Knowledge Summary Of Precision Testing Of Various Parts Of Machine Tools

How are straightness errors detected in the vertical plane of a cylindrical grinding machine table movement?

A: Check the straightness error of the cylindrical grinder table movement in the vertical plane.

Place a bridge supplied with the machine or a special homemade bridge (for inclined table surface only, bridge is not required for platform surface) in the center of the table.

Place a gradienter in the middle of the bridge parallel to the direction of the table movement.

Move the table, record the readings every 250mm (the short bed is inspected at the two ends and three positions in the middle of the maximum grinding length), arrange the readings of the gradienter in sequence and draw the motion curve of the table.

The maximum coordinate value between the movement curve on the length of 1000mm and the connecting line of the two endpoints is the straightness error on the length of 1000mm.

Make a parallel line to cover the movement curve, the coordinate value between the covering line is the straightness error value on the whole length of the guide rail.

How to detect straightness errors in the horizontal plane of a lathe slide movement?

A: If the travel of lathe slide carriage is less than 3000mm, the straightness error of the lathe slide carriage in the horizontal plane can be detected with a long cylindrical test rod.

In the front and rear center, a long cylindrical test rod is tightened and the dial gauge is fixed on the slide carriage to make the dial gauge be placed on the side generatrix of the gaging mandrel.

Adjust the tailstock so that the micrometer readings on both ends of the gaging mandrel are equal.

Move the slide carriage to check on the full range of the gaging mandrel.

The maximum difference between the readings on the 1000mm travel of the dial gauge is the straightness error.

When the gaging mandrel travel is more than 3000mm, it uses a taut wire parallel to the bed rail instead, and use a microscope (also available optical straightness meter) to detect it.

How to detect straightness errors in the horizontal plane of a long lathe bed working table or slide carriage movement?

A: When slide carriage travel of double housing planer, milling planer and horizontal boring and milling machines etc. is more than 2000mm, horizontal lathe, screw lathe and other slip plate stroke is greater than 3000mm, because the flat ruler over 2000mm is easy to deform and there are many difficulties in manufacturing test rods over 2000mm, tools such as wire and microscope should be used to detect.

The detection method is the same as the detection method of the straightness error of the guide rail, which can refer to the detection method of the straightness error of the guide rail in the horizontal plane by pulling the wire.

If possible, an optical flatness gauge can be used to detect.

The optical flatness gauge is placed at one end of the machine tool, and the reflector is placed on the slide carriage or working table.

At the two extreme positions of the stroke, the flattening gauge and the reflector is adjusted to make the bright cross image of the collimator coincide with the alignment of the movable reticle.

Every 500mm worktable movement is to take readings once and make a record, the readings will be arranged to draw the movement curve of the worktable, and then the error values on the length of 1000mm and the total length of the stroke are calculated.

How to detect the tilt error when the slide carriage moves?

A: To detect the tilt error when the slide carriage moves, the gradienter should be placed on the dovetail guide of the slide carriage near the knife holder, perpendicular to the lathe bed rail (i.e. the direction of slide carriage travel).

Move the slide carriage, record a reading every 250mm (or 500mm, or less), and check on the full travel of the slide carriage.

The maximum algebraic difference between the readings on the 1000mm stroke and the full stroke of the gradienter is the inclination error.

The tilt error is indicated by the slope or angle value.

How to detect the tilt error when the table moves?

A: For the detection of tilt error when moving cylindrical grinders, thread grinders, broaching grinding machine, double housing planer and milling planer etc., a gradienter is placed in the center of the table, perpendicular to the direction of worktable movement (if the grinder has an inclined table, the gradienter should be placed on a special pad).

When the worktable is moved, readings are recorded every 250mm (or 500mm, or less than this value), and at least three readings are recorded on the short lathe bed on the entire travel of the worktable.

The biggest algebraic difference between the readings on the 1000mm travel and on the whole travel of the gradienter is the tilt error when the worktable moves.

How to detect the tilt error when the beam moves?

A: The method for detecting the tilt error when the beam moves is to place a gradienter in the center of the rail of the beam, parallel to the beam.

When moving the beam, a reading is recorded every 500mm (or less than 500mm), at least 3 readings are recorded on the full travel of the beam.

The two vertical tool holders (or milling heads) should be moved to a symmetrical position on the beam when checking over the full travel of the beam.

The beam can only be moved from bottom to top, not back and forth.

This method is mostly used for the detection of the tilt error when the beam moves on the double housing planer, milling planer and vertical lathe etc.

Which machine tools require higher positioning accuracy? How should it be tested in general?

A: The positioning accuracy requirements of the jig borer are relatively high, so it is necessary to detect the positioning error of the table or spindle box after moving the coordinates positioning.

Various types of domestic jig borer positioning system have optical system and mechanical system (i.e. screw and calibration ruler).

Although the positioning system is different, the measurement method of positioning error is the same.

On the machine tool table, a precise scribing ruler is placed along the longitudinal movement direction (the scribing accuracy of the scribing ruler should have an error verification table, and the verification accuracy should be within 0.0005mm), the scribing ruler is placed in the center of the worktable, and the height should be l/3~l/2 of the maximum distance from the worktable to the end of the vertical spindle.

The reading microscope (reading accuracy is 0.001~0.002mm) is fixed on the spindle sleeve, so that the microscope can clearly observe the scribe lines on the scribe ruler, and the movement of the table in the specified length is detected (generally specified as one reading for every l0mm movement).

The table should be clamped during the readings.

The positioning error is the most algebraic difference between the actual values of the readings taken at any two positioning times.

How to detect the dividing error of indexing head?

A: The dividing error of the indexing head fixes the standard indexing disc to the spindle of the indexing head.

To keep the center overlap, the reading microscope is fixed on the holder of the inspection plate.

The determination of the starting position of the handle will align the reading microscope and the index plate to the zero position.

Then make a reading every 90° turn of the indexing head and record it.

When using optical indexing head for comparative testing, it should insert an inspection rod with Morse Taper at both ends, one end is into the optical indexing head spindle taper hole with closely fit, while the other end is closely inserted into the indexing head spindle taper hole to make these two indexing head into one.

When the center of the main shaft of the inspected indexing head and the optical indexing head are not equal in height, it should be flattened.

Disengage the indexing head and turn the handle of the indexing head to turn the indexing head to be inspected,  and the optical indexing head can be driven to rotate by the inspection rod at the same time.

When the indexing head is in the starting position, the rotation of the optical indexing head is recorded.

When the indexing head is in the starting position, the reading value of the optical indexing head’s starting position is recorded.

(1) When the errors of the indexing disc and indexing worm are not considered, the detection method and dividing error are calculated as follows:

The transmission relationship of the indexing system is that when the indexing head handle rotates for n revolutions, the main shaft rotates once, which is:

n = z2 (number of teeth of the indexing worm) ÷ z1 (number of heads of the indexing worm)

General indexing worm gear teeth z2 = 40, the number of worm head z1 = 1.

Therefore, when the handle turns every cycle, the theoretical angle of the indexing head spindle rotation is 360 ° / 40 = 9 °.

After detecting the position, the reading of the standard dividing disk (or optical indexing head) is recorded once.

The difference between the theoretical angle the spindle should turn and the actual reading in the optical instrument is the dividing error of the indexing worm during each cycle of handle rotation.

In the spindle rotation for one cycle, 40 indexing error values can be obtained, of which the largest algebraic difference of error values is the maximum indexing error when the indexing head spindle rotates for one cycle.

When detecting, the spindle should be rotated clockwise for one cycle, and then the same spindle should be rotated counterclockwise for one cycle and to detect again.

When considering the error of dividing disk and indexing worm, the detection method and indexing error are calculated as follows: the indexing worm handle does not turn a cycle but turn an α angle.

This α angle is also equivalent to the handle rotate 1/z cycle, that is, α = 360 ° / z, z is integer of 8 ~ 12,  which is determined by the indexing transmission ratio and the number of holes of the original dividing disk of the indexing head being inspected.

During detection, when the handle turns the α angle (i.e. 1/z cycle), a standard indexing disk (or optical indexing head) readings is recorded.

Recording and calculating according to the theoretical rotation angle and actual reading of the indexing head spindle, the algebraic difference between the maximum value and the minimum value is the maximum indexing error of the worm during one cycle.

When detection, the indexing handle is turned clockwise and counterclockwise each cycle to detect.

The comprehensive error value of the indexing system is the sum of the maximum indexing error when the spindle turns one cycle and the maximum indexing error when the worm turns one turn.

How to detect the dividing error of the rotary table using an octagonal gauge?

A: General rotary table is a milling machine accessory with low indexing precision, which can be used for testing octagonal gauge.

The external circle diameter of the octagonal gauge is 250mm

The positioning spindle of the octagonal gauge is inserted closely into the worktable tapered hole to ensure that the rotation center of the worktable coincides with the center of the circumcircle of the octagonal gauge.

The inspected worktable is fixed on the test plate, the flange on the base of the dial gauge against the guide groove in the test plate on the side of the guide groove is not available instead of a flat ruler, so that the dial gauge measuring head on top of one side of the octagonal gauge.

The micrometer is moved along the guide slot so that the micrometer reads the same on both sides (which is adjusted by turning the worm handle).

The table is then turned 45° (i.e. 360°/8) and the micrometer is checked over the full length of the other side, checking each side in turn.

The maximum difference between the meter readings on either side of the table is the dividing error.

This method is used when the indexing precision of the measurement is not high (the error is within 4′ to 8′).

How to detect the dividing error of rotary worktable by comparison with a precise horizontal turntable?

A: The dividing error of precise horizontal turntable is not as accurate as rotary table using the odolite to measure, but it is more convenient than theodolite with simple operation and high efficiency.

The method: The precise turntable is placed on the plate or machine tool worktable, with a gradienter for detection to make the turntable in a horizontal state.

The inspected rotary table will be stacked on the precise turntable, a dial indicator is used to find the parallelism of the working surfaces of the two turntables (use a cushion block when not parallel) to make the rotation center lines of the positioning holes of the two turntables coincide and fix the two turntables with screws to form a whole.

A locating piece is fixed on the surface of the turntable to be inspected, and the dial gauge is fixed on the plate (when tested on the machine table, the differential table can be fixed on the spindle of the machine), so that the dial gauge probe rests on the side of the locating piece.

The pointers of the reticle and dial gauge of two rotary table are in the zero position by adjusting the precision rotary table, the inspected rotary table and the dial gauge.

The handwheel of the inspection rotary table is turned to make the worktable rotate clockwise by a certain angle (taking integer value), then the handwheel of the precision rotary table  is turned to make the inspection table turn back counterclockwise with the precise turntable.

When it turns to the side of the positioning block and touches the dial gauge probe and the dial gauge pointer returns to the zero position (initial position), the precise turntable stops rotating.

At this time, the marking readings of the two turntables are recorded, and the difference between the two is the dividing error of the inspected turntable.

With this way, the test should be performed at intervals of 10°, 5° and 1°.

How to detect repetitive positioning errors in the fast feed mechanism of a grinding carriage on a cylindrical grinder?

A: The detection of the repetitive positioning error of the fast feed mechanism of the grinding carriage on a cylindrical grinder is to fix the micrometer on the machine table with grinding carriage in the feed position, so that the micrometer measuring head is placed on the axis of the grinding carriage near the grinding wheel, with fast feed of grinding carriage for continuous 10 times, the maximum difference between the micrometer readings is its repetitive positioning error.

How to detect the repetitive positioning error of the working stroke for relieving tool carrier?

A: Detection method of the repetitive positioning error of the working stroke for relieving tool carrier:

The dial gauge is fixed on the back of the tool carrier on the slide carriage to make the measuring head on top of the side on the tool carrier, rotate the driveshaft by hand to make the tool post reciprocate and test again.

The tool carrier reciprocates 10 times, the biggest difference between the readings of the dial gauge is the repetitive positioning error.

What are the main factors that affect the machining accuracy of workpieces in machine tools?

A: In machine tool machining, there are several factors affecting the accuracy of workpiece machining as follows:

(1) Tool geometrical form error and its misalignment on the machine.

(2) Misalignment of the workpiece on the machine.

(3) Errors in the machining principle of the machine tool.

(4) Vibration, elastic deformation, thermal deformation and tool wear of the machine tool and workpiece system during the cutting process.

(5) The geometrical form error of the machine tool.

(6) The transmission error of the machine tool’s transmission chain.

How to improve the accuracy of the machine transmission chain?

A: When designing machine tools, the methods to improve the precision of the machine transmission chain can be performed from the following aspects:

(1) Minimize the number of transmission elements in the transmission chain to reduce the sources of error.

(2) In the transmission chain, the descending speed arrangement is used from the first end to the end of the line, and the maximum transmission ratio for the end of the transmission pair is created (increase the number of worm gear teeth, reduce the number of worm head, reduce the number of threads and reduce the pitch of the screw).

(3) Try not to use helical gears, bevel gears or clutches near the final transmission pair.

(4) The exchange gear should be placed in front of the end transmission pair as much as possible.

(5) Try to use the gear transmission with transmission ratio of 1:1 to compensate for the transmission error.

(6)Improve the precision of transmission components.

(7)Improve the precision of transmission components and use the error compensation method when assembling.

(8) Adopt an error correction device.

Repairing or refitting the machine tool is different from the new design, which is difficult to improve the accuracy of the transmission chain by changing the structure of the transmission chain of the machine tool (such as reducing the number of transmission components, adopting a reduced speed arrangement from the driving part to the end, etc.) or improving the accuracy of the components.

The practical and feasible way is to improve the installation precision of the transmission parts, using the corresponding error compensation method and error correction device.

It also can be installed in the repair work to improve one level of the machine accuracy in the original basis, or to make it restore when the loss of precision is not too serious.

What kinds of machine tools use transmission chain drive to detect error? What are the methods for detection?

A: Any machine tool that processes gears and threads by the synthetic motion of the transmission chain, in order to obtain the correct dentoform, pitch and tooth graduation accuracy, the transmission chain must have a certain accuracy.

Machine drive chain transmission error detection methods are indirect and direct methods:

1) Indirect method

When processing a product such as a gear or a screw according to the machine tool manual requirements, the workpiece is measured by the method of testing the workpiece quality to determine whether the transmission error of the machine tool’s chain can produce the required accuracy level of the workpiece.

This method reflects the comprehensive error of the construction process, which includes both the transmission error of the machine transmission chain, as well as the errors of other factors.

(2) Direct method

There are static measurement methods and dynamic measurement method.

How to perform static detection of gear hobbing machine indexing transmission errors?

A: In the vertical hobbing machine precision test, the indexing transmission error detection is as follows:.

Firstly, configure the machine with an indexing change gear and adjust the indexing chain to make the number of indexing teeth be equal to the number of teeth of the indexing worm z.

The hob spindle is mounted with a standard dividing disk and a reading microscope is installed on the column, which is to determine the rotation angle of the standard dividing disk (i.e., the hob spindle).

Install a theodolite (or optical angle gauge) on the worktable, or a sight vane alidade (or collimator) on the outside support of the machine, or suspend a calibration hair thread away to determine the rotation angle of the worktable.

When the hob spindle rotates for a cycle, the worktable indexing worm wheel should theoretically turn over 360 ° / z.

When hob spindle rotates for each cycle, the theodolite will return to the original position, the actual rotation angle of the worktable is determined by the readings of the odolite.

The forward and reverse rotation of the worktable is detected once each.

The difference between the actual rotation angle of the worktable and the theoretical rotation angle is the indexing transmission error of the machine indexing drive chain.

How do hobbing machines dynamically measure transmission errors?

A: As the inspection gear shaper, dynamic measurement of gear hobbing machine transmission error can be performed according to the rolling principle.

Adjust the hob shaft of the hob holder parallels to the axis of the worktable.

Install a friction disc on the hob shaft and a fixed disc with a mandrel concentrically on the table, and set a friction disc over the mandrel.

The diameter ratio of the two friction discs is equal to the transmission ratio between the hob shaft and the worktable.

When the friction disk rotates, it relies on friction to drive the rotation of the friction disk, thus constituting a standard comparative mechanism.

When there is no transmission error between the hob shaft and the table transmission chain, the friction disc and the fixed disc can rotate synchronously;

But when the transmission error produced between the transmission chain, the fixed disk and the friction disk can not be strictly synchronous rotation.

An inductive probe is installed between the fixed disk and the friction disk, which can convert asynchronous rotation into electrical signals, and output, amplify, rectify and record the electrical signals.

According to the recorded curve, “qualitative” and “quantitative” analysis of the transmission error of the transmission chain is to determine the size of the transmission error and the source of the error.

How to achieve dynamic measurement of transmission errors on horizontal lathes and precision leading screw lathes?

A: Horizontal lathe and precision screw lathe transmission error dynamic measurement can be tested by precision nuts, dial gauge and standard screw according to the specification of professional precision standards for machine tools.

In the front and rear center, a standard screw with a precision nut is tightly placed, the nut should be precisely with the standard screw (or with a device to adjust the clearance).

It also makes the standard screw rotate, but the nut can only make axial movement without rotation.

The dial gauge is fixed on the slide to make the dial gauge probe on the end face of the nut.

Take the ratio of the standard screw pitch and the machine screw pitch as the transmission ratio from the spindle to the transmission screw.

Close the machine’s slit nuts, start the machine at a slow speed, and detect it with the lengths of 25mm, 100mm and 300mm, respectively.

The maximum difference of dial gauge readings is the transmission error.

How to detect repeat positioning error of turret lathe turret?

A: The repeat positioning error detection of turret lathe turret is to closely insert a gaging mandrel in the tooling hole on the turret, a dial gauge is fixed on the machine tool to make the dial gauge probe be placed on the surface of the gaging mandrel from the center of the turret L (L is specified by the inspection standard), and then turret is exited.

The turret rotates 360 ° to push it back to the original position, then measures it again after clamping for 5 times.

The maximum difference between 5 continuous measurement readings is the repeat positioning error.

Each tool hole in the turret should be detected.

For different shapes of guide rails, which plane straightness error should be controlled for each surface separately?

A: The common shapes of machine tool guideway are rectangular guideway and V-shaped guideway.

The horizontal surface of the rectangular guide rail controls the straightness error in the vertical plane of the guide rail.

The two sides of the rectangular guide rail control the error of straightness in the horizontal plane.

For the V-shaped guide rail, because the guide rail is composed of two inclined surfaces, the two inclined surfaces not only control the straightness error in the vertical plane, but also control the straightness error in the horizontal plane.

What are the common detection methods for straightness error of guide rails?

A: commonly used detection methods of guideway straightness error are: lapping spots method, horizontal ruler pull table comparison method, mat plug method, pulling wire detection method and gradienter detection method, optical flatness gauge (autocollimator) detection method.

What is called the lapping spots method?

A: When testing straightness error with ruler, a thin layer of red lead oil is evenly sprayed on the surface of the inspected guide rail, the ruler is covered on the surface of the inspected guide rail.

Use appropriate pressure to make short-distance reciprocating movement to lap the spots, then remove the flat ruler to observe the distribution of the lapping spots on the surface of the inspected rail and the density of the sparsest lapping spots.

Lapping spots are evenly distributed on the whole length of the guide rail, which means that the straightness error of guide rail has reached the corresponding accuracy requirement of straight-edge.

This method is called lapping spots method.

The flat ruler used for lapping spots method is a standard flat ruler, its accuracy level is selected by the precision requirements of the inspected guide rail, which is generally not less than 6 levels.

The length is not shorter than the length of the inspected guide rail (in the case of lower precision requirements, the length of the ruler can be 1/4 shorter than the guide rail).

Which types of guide rail straightness error detection are suitable for the lapping spots method?

A: When using scraping method to fix the straightness error of guide rail, most of them use lapping spots method.

Lapping spots method is often used in the testing of shorter guide rail, because the ruler more than 2000mm is easy to deform with manufacturing difficulties, which affects the measurement accuracy.

When scraping short guide rail, guide rail straightness error is usually guaranteed by the accuracy of the straight-edge, the density of the research point in the unit area also has certain requirements.

According to the accuracy requirements of the machine tool and the nature and importance of the position of the guide rail in the machine tool, it can be specified as not less than 10-20 points per 25mm×25mm (i.e. the number of points per scratch).

When using lapping spots method to detect the error of guide rail straightness, because it can not measure the error value of guide rail straightness, so it generally does not use lapping spots method for the final test when there is a gradienter.

However, it should be pointed out that, in the absence of measuring instruments (gradienter, optical flatness gauge, etc.), the inspection straight-edge produced by the mutual research method of three straight-edge can more effectively meet the detection requirements of the short guide rail straightness error of general machine tools.

Which types of guide rail straightness error detection are suitable for the horizontal ruler pull table comparison method?

A: The horizontal ruler pull table comparison method is usually used to detect the straightness error of the short guide rail in the vertical plane and in the horizontal plane.

In order to improve the stability of the measurement readings, the length of the pad moving on the rail under inspection is generally not more than 200mm, and the contact surface of the pad and the rail should be scraped with the rail under inspection to make good contact, otherwise, it will affect the accuracy of the measurement.

(1) The detection method of straightness error in the vertical plane

Put the straight-edge working surface into the level to the position next to the inspected guide rail, the closer the better, to reduce the influence of guide rail distortion on measuring accuracy.

A supporting scraping pad iron is put on the guide rail, micrometer stand is fixed on the pad iron, which is to make the micrometer probe be placed on both ends of the ruler surface, adjusting the straight-edge to make the readings of both ruler ends be equal.

Then the pad iron is moved, the micrometer value is read every 200mm, the maximum difference between the readings of the dial indicator is the straightness error within the full length of the guide rail.

During measurement, in order to avoid the impact of scratching points to get accurate readings, it is best to pad a block of measurement in the micrometer probe below.

(2) The detection method of straightness error in the horizontal plane

Place the working surface of the flat ruler next to the inspected guide rail, and adjust the straight-edge so that the readings of the micrometer on the two ends of the ruler are equal.

The measurement method and calculation error method are the same as above.

Which types of guide rail straightness error detection is suitable for the mat plug method?

A: Mat plug method is applied to the plane guide rail that has been ground and have low surface roughness.

A standard straight-edge is placed on the inspected guide rail, two equal height pad is supported in the straight-edge below at a distance of 2/9·L from both ends of the straight-edge, the amount of blocks and feeler gauge is used to check the clearance between the straight-edge work surface and the measured surface of the guide rail.

For example, horizontal lathe guide rail straightness tolerance is (1000:0.02) mm, which is equal to the thickness of an equal height pad plus 0.02mm of the measuring block or feeler gauge, any place on the guide rail within the length of 1000mm can not be inserted into it as qualified.

When measuring precision machine tool guide rail, it is appropriate to use a measuring block with higher accuracy, which helps to correctly measure the guide rail straightness error value.

This method can also use a dial gauge instead of the feeler gauge, but the thickness of the equal height pad should be increased to make the dial gauge enter the measurement mode.

What are the characteristics of the straightness error of the guide rail using the pulling wire detection method?

What issues should be noticed during operation?

A: It uses tightened steel wire as an ideal straight line to directly measure the straightness of the linearity error line value of each component on the guide rail.

It is a kind of line value measurement method like the horizontal ruler pull table comparison method.

This method can only detect the straightness error of the guide rail in the horizontal plane.

A length of 500mm pad iron is put in the slideway of the machine tool, a graduated reading microscope is installed on pad iron, microscope lens should be aimed at the wire and must be placed vertically.

A small sheave is fixed at both ends of the guide rail, with a wire less than 0.3 mm in diameter, one end is fixed on the small pulley, the other end is suspended by a heavy hammer.

The weight of the heavy hammer should be 30% to 80% of the wire pulling force/strength.

When adjusting both ends of wire to make the microscope on both ends of the guide rail, the steel wire coincides with the engraved line on the lens.

The reading of movable splitter handwheel on the microscope is written down.

Moving the pad iron and observing the microscope every 500mm to check that the wire coincides with the scribe.

If there is no overlap, it should adjust the handwheel on the reading microscope to make it overlap and record the reading.

It should measure on the whole length of the guide rail and record the readings in order.

It should arrange the readings on the coordinate paper and draw a graph of the pad iron’s movement.

The maximum coordinate difference between the movement curve and the line connecting the two end points at each 1000mm length is the straightness error with 1000mm length.

If the formed curve is a convex or concave line, the coordinate difference between the most convex or concave point to the two ends of the connection is the straightness error over the full length of the guide rail.

If the curve is folded line (i.e. there are points on both sides of the abscissa axis), it can use inclusive line method, taking the coordinate difference between the two parallel lines with the smallest distance as the straightness error on the whole length of the guide rail.

What issues should be considered when drawing the straightness error curve of a guide rail?

A: When drawing the straightness error curve of a guide rail, the size of the curve chart should be moderate, if the size is too large, it is inconvenient to draw and modify; if the size is too small, straightness error may be inaccurate in the calculation of guide rail.

It is recommended that when measuring medium and small machine tools, the length of 0 to x-axis should be 200mm, the longer lathe should be 200-400mm, and the extra-long machine tools should not exceed 500mm.

After the length of the 0-one-x-axis is set, the scale of the x-axis can also be set.

In fact, 0 to x-axis is a representative of the spacing of the gradienter pad iron, which can be drawn by 1:5 to 1:10, that is,  the measurement distance of 200mm is represented by 40 or 20mm.

The z-axis and y-axis is the precision error on behalf of the guide rail, which can be used from 1000:1 to 2500:1, i.e. the accuracy error of 1μm is represented by the coordinates of 1 to 2.5mm.

For special precision machine tool guide rail (generally shorter), it can take 5000:1, i.e. the error of 1μm is represented by 5mm.

For example, to measure the rail of a machine tool with length of 1000mm, the specification of the gradienter is 0.02/1000, the length of the gradienter pad iron is 200mm.

The reading is zero when putting the gradienter on the  0-200mm section of guide rail surface.

When the gradienter moves forward to the 200-400mm section of guide rail surface, the bubble in the gradienter moves forward one frame, with positive value, which means that this section of guide rail surface is inclined upward by 0.004mm.

When the gradienter is moved to the 400-600mm section of guide rail surface, if the bubble of the gradienter moves backward and returns to zero position, which means that this section of guide rail surface is parallel to the 0-200mm section of guide rail surface.

Due to the 200-400mm section of guide surface tilt upward, so 0-200mm and 400-600mm section of guide surface is parallel in the different plane.

When the gradienter moves to the 600-800mm section of guide rail surface, the bubble in the gradienter moves backward one frame, with negative value, which means the plane of this section of the guide rail is inclined downward.

The last section of 800 ~ 1000mm gradienter is back to zero position, so if it continues to measure until the whole guide rail measurement is complete, the curve formed by each line segment is called guide rail straightness error curve (or measuring tool movement curve).

What are the characteristics of straightness error of guide rail by using optical instruments?

A: The principle of measuring rail straightness error using collimators and automatic collimators (optical flatness gauge) is based on that the beam motion is a straight line.

The advantages of using optical instruments to measure are:

(1) The accuracy of the instrument itself is less affected by external conditions (temperature, vibration, etc.) during the measurement process, and therefore the measurement accuracy is higher.

(2) It not only can measure the straightness error in vertical plane (not equal level) like a gradienter, but also replace wire and microscope to measure the straightness error in horizontal plane.

Therefore, it has been commonly used in the manufacture and repair of machine tools.

But for measuring long guide rail more than 10m, because of the longer distance for beam to pass, light energy loss is larger, so the image is not clear enough,  which can not be measured directly, but must be in section length measurement.
How to detect the surface distortion error of single-guide track?

A: For the shape of the surface of each guide rail, in addition to the requirement of straightness in the horizontal plane and vertical plane, in order to ensure that the guide rail and moving parts cooperate well with each other and improve the contact rate.

It is also required to control the distortion error of the guide rail surface, which is especially important for large guide rails.

When scraping, in order to measure the parallelism error between guide rails, it is necessary to prevent serious distortion on guide rails used for reference measurement.

The detection method of the distortion error of the surface of the mono-rail: V-shape gradienter pad block is used for V-shape guide rail, flat pad block is used for flat guide rail.

It starts from any end of the guide rail by moving the gradienter pad block, the value is read every 200~5001Am, the biggest algebraic difference of the gradienter readings is the twisting error of the guide rail.

This error is required to be specified in the machine tool accuracy standard, mainly in the scraping and grinding process.
What are the requirements for measuring flatness errors of machine worktable?

A: The detection methods for flatness errors of machine worktable is followed the “two-point method” in the past, which is to use parallel motion protractor, dial gauge, contour block and frame type-level etc. to measure some straight parts along the worktable and understood the maximum straightness error of any cross-section.

However, it is inconsistent with the definition of flatness in the national standard for geometric tolerances, the current JB2670-82 “General Rules for Inspection of Metal Cutting Machine Tools” pointed out that the measurement for checking the flatness error is the distance between two parallel planes, which is the smallest distance that accommodates the actual surface.

This definition shows that the inclusion of the plane as an assessment benchmark, its location also needs to be determined according to the principle of minimum conditions.

Therefore, it is necessary to fully grasp the error situation of the measured surface at first, and then to determine the evaluation benchmark according to certain criteria.

This determines the measurement must be divided into two steps: the first is to measure the height of several points on the actual surface relative to any ideal plane (measurement reference), and then through methods such as datum conversion etc. to obtain the error value in accordance with the definition.

How to operate and assess the flatness error when measuring with an indicator?

A: When measuring the flatness error with indicator, the measured part with support is placed on the plate, with working surface of the plate as the measuring datum.

When measuring, it usually adjusts the farthest three points on the actual measured surface are the same height as the plate (leveling), so the algebraic difference between the maximum reading and the minimum reading measured by the indicator is the flatness error value evaluated by the three-point method.

It can also adjust the height of the two ends of a diagonal line on the actual surface to be equal to the plate, and then adjust the two ends of the other diagonal line to be equal to the plate, so the algebraic difference between the maximum and minimum readings measured by the indicator is the error value evaluated by the diagonal method.

But this leveling is more difficult, it can measure the measured surface according to certain wiring and record the reading at the same time.

Generally, the algebraic difference between the maximum and minimum readings can be used as the error value.

If necessary, the readings from each measurement point can be processed according to the minimum conditions to solve the error value.
What issues should be considered when measuring flatness errors with a gradienter?

A:The flatness error measured by level meter is based on the natural level as the measurement base, when measuring, the actual surface to be predicted should be adjusted to the approximate level first.

The gradienter is put on the slab bridge, then the slab bridge is put on the inspected surface.

The inspected surface is measured point by point according to certain routing, the readings of each measuring point (grid number) are recorded at the same time, and then the grid number is converted to line value.

According to the measured readings (line value), through data processing, the flatness error can be obtained.

This method can be used to measure the flatness of large planes.

What issues should be considered when measuring the flatness error with the autocollimator?

A: When measuring the flatness error with the autocollimator, the autocollimator is placed outside the measured parts on the base, the reflector is installed on the slab bridge, and the slab bridge is placed on the measured surface.

When measuring, the autocollimator should first be adjusted to be roughly parallel to the measured surface.

The readings of the measuring points on the diagonal should be measured at first with the method of measuring straightness error according to the meter type wiring, then the readings of the points on another diagonal and the rest of the cross-section of the points are measured, and these readings are converted to line values.

According to the measured readings (line value), it uses the intersection of the two diagonals to determine the ideal plane in accordance with the diagonal law, and then the flatness error value is obtained according to this ideal plane.

If necessary, the error value can be further solved according to the minimum conditions.

This method can not be used to measure the flatness of large planes.

How to evaluate flatness errors when measuring with an optical flat?

A: The application of optical flat to measure a small plane, the optical flat is sticked on the measured surface during measurement, if the measured surface is concave or convex, there will be a circular interference band.

The flatness error is expressed according to the product of the number of ring fringe and the half-wavelength of the light wave.

If the interference fringe are not closed, the optical flat and the measured surface can be slightly inclined at an angle to form an air wedge between the two.

The ratio between the curvature of the fringe and two adjacent fringe multiplying by half-wavelength is error value.

However, the error assessed by this method is actually a straightness error instead of flatness error.

In the past, an optical flat can only measure a small plane.

In recent years, there is a flat interferometer, the application of this instrument can also use flat interferometry to measure the larger plane.

How to detect the perpendicularity error of the horizontal milling head spindle axis due to the movement of the milling planer worktable?

A: The method to detect the perpendicularity error of the horizontal milling head spindle axis by the movement of the worktable on the milling planer.

When detecting, the horizontal milling head is fixed at the position close to the worktable surface, the spindle sleeve is clamped, the milling head with rotatable angle should be adjusted to zero position.

The working table is moved to the middle of the guide rail, i.e. the place away from L/2 of the spindle axis, and a special slider is put in the T-slot of the worktable, so that the slider flange is close to the side of the central T-slot.

An angle bar is fixed on the spindle to make the dial gauge probe be placed on the side of the slider, and the readings are taken down.

The slider is not moving, after moving the worktable L length (the L length is determined by the machine tool accuracy inspection standards according to different specifications of machine tools), it is placed on the spindle 180 ° to make the dial gauge contact again touch the side of the slider for detection.

The maximum difference between the two readings of the dial gauge is the perpendicularity error.

How to detect spindle cone hole oblique circular runout error?

A: The dial test indicator is fixed on the machine tools to make the micrometer probe be placed on the inner surface of the spindle cone hole, micrometer probe is perpendicular to the inner surface of the cone hole, rotating the spindle for detection, the maximum difference of micrometer readings is the oblique circular runout error.

This detection method is often used when inspecting the main spindle cone hole of an internal grinding head.

How to detect the and oblique runout errors of spindle centering journal?

A: According to the use and design requirements, the spindle of the machine has a variety of different centering methods to ensure that the workpiece or tool in the rotation with a stable state, so it requires that the surface of the centering journal and the spindle axis of rotation is coaxial.

The method of detecting coaxiality error is also to measure its radial and oblique circular runout error.

The dial gauge (micrometer is used when requiring high measurement accuracy) is fixed on the machine to make the dial gauge probe be held on the surface of the spindle centering journal (if it is a conical surface, the probe is perpendicular to the conical surface), and the spindle is rotated to detect.

The maximum difference between the micrometer readings is the value of the radial and oblique circular runout error of the centering journal.

It is measured in the direction of the surface being measured.

How should the straightness error be detected when the lathe slide carriage moves in the vertical plane?

A: Straightness error detection of lathe slide carriage moves in the vertical plane: shake the handle, move the frame to the central line, a  gradienter is placed on the slide carriage close to the knife rest on an equal footing with the lathe guide rail.

Move the slide carriage to the place near the spindle box, record the reading of the gradienter.

After that, every time the slide carriage moves 500mm (or less than 500mm) to the tailstock direction, the reading is recorded at least four times on the whole travel of the slide carriage.

The readings of the gradienter should be arranged in sequence to draw the movement curve of the slide carriage.

The maximum coordinate value between the movement curve and the line connecting the two endpoints on every 1000mm travel of the slide carriage is the straightness error on the 1000mm travel.

It should connect the line connecting the two ends of the motion curve, the maximum coordinate value from the motion curve to the line is the straightness error on the entire stroke.

Note: Before inspecting the machine’s motion accuracy, it should first adjust the machine’s installation level.

The lathe test slab bridge is placed on the lathe guide rail, two gradienters is put on the slab bridge, one is parallel to the guide rail, the other is perpendicular to the guide rail.

Check whether the machine tool is level or not at both ends of the guide rail, and the reading of both levels are not allowed to exceed the specified value.

For high precision machine, the specified value is (1000:0.02)mm, for common precision machine, the specified value is (1000:0.04)mm.

How to detect the straightness error in the vertical plane when the gantry planer table moves?

A: The straightness error detection of the gantry planer worktable moving in the vertical plane, on the central position of the worktable surface, a gradienter is placed parallel to the direction of the worktable moving.

The worktable moves from one extreme position to the other extreme position and the reading of the gradienter is recorded every 500mm (or less than 500mm) after moving the worktable.

On the whole travel of the worktable, the readings of the gradienter are recorded in each position.

The readings of the gradienter are sequenced, which helps to draw the motion curve of the worktable.

The maximum coordinates of the movement curve to the two endpoints of the line on the 1000mm travel length is the straightness error on the 1000mm length.

Make mutually parallel straight lines to contain the movement curve, the coordinates of the two parallel lines with the smallest distance is the straightness error of the guide rail on the whole travel length.

How to detect the perpendicularity error of horizontal milling head spindle axis when the worktable moves on the milling planer?

A: The method to detect the perpendicularity error of the horizontal milling head spindle axis is the movement of the worktable on the milling planer.

When detection, the horizontal milling head is fixed at the position close to the working table surface, then the spindle sleeve is clamped, the milling head with rotatable angle should be adjusted to zero position.

The worktable is moved to the middle of the guide rail, i.e. away from the spindle axis L/2, and a special slider is put in the T-slot of the table so that the slider flange is close to the side of the central T-slot.

An angular table rod is fixed on the spindle to make the dial gauge measuring head on the side of the slider, and the meter reading is recorded.

Without moving the slider, after moving the L  length of table (the length of L id determined by the machine tool accuracy testing standards according to different specifications of machine tools), the spindle is placed 180 ° to make the dial gauge contact touch the side of the slider again for inspection.

The maximum difference between the two readings of the dial gauge is the perpendicularity error.

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