Servo - December 2015

20 SERVO 12.2015

Types of Screws

Wood Screws

Wood screws — as the name implies — are primarily meant for use with wood, which itself is rarely the right material to use in your combat bot. While there may be only a few applications for wood in fighting robots, there are several applications for wood screws.

When fastening materials like UHMW-PE and HDPE, wood screws are a strong option as these materials (in at least a few critical ways) behave similarly to wood. The large coarse threads on the wood screws dig into the plastic, and are far less prone to stripping the threads that get cut into the plastic than most other types of screws.

Machine Screws

Machine screws are the all-around fastener option. You can get these in a wide range of material, head, and drive types. For any given thread size, these won’t be the strongest option, but they are typically very budget friendly and can be found almost anywhere in some form.

Hex Head Cap Screws

Hex head cap screws are the first step into the realm of industrial fasteners. At this point, you’ll often start seeing fasteners listed as a specific “Grade” or “Class” when you’re looking at your options for steel versions of screws.

In general, the higher this number, the stronger the fastener will be. For pure strength, these are hard to beat. However, you’re extremely limited on head styles, so there will be many situations where they’re not a practical option for your build.

Socket Cap Screws

Socket cap screws are another industrial grade option. Unlike regular cap screws, there is less choice when it comes to materials.

However, the materials used for these types of screws are generally much stronger than their machine screw equivalent.

The other perk of the socket cap screw over the hex head cap screw is that you’ve got several head style options to choose from, which makes them a much more versatile fastener.

Socket cap screws will more often than not be the right screw for the job.

Plastite Screws

Plastite screws are a specialized type of screw designed to hold well in plastic. The shape of the shank is triangular to resist vibration.

Like wood screws, Plastite screws have coarse threads that will create durable threads in plastics.

Head Styles

Flat

Flat heads are meant for applications where you need the surface of the part being bolted down to be flat. To use these fasteners correctly, you need to countersink the piece of material they’re holding down.

The countersinking requirement results in a minimum material thickness in most cases as the total head height needs to be contained within the height of the piece of material that it is holding in place.

You could countersink into the material that the screw threads into, however, this will greatly reduce the amount of material being held by the screw and increases the chances of mechanical failure.

Hex

Hex heads are the highest torque option since they can typically handle much higher loads before you’ll risk stripping the tool-to-bolt interface. The large exposed head does pose some risk in combat as they make for fantastic targets.

However, so long as you keep that in mind when planning their locations and you’ve got some spares handy should any heads be damaged in a fight, they’re a very good option.

These will typically be the heaviest screw for a given size and length due to the bulk of the head. So, if you’re expecting to be tight on weight, that may be a