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Changing Hammers in a Pin and Plate Style Hammermill

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Horizontal Grinder Hammermill

In this post we will describe how to change the hammers in your pin & plate style hammermill for your tub grinder or horizontal grinder. We will also provide time and money saving tips to help you get the job done quickly and efficiently as possible. 

Please note that these instructions have been adapted from instructions originally written for WHO and FHE grinders, but that the instructions will assist you with changing hammers in nearly all pin and plate hammermills.

Tips and advice provided in this post is intended to be a general guide although settle differences may exit such as the number of hammers or rods in your hammermill, or the method of pulling the rods from the hammermill. Please review these instructions completely before you begin changing your hammers.


Lubricant – WD-40, Diesel Oil, or other similar lubricating oil

2′ Pipe Wrench with Extended Handle

Electric Hand-Held Electric Grinder With 4” wheel

Extra Hammermill Shaft (or similar rod)



Vise Grip Pliers with Curved Jaws


Block of Wood


Using your lubricant (diesel oil, WD-40, or similar lubricating oil) lubricate the hammer retaining rods where they pass through the rotor plates. (note) Do not spare the oil here. Using an 18″ to 24″ long pipe wrench, rotate all of the hammer retaining rods three or four full turns until they are turning freely in the mill. (note) Rotate all the rods before trying to remove any of them.

The first step to change the hammers is to remove the hammer rods. Once they are fully lubricated and spinning freely, locate the hole at the end of the hammermill through which the hammermill rods will be removed. In most cases there is a cover over the hole which must be removed first.

Tub Grinder HammermillThe end plate on the hammermill is referred to as a slide plate, it rotates to align or misalign its holes with the hammermill rods. When misaligned, it acts as a retainer for the hammer rods. It is generally secured by a couple bolts. Look through the hole while having someone turn the hammermill until you can see the head of these bolts, loosen this bolt, then turn the hammermill to the remaining bolts and loosen them as well. When these bolts are loose the end plate of the hammermill may be rotated two to three inches allowing the holes in the plate to line up with the respective hammer rods. (note) The slide plate can sometimes be very difficult to rotate due to debris accumulating under and around it, so before trying to rotate it make sure that it has been lubricated very well.

Next, insert a rod such as an extra hammermill shaft into one of the holes in the slide plate, and while one person holds the rod and the slide plate from turning, another person using a spare rod or long pry bar can rotate the hammermill from inside the tub, forcing the slide plate to rotate. Once the slide plate begins turning it should be fairly easy to align the holes.

Install an eye bolt into the threaded end of the hammermill rod (spray wash the threads out first), then attach a come-a-long to the eye bolt and to the ring or hole in the machine frame just ahead of the main drive belts. The rod should then be pulled out carefully, rotating it occasionally if it should become stuck. Some tub grinders have a hydraulic cylinder installed to assist with the removal of hammer rods. (A handy tool for rotating the rod when removing it, and also when installing it, is a pair of vise grip pliers with curved jaws.) If a rod is extremely hard to remove even after lubricating and rotating it, it may have a slight bend or ridge in it caused by hammer wear. In this case it is usually more economical to replace the rod with a new one rather than reuse it.

(tip) If the hammer rod cannot be removed fairly easily with the come-a-long, then use a small hand grinder to remove any ridges on the shaft. Continue trying to remove the shaft and grinding ridges until the shaft comes out.

Before reinstalling the rods in the hammermill they should be cleaned well, and the holes in the rotor plates where the rods go should be completely clean. Also be sure to clean out the rear hammermill rotor plate where the rods seat. If the rods do not seat against the rear end plate they will interfere with the slide plate at the front end, making it difficult to rotate to the operating. If a rod is hard to get in and it is necessary to hammer on it, use a block of wood over the end of the rod to keep from flattening the end and ruining the threads.

The hammer pattern will vary by brand and application. Changing the pattern of hammers will affect production rates as well as how your hammers and tips will wear while grinding. The goal is to maximize production while wearing your hammers and tips as evenly as possible. Wearing out one side of the hammermill first will cause your hammermill to become unbalanced which can cause further damage to your hammermill and machine. Also, wearing your hammers and tips more evenly will reduce costly downtime to replace just a few of the hammers or tips. Regardless of the pattern you choose, hammers should always be installed opposite of each other in the hammermill to maintain mill balance.

Tub Grinder Hammermill Swing Hammers

Swing Hammers:

The following directions for installing swing hammers are based on a eight rod hammermill with fifteen plates.

On the fourth rod there is a change: on this rod you will put a bushing in the first slot, skip two slots, and put a hammer in the fourth slot. Then put a bushing in the fifth slot, skip two slots and so on. The reason for this change is that the hammer pattern repeats itself every four rods and four hammers. To install hammers and bushing on the fifth through eighth rods repeat the directions for the first through fourth rods.

Fixed Hammers:

The following directions for installing fixed hammers are based on an eight rod hammermill with fifteen plates.

To install fixed hammers first remove all hammers and rods currently in the hammermill. Begin installing hammers by putting a hammer in the first space, put the hammer on the rod with the rod through the hole nearest the cutting tip, then skip 3 spaces and put in the second hammer. Continue this spacing to the end of this rod.(note) While installing fixed hammers rotate the hammermill clockwise looking back from the engine.

Tub Grinder Hammermill FixedWhen installing the 2nd rod install the first hammer from the 1st rod first, then in the second space install a new hammer. Then skip 2 spaces, install the second hammer from the 1st rod, then in the next space install a new hammer.

Continue this procedure until all hammers are installed. When all the hammers are installed, rotate the slide plate at the end of the hammermill to the operating position, where the rod ends are covered by the plate, and tighten the bolts to secure the plate.

Re-install the hole cover where the hammer rods come through the front bulkhead.

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