Making A D Bit Single Flute Milling Cutter, by Clickspring\r
\r
The D Bit is a piece of old school shop tech that I absolutely love to use. Theyre perfect for profile milling cutters, countersinks etc. as demonstrated in this video. But they are particularly well suited to drilling very deep, straight holes. They are incredibly accurate, and can leave a surface finish that approaches what you expect from a HSS reamer - And thats from a shop made drill! \r
\r
The main project video that this video is related to is Spare Parts #9 - Making A Rectangular Bluing Tray: \r
\r
If you would like to help support the creation of these videos, then head on over to the Clickspring Patreon page: \r
\r
Ask Me A Question:\r
\r
\r
Follow Clickspring:\r
\r
\r
\r
\r
\r
\r
\r
Abbreviated Transcript:\r
\r
00:07 As essential as these commercially produced cutters are, there is another type of cutter that can often prove to be equally indispensable. The shop made D Bit.\r
00:17 Now the term D Bit has a fairly broad meaning, and can be used to describe a wide range of cutters with a D shaped cross section, but in this video Im going to make a milling cutter to form a V shaped groove in brass, so the geometry will need to be something like this.\r
00:32 Starting with this length of drill rod, the first step was to face it to length. The cutter Im making has an included angle of 92 degrees, and I do need it to be dead on, so rather than rely on the lathe protror, using a dial indicator to get it exly right.\r
00:50 The better the surface finish on the cutting edge, the better the finish the cutter will leave on the part, so Im using a shop made emery stick to give it a mirror finish before proceeding to the next step.\r
01:27 I remove the bulk of the stock using an end mill like this, and then rotate the work through 90 degrees to finish the rest of the stock removal, and create a recess behind the flat. This recess becomes quite helpful when sharpening the cutter, which Ill show you later.\r
01:40 With the flat just short of the half way mark for sharpening, the bulk of the metal removal is complete. A little bit of time on the coarse stone brings it even closer to the centerline, and also removes the burrs and tools marks in preparation for hardening.\r
02:01 A coating of boric acid and denatured alcohol, along with soft iron wire can help to reduce the oxidation scale that would normally build up during the heating process.\r
02:23 I used some emery paper to clean up the surfaces, and a quick test with an old file confirms the part is glass hard. At this point its much too brittle to be of any use, and needs to be tempered.\r
02:36 Ideally Id use a heat treating oven for this, but I dont have one, so instead I use the oxide colors as a guide. I heat it gently from the shank end, and let the heat slowly walk up the length of the cutter.\r
02:47 The oxide colors do roughly indicate the surface temperature, but I give it plenty of time for the heat to pass into the interior and transform the structure of the metal.\r
03:01 Emery sticks can again be used to brighte up the surface, and the cutter is ready to be sharpened, using the coarse medium and fine oilstones.\r
03:12 And you can see the recess ensures that the cutter naturally sits flat on the stones, so that the entire surface is being sharpened parallel to the axis of the cutter.\r
03:33 For one thing, quench hardened carbon steel cant compete with carbide or HSS, so I find its best to not be too ambitious with the depth of cut and feed.\r
03:42 And to be technically correct, a side cutting D Bit really should have clearance angles behind the cutting lip, much like an engraving cutter.\r
03:49 But its difficult to form the relief angles for this sort of profile without a tool and cutter grinder, and in price Ive found that if I keep the feed rate modest, I can get away with leaving them out, without too much penalty.\r
04:08 D Bits are an incredibly versatile and effective type of cutter, and there are many ways to use them beyond what Ive shown in this video.\r
04:17 Theyre particularly well suited to drilling very deep, close tolerance holes, and can be tailored to suit a specific requirement, for example in this case a square bottomed to the hole.\r
04:25 Theyre a great way to solve those unusual cutting problems that crop up from time to time, that might otherwise require spending money, on an expensive cutter.\r
\r
References:\r
\r
The Model Engineers Workshop Manual pg 94\r
George H Thomas\r
\r
The many forum posts on the subject of D Bits\r
by John Bogstandard Moore\r
\r
Making A D Bit Single Flute Milling Cutter, by Clickspring.
