 5 x 1.33 will give you 7 rings (6.65 rounded off) that have to be made. To install, slip the welded assembly of rings on over the shaft. You should have a beginning point where the first flyte starts. At this point weld the end of the flyte onto the shaft, at the point where it will be permanently installed, with a fairly strong tack weld. Don't weld too much at this point. 
     Once this has been done, go to the far end of the ring assembly and fasten a lug to the last edge of ring, or have a hole already in the ring to accommodate a shackle. Secure the shaft to prevent movement of any kind. You must also have a separate, suitable, anchor point to use to hook some type of puller onto. This anchor point must be located directly opposite of the end of the shaft where the shackle or lug is located. Using a puller, begin to pull the rings along the length of the shaft. If you marked the distance (pitch) between each flyte onto the shaft, you should be able to tap the flytes in place as you go along and tack them in place. They should pull into the required position. You are now finished, and are ready to begin the final welding of the flytes.