12inch over bore reamer for horizontal drilling

When my customer picked up the 6" casing puller he dropped off a short piece of drill stem and his 7" reamer that fits his smaller boring machine and asked me to make one to ream a 12" bore from the 5" bore hole his larger machine bores.
This is what I made for him;
based loosely on a 4inch flighting pitch the starting teeth are set at a more aggressive angle and progressively increase in cutting radius while the cutting angle decreases, with a semi ring attached to the last tooth to simulate an open auger flight for stabilizing the reamer in the bore hole. this in unlike the hodgepodge assembly of his existing reamer.
In the past when I was making foundation drilling tools I would have made a full solid flighted auger starting out with a smalle diameter and increasing until the desired major diameter was achieved. Horizontal boring is different than vertical bores in that small drills are used to make the initial bore then the reamer is pulled back through while turning and spraying with high pressure water to clean out the bore this is why the open design is preferred
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