When running large boring mills, one common problem is damage to the spindle bar taper. These bars can be upwards of 8 feet long and 7 inches in diameter, making them difficult to repair once they have reached the point of no return as far as in-place grinding.It is possible to grind and chrome plate the taper back to OEM specifications, however, due to the type of machining being performed and the natural flex of the bars, the chrome may start to flake. To remedy this problem, Locher, Inc. designed a process of modifying spindle bars to accept a Locher, Inc. -designed replaceable taper insert. They can be installed in 4” diameter bars and larger.The inserts can be manufactured to standard taper dimensions or set to use Big Plus Tooling from #40-#60 sizes. They function in machines with or without tool changers and with drawbolts or drawbars. We normally hold .0002” TIR on the inserts installed, but the spindle-bar run-out and condition of the bearings affect total run-out on the insert.In-place installation takes about 5 days. Installation at our facility will take about 3 weeks.A major benefit of the insert is that it’s replaceable in the event of a crash. It can be replaced in about an hour, minimizing down-time. We also recommend that tapered inserts be reground in-place as many times as possible before replacing.A major crash with the insert installed can still damage the ID piloting bore in the bar, so if a new insert is installed you may still have excess run-out. In this event the ID of the bar is still able to be cleaned up to a diameter and the insert made to the new larger piloting diameter in the bar and installed back to like-new condition. It allows end-users to repair the bar in-house without needing complete spindle-bar repairs which are costly and have extended down-times.