What prevention methods are in place in the small machining outfits at the edge of town, or for large factories? 

A lot of people subscribe to insurance programs that "should" compensate for blackout damages. It is all very well until a blackout occurs and the small print gets scrutinized.

Another method is to hope and leave it to deities that the blackout won't happen, to wish it away... This is one sure foot into the Blackout Club door.

 CNC Praying 

If a power cut happens during machining on CNC machining center, milling machine or on a CNC lathe, what often occurs is that the tool in contact with the metallic part whilst machining gets broken as the cutting speed and feed rate grinds to a halt in an uncontrolled manner when the machine runs out of juice.

 S33-MachiningCenter

Depending on a lot of parameters this can be either benign or horrendously expensive.

For instance, let's imagine, you are machining an aircraft wing spar or a wing skin. The billet size is about 30 meters long by 5 or 10 meters wide and 3 or 4 meters thick, from this you are machining a very large, time-consuming, expensive aircraft structural part. The manufacturing cost of this part is of the order of several hundreds of thousands of euros, so if a blackout causes a power down of the machining operation, this is going to be a huge problem. 

The part has to be scrapped, the tool is generally broken, sometimes the machine spindle is broken also. The area needs to be closed off to clean and repair the damage.  This can take days!

This is perhaps why Airbus has resorted to working independently from the grid to assemble the wings of the A380 Superjumbo. Airbus powers the West Factory wing assembly and painting hall in Broughton by using three 11 kV 1020 kWe natural gas-powered Aircogen units that provide electrical energy and heat to ensure the temperature remains close to 20°C.  These units also supply the temperature control for painting (18°C to 80°C )

A380

Without having to resort to such drastic measures, it is possible to make sure that your machine remains powered up enough time to stop cutting into the part in a controlled manner and record which program line it is at. 

An ultracapacitor module can provide enough power for several seconds and will cost only a small fraction of the potential damage and cost a blackout can incur.

SkelGrid and Rack and Modules can keep your commercial operation afloat for 1 second or more depending on power requirement, this is enough time to get your power backup solution up to speed, without enduring a blackout.