Under pressure to consistently produce high-quality parts and meet customer deadlines, shops often overlook the long-term accuracy of a milling machine’s spindle. While not typically a daily maintenance item, spindle integrity and inspection is crucial for reliable part production as well as for the overall health of a machine tool.
Many factors affect the dimensional repeatability of a machine spindle. Constant, three-shift machining, for instance, can quickly generate problems, as does heavy cutting in tough materials. Ignoring regular preventative maintenance is another contributor to unreliable spindle performance as is the use of worn or inappropriately large toolholders that create uneven forces and accelerate spindle wear.
Indicators of spindle wear include poor finishes on machined parts along with toolholders showing fretting and sticking in the spindle. Other symptoms include out-of-the-ordinary noise, vibration and excessive heat. A worn spindle can also lead to downtime for repairs or actual spindle replacement. Additionally, and what most shops are unaware of, is that runout from a worn spindle or one that is out of alignment can significantly reduce the performance of high-precision tool holders.
To take full advantage of an investment in high-precision tool holders, such as those from REGO-FIX, shops must regularly check the runout and parallelism of their machine spindles. To ensure they do, REGO-FIX has introduced its MasterBar test arbor product line for shops to check and align their machine tool spindles.
Consisting of a precision spindle interface and an extended arbor bar, MasterBar tools are quick and easy to use. Shops conduct a test procedure with a thorough cleaning of the spindle’s tool taper because when micron-scale measurements are involved, any particles, oxidation or other contamination will negatively affect the results.
Once the spindle interface is clean, shops chuck the MasterBar arbor (also totally clean) in the machine’s spindle. After measuring the arbor runout close to the spindle nose (~50mm from the interface) with a 1 µm or 2 µm scale dial indicator, the user turns the arbor by hand and observes the runout, comparing that result to the spindle manufacturer’s specifications. The user can then check runout at the bottom of the arbor and compare it to the spindle manufacturers’ specifications for runout at that distance from the spindle nose.
Next, to check parallelism, the user places a dial indicator in the middle of the arbor and jogs the spindle up and down in the Z axis. The corresponding arbor length used depends on the size of the spindle interface. Large interfaces like HSK 63 may require an arbor that is 300mm long, while for smaller interfaces such as HSK 40, an 180mm arbor will be appropriate because the smaller associated tools are not expected to run at extended lengths.
A shop can also use the MasterBar arbor to check spindle alignment after a crash. If runout and parallelism have changed after a crash, the shop itself may be able to realign the spindle or will know to call a service technician.
Storage of the MasterBar can affect its accuracy. This is why REGO-FIX ships the tool in custom foam packaging that supports its entire length. Without such packaging, simply storing the tool flat on a table will eventually affect its straightness and thereby its accuracy.
REGO-FIX grinds the outside surfaces of MasterBar arbors to the same specifications that it meets when grinding the inside dimensions of its tool holding products. Cylindricity of the entire length of the MasterBar is a maximum of 2 µm, while runout from the cylindrical part of the tool to the taper is always under 3 µm.
MasterBar arbors feature an aluminum ring laser-marked with the tool’s unique serial number and a QR code. Scanning the QR code enables a user to go to the REGO-FIX website and access technical information about that specific tool as well as its inspection certification. The information and certificate are always available, even if the originals are misplaced. MasterBar arbors are available in ST, CAT, BT+40, HSK-A, HSK-E and ATC-E interfaces, in lengths from 350mm to 70mm and diameters from 40mm to 10mm, depending on the size of the interface.
As with vehicles (and the human body), regular checkups are the key to long and reliable performance. For machine tool spindles, the REGO-FIX MasterBar ensures your spindles are always in tip-top shape and will never hinder your machining precision.