Underwater Chain Saw
A chainsaw (or chain saw) is a portable, mechanical saw which cuts with a set of teeth attached to a rotating chain that runs along a guide bar. It is used in activities such as tree felling, limbing, bucking, pruning, cutting firebreaks in wildland fire suppression, and harvesting of firewood. Chainsaws with specially designed bar and chain combinations have been developed as tools for use in chainsaw art and chainsaw mills. Specialist chainsaws are used for cutting concrete. Chainsaws are sometimes used for cutting ice, for example for ice sculpture and in Finland for winter swimming. Someone who uses a saw is a sawyer.
The chain saw, or “cutting chain”, is a key component of a chainsaw. It consists of steel links held together by rivets, and superficially resembles the bicycle-style roller chain, although it is closer in design to a leaf chain. Its key differences are sharp cutting teeth on the outside of the chain loop, and flat drive links on the inside, to retain the chain on the saw’s bar and allow propulsion by the engine or motor.
Saw chains (and chainsaws generally) are used for cutting wood. This may be for harvesting trees for pulp or timber, for tree surgery, or for processing firewood.
Whether for hand-held chainsaws, mechanical timber harvesters or chain mortisers, the saw chain has undergone dramatic development since its invention. Modern chains designed for high power, high-speed sawing applications will vastly outperform older designs, while allowing a far greater degree of safety and reliability in use.
The origin is debated, but a chainsaw-like tool was made around 1830 by the German orthopaedist Bernhard Heine. This instrument, the osteotome, had links of a chain carrying small cutting teeth with the edges set at an angle; the chain was moved around a guiding blade by turning the handle of a sprocket wheel. As the name implies, this was used to cut bone. The prototype of the chain saw familiar today in the timber industry was pioneered in the late 18th century by two Scottish doctors, John Aitken and James Jeffray, for symphysiotomy and excision of diseased bone respectively.
The chain hand saw, a fine serrated link chain which cut on the concave side, was invented around 1783-1785. It was illustrated in Aitken’s Principles of Midwifery or Puerperal Medicine (1785) and used by him in his dissecting room. Jeffray claimed to have conceived the idea of the chain saw independently about that time but it was 1790 before he was able to have it produced.
In 1806, Jeffray published Cases of the Excision of Carious Joints by H. Park and P. F. Moreau with Observations by James Jeffray M.D.. In this communication he translated Moreau’s paper of 1803. Park and Moreau described successful excision of diseased joints, particularly the knee and elbow. Jeffray explained that the chain saw would allow a smaller wound and protect the adjacent neurovascular bundle. While a heroic concept, symphysiotomy had too many complications for most obstetricians but Jeffray’s ideas became accepted, especially after the development of anaesthetics. Mechanised versions of the chain saw were developed but in the later 19th Century, it was superseded in surgery by the Gigli twisted wire saw. For much of the 19th century, however, the chain saw was a useful surgical instrument.
The first portable chainsaw was developed and patented in 1918 by Canadian millwright James Shand. After he allowed his rights to lapse in 1930 his invention was further developed by what became the German company Festo in 1933. The company now operates as Festool producing portable power tools. Other important contributors to the modern chainsaw are Joseph Buford Cox and Andreas Stihl; the latter patented and developed an electrical chainsaw for use on bucking sites in 1926 and a gasoline-powered chainsaw in 1929, and founded a company to mass-produce them. In 1927, Emil Lerp, the founder of Dolmar, developed the world’s first gasoline-powered chainsaw and mass-produced them.
World War II interrupted the supply of German chain saws to North America, so new manufacturers sprang up including Industrial Engineering Ltd (IEL) in 1947, the forerunner of Pioneer Saws. Ltd and part of Outboard Marine Corporation, the oldest manufacturer of chainsaws in North America.
McCulloch in North America started to produce chainsaws in 1948. The early models were heavy, two-person devices with long bars. Often chainsaws were so heavy that they had wheels like dragsaws. Other outfits used driven lines from a wheeled power unit to drive the cutting bar.
After World War II, improvements in aluminum and engine design lightened chainsaws to the point where one person could carry them. In some areas the skidder (chainsaw) crews have been replaced by the feller buncher and harvester.
Chainsaws have almost entirely replaced simple man-powered saws in forestry. They come in many sizes, from small electric saws intended for home and garden use, to large “lumberjack” saws. Members of military engineer units are trained to use chainsaws as are firefighters to fight forest fires and to ventilate structure fires.
Principles of chain saw operation
Saw chains operate by being propelled around a guide bar, removing material from the kerf by cutting chips from the side and bottom. In order to operate properly, the depth to which each tooth cuts must be limited to avoid it binding in the wood. Scratcher chain, like the teeth on a hand saw, simply uses a multitude of teeth to prevent individual teeth from sinking too far in without undue pressure on the bar. Chipper chain, and all subsequent designs, incorporate a depth gauge (also known as a “raker”) on each cutter link to limit depth of cut on each tooth.
This has two distinct advantages over scratcher chain – it enables the use of fewer cutters per unit length of chain, which allows for shorter downtime for sharpening, and produces a more “open” chain layout, allowing far better clearance of chips and debris from the kerf. Individual depth gauges on each tooth also enable the use of skip chain. Skip or semi-skip chain has a further reduction in the number of teeth and is used for applications where much debris is produced, such as ripping or cross-cutting very large sections of wood. Skip chain also absorbs less power from the motor per unit length of chain than full-complement chain, allowing the use of a longer bar/chain combination on any given motor.
Early chain saw designs
Very early chainsaws used tooth configurations very similar to conventional hand saws. These were very simple saw teeth following a wave pattern (left, centre, right, centre) with no depth gauges as such, relying purely on bar pressure to limit the cutting rate. They were inefficient and slow in use, and were soon superseded by chipper chain. They required great skill and a lot of time to sharpen in the field leading to extended downtime between sessions.
Chipper chain invented by Joseph Cox improved dramatically on the performance of scratcher chain. Chipper used a tooth that was curled over the top of the chain, with alternate teeth pointing left and right. Ahead of the tooth was a depth gauge, which allowed for good clearance around the tooth for chip clearing while limiting the depth of cut and preventing grabbing or overloading. Chipper chains are sometimes used for dirty work, since their very large working corner allows the cutter to retain its effective sharpness for a long time in abrasive conditions.
Modern tooth designs of Chain saw.
Modern Cutting Teeth
Modern chains saw for general use in forestry, tree surgery and firewood cutting come in three basic configurations: the full chisel, the semi-chisel, and the chipper chain.
The full chisel chain has square-cornered teeth, splitting wood fibers easily in the cut for fast, efficient cutting in clean softwood.
The semi-chisel chain has teeth with rounded corners formed by a radius between the top and side plates. While slower than full chisel in softwood, it retains an acceptable cutting sharpness longer, making it the preferred choice for dirtier wood, hard or dry wood, frozen wood or stump work, all of which would rapidly degrade full chisel chain. Variation of the semi-chain is “Chamfer chisel” chains by made by Oregon. They are similar to semi-chisel design but have a small 45 degree chamfer between the plates rather than a radius. Performance is similar to good semi-chisel.
The chipper chain is similar to the semi-chisel chain as in standard chain saw. The key differences between are the size of the radius at the working corner. In cross-section a chipper tooth looks like a question mark, having a full radius over the whole cutting portion of the tooth, whereas a semi chisel design is more like a number “7” with the top-right corner slightly rounded.
Chain saw arrangements
There are also different arrangements of teeth on the chain saw.
“Full Complement” chain has a left cutter, drive link, right cutter, drive link arrangement and is used for most applications.
“Skip” has a left cutter, drive link, drive link, right cutter arrangement. It has 1/3 fewer cutting teeth and is generally used on long bars (24″+) for added chip clearance or when a bar longer than ideal for a given power head is used. Fewer teeth require less power to operate.
“Semi-Skip” alternates having one or two drive links between pairs of cutters, for performance in between that of full complement and skip arrangements.
The terms used to describe chain arrangements can be confusing. Most modern chains do not have only cutter teeth and drive links. There are tie straps which separate the cutters from each other.
Chain saw specifications and dimensioning
Cutting chain saw comes in a large number of configurations, but these are reduced to a few key dimensions for replacement or specification purposes.
Gauge. The gauge of the chain saw is the thickness of the drive links, and is dictated by the gauge of the bar on which it is to be run. Usual gauges are .050″ (1.3 mm) – .058″ (1.5 mm) and .063″ (1.6 mm). Chain saw and bar gauge must match; a chain that is too large will not fit, one that is too small will fall sideways and cut poorly.
Pitch. The pitch of the chain saw is the average distance between two rivets. As the distance between rivets varies, the pitch can be measured by measuring between three rivets and dividing this distance by two. Usual pitches are 0.325″, 3/8″ and 0.404″. 3/4″ is used for harvester applications, and very rarely for handheld cutting. the pitch of the chain must match the drive sprocket, and the nose sprocket (if fitted).
Length. A chain loop must be of an appropriate length in order to run safely. This is described by the number of drive links. This number is determined by the length and type of bar, the sprocket size and the overall configuration of the saw. For replacement purposes, simply count the drive links on the old chain.
Specialised chains saw
A number of very specialised chain saw types have emerged over recent years. These include chains made of steel alloys optimised for cutting in extremely cold conditions, chains with tungsten carbide teeth for very dirty conditions and rescue work, ripping chains with altered blade geometry for making ripping cuts, milling chains for chainsaw mills, and underwater chain saw.
Chain mortisers, used to cut the mortice of large mortice and tenon timber framing use a number of chains, riveted side-by-side. They are used with a vertical tip-first plunge. Owing to the difficulty of resharpening the multiple teeth, these are usually made of long-lasting tungsten carbide.
Joining chain saw
Chains saw are usually bought ready-joined to length, to suit a particular bar. All chainsaws have adjustable bar mounts to allow their chain tightness to be adjusted, allowing for any wear in the chain linkages. There is no requirement to remove links to shorten worn chains, chains will wear out on their cutting teeth before wear in their pivots becomes a problem. The adjustment also permits enough slack to allow a chain to be installed, so there is no need for a “split link” when fitting, as for bicycles.
Large scale operators and retail shops may buy bulk chain on reels. This must then be cut and joined to length which is done by inserting rivet pins. These non-reusable pins are usually supplied already installed into a half-link and must be peened over against a half-link on the other side. As this peening is done with a bench-mounted rotary tool, rather than hammering, it is referred to as “rivet spinning”. The tool is usually hand-cranked, or may be electrically powered for mass production.
Special underwater type of Chain Saw
Underwater Tools are designed for a full range of subsea and marine applications including underwater construction, salvage and demolition. Whether for commercial companies, military or governmental organizations underwater tools are found everywhere from oil platforms and dam construction sites to mining explorations and archaeological expeditions.
How is it to operate a chain saw underwater?
Ever sliced through a tree with a chainsaw?
Try again, but this time…underwater. With limited visibility.
Randy Busby is the Divers Institute of Technology (DIT) instructor for hydraulic tools, salvage theory and practical. He defines underwater chainsaws as “pretty unusual.”
“Using a power tool underwater is not something people see or do every day; it’s not something a lot of people know even exists.”
At DIT, training with the underwater chainsaws is an experience classes enjoy immensely. They apply their cutting skills on a tree trunk: the student who slices it thinnest is deemed the winner. It’s not an easy task, but it’s one of the many in their hydraulics and salvaging training module.
Of course, a chainsaw doesn’t always cut it.
Commercial divers use a variety of hydraulic equipment and power tools on the job. Underwater construction that requires demolition or cleaning may require these types of tools. Specially if the job requires more than just brute strength.
How it Works: Power Tools’ Function & Application
“In my experience, underwater power tools are more used offshore, used to do everything from bolting up flanges, to drilling holes to plant explosives and scrubbing the hull of a boat. They are used more often offshore, but are also used for the same types of things in inland work on a smaller scale,” Randy says.
Here’s a few examples of jobs requiring underwater power tools:
- River dam demolition.
- Vessel hull and propellor polishing.
- Cutting through coral blockage.
- Driving in bolts/rods.
- Creating holes in dock pillars.
- Flange pipes.
Since divers use this equipment underwater, the equipment must have a tough exterior that can hold up under pressure and floating material. These tools are powered through hydraulics (fluids in pistons) and pneumatic (air pressure) application. Not electricity like underwater welding stingers.
These tools require large amounts of energy for small periods of time, and hydraulics and pneumatic power are perfect for applying this force in the wet.
Operation underwater versus topside is a bit different, as Randy explains.
“The main differences are the weight and leverage. Topside leverage is a lot easier than underwater leverage. If the tool gets away from you and starts to spin, it’s going to take you with it.”
Surface Team Responsibilities
In DIT’s course, students train with the underwater chainsaw, jackhammer, hammer drills, impact hammers, impact wrenches and hull scrubbers. And they don’t just train underwater. Surface operation is just as important to the proper application of hydraulic tools.
Randy “Buzz” Busby with his class during salvage
Randy points out that the responsibilities of surface teams are primarily focused on equipment maintenance, preparation and delivery:
Meet Hydraulic Tools
- Underwater Chainsaw: Precision is of the utmost importance in underwater use. Underwater chainsaws run off hydraulic power and cut through wood, plant growth or other entanglements.
- Jackhammer: Underwater, divers use jackhammers in a variety of different positions, but always grip the handles securely, focusing pressure toward the end of the bit. Several different weights exist, ranging from light to heavy.
- Hammer Drill: Used for much harder material like rock or cement, commercial divers often utilize hammer drills to clear out holes for bolts and other support systems. They use special carbide tips to get the job done.
- Hull Scrubber: Wax on, wax off. Divers polish and clean away rust, coral and growth on submerged metal. They don’t have the power of most of their high impact cousins, but are just as effective.
- Impact Hammer: Like the hammer drill, impact hammers chip away cement and masonry. They make use of various sizes and shapes of bits to cut, chip or break away debris.
- Impact Wrench: Impact wrenches use a powerful swing-hammer movement to tighten or loosen bolts. They come with two handles, one for the back and a bottom handle on the business end.
Ins & Outs of DIT Hydraulics’ Module
Students train with these power tools in month five of their seven month training. The hydraulics portion lasts for two weeks.
Students learn all aspects of power tools’ application, maintenance and safety.
They also study the how diesel engines to supply power to diving equipment. Sending power to hydraulic tools works similar to underwater wet welding, in which power is controlled through a knife switch.
“The tools are not always “hot” (on) when they are sent to the diver, the diver will call topside to give power to the tool. There is not a knife switch, but there is something called a squash plate (topside) which is similar, it gives power from the hydraulic power unit to the tool underwater.”
Importance of Safety
Like all aspects of commercial diving, safety is the number one priority in operating underwater power tools like a chain saw. Randy emphasizes several actions when he covers this portion of the course:
“Make sure all safety guards are in place while you are hooking up equipment. Watch your hand placement; make sure your gear is not floating up into the tool; make sure you are standing clear when the tool comes down, so it doesn’t hit you.”