Servo - May 2008

chemicals such as TapMagic will work better in most cases. Most plastics cut perfectly fine dry, just be sure not to cut at too high a speed as to melt the plastic (caused by overheating). If you are having a problem with the plastic melting, water makes a good coolant. However, mixing water and metal tools usually leads to rust, so be cautious.

When you are preparing to cut your material, there are a number of things you can do to help make accurate cuts. If you are cutting metal, spray it down with layout fluid, which is a bluish paint-like coating that allows scribe marks to be very visible. It also comes off easily with the correct chemical remover. Then you can use a machinist square and scribe to draw the line. After scribing the line, mark a large “X” on the excess material. Now when you go to cut the material, place the cutting blade such that the blade width is on the side with the X; this will keep your material from being a blade widths’ shorter than planned. It will also serve to remind you which part is the excess and which is the actual piece.

Cutting sheet stock is best done with a jig saw or a vertical band saw. Both allow you to make long straight cuts in addition to complicated curves. Just be sure you are using the appropriate blade type and tooth count for what you are cutting. These tools can be used to cut most metal, plastic, and wood.

Bar stock can be cut using a variety of tools but a horizontal band saw is usually the easiest. You can also use a vertical band saw, jig saw, sawzall, and chop saw. Just be aware that an abrasive disk on a chop saw should not be used for anything but ferrous metals (iron/steel). Also, these disks can fragment and explode, so always stand outside the path of the disk and wear full face protection.

Carbon fiber, Kevlar, fiberglass, and other composites require great care when cutting. The dust created when cutting them is very harmful and should not be inhaled. If you decide to work with these materials, be sure to use a proper mask to filter the air you breathe, do it in a properly ventilated area, and wet it to minimize the dust.

center of the X by deforming the material under impact. There are two types of center punches. You can use a spring-loaded, automatic center punch which you simply have to line up and push down until it pops, or a manual center punch which you line up and then hit the top with a hammer. Both work equally well but the automatic center punch can be more convenient.

2b) If you require high accuracy, a small center drill is the best way to start — and countersink — the hole you wish to drill. Center drills are unique in that they are very rigid with very little flex so they do not wander.

3) If you are drilling a large number of holes that need to be the same depth, an easy method is to put a “shaft collar” on your drill bit. Usually, this is a round collar that you set at the correct distance up the bit and lock into place via a set screw. If you don’t have one of these, then a thin strip of duct tape wrapped around the bit at the correct height will work also. This will give you a clearly defined stopping depth when drilling your holes.

4) Now you are ready to drill the actual hole. If you are drilling a hole with a diameter of 1/4” or less, you can simply use that size drill bit. For larger sizes, I recommend you start with a 1/4” drill and then work your way up in 1/4” increments to the size hole you need. When you drill these holes, be sure that the drill bit is perpendicular to the material. This can be done easily with a drill press as seen in Figure 2.

If you are using a handheld drill, then there are a few tricks. The first is to use two levels or machinist squares to keep the drill upright. Use one for keeping it upright front to back, and the other for left to right. An assistant is a big help while doing this because while you are controlling the drill, they can be continuously checking the orientation of it. If you have many holes to drill, then this method can be very time-consuming, in which case you can make a guide. A piece of metal with the right size hole

Drilling

Drilling a hole can be very straightforward and easy. However, doing it accurately and correctly is a different matter. A hole generally needs to be perpendicular to the surface of the material, placed correctly, and made deep enough. The following is a procedure I use when drilling a hole.