A CNC machine that is not levelled is not only a safety hazard, but will also significantly affect machining operations. Even a minor bed twist or uneven support will cause taper errors, premature wear and machining accuracy.
As part of our CNC lathe machine installation and operation guide series, today, we will explore how to level a CNC lathe machine professionally.
Equipment Required
As an industry best practice, you must choose the right tools and accessories to successfully level CNC lathe machine. Through this process, it’s easier to achieve a high degree of machining precision.
Therefore, for any CNC lathe leveling procedure, the most critical tools are:
· Precision Machinist Level
The leveling process of the CNC lathe cannot proceed without the precision machinist’s level. This is a highly sensitive tool that detects minute deviations in the bed. It requires careful handling and calibration to prevent errors. It works like a spirit level, but to a finer extent and in both traverse and longitudinal directions.
· Mounting Bolts
Mounting bolts support the CNC lathes by making fine adjustments to the bed height at certain points. Having mounting hubs from three to six points will allow you to distribute the lathe’s weight.
These bolts may have a vibration-damping mechanism and are effective when fine-tuning the CNC machine level.
· Torque Wrench
This tool allows you to secure mounting or anchor bolts according to the torque values of the machine maker. Note that over-tightening bolts or tightening to different torque levels may interfere with the leveling efforts. Correct tightening procedure prevents stress from overloading the frame.
· Feeler Gauges
While this equipment is not compulsory, it helps determine floor and leveling pad contact. Additionally, it can also help to determine the seating of support points. They feature thinly fabricated metal stripes with a defined thickness that determines gap measurements.
· Cleaning Materials
You’ll need cleaning materials to wipe down the surfaces, removing contaminants like dirt, oil and rust. Debris on the lathe bed can prevent the machinist’s level from sitting flat and as a result, hamper accuracy.
Pre-Leveling Preparation
Pre-leveling preparation helps to achieve accurate measurements by ensuring both the machine and environment are suitable for the leveling process.
Site Preparation
The ground on which you erect the CNC lathe is essential in determining stability. There are certain aspects you need to consider before positioning CNC lathe:
· Strong Foundation
The foundation should be rigid and not vulnerable to vibrations. It is typical to use reinforced concrete which ensures the flooring is formidable and even. This prevents movement under heavy load which can cause the machine to misalign.
· Load-Bearing Capacity
While a formidable floor is ideal, it should be at a level capable of supporting the CNC lathe’s total weight. Any slight shift in the ground will result in calibration issues that ultimately affect machining accuracy.
· Environmental Stability
Temperature fluctuations can affect components of the CNC lathe through expansion and contraction. The surrounding temperature must be stable.
· Positioning
When positioning the CNC lathe, provide adequate spacing around it for easy interaction during the leveling exercise and even later during maintenance.
Machine Preparation
Before any CNC lathe leveling procedure starts, you must do the following:
- Clean all the surfaces where you will take measurements such as the points of leveling and the bed. Remove any traces of grease, oil, dirt and dust since they can upset readings on the level.
- Remove the locks that come with it and the shipping brackets. While they hold moving parts during transit, they can introduce stress in the machine when left.
- Undertake a thorough inspection of the CNC lathe to ensure all the necessary parts are properly installed. Also, examine the leveling hardware, ensuring they are freely moving and undamaged.
Leveling Points and Procedure
Leveling points are positioned at the bottom of the CNC machine. They are adjustable supports and include screws, threaded bolts and mounts. It is from these leveling points that you can either raise or lower the machine.
In most cases, the leveling points will vary according to the machine’s support points. Among the most common options are:
- Three-Point Support: This is the easiest to level since it is simple and naturally stable. It is however, only ideal for small machines as it offers fewer support points for heavy or larger machines.
- Four-Point Support: This configuration offers an improved load distribution and is ideal for mid-sized machines. However, you need to balance points that are diagonally opposite which is challenging and can be susceptible to twisting.
- Six-Point Support: Common for large CNC lathes, this offers maximum support for lathe machine leveling setup. With multiple support points, it allows for complex adjustments as an important process in the CNC machine calibration.
The leveling procedure takes the following form:
- Position the precision machinist level on the machine’s bed parallel to bed ways ensuring full contact. Take the reading after the bubble stabilizes.
- Ensure the CNC lathe is level from the head to the tail sections by rough leveling longitudinally. Do this by observing the position of the bubble by gradually adjusting the leveling points at the front and rear.
- Level transversally by positioning the level at ninety degrees with the bed checking from left to right. The aim is to have the bubble at the center.
- Work incrementally, adjusting her and checking there since changes at one point will affect another point. Do not randomly adjust and go straight to tightening.
- Ensure the base is stable with the machine seated firmly on the leveling points in both directions with no instability.
Precision Leveling
Precision leveling succeeds rough leveling focusing on fine-tuning to attain geometric accuracy. This process entails the following interventions:
- Use the highly sensitive machinist level, preferably with a high resolution. Only take your reading after the bubble stabilizes fully. This will help to prevent the effects of disturbances like vibrations when taking measurements.
- Check the bed in multiple positions, usually near the headstock and tailstock as well as the middle of the bed. Ensure the readings taken from all these positions remain consistent.
- Use critical adjustment to eliminate twist by comparing readings at both machine ends. The readings should be similar. If not, it indicates a twist and requires adjustment of the leveling points that are diagonally opposite.
- Make iterative adjustments by measuring multiple positions, making small adjustments every time, re-measuring and repeating the process.
- Make corrective adjustments both longitudinally and transversally maintaining balance always.
- Establish final tolerance by ensuring the level indicates minimal or preferably no deviation across multiple points. Any differences should be within the accepted limits.
Twist Evaluation, Verification and Testing
· Checking for Twist
Start by determining the machine twist when the lathe bed is slightly slanted due to uneven support. This causes one end to be higher and geometrically distorted hampering accuracy levels.
Checking for twist will involve:
- Position the machinist level transversally close to the headstock and record the bubble position.
- Transfer the level close to the tailstock positioning it as before and also record the reading.
- Make a comparison of the readings. The readings will match in the absence of a twist and not otherwise.
Note that the direction that the bubble shifts towards indicates which point requires adjustment. Adjustment involves making small changes at one point while checking the other.
· Tightening and Securing
Locking the machine in place preserves the alignment achieved. Otherwise, an external force can cause a shift in the machine frame and induce twist. Tightening should be gradual and even ensuring equal distribution of force.
· Verification and Testing
Verification confirms your CNC lathe will consistently produce accurate results during operations. A test cut offers the ideal method for verification. Undertake a cutting operation along a workpiece’s length, measuring the diameter at both ends. Matching diameters means upright leveling otherwise, it indicates misalignment or twist.
Factors to Consider When Leveling a Lathe
Here are some important factors whose consideration is ideal in the success of your levelling efforts:
- Temperature: Causes thermal expansion or contraction of machine parts and components. Place the machine in tepid conditions and away from direct heat sources or sunlight.
- Floor Movement: Shifts in the floor may upset the established equilibrium from natural causes or heavy loads and alter leveling points. Always check periodically for the current levels.
- Workpiece Weight and Machine Load: Ultra-heavy workpieces can result in deflection at certain points. Also, having an uneven load increases localized stress.
- External Disturbances: You can have vibrations from external sources like construction works nearby. This can affect the leveling points and reduce accuracy in machining.
- Operating Conditions: Have a warm-up cycle before undertaking precision work to allow for thermal stabilization.
When to Re-Level a Lathe
Once in a while, it is important to conduct a comprehensive CNC lathe accuracy troubleshooting, which may require that you re-level the machine. This may be due to natural wear, environmental changes, and operational loads.
Other circumstances that may require a re-level include:
- When relocating or carrying out the CNC installation process
- After carrying out major CNC machine maintenance
- Upon completing a defined period as a form of preventive maintenance.
- When there have been changes in the immediate environment, such as the use of heavy machinery.
Mistakes to Avoid When Re-leveling
Mistakes in the re-leveling process can result in costly damage and losses. Some common mistakes to avoid by all means are:
- Adjustments should be small and controlled and made one at a time. Do not initiate large adjustments at a go.
- Always use a standard precision machinist level and not any other. Those lack the enhanced sensitivity required for leveling a CNC lathe.
- Avoid tightening the bolts early at the initial stages. It introduces internal stresses to the frame. Tightening should be gradual and only after verification of leveling.
- Consider twist as you check your level. Compare the readings at both bed ends, making adjustments diagonally opposite.
- Do not take measurements on an unclean surface. Even small amounts of dirt can upset the machine calibration.
- Leveling is susceptible to environmental factors, and as such you should not ignore things like temperature changes.
- Avoid having an uneven distribution of load as it results in distortion from stress concentrations.
FAQs
Does leveling affect accuracy in CNC programming?
No, CNC programming precedes leveling. However, a correct program can be improperly executed by a CNC lathe with poor leveling.
Can you level a CNC lathe without a precision level?
Yes, but for the best results, the precision level is recommended.
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