Anodising

[TerrydParticipant @terryd72465]

Lovely work Ramon!  Well done. 

 

Regards

 

Terry

[ZigFireParticipant @zigfire]

Well done Ramon,

 

Practice makes perfect eh!.

 

Cheers

Michael

[Ian S CParticipant @iansc]

Went into town today, and after I had done all the important things I started looking around the second hand shops, and what I found made me think of you, about twenty 1lb packets of Brunswick Green dye, don’t know its condition and I didn’t buy it. Don’t know if it was metal or fabric dye, and by the look of the packages it would be at least 50yrs old, but interesting what you find when you’r not looking for it. Ian S C

[CirclipParticipant @circlip]

Would also like to know how close in chemistry “Parkers Green Ink” is to the inkjet printer inks??

 

  Regards  Ian.

[TerrydParticipant @terryd72465]

http://www.misterinkjet.com/inks.htm

 

Some information about inkjet inks

[TerrydParticipant @terryd72465]

http://www.signindustry.com/flatbed_UV/articles/2008-04-SGIA-Cahill-Printheads_and_Ink_Working_Together.php3

 

and here

[TerrydParticipant @terryd72465]

Apparently pen inks become long lasting and permanent when combining with the cellulose in paper (or cotton shirt.  See here:

 

http://www.marcuslink.com/pens/ink/index.htm

 

Oe of eh best ink sites I have come across.

[MartinParticipant @martin]

I'm just completing the Hemmingway Centering Microscope and would like to anodise the parts once completed.

However I have made the male and female threads to a really good fit, I'm concerned that after anodising the treads will be too tight.

When anodising, is there a process whereby curtain areas of a component can be protected from being anodised ie. close fitting parts?

Martin

[Ramon WilsonParticipant @ramonwilson3]

Hi Martin,

I have not had to worry about this situation and as such cannot tell you if dimensions grow slightly or indeed reduce some. I would hazard a guess that if it does it will be microscopic but that may be enough if your fits are that close.

You could mask the external threaded area using tape possibly PTFE thread tape so that the tape forms to the thread but what you could use for the internal I'm not sure – possibly silcone grease or a layer of silicone sealant allowed to cure – that would certainly be easy enough to remove. Watercolourists masking fluid may do the trick too but these are suggestions – nothing positive based on past experience.

Perhaps others may be able to help.

Whatever perhaps you would be good enough to report back on the method you use – successful or not as that way we all get some benefit

Regards – Ramon

[jason udallParticipant @jasonudall57142]

Martin
My understanding is that the parts shrink when annodised ( the oxide is denser that base metal thats why it is impervious ..like cromium and unlike iron who's oxide is less dense and thus larger) thus threads "loosen"… about 5-10 microns.
Manufactured thousands of anodised parts and never needed to use "preplating" gauges for fit. but home anodising ? sorry can't say..

[The Merry MillerParticipant @themerrymiller]

 

If components are "hard anodised" then you you will finish with an increase in dimension on outside surfaces.

Eg. If you want .002" hard anodising you will get approx. .001" growth and .001" penetration.

This is not an exact science and the figures can vary usually  between 50-60%

Len. P.

 

Edited By The Merry Miller on 09/12/2012 14:26:45

[ToolParticipant @tool]

Have built Centering Mic – my threads were to good a fit and siezed on screwing together.

The anodised finish was extremely hard and could not be easily machined. I had to make some parts again!

Tool

[MartinParticipant @martin]

My thoughts were to use some kind of tape, grease or even paint, but having not yet done any anodising I was unsure of the reation/contamination with the acid.

Martin

[The Merry MillerParticipant @themerrymiller]

It's worth looking at this video clip that highlights the problem that occurs when anodising screwthreads.

Len. P.

[MartinParticipant @martin]

The fits I have achieved will not allow for any further interference to be introduced, further more it appears that there is no fast and hard rule as to controlling the thickness of anodising when using a home setup.

Therefor I think I may have to settle for a good quality primer/etcher followed buy a number of hard coats of paint. At leased with this method I can mask out the areas that I need to keep natural.

To all that contributed to my post. Thanks you!!!!

Martin

[Dave MartinParticipant @davemartin29320]

Posted by Martin on 09/12/2012 13:09:58:

I'm just completing the Hemmingway Centering Microscope and would like to anodise the parts once completed.

However I have made the male and female threads to a really good fit, I'm concerned that after anodising the treads will be too tight.

When anodising, is there a process whereby curtain areas of a component can be protected from being anodised ie. close fitting parts?

Martin

 

Hi Martin,

Anodising does minutely change the dimensions – but depending on your items, you may well not notice them. Anodising is a surface-conversion process – you are converting the surface of the metal into a honeycomb matrix which you can then, if desired, fill with dye and then seal the surface to keep the colour in. There are some notes here which give some background on the process.

Using type II anodising, for a light colour (blue, red, green) you typically need about 0.5 thou total layer thickness; to pack in enough black you need nearer 1.0 thou total thickness. When you're building the ano layer, the very surface is both consumed & converted – its about 50/50 (its actually nearer 60:40 but I can't remember which way!). So, if you're going to colour anodise with a 0.5 thou layer, the item will grow by 0.25 thou for each layer – i.e. 0.5 thou on the diameter.

There is no easy way of masking that doesn't carry risks; and you need to be able to flush out nooks & crannies such as threads between process tanks, so normally threads are left exposed. You will see multi-coloured anodising, or items with some coloured and some left natural – but in these case usually the whole item has been anodised and it has been masked or bleached when it is dyed.

You also asked about the predictability of the coating thickness. Like many engineering processes, if you keep the environment and process constant you can get remarkably consistent results. Using the Constant Current / low current density method, with temperature controlled tanks, we get pretty consistent results (within 0.1 thou or better). Spot checks with our Elcometer show, within the meter's resolution, less than 10% variation in thickness and often better – and the colours match between runs which is our other major criteria.

Depending on how you've cut your threads, you may also find the crests shed their coating and revert to near as small as before coating. Anodising builds a matrix at right angles to the surface, and doesn't take kindly to absolutely acute edges (imagine trying to bend a honeycomb from a beehive around a 90 degree corner). For successful anodising edges need to be 'broken' – radius can be as little as, say, 0.2mm. If you've cut your threads with a full-profile tool, it should be OK; but if the crests have been left sharp they may shed the ano.

Dave

Edited By Dave Martin on 11/12/2012 13:38:51

Edited By Dave Martin on 11/12/2012 13:41:09

[Sub MandrelParticipant @submandrel]

I would be worried if threads need to be cut so tightly you can't fit in a thou of anodising. There is a chance they will fret together. It could be be that you can't get them apart again in a few months.

I don't know the Hemingway design, but the design should not rely on threads to achieve accurate positional relationships. Typically either concentric registers and flat surfaces or coned joints to get alignment both axially and laterally.

I would make a test piece and measure the enlargement you get with your process, then make threads that much undersize.

Neil

[Clive HartlandParticipant @clivehartland94829]

I must say here I have never had a problem with threads and anodising, cut to standard dimensions and then anodised they have always worked and fitted fine.

The only proviso was that the thread was lubricated with a kilo poise type lube. or a very tenacious Silicon typelube. These were used on all the eyepiece threads and focus thread drives and lasted for years. Some of the Lubes were usable to -50C as the instruments were used in arctic conditions and left out 24/7.

Also that I have seen Kilopoise grease used that was too thick and when cold you could not turn the spindle and in fact once had one snap off.

[MartinParticipant @martin]

Is it feasible to anodise the assembled unit and disassemble it after to fit the lens etc?

For those who are not familiar with the microscope see below picture.

Martin

[Clive HartlandParticipant @clivehartland94829]

Martin, every part should be anodised seperately at the same time in the bath. If its anodised as one item the internal threads and inserts will not get anodised.

The tubular parts will be put on the jig with internal clips so marks will not show on the outside.

The anodising figure for what you want doing should be AA5 – AA10, this will be perfectly adequate for the use it will be put to.

Clive

[Dave MartinParticipant @davemartin29320]

Posted by Martin on 12/12/2012 00:45:44:

Is it feasible to anodise the assembled unit and disassemble it after to fit the lens etc?……

Martin,

you might just be able to – but I would strongly advise against it.

Firstly, as well as the lens, you would need to remove any ferrous or other non-aluminium components (I suspect the arbor is steel, plus any ferrous fasteners etc.).

Secondly, with the assembled structure there will be significantly higher risk of carry-over. The anodising process traverses a number of process tanks, and it is absolutely essential that the item is purged off one chemical before it enters the next tank. This is often done by a combination of dipping in / spraying with pure water (reverse osmosis / de-ionised or distilled etc.). Carry-over of chemical from one tank to the next can, in extreme cases, "poison" the following tank, but far more likely is an inferior finish. A little acid carried over into the bulk of the dye tank and affecting the bulk pH will have a slight impact on the dye's performance; far more worrying are small localised amounts. If the workpiece isn't thoughly purged of acid, and a little seeps-out during the dying, you can get symptoms like white whisps or streaks or spots.

Thirdly, it would also be harder to guarantee the readiness and that all the wetted surface area would pass the water break test.

Fourthly, if there are, say, any small aluminium retaining rings or collars, there is a possibility that during the anodising run, if they aren't individually racked then they may loose contact and that component wont anodise properly.

For all the above reasons, when we have camera housings, composite lens mounts etc. to anodise they're always racked as individual items.

Anodising isn't really anything to be scared of if you take your time and common sense precautions.

However, if you take it fast & loose then you can spoil things – e.g. inadequate cleaning resulting in un-anodised patches; or excessive etching beforehand giving a matt surface; or anodising too cold and build up a hard layer that won't take dye; or anodising too warm so you get dissolution and a chalky finish; or touching the item part-way through and getting fingerprints; etc. etc.

I think you're right to be scared of, say, the battery-charger/"let her rip" approach which may give variable/dis-appointing results.

BUT if the item is well made, properly prepared and anodised carefully the impact on the dimensions will be minimal and I really doubt you'll have significant issues.

Dave

Edited By Dave Martin on 12/12/2012 14:43:13

[Bill PudneyParticipant @billpudney37759]

When I had to work for a living, one of the products was a gunsight. The metal parts were all 6061 T6 al. alloy, and they had to be anodised a uniform satin black. There were also many male and female threads that were all 0.5mm pitch, the diameters varied between about 12mm and about 20mm. The customer required that the assembly operations be completed in a clean room, to prevent the ingress of foreign objects such as dust and stuff. The customer also required that the assembly be achieved without the use of grease, to ensure that there could be no contamination of the optics. All this required the threads to be pretty close to "cock on".

In a post above Dave talks about dimensional change. This is real, we had to initially develop a repeatable process which would provide an acceptable "satin black" anodising. The dimensional growth was then established, and the NC programs adjusted as required. From memory it was 2/3 "in" and 1/3 "out", so that for instance if the required spec. of anodising was found to be 0.015mm thick per side, then the dimensional growth would be 0.005mm per side. Before anyone jumps up and down, the 0.15mm and 0.005mm were arbitary numbers.

There were many thousands of sights produced so we must have got something right!!

cheers

Bill

[MartinParticipant @martin]

Well, you have convinced me to "give it a try". I have made a shopping list and I'm off to buy the bits.

I also considered powder coating, but it is a bit messy and the fumes from the oven are a bit dodgy, positive side is one can coat many different materials.

I will cut a few threads of similar dimensions and anodise them as a trial first.

One other question, if the threads are found to be too tight after anodising, would it be possible to lap them in, or is the anodising even too hard for this?

Thanks for your input.

Martin

[MartinParticipant @martin]

Gents,

Just a couple of question.

I have had problems obtaining suphuric acid (Perth Western Australia is the most remote city in the world). However I managed to find some today, but it is only 34% suphuric acid, is this normal and if not what ratio should I mix?

Gloves are another issue, do nitrile gloves provide the same protection as vinyl? I know with my experience dealing with conveyor belt, that nitrile was always recommended where oil or acid was present.

Martin

[AndyfParticipant @andyf]

Martin, I use about 15 or 20% for anodising, so adding your acid to the same volume of water (add acid to water, NOT water to acid) would get you there.

I have had perfectly acceptable results using the acid from dead car batteries given to me by a local garage, added to the same vol of water, but that's difficult now that most car batteries are sealed.

Andy

[Author]

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