When hatchets and handsaws ruled the day, dealing with wood waste often meant backbreaking labor. It took armies of men to cut it up. Bonfires were the primary means of disposal.

Thankfully, times have changed. Today, wood grinders handle a wide variety of wood and organic waste, making wood recycling, forestry, tree care and cleanup operations much easier than ever before. And with dozens of purpose-built, excellent machines on the market, choosing the right grinder for you may be the toughest part of the job.

Before you race off and buy a grinder though, there are plenty of things to consider. Becky Smith, Communications Manager for Peterson Pacific Corp. in Eugene, Oregon points out, “Wood grinders are a significant investment for most customers, so it pays to be informed. Potential buyers should have a thorough understanding of their needs and know exactly what the machine will be used for. They should also collect and sort through information from various manufacturers before moving ahead with their purchase decision,” she said.

Wood grinders were developed to assist in land clearing and logging operations, reducing unsightly wood debris and other organic waste to manageable volumes. However, more recent refinements are enabling grinders to produce mulch, ground cover and other saleable products. In general terms, they can be divided into two distinct categories – tub grinders; and horizontal feed recyclers. We’ll look at tub grinders first.

Tub grinders originated in agriculture, producing livestock feed and related products for use on the farm. Over the years, their ability to reduce large volumes of bulky materials eventually drew interest from the recycling community. In the 1980s, tub grinders began showing up at landfills across the country.

On the jobsite, raw materials are usually gathered by crane and placed in a large, rotating hopper or tub, where gravity delivers them to the hammermill. Inside the hammermill, rows of heavy, rotating hammers equipped with replaceable cutting tips break the material down and force it through changeable grates or screens. An auger system then delivers finished material to a discharge conveyor that moves it safely away from the grinder.

According to Dan Brandon, Marketing Manager for Winn, Michigan based Morbark, Inc., manufacturers of a complete line of wood recycling, forestry and sawmill equipment, “Tub grinders are versatile units and well suited for the heavy stuff. Large stumps, tree roots and other items are easily consumed and reduced.” They also tend to be large, with impressive productivity to match. “Some models can weigh up to 50 tons and process more than 500 cubic yards of throughput per hour,” said Brandon.

Tub grinders are good choices where a wide variety of material is processed and when high productivity is important. Due to size and space requirements of the design, they can normally be found in more controlled environments such as mill yards and municipal landfills or transfer stations.

But wood grinders are becoming increasingly more visible along roadways, in subdivisions and in places where tub grinders just can’t access as well. “Those are horizontal feed recyclers,” said Becky Smith, of Peterson. Horizontal feed recyclers are similar to tub grinders in that both use hammermills. The difference is in the feed method. In place of a large, rotating tub, horizontal feed recyclers use an infeed conveyor to move raw material through an upturning rotor in the grinding chamber where fragmentation occurs. Next, the material is sized by grates or screens. Material that does not fall through the grate area is ground by the rotor until the right size of finished product is achieved. Finally, high value end products move along a discharge conveyor.

“It’s a positive feed system,” said Smith. “The primary advantage is increased safety with high productivity - equal to or exceeding tub grinders,” she added. Due to a smaller footprint, horizontal feed recyclers are often deployed where safety and limited working space are considerations.

Like with any capital equipment, good maintenance is essential to protect the investment and guarantee the most favorable outcomes. “The most important maintenance consideration involves hammer tips,” commented Dan Brandon, of Morbark. “The tips are usually tungsten carbide. They’re very hard and hold a sharp edge, provided the inbound material is kept clean. Hammer tips should be inspected on a regular schedule and replaced as often and quickly as needed. Otherwise, hammers and other parts will wear, and the quality of material produced will decline,” he said.

Other maintenance items include lubrication, filters and general mechanical systems. Radiators should be kept clean, belts and chains must be adjusted and all facets of the grinder should be inspected on a regular basis, following the manufacturer’s service recommendations.

But it doesn’t end there. After-sale support can play an important role in choosing the right wood grinder as well. “Depending on how the equipment is used, maintenance costs and the availability of parts may help determine which machine is the best choice for a buyer,” notes Michael Weible, Marketing Manager for Diamond Z Manufacturing, Inc. of Caldwell, Idaho. “If a grinder isn’t maintained well, replacement parts and downtime can become the most costly part of owning the machine,” he added. “It’s important to have a local dealer that knows the product and keeps a good supply of parts on hand if needed.”

Grinders have become an essential tool for wood recycling and the future looks bright. Recent trends include a movement toward larger, more powerful engines, better emissions controls for the environment and advancements in power transmission systems. And with more and more markets being developed for recycled wood products, these trends will likely continue.