Machining before plating

[ctopher]

I started this job early this year. They have most parts machined with a note on the drawing "All dimensions are after plating". Majority of plating is nom .0005.
If I were machining the parts, I use CAM and deduct this amount.
I'm curious how would others do it? I'm trying to reduce cost and errors.
Thanks.

ctopher, CSWP
SolidWorks '17
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[looslib]

If your tolerances are enough, machine to the print dimensions and let the plating add that little thickness.
If you have really tight tolerances, subtract the plating thickness before machining.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[ctopher]

Thanks.
That is what I do, most are tight.
Unfortunately these parts are made in Thailand for us. Terrible machining practices.
I was curious how others manage this.

ctopher, CSWP
SolidWorks '17
ctophers home
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[JNieman]

Same as looslib. Hard-coat anodizing has larger buildup and that's almost always accounted for, unless it's comparatively large tolerances, but if the plating is less than 10% of the tolerance I might not worry about it. Depends on your expectations from your machines and machinists, on whether you hold tight to 10% (or w/e is a safe rule of thumb for you)

If I'm dealing with +/- .002 or .005 I would absolutely account for .0005 or .0010 of plating. For +/- .001 or tighter, I think I'd be looking into exactly what that plating is, or honing/polishing after plating.

 

[MikeHalloran]

You will continue to get whatever you accept.

Cost of inspection should be included for offshore sources.
That may change your onshore/offshore decisions, but that's a management problem, not an engineering problem.



Mike Halloran
Corinth, NY, USA

 

[ctopher]

Mike,
I agree, working on it.
I'm curious how others manage the machining part of it.

ctopher, CSWP
SolidWorks '17
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[MikeHalloran]

Of course, I can provide a counter-example:

We were buying a stainless casting from a domestic foundry, and having it machined by another outfit entirely.
We could not find a domestic single source for the finished product, and these particular vendors
could not seem to work together to produce satisfactory finished products.

So we reluctantly tried a Chinese source, which provided 100 pct perfect parts,
every lot, every time, at less than half the cost of the domestic product.

I was so disappointed in, well, us.



Mike Halloran
Corinth, NY, USA

 

[ctopher]

I have used good machine shops in China. Thailand, not good.
Here in the US it's getting worse. Difficult to find reliable and experienced machinists. Also less people everywhere that can read a drawing.

ctopher, CSWP
SolidWorks '17
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[CWB1]

I would apply -/- logic to it. The design team told you exactly what they want - coated parts w/dims measuring X after coating. When in doubt, machine the parts undersize and build up with plating then statistically optimize the plating back to minimal thickness through a quality plan.