Irwin vs Jennings auger bits.
I did a quick search of the Internet to see what the prevailing wisdom on Jennings vs. Irwin auger bits is. Here are a few snippets of what I found.
„Jennings bits with fine pitch are the ones to have if you're going to be working with hardwoods.“
„The Irwin bits have a coarser screw and some of the smaller sizes have bigger diameter lead screws than the Jennings, probably to make up for the coarser pitch. They work quickly in softwoods but can be really rough to use in hard dry hardwoods,“
„I would get Jennings if you work with hardwoods.“
„I have both the Irwin and Jennings bits. I consistently reach for my Irwins. I just drilled a 1“ hole in 4/4 QSWO yesterday with an Irwin and 12" throw brace and it didn't leave me wanting anything else. The Jennings will get their threads clogged in softwood, so I say the Irwins are the better all-around bit."
„I use my fine thread RJ s for hardwood and my Irwins for carpentry work.“
„Soft woods, e.g. pine, spruce etc., have soft & coarse grain and lend themselves better for a coarse thread for better grip and pull. In addition, as the wood is soft, it “allows” for faster “RPM” with coarse and larger chips and a single-flute bit for clearing volume is better here. Irwin (like) bits come to mind…“
„As hard woods typically have much finer and denser grain, a fine threaded lead screw is usually preferred for better grip and pull. Naturally, this results in lower “RPM” but with more force-gain per turn. With finer shavings, the clearance volume is realized here with a parallel/double flute. Russell-Jennings (like) bits come to mind here…“
„Irwins are for softer gummy woods (pine Doug fir). Think quick dirty holes for construction work. They have large pitched lead screws that have a tendency to strip out and not grab in hardwoods.“
„What you want to look for are auger bits with a fine pitch lead screw. The coarser pitch lead screws are for soft woods.“
„I was taught that Russel Jennings type augers were best in hardwoods due to the fine thread of the lead screw and fine pitch flutes. Irwins were better for softwood because of their coarser lead screw and flutes. Irwins were used primarily by the "building“ trades since most house framing was done with softwoods. Cabinetmakers, stair builders and other „fine“ woodworkers used Jennings."
The consensus seems to be that the Jennings has a fine pitch lead screw and is better for hardwoods with one exception and that person said Jennings clogged in softwoods. I decided to try it and find out.
Here are the four bits I selected for my trial. Two Irwins with different Logos on them, a Russel Jennings and a Greenlee in the Jennings pattern. I bored holes in different types of wood. Each 3/4" hole was bored with ten cranks of the brace after the bit began to take a shaving. I sharpened all of the bits before I started. Here is a photo of my results. The woods are White Pine, Ash, Cherry, Basswood, Hard Maple, Walnut, Mahogany, Hemlock? (construction lumber) and White Oak. For the most part my effort on each hole in each type of wood felt similar. Some sort of torque gauge would be a better way to know for sure. The line below the holes is 3/4" down from the edge.
The Irwins were very consistent in all the types of wood with one 7/16" deep hole, eight 1/2" deep holes and nine 9/16" deep holes. Really a variation of only a 1/16". The Jennings bits showed more variation with two 1/2" inch deep holes, four 9/16" deep holes, seven 5/8" deep holes and five 11/16" deep holes, a variation of just over 1/8". While my results are a small sample, far from scientific and run counter to the prevailing wisdom, what I see is the Jennings bit consistently boring almost 1/8" deeper in each type of wood, with the exception of the White Oak, telling me that the Jennings bit takes a thicker shaving, has a coarser lead screw and therefore cuts faster. The Jennings lead screw appears to be finer, and appearances can be deceiving. The Jennings bit has a double twist on the lead screw so it is in reality coarser. My take on it would be use what you have and use it sharp. Since Irwins are cheaper and more abundant it would make sense to buy them, but I wouldn't pass on a good set of those fast cutting Jennings bits either.