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!!

 

[fcsuper]

Well, joebk, then I'd say it seems in your case there's need to call out the thickness. Notice I didn't say not to call out a plating thickness...just that the note saying what the dims represent was unnecessary in most cases.

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

 

[fcsuper]

Just for clarification, ASME Y14.5M-1994 Paragraph e states "The drawing should define a part without specifying manufacturing methods." Paragraph f states "It is permissible to identify a nonmandatory certain processing dimensions that provide for finish allowance, shrink allowance, and other requirements, provided the final dimensions are given on the drawing. Nonmandatory processing dimensions shall be identified by the appropriate note, such as "NONMANDATORY (MFG DATA)".

Basically, the standard states that it is the processing dims that need identification, not the final dims; and that in either case the final dims have to be provided along with any included process dims.

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

 

[KENAT]

Fcsuper (and others), take a look at ASME Y14.5M-1994 Section 2.4.1 and see if it changes your mind.

2.4.1 Plated or Coated Parts. Where a part is to be plated or coated, the drawing or referenced document shall specify whether the dimensions are before or after plating. Typical examples of notes are the following:

(a) DIMENSIONAL LIMITS APPLY AFTER PLATING.
(b) DIMENSIONAL LIMITS APPLY BEFORE PLATING.
(For processes other than plating, substitute the appropriate term.)

I came across it by chance when looking for something else.


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

 

[israelkk]

KENAT

"Typical examples of notes" meaning not mandatory. We can all do a flip flop as much as we like but every process has its tolerances. If a final dimension with a specified tolerance is needed there is no way to manufacture it without deciding how the tolerances for each process will be specified. We can try to hide it by throwing the burden on the plater but no plater in the world can make a plating with zero tolerance as no machining house can do a zero tolerance dimension. If for example the final outside diameter dimension or a part is 30 mm -0.010 mm and the minimum zinc coating is 0.005 mm, the part must be machined to 30 mm -0.001 to 0.002 to allow the zinc plater to reach the final dimensions unless he will plate, remove and re-plate over and over until he will (hopefully) succeed.

 

[KENAT]

israelkk

the drawing or referenced document SHALL specify whether the dimensions are before or after plating

The form of the note is not mandatory. Having a note, or otherwise indicating when limits apply, apparently is mandatory as indicated by use of the work shall.

As regards the rest of your post, I've previously written that depending on what the specific plating spec says it may be necessary to at least state a minimum required plating thickness.

I've also posted that I think it's probably best left to manufacturing to determine the divide in tolerance between plater & machine shop. It could potentially vary between different platers so I'd probably leave it or ‘pre treatment’ dimensions off the drawings, although as fcsuper pointed out in a previous post ASME Y14.5 does allow for it to be on the drawing if required.

However, I didn’t put my previous post to restart the general debate, just to share information I’d found that states unequivocally (assuming you follow Y14.5) that an indication of whether dimensions apply before or after treatment is required.


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

 

[Heckler]

I've also posted that I think it's probably best left to manufacturing to determine the divide in tolerance between plater & machine shop.

Exactly what I said in my second post. In most high end aerospace/defense companies their manufacturing engineers with the sole purpose of doing process drawings. I don't think it's common in other industries.

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

 

[israelkk]

Look what I have found in MIL-S-7742D para. 3.4.5 and 3.4.6 Where the MIL actually dictates how much undercut or overcut for external and internal threads machining before plating.

See:

http://assist.daps.dla.mil/docimages/A/0000/0000/6581/000000019144_000000011730_YTVZRXWRPJ.PDF

 

[ctopher]

Inspecting a thread before and after plating that has special cutting can be a nightmare.

Chris
SolidWorks 07 4.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 10-07-07)
ctopher's blog

 

[ajack1]

If the thickness of the plating is not stated and can vary between suppliers, how exactly are the guys in the machine shop supposed to know what size to make anything before plating?

 

[ctopher]

I have always designed the part for before plating. The plating spec calls out the thickness and tolerance.

Chris
SolidWorks 07 4.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 10-07-07)
ctopher's blog

 

[Heckler]

If the thickness of the plating is not stated and can vary between suppliers, how exactly are the guys in the machine shop supposed to know what size to make anything before plating?

A good manufacturing engineer that's creating process prints from a released CAD drawing will solve these types of problems. This is nothing new here people

Heckler
Sr. Mechanical Engineer
SWx 2007 SP 4.0 & Pro/E 2001
o
_`\(,_
(_)/ (_)

This post contains no political overtones or undertones for that matter and in no way represents the poster's political agenda.

 

[ajack1]

Sorry Heckler I have not come across this before, are you saying that the design and checking team create a component drawing that includes plating, and it then goes to a process engineer who creates a separate document for before plating?

 

[vc66]

If you need a plate to be .5" thick +/- .001 for some reason, and it is plated, powder coated, electropolished, or any other process that adds or takes away material - it is my feeling that you specify what you need in the END condition, and then the manufacturing engineer is there to figure out what the finished MACHINED part thickness is to account for the secondary processing.

Although now that I see it, I don't supposed specifying that the dimensions apply after all finishing processes is such a bad idea.

V

Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."

- R. Buckminster Fuller

 

[joebk]

I do not have the luxury of manufacturing engineers and our manufacturing folks either refuse to develop this information or aren't capable of doing so. If we don't spell out every detail for them the entire system grinds to a halt. Sucks but true.

To resolve the issue I need to include limits for the thickness of the plating so that our manufacturing folks can control their machining processes accordingly. I don't like this situation but I have little choice at this time.

I think my best option is to consult with a few plating vendors and specify a thickness range based on their recommendations and our corrosion resistance requirements and let the manufacturing guys sink or swim. I was hoping there was some sort of "industry standard" for this but apparently not.

Please note that I am not bashing manufacturing in general, just the chuckle heads I have to deal with.

Thanks for all of the feedback.

JBK

 

[ctopher]

Another option is to have a machine dwg (before plating) and a plating dwg separate. This way the machinist does not have to worry about the plating, the plater does not worry about the machining. Just an option.

Chris
SolidWorks 07 4.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 10-07-07)
ctopher's blog

 

[vc66]

I agree with ctopher. If there is no manufacturing engineer, then to make it easiest, have two drawings. Or maybe, sheet 1 and 2 (1 being machined condition, 2 being plated condition), with a note stating, "Send only sheet 2 to plating vendor."

V

Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."

- R. Buckminster Fuller

 

[KENAT]

The effect of coatings on threads is something to consider. ASME B1.1 talks about it for UN threads. If I recall correctly, then for class 1 or 2 threads by default the dimensions given in the standard actually apply before treatment. The finish can take it upto class 3 (line fit). The standard says a lot about this and I haven'rt looked in detail but I think this is more or less right.

ajack, while not normally a complete drawing I have seen it done that way. The design team came up with the drawing for the finished item. Manufacturing then determined any dimensions that needed to be made deliberately undersize etc and either came up with their own partial plan (drawing) or notes on a travelor or similar/equivalent. It was definitely like this where I worked in the UK.

A lot of the time my guess is if the tolerance is say +-.005" while the plating is say less than .001" they don't really do anything except try and stay nearer the middle of the tol zone for the machining.

vc66, I personally hate the sheet 1 & sheet 2 being treated as almost separate drawings. To me the possibility of confusing as to what state a part is at, either sheet 1 or 2 outweighs the advantages. I've seen it cause problems.

What this thread and related threads/conversations etc has made me realize is just how important it is for the designers to know what the finishing spec says. Some do define thickness, others give recomendations but seem to say that the drawing should state the thickness while if I recall correctly some perhaps don't even go that far.



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

 

[ewh]

I have often seen the finish note include the statement "DO NOT PLATE INDICATED HOLES", greatly simplifying the manufacturing engineers job

 

[BARM]

joebk (Mechanical)

I would NOT leave a plating thickness spec off my part drawings. Doing so would leave yourself open to receiving out of spec parts from your plater. What are you going to gauge your parts to pre & post plating if the proper spec is not called out? That may come back to bit you later.

I recall the ANSI Standards book for threads calling out the proper method for calculating the new BEFORE PLATING sizes.

Hope this helps. There is also another thread in this forum dealing with plating callout on drawings.

 

[KENAT]

You know, if we could come to agreement I'm pretty sure a FAQ on this would be a good idea;-)

The threads (no pun intended) on this subject really have reminded me just how important it is to know what the spec you call up says and what it says about how it should be called up on the drawing. I also realize that it turns out that some of the information in my earlier posts was possibly wrong.

Some specs definitely do say that you should give the thickness, or at least the minimum thickness, on the drawing.

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