Correct Calculations?

[VillainMotorsports]

I haven't started my ano line yet, just want to get an idea of how big of a power supply I need by measuring a few scrap pieces I have laying around. I just wanted to make sure I'm calculating the surface area correctly, so if someone could double check this for me would be great, thanks



This is a piece of aluminum pipe
2.9" outer diameter
2.5" inner diameter
2.35" hight
.2" wall thickness

2.9x3.14= 9.11" Outer Circumference
2.5x3.14= 7.85" Inner Circumference

9.11x2.35= 21.41" outer surface area
7.85x2.35= 18.45" inner surface area


2.9/2=1.45" outer radius
2.5/2=1.25" inner radius

(A= pi r2) 3.14(1.45x1.45)= 6.6" surface area of outer circle (top/bottom)
(A= pi r2) 3.14(1.25x1.25)= 4.9" surface area of inner circle (top/bottom)

Subtract inner circle area from outer to get wall surface area x2

6.6-4.9= 1.7 x2= 3.4" top and bottom edge surface area

3.4 + 21.41 + 18.45 = 43.26 square inches?

43.26 x .0069 = .3 square feet?

720 rule calculator
at 4.5 ASF @ 1mil = 1.35A for 120mins?

Any easier way to do this? My brain hurts...

What do you guys do for irregularly shaped objects? This was a simple piece and took some serious brain power even with a calculator! I'm sure it'll get easier the more I do it though.

[pyroracing85]

To be honest with you that part is soo small. I would just do the outter minus the inner..

[VillainMotorsports]

Ok, this is actually a pretty big piece in my eyes for the kinds of things I will be anodizing, so I think I'll order up just a 5A power supply. But, maybe 10A if the price is right so I can expand.
So, does the surface area have to be exact to the .01"? Or is it just a quick going over with calipers and a little guess-timating along with a calculator?
I guess what I'm asking is do I have to be as thorough with my measurements as I was with this piece pipe?

[BobFrapples]

Unless the wall is very thick, Dont worry about it.
I do (for piping) SA of the outer, + SA of the inner. Two basic equations.

[ddrink]

Unless the wall is very thick, Dont worry about it.
I do (for piping) SA of the outer, + SA of the inner. Two basic equations.

I would agree if doing a couple of parts. I normally do batches of the same part, if is skip smaller areas like the wall thickness of your part on all of them parts in the run, it can add up to a bite of surface area.

[BobFrapples]

I would agree if doing a couple of parts. I normally do batches of the same part, if is skip smaller areas like the wall thickness of your part on all of them parts in the run, it can add up to a bite of surface area.

Yes, ddrink is right, if its a couple parts its fine. But if your doing lots of parts and ignoring the wall thickness, just calculate for one, and multiply by however many parts you have.

[pyroracing85]

Did you say a 10amp?

That is pretty small?