Maintain A Cutter Bar On A Disc Mower

If you’re in the hay cutting business then knowing how to maintain a cutter bar on a disc mower is a critical skill. For our purposes, we’ll be working on a DM5070 Disc Mower (US CA), the largest in Frontier’s line of disc mowers. It has 7 knife mounting discs. Inside each one we’ll find the knife blades and the entire spindle unit assembly.

Changing blades.

We’ll start with how to change blades. Blades can be flipped over for extended wear life or entirely replaced. Either way, the process is the same.

First, using a socket wrench, loosen and remove the nut and bolt that attach the blade to the knife mounting disc. Simply flip or replace the blade, depending on its condition. If you’re replacing a blade, make sure to match the lift angle of the new blade with that of the old blade, and make sure they’re properly oriented as Right Hand Knife or Left Hand Knife (See your Operator’s Manual). Then replace the washer, bolt, and nut, and tighten with the socket wrench.

More serious trouble.

There are also other reasons you might need to maintain a cutter bar. For example, if the cutter bar has hit an obstacle during cutting, the spindle unit can become damaged, or shear, and need to be replaced.

First, place a block of wood between any two discs to lock all discs on the cutter bar in place.

Remove the cap on top of the knife mounting disc. Then remove the large nut and washer holding the disc in place. Using a pry bar, remove the splined mounting disc and you’ll see the spindle unit.

Remove the 6 bolts holding the spindle unit and remove it. You may need to use a pry bar.

Clean the area around the surface of the cutter bar, making sure debris doesn’t fall into the bar.

Make sure the O-ring on the bottom of the new spindle is properly aligned with the groove in the casting. Insert the new spindle, and secure it with the 6 bolts.

Next, re-install the splined mounting disc. This step resets the timing of the unit. So you’ll need to make sure the timing is correct before operation.

Replace the large washer and retaining nut on the spindle shaft and tighten. Make sure the washer cup points toward the bottom.

Replace the knife mounting disc with blades and top cap. Make sure the knife mounting disc is oriented properly for your DM50 model as shown in the operating manual, and insert the 6 bolts. At this point you may have to adjust the position of the splined mounting disc to set the timing properly. Incorrect timing will damage the disc unit upon start-up.

When you’re sure the cutter bar timing is set correctly, tighten the 6 bolts in the top cap, and get back to cutting hay.

Proper maintenance equals better performance.

How well you maintain a cutter bar on your disc mower will make a big difference in its performance in the field.

Frontier has more than 400 implements that are available only from your John Deere dealer, the place to go for advice and equipment.

So remember, for implements that help turn your tractor into the workhorse it was built to be, think Frontier and your John Deere dealer.

And lastly, always read the Operator’s Manual before operating any piece of equipment and follow all operating and safety instructions.


Helpful Links:

Frontier Hay & Forage Equipment (US CA)

Frontier Disc Mowers (US CA)

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Frontier DM50 Series Disc Mowers

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