The following procedure discusses balancing used cutters that will be installed on heads having either an even number of bolts where opposing cutter stacks are identical or on heads having an odd number of bolts or a staggered set up.
This procedure is identical to balancing new cutters. Balancing used cutters can be more challenging as they have been previously ground.
Before you begin balancing:
- All cutters, spacers, and washers should be cleaned, de-burred and dried at this point.
- Arrange cutter stacks as they will be installed on the head. Be sure to include donut spacers or washers when weighing each cutter stack. Dogbone, mastlock or pie spacers need not be included in the weighing process. Nuts are factory balanced in pairs and do not need to be included in the weighing process.
- It is helpful to label balanced pairs and keep knife stacks together during the disassembly and cleaning process. This procedure will speed up the balancing process as the stacks should still be relatively matched.
Determining correct washer thickness:
- Before weighing, balancing, assembly and grinding can commence however, the correct washer thickness must be established. The end goal- after the heads are assembled and the bolts are torqued- is to have the nut be flush or very close to flush with the end of the bolt. The correct washer thickness needs to be established as a preliminary step before beginning the balancing process. Having the nut rest at or near the end of the bolt offers protection during the jointing operation and prevents damaged bolt threads from complicating the head dis-assembly process. The correct washer thickness also keeps debris from collecting on the exposed threads of the bolt.
Step 1: Install one complete stack of cutters on a bolt, including spacers if required. The stack height needs to be identical to what will be installed in the working head.
Step 2: Install the top plate and thread a nut onto the bolt until the top of the nut is flush with the end of the bolt.
Step 3: Measure the distance from the bottom of the nut to the top plate. That measurement determines the thickness of the desired washer. After determining the correct washer thickness, back the nut off the bolt and install the washer or washer combination on the bolt and reinstall the nut until finger tight. The end of the nut should be flush or close to flush. Caution- the top plate should never protrude above the end of the mast of the head body.
AceCo’s hardened washers are available in 1/8”, 1/4”, 3/8”, 1/2” and 3/4″ increments. Any combination of washer thicknesses may be used.
Consideration: If the stack height of the cutters exceeds 3.00” (76mm), it is highly recommended that a locking device (pie spacer, mastlock spacer or dogbone spacer) be installed between the cutters at 2.00” (51mm) intervals to prevent cutter movement. Some applications may require use of custom cutters on either side of the spacer.
Balancing even number of cutter stacks:
- Weigh each cutter/washer stack and record the weight.
- If the weight of each cutter stack exceeds the scale capacity, stacks must be weighed and balanced in groups and the totals added together.
- Compare stack weights and pair any stacks that have weights within +/- .1 gram.
- Of the remaining cutter stacks: select the two stacks that are closest in weight. This is now considered a “pair”
- Place the lighter stack of the pair on the scale and set the scale to zero.
- Remove the lighter stack and replace with the heavier stack of the pair. The number displayed on the scale is the weight difference between the two stacks.
- Remove a cutter from the heavier stack and replace with a cutter from the lighter stack.
- Repeat this procedure until the weight difference has been reduced by exactly half.
- Both cutter stacks should now be within .1 gram of each other. Reset scale to zero and verify weight of each stack.
- Repeat this procedure on the remaining pairs.
- The desired result, with this method, is balancing all cutter stack pairs within .1 gram.
- If grinding is necessary to achieve balance between a pair of stacks, grind the lower back of one of the cutters from the heavier stack. If the stack consists of a combination of thin and thick cutters, grind material from the thick cutter of the heavier stack to gain balance. This will prevent having to grind material from several thin cutters to achieve balance. Never grind the index surface of the cutter.
Balancing odd numbers of cutter stacks / Staggered set up: Follow the same steps as listed above for a standard set up. Instead of cross balancing the stacks, all stacks must be of matching weight (+/- .1gram).
Getting all stacks to match by switching cutters between stacks will be nearly impossible, so removal of weight via grinding from the heavy stacks will be necessary. To reduce the amount of grinding, cutters can be switched between stacks to bring the stacks closer to a common weight.