CNC Lathe Headstock - Alignment and Checks
Continuing our series detailing alignment checks and adjustments that may be required after a visit to Crashville ... this post deals a little with the other end of your CNC lathe ... the tailstock.
The tailstock may end up getting a bump in variety of ways and for a variety of reasons ... sometimes it doesn't even have to be involved in the cutting !! Sometimes just sitting somewhere on the bed ... it can be bumped or hit with the turret body. These kinds of "crashes" will inevitably cause the tailstock spindle to fall out of alignment with the main spindle ... the result? ... taper when cutting a workpiece that is held in the chuck and supported by the tailstock.
However ... if you perform any main spindle alignments as outlined in the post above ... you definitely will need to re-check the tailstock alignment. Shifting and adjusting the main spindle will surely result in a mis-alignment with the tailstock.
The easiest way to check the alignment of the tailstock is to test cut on a piece of material the length of which you feel is appropriate ... with one held in the chuck and the other end supported with the tailstock. The stock should have a precise center drill hole to accept the tailstock center. Obviously the longer the piece of stock used for cutting will result in the closer the alignment adjustment ... so you should select a diameter and length of stock that is appropriate ... you're a machinist ... you know what will work best.
Make sure to take enough stock to insure the bar OD has been "cleaned" ... then take a light finish cut the appropriate length and measure both ends. The difference in diameters at the headstock and tailstock end will tell you the amount of mis-alignment.
If you reviewed our headstock blog post ... you are already familiar with the type of construction used on most tailstock assemblies ... which is similar to the construction used on the headstock assemblies. As the pic below illustrates ... the tailstock body is usually bolted to the tailstock base. There are usually "push-pull" bolts similar to the headstock assembly that can be used to push-pull the body on the base for alignment.
One way to make the adjustment ... and should be the starting procedure ... is to mount an indicator on the chuck face ... move the tailstock all the way up to the chuck so you can sweep the tailstock spindle with that indicator mounted on the chuck ... and adjust the tailstock body until you get a zero reading. This is a fairly good place to start ... but you should still conduct the test-bar procedure below to insure that the whole tailstock body is "square" with the spindle. Performing only this tramming procedure will not insure that the tailstock body is out of square ... and may still result in a taper when the tailstock is employed in shaft cutting.
- Mount an indicator somewhere on the tailstock base against the tailstock body to measure the amount of movement you will employ in the steps below.
- Crack the hold down bolts loose.
- Use the push-pull bolts to adjust the body in the direction and by the amount you deem appropriate.
- Make sure the hold down bolts are fairly snug.
- Take another test cut.
- Measure again the headstock and tailstock diameters ... repeat steps above as necessary.
As mentioned above ... whether it is a visit to Crashville involving the tailstock ... or a re-alignment of the headstock ... the above re-alignment of the taistock is just as critical to accurate machining as any other check and adjustment. We hope that the clues and tips here can help you get back on track with accurate machining with your CNC lathe.
Until Next Time ... Happy Chip Making !!