Pallet change alignment procedures for CNC
Rotary type CNC pallet changers
There are many different designs but the following sequence of events are usually somewhat the same. These type of pallet changers usually are on Horizontal machining centers with a B axis
- Check the alignment of each pallet when at Zero in the machine. Notice any difference This difference should be repaired first. This can often be caused by crashes which change the mechanical alignment with the pallet and engagement ring found underneath.
- Next if the indicator reading across the front of the pallets is not true a B axis alignment will be required. This can be a difficult procedure and varies greatly.
- If it is straight many pallet changers use a lifting type system. Often there is a set of tapered cones or round rod protruding into recesses in the pallet. These pins or cones will often have some bolts that can be loosened to adjust cones center position.
- Move the machine to pallet change position. Note: you may have to adjust the axis home position if the misalignment is off equal for all cones or alignment pins.
- To adjust actuate the pallet changer in the motion to move it up and down and view any rotation of the pallet or movement as the pins slide into the holes. Many times you can just loosen the cones and move the pallet changer up and down to self center them.
- Make sure you check and adjust both pallets.
Side by Side pallet changer alignment
This type of pallet changer is often found on Vertical CNC machining centers. They often require alignments about every 6 months to a year. This is because they are often hit with carts or fork trucks, concrete settles or problems with the pallets moving in and out of the setup station. Some of these problems can be avoided by doing some of the following.
- Install extra angle brackets around pallet changer feet anchored to the concrete.
- Install metal posts at the corners to prevent slamming part baskets and fork truck accidents
- Take the time to align the pallet shuttle as close as possible the first time.
- Improper alignment procedure
- Machine Tool is moving. Anchor to floor or at minimum install a couple toe clamps and check for soft foot.
The proper way to align this type of pallet changer varies depending on the mechanical design. One of the most common types which I will explain here, is a swing arm with a Cam follower that runs in a groove on the pallet while it shuttles into the machine.
Many people try to adjust the alignment by just shuttling manually stepping through the CNC control or shifting the hydraulic valves manually. This is not the right way to do this!! The right way is to remove the Cam or cam attachment and push in and out of the machine manually by hand. Below is a step by step procedure.
- Get machine in a pallet change state
- If its a new installation. If equipped move the adjustment bolts to center the Pallet changer to the base plate which will be anchored to the floor to give the most adjustment as possible in either direction.
- Move the machine to Pallet change position.
- Unclamp pallet- either through control or by pushing hydraulic valve
- Remove the Cam from the swing arm
- Push the Pallet in and out of the machine and adjust pallet changer.
- In the following alignments push the entire base around to get close. DO NOT ANCHOR THE PALLET CHANGER YET!!
- Align the distance the pallet changer is away from the machine. Move the swing arm furthest into the pallet changer and hold up the Cam assembly you removed and adjust the pallet changer to get the CAM to align with the groove on the pallet so the lock pin shoots in properly.
- Rough align pallet A-side to side alignment.
- Rough align pallet B side to side movement. Note the amount off and what direction and check A pallet again. You may need to adjust the pallet change position if it is to far off, but usually not required unless new installation or severely damaged rails.
- This can and usually takes 2 to 4 hours to align the first and second time from scratch.
- Note: Many people have a tendency to raise the pallet changers farthest side away from the machine to much. It is often smoother if this side is lower than the side closest to the machine.
- Now fine tune the alignments
- Check the CAM alignment to be sure it is still correct.
- Check any lock pin engagement on each pallet
- Anchor the Base to the concrete if necessary