Anatomy of a Tailstock Rebuild-Repair

A new bearing assembly with the old-style solid nose, prior to redesign of the nose. (Image courtesy Riten Industries)

Riten Industries applies a mix of inspection, analysis, engineering execution, and inventory backup to eliminate costly machine downtime due to tailstock failure.

February 2024

The following article was contributed by Riten Industries, Inc.

WASHINGTON COURT HOUSE, Ohio—Riten Industries, Inc. is reported to be the largest domestic manufacturer of live centers, dead centers, and face drivers in the work holding industry. Riten’s quality management system is ISO 9001:2015 certified for the design, manufacture, and repair of work holding devices and machine tool accessories, according to the company’s certificate of conformance.

A growing part of Riten’s re-engineering platform consists of solutions to eliminate costly machine downtime resulting from tailstock failure. Why? A large amount of machinery becomes obsolete before the end of its service life, but the original manufacturer (OEM) of the machine may no longer exist—and therefore cannot provide timely replacements.

If a machine becomes obsolete, Riten has developed a dedicated tailstock “rebuild-repair” program. It includes a bearing assembly inventory platform that allows manufacturers to strategically schedule downtime.

An old bearing assembly showing six bearings separated by a spacer, with replaceable nose. This is a used assembly in for repair. (Image courtesy Riten Industries)

Riten’s Tailstock Rebuild-Repair Process

Some tailstock projects are quoted by Riten based on existing lathe assembly drawings. A budgetary proposal is provided for a repair based on these drawings, with the understanding that it is subject to change based on the condition of the tool as received. From there, Riten executes its established tailstock repair process.

Following is a step-by-step overview of the process.

Step 1

Upon receipt, the tool is photographed and a project folder is assigned. The project folder contains detailed inspection forms tailored to the scope of the project. Riten’s repair department then disassembles the tool—documenting the process with notes and photographs specific to each step.

Once the tool is fully disassembled, a bill of material is created detailing all of the essential components.

Step 2

The components go to the inspection department, where a visual review is performed in addition to taking vital measurements. All of the key inspections and fits are documented in the project folder, which details both the inspection process and the expected inspections. Key inspection variables include the following:

• The fit between the quill OD and the tailstock ID
• The fit between the quill ID and the OD of the bearings
• The spindle bearing journals and the bearing ID
• The spindle point and the bearing journals between centers to determine concentricity
• The Morse taper ID (if the spindle has an ID taper instead of a point)

Step 3

The folder goes to quoting, where an engineer reviews the scope of the project and the inspection findings. A quote is then created based on the condition of the spindle as received.

Step 4

The inspection findings and the preliminary quote are presented to the customer. Based on feedback from the customer, the scope of work is finalized. Also, if it is determined that the parts don’t exist, they will proceed to retrofit, rebuild, and redesign of headstock or tailstock assemblies.

A Rebuild-Repair Application Example

Since 1912, Deister Machine Company, Inc., of Fort Wayne, Indiana, has been a major manufacturer of high-quality specialized vibrating equipment for the mining, quarrying, and allied industries. The family-owned and operated company is a preferred manufacturer of vibrating feeding, scalping, and screening equipment.

Deister is known for delivering reliable separating and sizing equipment that is engineered to operate hour-after-hour, day-after-day, with minimum attention and maintenance. The company’s products are uniquely engineered to  significantly increase efficiency and productivity within key aggregate industries, including crushed stone, sand, gravel, asphalt, coal, coke, slag, and ore processing.

Deister’s dedicated aggregate capital equipment portfolio includes machinery for inclined screens, high-speed screens, horizontal screens, asphalt-batch plant, asphalt-drum mix, de-watering screens, feeders and grizzly feeders, and electro-mechanical feeders. In 2006, Deister realized that its lathes required excessively frequent maintenance, which was affecting its  production output and resulting in costly downtime.

The company contacted Riten, which swiftly performed essential inspection-and-failure analysis on one of its two lathes.

Based on its findings, Riten designed and manufactured a new quill with an upgraded four-piece bearing design. This new design was an upgrade with more capacity than the existing bearing design. Riten also designed and manufactured a replaceable point spindle instead of the existing solid spindle, because the customer noted that the spindle points of their existing lathes were easily damaged. This new design was highly efficient and performed much better than the old design.

A year later, however, Deister came back with a desire to achieve additional bearing life. Riten then initiated a review of the application on-site and discovered that part of the process involved an eccentric load that they were not aware of. Eccentric loads are very hard on both the bearing assembly and the spindle of the lathe.

The review revealed that Deister was turning shafts that weigh between 1,500 pounds and 3,000 pounds. Once the turning is complete, they cut a new center hole that is offset (not on-center), and they turn a new bearing journal—resulting in a shaft that is unbalanced. In effect, a heavy, eccentric shaft spinning at high RPM can literally walk the machine across the floor, which is extremely hard on the equipment and its effective lifespan. However, this shaft design is key to the performance of equipment Deister is known for.

Again, after reviewing the application on-site, Riten suggested key changes to both the process and the selection of dead centers. In addition to premature wear on the bearing assemblies, dead centers were breaking—a vital safety concern. In many cases, the center hole sizes were inadequate; therefore, charts were provided that specified minimum center hole sizes based on the weight of the part.

Additionally, the bearing assembly in the new unit was upgraded to a matched set of six angular contact bearings. The existing four-bearing assembly was replaced with a six-bearing assembly in the same custom quill. During design of the quill, room was left in the assembly for additional bearings if they proved necessary.

Another key downtime dilemma is delivery on a bearing assembly, which can be anywhere from 12 to 20 weeks, depending on availability of the base bearing. The bearing manufacturer starts with a standard high precision bearing and reworks them into a six-bearing matched set. Riten orders and inventories a spare bearing assembly with every customer repair. This is essential for limiting production downtime for a repair—reducing downtime to 2–3 weeks, versus 3–5 months for the repair.

A complete tailstock showing a replaceable point. (Image courtesy Riten Industries)

Final Thoughts

Between 2006 and 2010, Riten upgraded a total of three Deister lathes, two of which are identical. They all share the same bearing assembly and replaceable point. The upgrade included manufacturing new quills with replaceable point spindles and honing the tailstock to fit. Notably, the new tools were installed on-site.

With this established “shut-down elimination” program in place, Deister continues to have Riten refurbish one of its lathes each year during its slow season. Each lathe is refurbished approximately every 2–4 years depending on its usage.

“It’s imperative for companies to perform critical maintenance during seasonal downtimes on their lathes,” said Riten Industries Vice President of Manufacturing Mitchell Kirby. “Depending on business levels, more companies send us their damaged units annually for either refurbishment and/or replacement. We also manufacture spare identical quill assemblies for inventory. With this in place, we can limit their downtime to 3-5 days to remove the existing unit and mount the spare, whereas delivery on a replacement unit could be 14-18 weeks.”