Anatomy of a Tailstock Rebuild-Repair

Established in 1969, Riten Industries, Inc. is a manufacturer of live centers, dead centers and face drivers. A growing part of its re-engineering platform is leveraging solutions to eliminate costly machine downtime due to tailstock failure.

"The fact is that a lot of machinery becomes obsolete before its time, and the original OEM may not exist anymore to provide timely replacements," said a company spokesperson. "If a machine becomes obsolete, Riten has developed a dedicated tailstock rebuild-repair program that includes a bearing assembly inventory platform that allows manufacturers to strategically schedule downtime."

Riten 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.

Step one: Upon receipt, the tool is photographed and a project folder is assigned containing 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 the essential components.

Step two: The components go to inspection, 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 the inspection process and the expected inspections. Key inspection variables include:

• 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 three: 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 four: 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 if the parts do not exist, they will proceed to retrofit, rebuild, redesign headstock or tailstock assemblies.

Deister Machine: Rebuild-Repair Case-In-Point

Since 1912, Deister Machine Company, Inc. has provided vibrating equipment for the mining, quarrying and allied industries. The family-owned and operated company is a 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 in 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, dewatering screens, feeders and grizzlys and electro-mechanical feeders. In 2006, Deister realized that its lathes required excessively frequent maintenance, which was affecting production output and resulting in costly downtime. They contacted Riten who swiftly performed essential inspection-and-failure analysis on one of the company's two lathes.

Based on its findings, Riten designed and manufactured a new quill with an upgraded four-piece bearing design. This new design had more capacity than the existing bearing design. Riten also designed and manufactured a replaceable point spindle instead of the existing solid spindle, since 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 of which they were not aware. Eccentric loads are very hard on the bearing assembly and the spindle of the lathe.

The review revealed that Deister was turning shafts that weigh between 1,500-3,000 lbs. Once these are turned complete, they cut a new center hole that is offset (not on-center) and 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 for which Deister is known.

After reviewing the application on-site, Riten suggested key changes to the process and their selection of dead centers. In addition to premature wear on the bearing assemblies, they were breaking dead centers-a vital safety concern. In many cases, their 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. When designing 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 12-20 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 two to three weeks vs. three to five months for the repair.

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 their slow season, with each lathe being refurbished approximately every two to four years depending on their usage.

According to Riten's V.P. of Manufacturing, Mitchell Kirby, "It is imperative for companies to perform critical maintenance during seasonal downtimes on their lathes. 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 three to five days to remove the existing unit and mount the spare, whereas delivery on a replacement unit could be 14-18 weeks."

Authored by Kent Hizer, Riten Industries, Inc.

For more information contact:

Riten Industries, Inc.

1100 Lakeview Ave.

Washington Court House, OH 43160

800-338-0027 / 740-335-5353

www.riten.com/services/tailstock-repair