plating tolerance 3

[joebk]

We typically specify zinc plating according to ASTM B633 including the thickness of the plating. We do not specify a tolerance for the thickness and I haven't been able to find anything that indicates what "standard" tolerances are for zinc electroplating.

Does anybody have any standards or experience with this you would be willing to share?

Thanks!!

 

[ctopher]

If you are looking for calling out the plating tol on a dwg, I suggest leaving it off. Let the plater worry about the tol per the spec.
It depends on the type of plating and material.
A Google search shows a lot of data on this.

http://www.finishing.com/224/09.shtml

Chris
SolidWorks 07 4.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 04-21-07)

 

[Heckler]

I think the Key here is finding a good plater. I've had sloppy platers that leave parts in the solution until the edges smooth over.

Heckler
Sr. Mechanical Engineer
SWx 2007 SP 3.0 & Pro/E 2001
XP Pro SP2.0 P4 3.6 GHz, 1GB RAM
NVIDIA Quadro FX 1400
o
_`\(,_
(_)/ (_)

(In reference to David Beckham) "He can't kick with his left foot, he can't tackle, he can't head the ball and he doesn't score many goals. Apart from that, he's all right." -- George Best

 

[Heckler]

Here's an interesting link. I have never used this plater but they have some good information on their website.

http://techplate.com/tpeprice.htm

 

[israelkk]

ctopher

What would you do if you need to manufacture a plated 3A or 3B class thread on bolt or on tnternal thread? There is no way to do it without giving the thread tolerances before plating and after plating. The pre-plated tolerances dictate the desired plating tolerances. From my experience the tolerances for Zinc electorplating a tolerance of 0.003 to 0.0004 mm is common. For internal thread or holes an electrode inside the thread/hole may be necessary.

For example QQ-Z-325C federal standard dicatates 0.005 mm for Class III and 0.013 for Class II. These are minimum plated thickness insure the 12/96 hours at salt spray bath. Therefore, you have to give tolerances to the plating if you manufacture parts such as class 3A and 3B bolts and threads.

 

[KENAT]

I've rarely seen the thickness on a drawing, and if I recal when I did it was either on very old drawings or drawings that didn't reference an industry spec.

However, I often see 'Dimensions apply after plating' as part of the plating note.


Probably not much help, sorry.


KENAT, probably the least qualified checker you'll ever meet...

 

[joebk]

The problem is that the ASTM B633 spec does not indicate a tolerance only 4 commonly used nominal thickness values. We specify a thickness because this effects salt spray resistance and the cost of plating. But how much is enough or to much?

We have some parts that have some tight tolerances so this can become very critical and chops away at the tolerances afforded to our manufacturing guys.

The link posted by ctopher seems to indicate to me that +/- .00015" on plating thickness is reasonable but I don't know if this is actually easily produced using standard (i.e. low cost) plating methods.

 

[Heckler]

We do not put plating thickness on mechanical drawings. We use note "Dimensions apply after finishing". Then our manufacturing engineers create what is called a processing drawing in which they account for finishing tolerances in the part creation.

Like I mention above.....find a good plater and talk with them about their process and ask good questions.

Heckler
Sr. Mechanical Engineer
SWx 2007 SP 3.0 & Pro/E 2001
XP Pro SP2.0 P4 3.6 GHz, 1GB RAM
NVIDIA Quadro FX 1400
o
_`\(,_
(_)/ (_)

(In reference to David Beckham) "He can't kick with his left foot, he can't tackle, he can't head the ball and he doesn't score many goals. Apart from that, he's all right." -- George Best

 

[ctopher]

I agree with Kenat using the 'Dimensions apply after plating' note. I have tried at various companies and designs using different types of plating, it can be very difficult to meet a thickness requirement indicated on a dwg. The tolerance you call out may work with one plater, but not another. Plating can be especially difficult to meet or inspect on threads.
Every company I have been with, the outcome was to leave off the tol on the dwg and call out the appropriate spec with type of plating.
I suggest calling your plater and ask them what their recommendation is.
My experience.

Chris
SolidWorks 07 4.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 04-21-07)

 

[MintJulep]

Plating thickness is a function of the part geometry and topography, among other things.

There is no way to have a "standard variation" for plating thickness without also defining a standard test coupon.

I agree with the others that the finished part has its necessary tolerances defined by the part design engineer, and that the tolerances apply after plating.

A good plater will have a decent idea of what thickness variation to expect based on geometry and topography, and will work with you to suggest changes to the unplated part so that the finished part will be what you need.

A bad plater will feed you a line of BS about "standard plating thickness tolerances".

 

[PSE]

We also utilize a "Dimensions apply after finishing" note. The main reason being the variability in processing as indicated by previous posters. For highly toleranced parts, work to select a supplier and then help them develop the appropriate process controls for running your part. For our more critical components, we have worked with the supplier (one who maintains excellent control on their bath chemistries) on racking locations and established standard lot sizes per run in addition to the more standard parameters such as masking locations.

Finding a good supplier and keeping communications going with them has proven beneficial to the results. The trick then becomes keeping them from being cut out as a result of someone elses cost reduction efforts (unless the alternate source proves equally as capable)

Regards,

 

[israelkk]

Asking for dimensions after plating is a "smart and hidden" way to ask for a tolerance on the plating thickness. The part before plating has its tolerances. The combined tolerances of the part and the platings gives the total tolerance. We do the same and give dimensions before and after plating but by doing so we actually dectate how to divide the tolerances between the machining and the plating.

 

[KENAT]

For most applications I would have thought the 'dimensions apply after plating/finishing' is the better way of doing things from the designers point of view. It leaves it up to the manufacturer to determine the pre treatment machined dimensions, dependant on their plating process.

For certain critical applications I suppose you may need more, is this what the OP is asking about?


KENAT, probably the least qualified checker you'll ever meet...

 

[fcsuper]

My own preference, as an Engineer, on calling out plating thickness is that I never do it. Platers know what they are doing with the part. The machine shop is responsible to adjust their work to meet your final spec. This is why I don't even use the instruction "Dimensions apply after finishing". It is technically a process instruction in my mind, and process notes do not belong on drawings. The part has to match the print when it comes in, period. It's up to the vendor to make sure that happens by whatever means necessary (unless their is a case where process is important to the design, in which case, ASME covers those times with a special note).

Matt
CAD Engineer/ECN Analyst
Silicon Valley, CA
sw.fcsuper.com
Co-moderator of Solidworks Yahoo! Group

 

[KENAT]

fcsuper, I agree that process don't normally belong on the drawing per ASME standards.

I don't see "Dimensions apply after plating/finishing" as being a process. It's just a clarification of requirements.

KENAT, probably the least qualified checker you'll ever meet...

 

[Heckler]

The note "Dimensions apply after plating/finishing" is no less a process as any other note on a mechanical drawing. If left to their own devices our inhouse machine shop would ignore notes.....it's our manufacturing engineers that develope process drawings that guide the machine shop. They have all the information to make those adjustments to account for the finishing or plating.

Heckler
Sr. Mechanical Engineer
SWx 2007 SP 3.0 & Pro/E 2001
XP Pro SP2.0 P4 3.6 GHz, 1GB RAM
NVIDIA Quadro FX 1400
o
_`\(,_
(_)/ (_)

(In reference to David Beckham) "He can't kick with his left foot, he can't tackle, he can't head the ball and he doesn't score many goals. Apart from that, he's all right." -- George Best

 

[fcsuper]

I don't see it as clarification as much as over stating what is already clear. If the final part does not meet the specs on the drawing, then it is not to spec. The one time I had a vendor not pay attention by not accounting for it, he called me before the plating process cuz he know his guy screwed up. He tried to pull that argument with me but he backed down the instant he know he wasn't going to sell me snake oil that day. The drawing shows the part in its final state. This is per ASME. State what you need. How the shop gets there is up to them (under normal circumstances, of course).

Matt
CAD Engineer/ECN Analyst
Silicon Valley, CA
sw.fcsuper.com
Co-moderator of Solidworks Yahoo! Group

 

[joebk]

I have to spec out thickness because this ties into salt spray requirements. In addition, without some sort of thickness spec our manufacturing folks have no idea what thickness they need to account for in machining operations.

I would argue that without a thickness spec defined by design engineers and complete dimensional requirements for the final part how can the part be produced without someone making an assumption at some point? Granted the plating thickness is typically very small but can and has created problems for us.

All drawings do contain the note "dimensions and tolerances apply after plating or painting unless otherwise specified".

Of course I could be way off base here - wouldn't be the first time.

We manufacture most parts in house and send out for plating/painting when required. The only information on drawings are the final requirements and thickness of plating/painting so in process stuff is up to the manufacturing guys - they can do whatever so long as the end result meets spec.

 

[KENAT]

In that case do you actually need to specify the tolerance or just the minimum plating thickness?

To meet the salt spray test maybe just specify minimum thickness.

I'm not familiar with ASTM B633 but I just looked at the UK defence standard we used to use in UK

http://www.dstan.mod.uk/data/03/020/00000300.pdf

and it actually says that you should specify the thickness of the plating on drawing (or in PO etc), so I was doing it wrong for a while. However, it does only give minimum thickness where it talks about thickness for different applications, not a range/tolerance.

So I’d take a look at ASTM B633 and assuming it’s similar to the Def Stan I’d put a minimum plating thickness as required to meet whatever your salt spray test is. I’d also still include the ‘dimension apply after plating’ note (sorry fcsuper, have to agree to disagree this time).

I’d still say it’s up to manufacturing to determine the actual machined dimensions/tols in coordination with the plating vendor but they would now have the minimum plating thickness as a start point.


KENAT, probably the least qualified checker you'll ever meet...

 

[ctopher]

The part should be designed based on the plating thickness. The engineer should know the spec.
Also, If you model the part, model it minus the plating for machining purposes. Some parts are machined after some plating. If the parts plating has to be precise for fit, make it a separate part to include plating, if needed.
Otherwise, create the part dwg, add the plating spec on the dwg. Some military programs require a similar note to the "dimensions and tolerances apply after plating or painting unless otherwise specified" note. It varies.

Chris
SolidWorks 07 4.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 04-21-07)