Adjust dimensions for powder coat thickness?

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john12ax7

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Oct 15, 2010
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When you get something powder coated do you need to adjust for the thickness in the mechanical drawing? Or is this something a machine shop automatically handles?

Example: You want a 0.250" finished hole, should you spec a 0.260" hole to account for 0.010" powder coat thickness? Is there a typical value to use for the thickness?
 
I never thought much about that... powder coat is pretty thin ( 0.006-0.012") so typically not significant if you already have some clearance factored into the design.

Designing +/- metal with zero clearance can end badly (no go interference if tolerances of both parts go the wrong way).

JR
 
I've had issues with some commercial gear that is modular on a grid,  like 19" racks or 500 series. Sometimes the faceplates are too big.

A range of .006-.012" gets me in the ballpark. Though it seems there is not any universal standard so need to discuss with the specific shop used. 



 
If you are talking "lots of clearance" stuff such as switch/pot/jack holes, no big deal, acceptable tolerance is usually way larger than paint thickness.

Now in speaker magnetic circuits, where tolerance is 1/100th of a mm, powder coat thickness is way too much.

Much used because of low cost BUT gaps must be enlarged a lot to accomodate it and you lose a significant amount of magnetic field density ... a lot of it, which also affects efficiency/sensitivity big time.

That´s why many cheap Chinese speakers sport impressive size magnets ... but then are inefficient and muddy.
 
My two cents:  Thickness will vary with desired scratch resistance.  Company I bought powder from said if the part was for instrument panels, they recommended a 2nd clear coat over base or, hit the part twice with same color, but before it entirely cools down.
 
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