03/03/2016 17:03:22 Categories: Tips
As many of you have asked about my CNC dowel drill bits, I am gonna try to explain a bit the differences and benefits over the classic ones.
This is the brad point bit. They are usually made of chromium-vanadium steel and and they have a center spur to prevent walking when it penetrates the surface.
This is the twist bit. It is typically used for metal but a lot of people use it in wood surfaces too. They are made of high-speed steel. They also have two cutting edges but they don't have the center spur.
And the last one is the drill bit this is all about, they are made for being used in CNC machines or drilling and tapping centers. But more and more people are using them in Column drills or 3D Routers as mine.
There are a lot of types, through hole, blind hole, left or right hand, and of course different diameters. You can use them in all kind of wood and wood based composites. It is made of super-strength steel and it has two precision ground cutting edges and a center spur. They also have a special coating to help keeping the bit from collecting resin, pitch and other residues .
Ok, let's try them so we can see the results. As you already know the biger the size of the bit the lower must be the revolutions of the machine. I am using a manual two speed drill that can work at 650 and 2000rpm, so in this case with small bits I am gonna go with the faster one. Let's start with the hard plywood and the brad point bit. I am making a blind hole and then a through hole. As a rule we should use a block under the plywood to avoid splintering but I am not using one here so we can see the real difference between all the bits.
As you can see the bit does the job but the back does not look good.
Let's continue with the twist bit, it has the disadvantage that it is no as easy to find the center point but the result is also good. You can see it looks better, but still not perfect.
Finally these are the CNC dowel drill bits. First the through hole. It goes smooth and centered. And as you can see, no splintering at all.
Let's try now the blind hole. Perfect!
Here you'll see it better, the Brad Point Bit made a lot of splintering in the back. The twist bit did it so much better and the CNC bit did a perfect job. Let's do now the same test in a more delicate material. MDF with melamine in both sides.
With the brad point bit, the upper side is perfect, but there is a bit of splintering in the back. With the twist bit, as it doesn't have a center spur, the material is slightly domed. The back, is surprisingly well. Finally with the CNC bit, both front and back are perfect as you can see.
In my opinion, for a column drill or a 3D Router like mine, and using these materials, this bit is the best, buy they are not easy to find. In fact I couldn't even find them without the flat part they have for the connection, so If you're planning to use them with a drill chuck like mine, you must be careful of keeping this part between the legs as I am doing here.