Upgrading machine tools during a market uptick: these guidelines aim to help shops determine whether it is in their best interests to revive existing metalcutting equipment of to buy new machines

Modern Machine Shop, April, 2004 by Derek Korn

Mr. Green says some shops have a perception that restorations are very inexpensive, or that any of their machines could be restored. While it is true that just about any machine could be restored, not every machine should be restored.

The 60 percent rule is the industry's fundamental tenet for determining whether to restore or replace a machine. Simply stated, if the cost to restore is less than 60 percent of a comparable new machine's price, restore it. If the cost is above that, buy new.

Retrofits and rebuilds usually have no problem getting under the 60 percent limit. In fact, retrofits sometimes cost only 30 percent of a new machine's price, according to Mr. Green.

Because of the amount of work involved, complete remanufactures come closest to hitting the 60 percent ceiling and often exceed it if the machine is relatively small. This is why remanufactures typically are reserved for sizable machines like boring mills, large-chuck lathes and big-table horizontals. This is also what nixes any notions of remanufacturing small VMCs or HMCs. As new machines continue to shrink in price and improve in terms of speed, accuracy and multitasking capabilities, it is nearly impossible for small used machines to gel under the 60 percent limbo pole.

"Understandably, small shops may have an emotional attachment to their first machine," Mr. Green explains, "perhaps a $30,000 VMC they mortgaged their house to buy. They must realize that it would take more money to restore it than to buy new. Some have a hard time dealing with this. Part of our job is explaining to them that restoring the machine is not in their best interests."

Mr. Green identifies four commonly remanufactured machines and suggests the following respective minimal sizes to meet the 60 percent rule:

* HMCs should have a minimum of an 800-mm table.

* Vertical boring mills should have a minimum of a 48-inch diameter table.

* Horizontal boring mills should have a minimum of a 5-inch diameter spindle.

* Horizontal slant bed lathes should have a minimum of a 28-inch chuck. The exception to this is very long-bed lathes commonly used in the oil industry.

The 60 percent rule is not absolute, though. Consider new machine ancillary costs. Will you need to add a foundation of rearrange the shop? Will you need to purchase new tooling or fixturing? Will you be able to run the same part program, or will you need another post processor to generate the correct code to match a new CNC? These "little" things add up quickly in terms of cost and complications, and they may make restoration a more attractive alternative, even if you are close or over the 60 percent limit.

From a mechanical standpoint, a restored machine's basic components likely won't be altered unless the machine design is dramatically customized. That means the maintenance crew will have an instant comfort level with the machine after restoration. But with a new machine, there may be a mechanical learning curve, especially if the machine has components such as linear guides of linear motors that the previous machine didn't have. Maintenance might not want to touch it.