Plating allowance on threads

[5 AX]

I am thread milling a part that will get .0025 thickness of plating on it. In the past I have adjusted the pitch diameter by two times the plating thickeness. A coworker has suggested only 1x the thickness. I can't find a definitive answer. What do you guys do?

[strabe]

I believe you are right. .0025" per side or .005 total.

[crazy^millman]

Nope you allow 4 times for plating when doing threads. If you are getting .0025 per side then you are getting that on 4 sides. The 2 walls on the one side of contact of the thread and you are getting it on the other 2 sides of contact of the thread.

 

One other suggestion is making a plate or part with several holes at different sizes. Send it to plating and then check them when they get back.

 

HTH

[5 AX]

Millman,

I have heard that arguement also. But the thickness is applied on the thirty degree sides of the thread. this is why I was thinking it would only move the pitch diameter 2x.

[Newbeeee™]

Definately 4 x for threads with 60 degree inclusive angle (ie unified and metric)

[strabe]

Ron is right. It's 4x for threads.

 

Linky

[crazy^millman]

Well what we have seen in that the major of the thread will sometimes get excess. This excess will form a radius and even though we allow 4 times we still sometimes have to chase holes with a tap. We do 100% on all threaded holes and parts so yes it is a pain, but insures we send out the best part possible.

 

HTH

[5 AX]

Thanks everyone! I will go with 4x.

[Newbeeee™]

Just dug out a design guide from a hard anodising company.

Their quote:-

 

The major and minor dia will increase 2 times the amount of growth. The pitch dia for threads having an included angle of 60 degrees will increase 4 times the amount of growth.

For threads having an included angle other than 60 degrees, the pitch dia will increase by 2 times the amount of growth divided by the sine of 1/2 the included angle.

 

Cheers

[CAM-mando]

Class 2 threads have "some" coating allowance built into them already.

 

Class 3 threads should be compensated as follows:

 

Reduce the max PD by 4 X MAX coating thickness

Reduce the min PD by 2 X MIN coating thickness

Reduce the min major dia by 2 X MIN coating thickness

Reduce the min minor dia by 2 X MIN coating thickness

Reduce the max major dia by 2 X MAX coating thickness

Reduce the max minor dia by 2 X MAX coating thickness

 

This probably doesn't impact you but some thread specs (such as MIL-S-8879) also have a maximum amount you are allowed to undercut for plating compensation. It is based on a percentage of total PD tolerance.

[specv]

We usually do 4x the build-up, Is that .0025 build-up or total plating thickness with allowance for penetration?

[5 AX]

.0025 build up. It is Electroless nickel. I do not believe that penetrates.