Tips to Help Un-Stick Your Stuck Tools

Occasionally during the machining process on machining centers, some tool holders may become stuck inside the spindle taper after the machining process for that tool is completed. This phenomenon happens when the taper of the tool holder wedges into the spindle taper and the unclamp cylinder device cannot knock the two tapers apart. This happens across the spectrum of machining centers and is not specific to any one brand of machine or builder. It happens across the industry and no one builder is any worse for this than another. Below are a few things that can be checked or performed that may help alleviate this or lessen its occurrence.

1. During an ATC tool change, make sure that the spindle air blast is working. This air blast is incorporated into the ATC cycle for cleaning out the spindle taper to help remove as much excess coolant runoff as possible while the finished tool is being removed and the next tool is being inserted into the spindle.



2. Check the tool knockout stroke. By placing a tool holder (with no cutter) into the spindle and an indicator attached to a mag base, set up the indicator to where it is touching the bottom of the holder. There you can measure the amount of knock-out stroke the machine's knock-out cylinder has. In order to check this correctly, the tool holder will have to be clamped in the spindle. Then with the assistance of another person unclamp the tool holder while pushing the holder against the spindle by hand. Looking at the indicator, measure the amount of movement the knockout cylinder pushes on the tool. Please exercise caution when checking the knockout. Okuma’s specification is 0.800mm to 1mm. If this is not what you have, contact Service for further instruction.



3. If there is a tool that is always in a cut for a long period of time and sticks in the spindle after the cut is finished spraying the taper of the holder with MolyKote 321 will help the tool to release from the spindle taper easier.



4. Never leave a tool in the spindle when the machine is not being used. If the machine is going to be down for an extended amount of time or overnight it is a good idea to remove the tool from the spindle then clamping the spindle before shutting the machine down.



5. Keep the spindle taper clean. When possible and an opportunity arises, remove the tool from the spindle and wipe the taper of the spindle out with a clean cloth. Wipe the tool holder taper down before inserting it back into the spindle.




6. Check the pull force of the spindle. If the pull force is over the high limit, it might be a good idea to have someone from Service come in and take a look. High pull force on the tool holder can cause the knock out cylinder to have to work harder to overcome the excessive force on the drawbar before striking the end of the pull stud to break the two tapers loose.



7. Perform visual spindle taper and contact checks. It is also a good idea to check the taper contact of the spindle taper. Using a high-quality holder, apply blueing to the taper of the holder and clamp the holder into the spindle. Unclamp the holder and check the contact of the two tapers. If there is close to 100% contact see Okuma Service. Okuma uses an 85% contact as a standard. By using 85%, this keeps the holder rigidity but also keeps the contact to a level that helps release the tool.



8. If the machine has a BIG-PLUS style spindle it is a good idea to use BIG-PLUS holders especially if the holder is going to be in the spindle for a long period of time, the spindle speed is high and if a lot of side load will be applied to the cutter. By using BIG-PLUS, this type of tooling gives you both taper and end face contact. This can increase rigidity but at the same time help in keeping the tool holder from wedge locking inside the spindle taper. Make sure the tool holder is a certified BIG-PLUS holder.




9. Check to make sure that the hydraulic unit is functioning correctly when a tool is being unclamped. A good way to check this is to remove any tool holder that may be in the spindle then clamp the spindle back. Find the hydraulic unit and look for the pressure gauge. Have someone else unclamp the spindle while watching the pressure gauge. If the pressure of the hydraulic unit drops tremendously while the knockout cylinder is moving, contact Service to have this checked. Some Okuma vertical machining centers may have the hydraulic unit mounted on top of the Z-axis ram. If this is the case, this unit will not have a pressure gauge. With the machine off check the oil level in the unit and add if needed. Start the machine up and with no tool in the spindle, cycle the clamp unclamp cylinder several times and listen for any unusual noises when unclamping the spindle.