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Old 03-18-2013, 11:43 AM   #1 (permalink)
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Measuring parts surface area for cc anodizing ???

I am going to try to do some anodizing using a constant current rectifier and I know that in order to calculate the current and time needed for anodizing I need to know the surface area of the parts.

How do you measure or calculate the area for complex shapes like gun bodies or frames?

Is there an easy way to estimate the measurements?
If not, how do you measure this stuff?

Thanks!
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Old 03-23-2013, 01:44 AM   #2 (permalink)
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this seems like a job for Multivariable calculus! This is actually a very challenging problem to do by hand. The techniques I will present will require a background in statistics (techniques of regression specifically) and multivariable calculus with analytic geometry.


Last edited by davehome333; 03-23-2013 at 01:24 PM. Reason: changed order of integration. changed limits of integration.
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Old 03-23-2013, 01:53 AM   #3 (permalink)
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Thanks for the information, but there are 2 small problems.
- I don't think you accounted for the internal surfaces
- this is way too complicated for my limited knowledge of those subjects

Thanks for the drawing and equations thought!
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Old 03-23-2013, 02:01 AM   #4 (permalink)
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you are correct in your assumption that i did not account for the internal surface area of the parts. I was just outlining the general ideas behind measuring surface area of complicated shapes. additionally, it is impressive that you made at least this observation given that you do not have knowledge of these mathematical techniques.

here is a joke for you:
3 people are asked a difficult question. one is an engineer, one is a physicist, and one is a mathematician. 5 minutes later the engineer comes back and produces the answer approximated to 3 decimal places! 30 minutes later the physicist comes back and produces the answer approximated to 20 decimal places! several days go by and the mathematician comes back and has proven that the answer exists.
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Old 03-23-2013, 02:17 AM   #5 (permalink)
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LOL

I may not know much about the math, but I did have to take Calculus in college. I only repeated it 3 times before passing so I could recognize some of it.

The folks at the caswell forum suggested I break down the body in to simple shapes and calculate the area for each segment separately.
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Old 03-23-2013, 02:35 AM   #6 (permalink)
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What type of tolerances are you allowed within the process? I would imagine that there is a little bit of wiggle room, otherwise nothing would ever get done due to needing a near perfect calculation. I would break it down into basic shapes (squares and circles) and tally them all up and call it a day. Otherwise, you'll be doing a whole lot of number crunching and there is a decent chance that it's not necessary.
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Old 03-23-2013, 03:09 AM   #7 (permalink)
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how accurate do you need to be? I would need to know the relation between surface area and current. that seems to be the missing link. approximating surface area is something you could do with just geometry and a ruler. all functions of area boil down to length times width.

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Old 03-23-2013, 03:18 AM   #8 (permalink)
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Originally Posted by desertT1 View Post
I would break it down into basic shapes (squares and circles) and tally them all up and call it a day.
what you are describing is called "The Method of Exhaustion" and is one of the underlying ideas behind integration techniques dating back to the time of Archimedes. take note of the smaller and smaller triangles:


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Old 03-23-2013, 05:33 AM   #9 (permalink)
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If you can draw it up in SolidWorks or a similar program it can calculate the surface area for you.
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Old 03-23-2013, 06:18 PM   #10 (permalink)
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The Caswell forum is a good resource.

Variational calculus only works if you have a continuous equation to feed it.

If you had to model every part you ano'ed, you probably wouldn't bother. On the other hand, a library of parts would be nice if you work on similar parts more than a few times.

Take the engineering solution and approximate it. There are plenty of other variables to render high precision useless. The Egyptians used to calculate taxes based on the area of the sum of the triangles in a farm. After you get your current (which can vary from 3 amps/sqft to 12 amps/sqft depending on the setup) watch your voltage and see how it does over time. The curve is different depending on your current and setup, but it is distinctive on a good layer.

I usually just measure the bores, outside cylinders, and rectangular sections. Most paintball parts are good with that except frames, which need a lot of little calculations. Use a spreadsheet to keep track of your parts. I also use the spreadsheet to gather up multiple parts into batches. Keep the calculation for later reference. After you calculate a few, you get a feel for the surface area and how it works in your bath. When calculating surfaces with lots of threads or surface features, be sure and add some area for those details. Threads can double the area in that spot.
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