MIKE BREEN ON PREVENTIVE MAINTENANCE

A Closer Look At
Spindles And Turrets

by Michael W. Breen

Michael W. BreenLast month we began to talk about checking machine tool accuracies, specifically those related to the axis. We will continue to address accuracy by looking at the spindle and turret.

All lathe alignments are directly related to the spindle. For example, if the headstock alignment is off, the Z-axis zero point will be off as well. It affects the turret’s rotational alignment (especially on slant beds) and can cause taper problems. If the spindle is out of alignment, all types of problems can occur.

Checking Spindle Alignment

Check spindle alignment by chucking up a piece of material and performing a cut. It is best to use the same type of material that the machine normally runs or you could get a false reading. The material should be 2" in diameter or larger and around 9" in length. You do not want any more than about 6" extended from the face of the chuck. If the diameter of the material is too small or the material is too soft, it could deflect.

Once the material is safely chucked up, start cutting. Make sure the cuts are not too heavy, and continue executing a series of passes until the circumference and length of the part is completely cleaned up. Then, measure the piece with a micrometer at the tip and the chuck side of the part and record both findings. They should be within a couple of ten-thousandths of each other. Your machine tool manufacturer should provide you with the runout allowance.

If the chuck side is larger than the tip, then your spindle is angled towards the turret. If the chuck side is smaller than the tip, then your spindle is angled away from your turret. As far as repairing this problem, refer to your machine manual and follow their recommendation. Adjusting headstocks for the first time can be a little tricky. I should warn you: do not do anything without mounting an indicator on the piece first. We will get into the repair down the road; there is quite a bit to it. Remember a PM is an inspection with minimal repairs done during the PM. All major repairs should be scheduled for a later time.

Checking the Turret

Once the spindle is checked, the next thing to look at is the turret. This task will require a magnetic base and an indicator. First, check the squareness of the turret by mounting the indicator in a place where you can sweep across the face of the turret. The indicator should not move. If it does, you will have to remove some covers, loosen the mount bolts, and square it up. Look at the print first for a pivot or location pin. Just as with the spindle, you may want to call in someone the first time you have to make this repair.

Rotational Check

Most turrets have a slot milled or ground into them for the mounting of form or groove tools for the rotational check. This slot should be parallel to the axis on which the turret is mounted. Usually it is mounted on the X-axis. If there are no slots in the turret, you will need to use a coaxial indicator to sweep the bore. First, zero out the indicator in the X-plane, then sweep the bore from top to bottom. The top should match the bottom. If it does not, the turret will have to be aligned. If you have both milled slots and bore toolholders, still use the slots as your reference. As far as the actual rotational alignment of the turret goes, contact your machine tool builder. There are many different styles and concepts when it comes to the turret.

The best way to train maintenance personnel to perform these checks and repairs is to invest in a service call. Training with an engineer in these areas will enable your staff to complete these tasks correctly and with ease. Once these checks and repairs are completed, your tooling cost will decrease, scrap will decrease, drills will last longer, and programmers will not have to spend time trying to manipulate programs to make a straight cut.

Next time, we will try to finish with the subject of accuracy. We will look at zero points, tailstocks, and sub-spindles. Talk to you next month.


Mike Breen started his career as an aircraft electrician in the U.S. Army’s 101st Airborne. A Certified Electronic Engineer with 14 years’ experience in machine tool repair, he is presently a Field Service Engineer with Ellison Machinery Company of Wisconsin. Mike has held this position for more than six years, during which he has designed and implemented complete preventive maintenance programs for many successful companies resulting in significant increases in their machines’ performance. For comments and inquiries about these articles, his e-mail address is mbreen@ellisonwi.com.

- December 2000