Trouble Maker Moon

This is a graphical representation of the moon taking a bite out of diamond turning accuracy.

This is a graphical representation of the moon taking a bite out of diamond turning accuracy.

When the Large Optics Diamond Turning Machine (LODTM, the most accurate “instrument” ever constructed) was being developed at LLNL during the mid-1980s, a team of engineers had to work meticulously to decide on many hundreds of possible error sources that could decrease the accuracy of the unit during use. Many machines designed by precision engineers have an error budget (more on this topic in a later blog). Depending on the amplitude of the error it would either require some sort of compensating or have some solution for correction. Of course, temperature was one of the issues, but this was much before the birth of Praecis. 

This is what happens when the moon goes on vacation... -___-

This is what happens when the moon goes on vacation... -___-

One morning one of the engineers working on the project had an epiphany, the moon might have an effect on the LODTM’s results! This wasn’t considered by any of the engineers yet but it made perfect sense. Think of how the moon has a direct correlation with the high and low tides. An engineer was then assigned with quantifying the resultant error.

 

The error from the moon’s gravitational precession about the earth was both indeed quantifiable and measureable. This meant that an algorithm would need to be created and implemented to compensate for this error and added the the many hundreds of other calculations. Fortunately, the amplitude of error was below the threshold for consideration of the error budget. Whew! Time to wipe off the sweat! Writing those equations and algorithms would be incredibly complex and time-consuming.

Temperature, on the other hand, does not play as nice or consistent as the moon and its effects are much greater and cannot be ignored. In fact, temperature is constantly and rapidly changing. This makes temperature control a nightmare for anything outside of a highly sophisticated HVAC system with may often cost several hundred thousand dollars to purchase and install.

 

For best results in diamond turning, use Praecis Air Temperature Control systems.

For best results in diamond turning, use Praecis Air Temperature Control systems.

Thankfully, there is a cost effective way to satisfactorily reduce error caused by thermal variation. Praecis has introduced state-of-the-art ultra precision temperature controlled enclosure systems 5 years ago and can stabilize temperature as precisely as ±0.002 ºC or a factor of at least 50. By using such an extreme degree of temperature control any heat generated from cutting a part would quickly return to its designated ‘set-point’ and thermal expansion on a given part would have no effect on the cut (as the temperature variation is too little and brief to allow for any changes whatsoever). Praecis designs the best known temperature management systems and offers the most comprehensive extended warranty packages.

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