Lathe Nose Spindle Repair

CHALLENGE

Northland Tool & Electronics recently received a lathe spindle for repair from one of our customers who manufacturers surgical implants. The customer was experiencing unacceptable chatter on the surface finish of their parts, but was unable to troubleshoot the issue in house. When the spindle arrived at Northland we completed a full evaluation and test run before disassembling the spindle. All our testing, vibration analysis, measurement of run out on critical surfaces, and motor testing showed the spindle to be within specification and healthy.

SOLUTION

We are always reluctant to disassemble a spindle that tests well, so we contacted our customer for additional details and to provide technical support. We visited the facility to get a first-hand look at their process. While we were there, we performed additional vibration analysis on similar machines to gather a baseline for analytical purposes. After meeting with their group in charge of this project we agreed to continue testing on the spindle with some tooling they provided for us.

Our next step of the project was to run the spindle with the tooling provided to see if it was influencing the performance of the spindle. During this process, our technicians started noticing odd frequencies showing on the vibration analysis, which pointed to mechanical looseness. We discerned that the tooling provided was indeed out of balance. Knowing this is a direct contributor to part finish we balanced the tooling to eliminate this as a factor in the part chatter. As we had not experienced this before we added the tooling into the equation, we dug deeper into its cause.

When we brought the customer’s tooling to our grinding department to check all of its critical surfaces, they found that the relationship between the taper and face of the mounting surfaces on the tooling were out of specification from the tooling manufacturer. The tooling taper was not ground correctly, preventing the tooling from meeting the face when tightened.

RESULT

After disclosing our findings to our customer, we discovered they had had five sets of tooling made recently and they decided they would like to send them all in for requalification. After initial inspection we found that three of the five had the same issues with taper-to-face contact. We were then able to kiss grind the tooling back into specification on our Kellenburger grinders. We balanced all five sets after the grinding process and returned the spindle and tooling to the customer.

Once we installed the spindle with the balanced and requalified tooling, the customer stated that they were not experiencing any part quality issues with the machine or that spindle anymore.