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Drill bits for use on mini-lathe, micro-mill and mini-mill

Elsewhere on this website we have discussed drilling on the mini-lathe. But what about the drills themselves? There are broadly three types of drill that we use on the mini-lathe and the micro-mill.

The most common type of drill bit available today is the twist drill. Such drills work best when the cutting edge is very sharp. This normally happens when the drill is very new. After some abuse on the mini-lathe, a drill bit is apt to become a blunt. When this happens, you have two options. You can either sharpen the drill bit, or, if the given their relatively low cost, simply buy another one! Twist drills are used for most of the work we do to on the mini-lathe.

Center drills are also very important on the mini-lathe. A long twist drill is apt to bend and skate across the surface of the job we are trying to start the hole in. A center drill will allow us to start a hole in a job without these problems. A center drill takes the form of a very short stubby drill bit. It is a relatively inflexible. A center drill is only used to drill the first couple of mms into the part, after this we swap to a normal twist drill. Center drills can be purchased for virtually no money on Ebay, therefore you have no excuse. They are used such a small amount that three of them will probably last to a year or so and will save a great deal of frustration.

Indexable drill bits are also available for use on them in the late. However, I have neither owned or used one therefore cannot comment further.

Another class of drill bit which you may hear mentioned are blacksmiths drills. I do not know what a blacksmiths drill technically is, but all use the term to refer to drill bit where the shank of the drill bit is of reduced diameter. Most chucks on a mini-lathe will only hold drill bits with the shank diameter of ten or 13mm. If you want a bigger hole, find a blacksmiths drill which has a 13mm Shank of but perhaps a cutting diameter of eighteen to 25mm. Personally I have a straight shank 13mm drill bit which I use on the mini-lathe, followed by my 18mm blacksmiths drill. After this we are into boring territory.

Most of the drill bits we use on the mini-lathe are going to be made from HSS, high speed steel. These are very resistant to heat and cut a wide variety of materials. It is also possible to get colbolt steel alloy drill bits. Although these are more brittle than HSS, they have the advantage of better heat resistance. They are used for cutting harder metals such as stainless steel.

On some drill bits you’ll notice a funny gold coating. This is titanium nitride (TiN). As far as I can see this as three purposes. It is a little more hard wearing, the material is more self lubricating than HSS, and of course it looks pretty as well.

The best drill bit purchase you can make for your mini-lathe is the commonly sold 25 piece HSS drill bit set. This gives you all the drills between 1mm and 13mm in 0.5mm steps. Usually they come in a nice metal tin. Now, you are not going to use some of those half sizes is very often. On the other hand, some sizes you would use very often. Therefore I recommend purchasing several drill bits of the more commonly used sizes and keep them in the bottom of that tin. This way you can simply throw away a drill bit which has become blunt and replace it with one from the bottom of the tin. I mean, how often do I use my told 12.5mm drill bit? Well, usually it is when I can’t find the 13mm drill bit! On the other hand, a 2.5mm drill bit is used a great deal. This is because it is one of the size is used when drilling a hole which is going to be tapped. Therefore I recommend buying half a dozen 2.5mm drill bits and also half a dozen 4.2mm drill bits for when you want an M5 tapped hole. I have standardized most of my fixings and fastenings so that am using M3 or M5. I do have an M2 tap and the associated 1.6mm drill bits. I keep these together in a small plastic box and only use them when I really really want to.

It is possible to buy drill bits sets containing over 100 pieces. I really do not see the point of these. Some of the sizes you’re simply never going to use.