Sunday, October 1, 2023

How is the Alesometer used?

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As mentioned in the article “dial gauge”, the alesometer, alexometer or interior checker It is a kind of comparator watch, suitable for the measurement of inside diameters by comparison.

The largest application of alesometer is found in machining, where it is the specific tool to measure not only the inside diameter engine cylinders, but also the oval and the taper that exist on cylindrical surfaces. The oval is the difference in diameter that the cylinder has at the same height, as a result of lateral thrust forces generated during combustion on the piston. The conicity is the difference in diameter that the cylinder has at different heights, since it wears more in the upper part than in the lower part due to the increase in combustion pressure, the high temperature generated and the reduction in lubrication. The use of alesometer allows you to check this difference by comparing cylinder diameter measurements at different heights.

Although various types of alesometers, both analog and digital of various designs, we can outline their basic parts according to the following image:


The measuring instrument at the top is nothing more than a dial gauge coupled to the Body, mango or vertical bar by means of a clamp or a fixing nut. This dial gauge can be graduated in fractions of a millimeter or inch and has a steerable sphere that allows the reset.

The mango Clamp, generally constructed of steel, is coated in a coating that reduces heat transfer from the hands to the instrument, minimizing the possibility of inaccurate readings caused by thermal expansion of the metal.

The head or horizontal bar is composed of a sensitive contact or fixed probe, two centralizing contacts, a extension piece or mobile probe interchangeable and a internal mechanism that transmits the movement of the fixed probe (which detects variations in the surface) to the Watch face comparator. The centralizing contacts maintain the correct position of the fixed probe on the diameter to be measured by means of a spring device.

Everything alesometer comes supplied with a set of extension pieces removable that by means of calibrated washers The device is adapted to measure different sizes of diameters. By adjusting and locking these extension pieces, the resetting the dial gauge when measuring a diameter of known dimensions.

As always for these precision instruments, extreme care must be taken to make accurate readings and protect the delicate mechanisms. To do this, a series of steps is followed, of which below we provide an example of typical use, that is, the measurement of the diameter of a cylinder with a alesometer.


Steps to measure a cylinder with an alesometer

  1. We look in the manufacturer’s data sheet for the nominal length of the diameter of the cylinder that we want to measure.
  2. We select the extension piece suitable for this diameter measurement, taking into account that the total length of the head (see image «parts of an alesometer), including the maximum tolerance, should be slightly larger than that diameter to ensure that the probes are in permanent contact with the cylinder.
  3. We assemble the alesometer as indicated in the manufacturer’s manual and we adjust the clamp or fixing nut.
  4. We graduate a micrometer, suitably mounted on a suitable support, to the nominal diameter of the cylinder.
  5. We introduce the head of alesometer inside the claws of the micrometer and zero the dial gauge. We gently move the alesometer from left to right (or vice versa) until we obtain a minimum measurement that we will take as a reference (Figure 1).
  6. We disassemble the alesometer of the micrometer and introduce it into the cylinder to measure (Figure 2). We must be careful that the alesometer Enter the cylinder in an inclined position, as this will not damage the styli.
  7. Once inside the cylinder, at the correct height and direction, we align the handle of the alesometer with shaft of the cylinder and take the reading of the dial gauge.
  8. Once again, we move the alesometer from left to right (or vice versa) until you find a inflection point which is the exact point of measurement. If that point coincides with the preset zero on the scale, the measure we are comparing will match exactly. If, on the other hand, the inflection point coincided, for example, with 5 on the scale, the compared measurement would be 0.05 mm more than the preset measurement.
  9. To extract the alesometer We must do it again with the body inclined to avoid damage to the dial gauge.


To obtain reliable results, it is necessary to take a sufficient number of measurements. For example, three measurements at three different heights (nine in total) will give an excellent approximation of the wear condition of the measured cylinder.

The video that follows these steps explains in detail for fans who want to learn how to use the alesometer.

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