john12ax7

Adjust dimensions for powder coat thickness?
« on: October 18, 2018, 02:07:51 AM »
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?


gyraf

Re: Adjust dimensions for powder coat thickness?
« Reply #1 on: October 18, 2018, 03:32:22 AM »
if precision is important, you should ask your powdercoater - but be aware it's not an exact science
..note to self: don't let Harman run your company..

JohnRoberts

Re: Adjust dimensions for powder coat thickness?
« Reply #2 on: October 18, 2018, 10:25:00 AM »
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
John Roberts
http://circularscience.com
Tune it, or don't play it...

john12ax7

Re: Adjust dimensions for powder coat thickness?
« Reply #3 on: October 18, 2018, 04:09:43 PM »
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. 




JMFahey

Re: Adjust dimensions for powder coat thickness?
« Reply #4 on: November 16, 2018, 10:23:01 PM »
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.
Design - Make - Service Audio Equipment since 1969.

john12ax7

Re: Adjust dimensions for powder coat thickness?
« Reply #5 on: November 18, 2018, 09:09:35 PM »
As a follow up,  one fabricator said to oversize holes by  . 005" to account for the powder coat.

boji

Re: Adjust dimensions for powder coat thickness?
« Reply #6 on: November 26, 2018, 11:41:47 AM »
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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