Sharing Our Know-how

We're proud of our work. And we're confident in the knowledge that backs it up. Below you'll find information about rebuilding, retrofitting, remanufacturing or maintaining machine tools.  We post new articles frequently, so visit often.

The piece below was written by Jim Leigh, Pyramid co-owner. Jim has more than two decades of experience in this business. He also is named on U.S. and foreign patents and has served as an expert witness on machine condition and repair.

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(The material below is copyrighted by Pyramid Rebuild & Machine LLC.)


Proper tailstock alignment is vital
 by Jim Leigh, Pyramid Rebuild & Machine co-owner

When operators are having difficulty maintaining consistency on turned or ground work-pieces, a culprit that's often overlooked is the machine's tailstock. A misaligned tailstock can cause taper, inconsistent size, oversize holes, out-of-square shoulders and a lot of frustration for you and your operators.

On both lathes and grinders, the tailstock must be concentric with the work-piece spindle and parallel to the bed ways in two planes simultaneously.  In addition, the guide surfaces on the tailstock base must fit properly on the bed's guide ways, which must be straight and true to the spindle.

Make sure the tailstock quill fits properly within the housing. A loose-fitting quill will cause the same problems as ill-fitting ways.

Before checking the tailstock's alignment, make sure the machine bed is level, and if you're checking a grinder, make sure the sub-table is set parallel to the bed. Next, clamp the tailstock down, extend the quill and lock it.

Mount an indicator on the cross-slide of a lathe or to the wheel-head of a grinder. Set a zero with the indicator needle touching the top of the quill. Now move the slide and read the indicator along the length of the quill. Record the measurement and take a reading on the side of the quill. On a lathe the readings should be within .001 inches per foot. On a grinder they should be half of that. If they aren’t, you have an alignment problem. If you find that you must always adjust the tailstock from side to side every time you move it, it's because the tailstock is not true to the bed-ways.

Now turn or grind a piece between centers in the machine. If you have a pre-ground mandrel with centers in it, you can use that instead. With the mandrel or test piece mounted between centers, run an indicator along the top of it. As earlier described, the indicator should be mounted to the cross-slide on a lathe or to the wheel-head of a grinder. Record the error. Assuming the piece you are checking is straight, the error should be less than .002 inches. Ideally the tailstock end of the work-piece will be slightly higher than the headstock end.
 
Finally, insert a tool or test bar into the taper of the tailstock quill. Indicate along the length of the tool or test bar on both the top and side. These readings should match the readings you took on the quill. If they don’t, then the tailstock taper is not in line with the quill's outside diameter.

If the tailstock alignment errors exceed the tolerances shown, you should consider a realignment. This is a fairly common problem on lathes and grinders on which the tailstock is used extensively. The ways of the tailstock wear more quickly because the lubrication system on most tailstocks is suspect, at best, and because dirt and grinding grit get under the tailstock when it's moved.

The tailstock is subject to a lot of contamination because it's always unclamped when it's moved. If the guide ways haven’t been wiped off prior to moving the tailstock, then dirt creeps in. To make matters worse, some operators clamp the tailstock down on the dirt, embedding it in the slide and worsening the problem.

So, if you do a lot of work between centers, or need to drill and ream precision holes using your lathe, check out that tailstock alignment and have any realignment issues remedied.

Whatever you do, I recommend that you maintain a metal-to-metal fit between the tailstock and the bed of the machine. Do not allow anyone to “build up” the tailstock ways with a non-metallic way liner. These materials will not hold up to the dirt and repeated clamping cycles.