Re: 720 rule vs LCD
They are basically just different paths to the same place. I don't know the exact origin of the 720 rule but if memory serves Fibergeek tested it to considerable lengths and found it to be correct. Kebo found it to get within +-7% of the target thickness. So scientifically it must be sound. At 1A per square foot current density anodic coating will grow to 1 mil in 720 amp minutes. From this, the only way to effect run time is to vary CD or the thickness of the coating. What needs to be understood also is the effects of different CD's on the coatings growth. ie: pore size. It's my opinion that if you only do a hand full of parts or a part once in a great while you may be able to get by not knowing all the ins and outs but to truly do it right it's almost a necessity to know and understand the process including the calculations. How else can you accurately diagnose a problem if one should arise. The only problems I have had that I did not know how to handle completely have been due to material grade, primarily cast parts. The other problems have been few and far between with little doubt as to their cause.
If you work all the numbers, all the methods are working off current density. The difference is perspective.
These figures were started by MCaswell to try and alleviate newbies confusion with the calculations. To simplify if you will and make the calculations in line with the other plating.
1amp for 50 sqin for 240 minutes = 1mil ( a 2.88 CD )
1amp for 25 sqin for 120 minutes = 1mil ( a 5.76 CD )
Your old method took me a little to sort out but was close in line with the 720 rule. It appeared to me that you were looking more from the perspective of what your PS would do and the time you wanted to do it in while possibly overlooking the basics or not concerned with them as in the CD being run. I mean no insult nor disrespect by what I say just letting you know how it looks from my point of view. You could not be that far off to have gotten the results you have for the time you have been doing anodize. You just had a different approach than I.
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