having problem holding tolerances after anodizing

SDConcepts · Jan 22, 2014

hey guys, I've got a group of parts that one of my customer specs and there are some holes that are tolerance 6mm h7 and 8mm h7. I can hit the tolerance coming off the machine and I even try to allow enough clearance for the anodize process, however, I use the same anodizer all the time, and they can't seem to control their process. this time around the holes are too tight coming out at 5.969mm and the customer wants a slip fit, but not so the pins fall out. they don't want to have to press them in.

any ideas on how to maintain the tolerance on these holes. I really don't want to have to ream after anodizing, but if I did, I guess I would need to go over size, let it anodize, then ream and then inspect and ship to customer. any other ideas? is my customer being too damn picky?

Finegrain · Jan 22, 2014

SDConcepts said:
... the customer wants a slip fit, but not so the pins fall out. they don't want to have to press them in.

This is impractical. If the pins don't fall out, they're held in by some force, albeit a small one. That means they had to be pressed in, albeit with a small pressing force.

I get this from customers regularly. They want it both ways -- easy to assemble, but stays in place somehow. I tell them they can have one or the other: either the part slips in (and slips back out), or it has to get pressed in, then it's harder to get back out.

Loctite retaining compound is a path to having it both ways.

BTW, lowercase tolerances (h7) are for shafts/pins, uppercase tolerances (H7) are for holes.

Regards.

Mike

spin-tek · Jan 22, 2014

With tight tolerance holes, we always give our plater pin gauges to check while he's plating the part. So far, we've had pretty good luck with that.

SDConcepts · Jan 22, 2014

I will try giving them the pin gauges and see if they laugh at me. I don't think these guys are going to do it, but we'll try. and yes your right about the capital vs small letter, typing to fast over here.

spin-tek · Jan 22, 2014

If your plater is unwilling to do it, then walk away and find one that's willing. That's what we did... :-)

specfab · Jan 22, 2014

In many cases, it's better to plug (mask) the holes than try to control a precision fit through the anodizing process. Plugging holes is more costly at the plating shop, but you know what you are going to get if you have supplied parts to the plater. with in-tolerance holes. On the other hand, I have worked with a plater who does have good control of plating thickness deposition, and it's not THAT hard from my observations.

RJT · Jan 22, 2014

Masking is the only way to guarantee the results. I have never been able to count on plating thickness 100% of the time.

Dave K · Jan 22, 2014

Maybe someone in anodizing can pipe in here, but here's what I've been told. Hard coat anodizing will build up on the surface, but plain old anodizing should not build up at all, in the end.
Before anodizing, there is a process that's called "etching". This process will open up that hole, just a tenth or two. The anodize then should build that back to where it was before the etching was done, thus, your final product should see no change in hole diameters.
I've been going off this method for years, and haven't had any problems. The only other possibility is you can have them anodized without the etching process, but then you will get some build up on the surface.
You may want to run this all by your anodizer, and see what he says about it.

rnmmhunter · Jan 22, 2014

You need to plug the holes. If there any problems at the plater and they have to strip them, there is your problem they will never tell you they plated them twice.We had a job where the pins were fine customer rejected the plating had them replated pins fell in.

vettedude · Jan 22, 2014

you need to mask or reem after anodizing, thats not a controllable process in that way. I also think your customer could give a little too. I think masking is the best solution!

sean9c · Jan 22, 2014

If you're expecting an anodizer to get identical results every time you're kidding yourself. Just like you won't get a plater, heat treater or just about any outside processor to repeat results. The sooner you realize this and adjust your manufacturing processes the better.

scadvice · Jan 22, 2014

This outfit use to do plating for me using My gage pins plus .0005 minus nothing all day long. That was a few years back and they are a bit far from you.

ANODIZERS INC
1709 E BAYSHORE RD
REDWOOD CITY, CA 94063-4154
(650) 366-3749

WDW · Jan 22, 2014

Type II anodizing (standard anodizing) builds up and also penetrates and equal amount usually around .0001-.0002. the plater does etch the part this removes material. We do a lot of parts that have close tolerances in various finishes that I have to account for plating buildup. You have 2 options first as other people have said mask the holes this should be the fool proof option. If the holes can not be masked make the holes to the high end of the tolerance or slightly over by .0001-.0002 and when you send to the plating company tell them the part has a tight tolerance and to minimally etch the part. The last option is to do a small test run to see how much the holes change and you can adjust the size of the hole before running the full run. Your plater should allow you to do this at no cost and they should be fairly consistent on the build up from run to run, if not its time to find a new plater.

Dave K · Jan 22, 2014

... and they should be fairly consistent on the build up from run to run,

I thought so, because there's a mil spec they're supposed to adhere to, isn't there?

Milland · Jan 22, 2014

SDConcepts said:
hey guys, I've got a group of parts that one of my customer specs and there are some holes that are tolerance 6mm h7 and 8mm h7. I can hit the tolerance coming off the machine and I even try to allow enough clearance for the anodize process, however, I use the same anodizer all the time, and they can't seem to control their process. this time around the holes are too tight coming out at 5.969mm and the customer wants a slip fit, but not so the pins fall out. they don't want to have to press them in.

any ideas on how to maintain the tolerance on these holes. I really don't want to have to ream after anodizing, but if I did, I guess I would need to go over size, let it anodize, then ream and then inspect and ship to customer. any other ideas? is my customer being too damn picky?

When you're getting down to the micron range there better be good measuring temperature control at both ends (shop and customer). Do you track the manufacturing temps, and what does the customer measure at? Do they have a proper metrology lab at 20C/68F? It may not be the anodizer at all...

Rstewart · Jan 23, 2014

Dave K said:
I thought so, because there's a mil spec they're supposed to adhere to, isn't there?

http://www.wbdg.org/ccb/FEDMIL/a8625.pdf

It's really hard to find an Ano place that can hold better than .0005 tolerance. They're out there, good luck finding them...

Tom3197 · Jan 23, 2014

Milland said:
When you're getting down to the micron range there better be good measuring temperature control at both ends (shop and customer). Do you track the manufacturing temps, and what does the customer measure at? Do they have a proper metrology lab at 20C/68F? It may not be the anodizer at all...

X2... there really are too many variables involved and I also agree that your customer can't have it both ways here... That pin is going to have to press in, or its going to easily slide right out...

TimD · Jan 23, 2014

It's been awhile since I've dealt with it so my terminology might be a bit off.

Most anodizers use a constant voltage power process. This doesn't give the most consistent results but it much easier to run. They can take parts on and off the power supply at will and it will adjust the current.

A more controller method is to use constant current. The down fall to that is that you need to know the total surface area of all the parts that are running off of the power supply. You set the current based on that surface area. So a batch of 20 parts needs a different setting than a batch of 50. You can start to see why most ano shops don't use it. In my limited experience it is primarily used in captive anodizing departments rather than an ano job shop.

If you need more consistent results try finding a shop that can do constant current. Don't be surprised if most shops you ask don't even know what you're talking about. Even if they tell you yes make sure that are wanting to know the surface area of your parts or...another option would be to try and find a shop running this system:
Anodize USA : Anodizing Systems

That being said I would op for plugging if you can. My ano shop charges $0.10 per plug on top of the standard ano price. Pretty cheap when you consider the hassles otherwise...

FredC · Jan 23, 2014

We have aluminum parts several different parts that get annodized with close tolerances. With the first plater I would take the parts and gauges. I would guage parts till we got the etch process down. The annodizing it self is fairly consistant as it builds up it starts to limit the current especially with clear. The etch on the other hand can cause large size variations with temperature and time of etch. It was not long before I was helping rack and unrack the parts.
With our new plater we sometimes take guages till we are certain things are going well. On our newer products we clean the parts thoughly and the platers just does a heated detergent cleaning instead of an etch. These parts are black annodized and grow about .00015 to .0002 on an OD which we allow for.
Annodizing in small holes is another variable. If the hole is blind there will be more build up near the mouth than the bottom. If it is through you will have less build up in the center of the hole. Either way it makes it harder to get your slip fit.
With all that said in your case the difference between a light friction fit and a gauge that will fall out under its own weight is probably .0001 to .0002! How close are the pins fitting in these holes plus 40 millionths minus nothing?
I have never been able to ream to the tolerances you need, honing or a fixed diamond lap, probably.

carl laniak · Jan 23, 2014

Definitely agree that masking the holes is the way to go in most cases.

Alternatively, if there aren't other constraints, your customer could assemble their components using roll pins or spring pins.
If my chart reading skills are correct, your holes came back from anodizing about .0012-.0015" too small.
For a roll pin, you could probably just ream the hole +.002" and let the anodizer do their thing..... assembly would just require a thumb, or perhaps a light tap with a brass hammer.

having problem holding tolerances after anodizing

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Titanium

Titanium

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Cast Iron

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Diamond

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