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What's a contractor to do when he has wood waste to grind? Well, he really has only two choices -- a horizontal grinder or a tub grinder -- but there are numerous things he must consider before deciding on a machine.

Similar Yet Different

What’s a contractor to do when he has wood waste to grind? Well, he really has only two choices — a horizontal grinder or a tub grinder — but there are numerous things he must consider before deciding on a machine.

 Manufacturers have differing opinions on whether contractors should only consider one type of grinder or if both have a place in the wood waste market. Some say that tub grinders were the old way of doing things, and horizontal grinders are the new and better way. Other manufacturers see the advantages of both machines, depending on the type of material contractors are looking to grind and jobsites where they plan to operate the machine.


Basic differences

There are significant differences between a horizontal grinder and a tub grinder, said Cory Gross, large equipment regional sales manager for Bandit Industries, Inc. For starters, a horizontal grinder utilizes a positive feed system — contractors place material into the grinding chamber. However, a tub grinder relies on gravity to work the material down to the grinding head, which is much slower than the positive feed of a horizontal grinder. Also, the mill in a horizontal grinder turns at a lower RPM, which is accomplished because of the aggressive positive feed and the larger mill diameter. The balance of the mill is much less critical with a horizontal grinder, due to the slower speed of the mill. Gross says a tub grinder needs to be perfectly balanced because the mill is turning so fast.

Horizontal grinders also have a lower loading height. Due to the design of a tub, the loader height is much higher, often requiring some type of ramp to reach high enough to dump wood material into the tub, which is especially true when using a front-end loader. “Many tub grinders have a cab and loader, making the grinding process a two-man job,” said Gross. “A horizontal grinder can be fed with the machine forwarding the material, making it a one-man job.”



What will you grind? Where will you grind?

Another significant difference is the material that can be processed in a horizontal grinder versus a tub grinder. “Horizontal grinders can process material regardless of length, whereas a tub grinder needs tree-length material to be cut down in length in order to fit inside the tub,” said Gross. That said, horizontal grinders work best for grinding long tree limbs and brush, and tub grinders generally work best with grinding tree stumps, large logs and root balls.

The type of material and the job sites that they’ll be working on are the two main factors contractors should consider when deciding between a horizontal and tub grinder. “If any contractor takes a look at these two factors before they buy a machine, they can and will get the best machine for their site and their job,” said Todd Roorda, environmental segment solutions specialist for Vermeer Corp.

Once contractors have identified the material that they will typically grind and the application for which the machine will be used, they must then consider where they’ll most likely be operating the machine. Will it be on an open land-clearing site, or will it be in an urban area with houses and other buildings nearby?

“In a rural area where you don’t have neighbors, you don’t have roads and you don’t have buildings around, you could probably get by with a tub grinder simply because the machine’s thrown object area is much larger than with a horizontal grinder,” said Roorda. “As you start getting into more confined areas where you may have a road that goes by that’s heavily traveled, you might want to stick with a horizontal grinder because its thrown object area is smaller.”


Weighing the pros and cons

Even in the right job application and when grinding the proper material, each machine has its advantages. That’s why contractors should come up with their own list of benefits they would like their machine to provide. Often, that list includes such items as productivity and cost

 of operation.

In addition to being safer to work around, horizontal grinders tend to be more productive for the same amount of horsepower in terms of tons per hour, said Vince Hundt, vice president of sales for Rotochopper, Inc.

In regard to cost of operation, manufacturers differ once again, with some giving the nod to horizontal grinders as being less expensive to operate. But Chris Edmonds, assistant regional manager for Morbark, Inc., contends tub grinders have the edge in this category because horizontal grinders have more maintenance parts. “Dollar for dollar, production for production, a tub grinder is a little less costly to purchase and maintain when comparing machines with similar horsepower,” he said.

Another tip for contractors is that they should dissect both grinders all of the way down to their cutter drums to get a clear idea as to the maintenance items of each and the time that will be required to keep the machine running. “Because, obviously, if the machine is down, downtime doesn’t pay,” said Roorda. “So the quicker you can get it up and running and maintain your cutter drum, the better off you’re going to be in the long run.”

When you spend hundreds of thousands of dollars on a machine, you want to make sure that you’re not only getting the right machine for the task at hand, but that you’re buying from a manufacturer with a good reputation.

“Shop around, but don’t shop for price, shop for value,” said Edmonds. “Some of the value is just not in the capital cost, it’s also in the company’s reputation for standing behind the equipment. Because the one thing that kills a contractor out there — especially somebody that’s getting started or expanding their business — is having a machine down and not having the support or company that can get them back up and running quickly.”

So although there may be only two kinds of machines when it comes to grinding wood waste, there are several variables contractors should consider before making a purchasing decision. In the end, both machines create a similar end product, but contractors must not lose sight of all the different moving parts it takes to get there.


Tara Deering-Hansen is a freelance writer, TDH Writing, West Des Moines, Iowa.

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