Dimensions apply after plating... 2

[ModulusCT]

... Well, for this particular project I'm working on, plating tolerances add up to a whopping .003" per surface!

So what I would like to do is have a not saying that all dims for features of size apply after plating and all dims for location apply before plating (for hole locations specifically).

Any precedence for this?

 

[KENAT]

Could you explain the logic?

How about inspection?

Surely in the end item you want the holes at the specified dia in the specified location.

If you split the two how the heck does MMC work, if you use GD&T.

This sounds like a dubious idea.

The general topic of 'Dimension Apply After Plating' has been discussed a few times, you may want to try and find them, though I don't think they answer your specific question.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[ctopher]

Have a machined drawing, and a plating drawing calling out the plating spec(s), separate.

Chris
SolidWorks 09, CATIA V5
ctopher's home
SolidWorks Legion

 

[drawoh]

ModulusCT,

Your note is perfectly reasonable. Lots of people do this. You have no interest in the state of the part prior to plating.

The ±.003"[ ]tolerance is an issue. Your tolerances must be significantly looser than ±.003" if the vendor is to easily fabricate your part. This is no different than applying tolerances to a sand casting where tolerances are in the order of ±.005"/inch. If you want ±.002" over a 10"[ ]length, the process simply will not work.

If you require an as-plated tolerance of ±.002", your vendor is going to have to machine off the plated part, or find a plating process that is more accurate. The extra cost will be passed on to you, of course.

Your other option is to review why you are plating the part. If you cannot control the zinc plating on a steel part, maybe you should fabricate out of stainless steel.

JHG

 

[dgallup]

I see a problem with having two conditions called out for a single part. I think you have to decide on one or the other. Either you have all dimensions inclusive of plating or all dimensions exclusive of plating. For critical work I do as ctopher suggested and have both pre-plated & post-plated drawings.

 

[ModulusCT]

drawoh, I think that's what I was looking for.

Our customer is requiring us to plate with a nickel strike, followed by copper, further by nickel, and lastly by tin-lead.

The plating thickness can vary from between ~.001 and ~.003. My problem is that the inside of some plated holes are going to get an effective buildup of .006" of plating potentially (both sides of the hole). There is a part that then gets soldered into that hole and it's position is important.

Now this hole needs to be produced oversized for the part being soldered in it because of the large plating tolerance. How else can I control the misalignment of the soldered in feature when the hole is produced at LMC? The only way I can think of is to control the position of these holes more tightly, not at our standard ±.005" but at something more like ±.002.

Unfortunately, the plating tolerance alone could violate this location tolerance (or vary nearly - leaving nothing left for the machinist) if the dims apply after plating. How can our machinist hold the position of a hole to within ±.002 when the plating is using ~.003+ of the .004" tolerance zone right from the get go?

So my proposed solution is to specify that the position dims for these holes apply before plating, where I can more accurately control their position.

Does that make sense? Maybe I'm over complicating things... I think drawoh understood my issue.

Thanks for the input guys.

 

[ModulusCT]

dgallup, I understand what you're saying. Here's the thing... We don't actually inspect any of our parts. We do a first article inspection, meaning that when the assembly is ready to go out the door, we measure the assembly to a layout drawing (overall assy dims).

So having a pre and post plating drawing wouldn't be useful for these wacko's I work for.

 

[ewh]

If a part is going to be soldered into the hole, is the plating of the hole itself that important? Couldn't it be machined to it's final size/location after plating? I have seen this done often.
I don't know enough about your situation, that's why I ask.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[SDETERS]

Can you have the Plater Plug the holes while the part is getting plated? I do not know much about this process but I would think a simple plug in the hole would eliminate any plating getting into that hole. We have dual prints one for plating that the plater has to meet then a final part. The plater is able to control build up on certain surfaces during his plating process. But we are only zinc plating our parts. Your plating process could be more difficult to control than a zinc coating.

 

[ModulusCT]

Unfortunately, our customer has strict requirements, which include plating every surface of our part.

Another idea might be to have the plater verify the plating thickness at certain points on the part (as defined by me on the drawing) so that we can measure the location of these critical holes independently of the plating.

Anyone know how I might go about that? Would I use datum points to indicate where verification should be taken? Mark out an area on the side where a plating thickness report would focus?

Again, plugging or masking the holes would be the easiest thing (and we're even soldering the mating part in with tin-lead soler!), but our customer won't have it.

Thanks

 

[drawoh]

...

So my proposed solution is to specify that the position dims for these holes apply before plating, where I can more accurately control their position.

The "DIMENSIONS APPLY AFTER PLATING" note goes on a drawing that goes out to a vendor who is expected to plate it after fabrication. The vendor must understand how the plating will work, and adjust his fabrication process accordingly. If your parts work, you don't need to know how they did it.

The alternate scenario is that you send your fabrication drawings out without finishing. You inspect everything, then send it out for finishing. You understand how the finishing will work. You fiddle the tolerances on your drawings to account for the finishing. You write clear instructions to the finisher, specifying how thick the finish can be. You inspect the finished parts, verifying that the finisher did what you specified. I think this is way more complicated.

I can see how the plating affects the hole diameters. Is the plating in the holes that uneven that it drastically affects postion?

JHG

 

[KENAT]

Do you even use GD&T position tolerance with MMC on these holes? If so I can't see how your idea will work. That said you only mention +- so I guess maybe you don't.

I'd suggest an inseparable assy where you just worried about the location tol of the parts being soldered in but your customer requirements seem to prevent this, or at least complicate it.

Drawoh, I've seen the note "Dimensions Apply After Plating" and it's in the standard. I have no problem with this and in most cases believe it is the way to go. However, the idea of splitting location and size tolerances so that one applies before and one applies after plating sounds questionable. I have never seen this.

OP - Why not just have loser location tolerances on the holes to accommodate the plating shift, assuming function allows this, and make the tolerance apply after plating. This is effectively what you're doing anyway, you're adding the potential .003 to you location tolerance.

Maybe you could even take advantage of what ASME Y14.5M-1994 1.4 f says about adding non mandatory process dimensions, although in this case it would be a 'process tolerance'. Put a tighter tolerance for before plating qualified by the "NON MANDATORY" note. I believe this would be subtly different from a ref dimension which wouldn't have a tol.

If you aren't using GD&T position for these holes I'd seriously consider it as in most cases it will actually allow more usable tolerance for the same functional requirements.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[fcsuper]

A basic answer is that ASME Y14.5-2009 Paragraph 2.4.1 requires a statement on a drawing that either says something like:

DIMENSIONAL LIMITS APPLY AFTER PLATING (or whatever finishing process is used)

-or-

DIMENSIONAL LIMITS APPLY BEFORE PLATING

But, KENAT's comments about the implications of using BEFORE option should be taken into consideration.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[ModulusCT]

Sorry, management in their infinite wisdom has determined that our parts are not critical enough to warrant GD&T (in other words, they don't understand it and don't really want to learn it). Although, they obviously are.

I'm slowly winning some ally's in the fight for GD&T, but it's a long process. We use flatness from time to time, but that's about it.

"OP - Why not just have loser location tolerances on the holes to accommodate the plating shift, assuming function allows this, and make the tolerance apply after plating. This is effectively what you're doing anyway, you're adding the potential .003 to you location tolerance."

I guess my worry is that our machinist will see the larger pos tol on these holes and not locate them while keeping in mind that the surface that they're measured from will be subject to plating tolerance.

Maybe I'll give him a call.

 

[drawoh]

...

Drawoh, I've seen the note "Dimensions Apply After Plating" and it's in the standard. I have no problem with this and in most cases believe it is the way to go. However, the idea of splitting location and size tolerances so that one applies before and one applies after plating sounds questionable. I have never seen this.

The plating note applies to everything or nothing. I do not think there is a practical concept of gray area.

I am not splitting location and size tolerances. In my alternate scenario, the fabrication drawing does not specify finish. I have a separate finish drawing that calls up the fabricated part as material. This is how I would implement it if I had to. I would try desperately to find some other way.

The OP feels he has problems with location, but not size. This is something independent of drafting standards. The only way this could happen on a hole is if the plating thickness varies from one side of the hole to the opposite side. Just doing the math, it sounds a little weird to me. There is not much point in accurately locating an otherwise sloppy hole.

JHG

 

[ModulusCT]

Well, I've decided to go with the larger positional tolerances and count on my vendor to do his job and figure in the plating tolerances when finding his centers.

I've attached a pdf to help explain what I'm doing here... drawoh, hopefully I've cleared things up.

 

[dgallup]

Quote Drawoh

"The OP feels he has problems with location, but not size. This is something independent of drafting standards. The only way this could happen on a hole is if the plating thickness varies from one side of the hole to the opposite side. Just doing the math, it sounds a little weird to me. There is not much point in accurately locating an otherwise sloppy hole."

That's not true because the datum surfaces will change with the plating buildup too, causing the position to shift.

 

[KENAT]

Drawoh, in your first response you said the OP's proposed note was "Your note is perfectly reasonable."

It was this I was questioning since his proposed note included the bit about some tols being before plating and some after.

You seemed to change your intent a bit with your second post but the OP seemed to be going with your first. My guess is you didn't mean it the way I read it but I wanted to clarify.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[drawoh]

dgallup,

The plating on the datum face is a problem if the hole position from the datums is an issue. Usually, the hole pattern itself is critical, and the distance from the datums is less so. ASME Y14.5 easily describes this.

KENAT,

Actually, you are right. I skimmed the first message, and I picked up the first plating note. My second comment is right.

ModulusCT,

This is where good drafting practice saves your butt. You specify the necessary diameters and positional tolerances on the feedthru holes and you keep everything else sloppy. The fabricator sees what is critical and he finds some way to solve the problem. Perhaps the plater can control the plating thickness in certain holes. Perhaps the fabricator will have to do a little machining after plating. You get parts that work.

So many people slap accurate tolerances all over everything. Fabricators can see that they do not really mean it.

JHG