For example, the drill chuck not hold the drill to be parallel with the axis. The actual part to be measured make continuous rotation around the reference axis without axial movement, and the indicator moves continuously along the ideal prime line. The difference between the maximum and minimum readings measured by the indicator in a given direction is the total runout.
The tools required for measuring lathe runout are a dial test indicator and a magnetic base, or other bases to hold the indicator. To do this, rotate the rotor in the direction that the dial indicator tip is pointing. Next, watch the needle for the lowest and highest number reached during one revolution. The runout number will be the difference between these two numbers. For example, if the lowest reading was 65 and the highest was 69 the runout is.
Next, loosen the set screw and rotate the black dial until the needle point to zero. Finally, rotate the rotor a complete revolution and note the amount of runout. As a result, the needle will start and stop at zero without going below it. Bonus Tip: It takes less than 60 seconds to measure rotor runout and KNOW whether the rotor runout will be an issue in a vehicle that comes back with pulsation. The group is a place for mechanics from all skill levels to interact, rant, and help each other.
Otherwise, consider checkin out some of our other articles:. How to perform a Rotor Runout Measurement. Systems that capture these peaks have to be periodically reset to keep the value current should it decrease. If using Elite Series capacitive sensors for shaft runout measurement, the MM Meter and Signal Processing module can capture and display peak values. The MM also has Tracking TIR which captures peak values but allows the values to decay with time; this way, the displayed value is kept current without a reset being necessary, even when the runout is decreased.
The MM is not an option for eddy-current sensors. Eddy-current sensors are calibrated for a unique material. To maintain precision, the sensors must be used with that specific material. Eddy-Current sensors are normally calibrated to a flat target. Shaft diameter should be times larger than the eddy-current probe diameter to provide a sufficiently flat target for accurate measurements. Magnetic materials have a property called electrical runout.
Small localized differences in magnetic properties within the material affect the interaction with eddy-current sensor magnetic fields. The differences result from local chemical composition, crystal structure and magnetic domains which are affected by heat history, degree of cold work stress, surface treatments and exposure to magnetic fields.
The greater these differences, the larger the electrical runout. As the magnetic steel shaft turns, the eddy-current sensor output will change in response to the electrical runout of the material even if the gap between the sensor and shaft does not change no mechanical runout. Images at the right compare a capacitive sensor and eddy-current sensor measuring the same magnetic steel shaft.
Non-ferrous materials like copper and aluminum do not have this phenomenon at any significant level. Non-magnetic steel, while better than magnetic steel, still exhibits a small electrical runout. In some applications, the electrical runout is small in comparison with the baseline runout of the shaft and therefore does not introduce any significant error in the total shaft runout measurement.
If your shaft runout measurement need be so precise that electrical runout will be a significant error, you will have to address the problem.
The best way to eliminate electrical runout errors in magnetic shafts is to use capacitive sensors. But shaft runout sensor applications are often in a wet and dirty environments that require an eddy-current sensor. Here are some methods for eliminating or reducing electrical runout. Use the largest probe possible.
The sensing field of an eddy-current shaft runout sensor is three times larger than the diameter of the probe. The probe output is an average of everything within that field. Suppose you know the direction of maximum runout for your spindle you can measure it!
Now measure runout on a toolholder perhaps using V-Blocks on a surface plate and mark the maximum runout position with a Sharpie. The two are at least partially cancelling each other out and the tool enjoys reduced runout. Not every taper has them, but many do. You might think spindle orientation is only about lining up the drive dogs with toolholder notches, but I recently learned differently. Dave Decaussin, one of the original founders of Fadal, recently remarked on a video I was watching that spindle orientation is also essential to maintaining tolerances while machining.
When you maintain the same spindle position relationship to the toolholder, you ensure that whatever runout there is will at least be consistent—either consistently good or consistently bad. Consistency is the main thing, because if it is consistent, we can compensate for it. If you think about it, the runout just makes the endmill act like it is a slightly larger diameter as it wobbles in the cut.
If that effective diameter changes every toolchange, the CNC machinist will have a tough time maintaining tolerance. But if it is consistent, there is hope. You can use your wear offsets to just enter the effective diameter of the tool and cut accurately despite that runout. Retention Knobs are a consumable that sits atop the toolholder. Worsening spindle runout over time is an indication of wear problems on your spindle. If runout gets bad enough, it may be time to rebuild your spindle.
Runout can dramatically reduce tool life, but now you know how to measure it, and you have some tips on how to reduce it.
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