Better than Blued finishes - halfway decent how-to guide
OK guys, first of all when pasting from Word to Yellow Forum, first
post to a text file, save and close it, re-open it and paste from it to
avoid syntax errors, Now:
as mentioned before on this forum there are some reasonably inexpensive
coatings that adhere reasonably well to metal sold by Brownells and
others in a DYI format. But I'm not writing about these today, because
the directions for these are on the back of the can. Today I want to
talk about the next step up - sending your parts to get professionally
finished. The first and most important question to ask is, why bother?
Well, personally, my Russian heritage makes me genetically predisposed
to Vodka and anything that makes a gun more rugged, reliable, and
maintenance free. I did spend a lot of time in Texas growing up, so now I
actually prefer Tequila, but my quest for more rugged guns continues. I
have traveled for work from just south of Canada border to New Mexico
for the past 3 years, and always at least one airgun has been with me.
Needless to say I have done everything from dropping them in snow and
mud to spilling pop on them, so I have no use for a pretty gun that
won't hold up. For that reason I became very interested in making guns
that can keep up with me. Now on steel, about the best thing that
bluing can do for you is hide beginning of rust as it starts to eat your
toys - it is not a terribly effective corrosion barrier. Bare aluminum
surfaces tend to gall when in dynamic contact with other metal, and other
metals like brass form oxide layers that only look good on roofs. So,
with that in mind, here are some alternatives:
Quick interlude:
When I posted the inquiry on the yellow forum about whether I should
get the info together for this post I got an e-mail from Matt, who, I'm
sure, will chime in if he would like to. He offered his help with this
post and I ran some drafts by him to make sure we didn't leave out any
helpful information. Also he pointed to some more resources, and I
have downloaded some PDF documents that basically go more in depth on the
subject for this post. Shoot me an e-mail if you'd like a copy.
Anodizing:
This is, of course, a controlled generation of an Aluminum oxide layer
(harder than just about anything other than Diamond and a few ceramics)
on the surface of your part - basically a controlled corrosion
process. After the porous oxide layer is formed the parts may be dyed in your
color of choice, and the porous surface is then sealed (how I'm not
sure). There are 2 commercial finishes Type 2 and type 3. For Type 2,
or color anodizing, a 0.0005" to 0.001" layer is formed. Roughly half
of this layer is below the original part surface and half is above it.
Not being very thick this layer mainly serves an aesthetic function, as
a tougher than paint color layer. It does protect against light
abrasion, but deteriorates easily, especially around corners. Unless
otherwise specified you can expect that the factory anodized aluminum part
you have is Type 2. As of 2 years ago a now defunct outfit out of Fort
Collins, CO charged me $40 to do a type 2 batch of 120 mixed size parts.
Type 3 anodizing is a 0.0025" to 0.0035" wear resistant surface.
Again, roughly half of it is above the original surface and half below.
Make sure you account for the dimensional growth of the finished parts
(like using oversized taps for threaded holes or masking the threads for
anodizing) before making them. The above mentioned outfit also
charged me $60 for a type 3 mixed batch of 80 gun parts. Either of these
finishes make your final product more professional looking, and, for me,
are a requirement to consider the Aluminum part finished. Anodizing
does have its problems. Aluminum Oxide is a type of ceramic, so it is
very hard but very brittle which makes it chip when flexing. Also, if it
does wear off between dynamic bearing surfaces it becomes an abrasive
that accelerates part wear. Matt has pointed me to a Teflon impregnated
Anodized finish with improved mechanical properties, but I haven't yet
located a firearms oriented vendor. I do have some specs on this
finish I can send you. Also, keep in mind that because this finish is hard
but brittle it will chip easily from sharp parts corners. On sharp
inside corners, blind and small holes finish thickness will also be
reduced, because of poor solution circulation in these areas. Below are
pictures of Crosman 7075 T6 AL Type 3 anodized breech prototypes I made.
Note the radiused corners for increased strength and anodizing design
considerations listed above.
src="http://i56.photobucket.com/albums/g191/dsmush/Crosman2240.jpg">
Here Matt has some good info on anodizing:
"MIL-A-8625F defines the different types and classes of anodize the
type specifies the basic process used to create the oxide layer. Type I
specifies chromic acid anodize Type II specifies sulfuric acid anodize
(most common as far as I know) Type III specifies hard anodic coatings
(there are others but they are sub-sets of the above). The class
indicates dyed or non dyed. Class 1 specifies non dyed Class 2 specifies dyed
the mil spec does not define the type of electrolyte that is to be used
for Type III. It says that any process that can provide a heavy,
dense coating of the specified thickness can be used. It also indicates
that Type III coatings should not to be applied to alloys with copper
content over 5% or a silicon content over 8%. There is an abrasion
resistance specified for Type III of 1.5mg/1000 cycles except for alloys with
a copper content of 2% or higher. Then the spec is 3.5mg/1000 cycles.
Due to the porous nature of anodize, Type I & Type II anodize are
normally sealed to improve corrosion resistance. Sealing can be done with
numerous solutions. In my experience boiling water and nickel acetate
are common. Depending on what you want, corrosion resistance or
abrasion resistance, Type III may or may not be sealed. Sealing is omitted
for maximum abrasion resistance. If the best corrosion resistance [is
desired] with Type III is obtained when it is sealed. Sealing solutions
are similar to Type I & II. Parts will need to be racked for
processing. Specifying appropriate racking areas ahead of time will help
eliminate exposed racking marks or scratches from removal from racks. Racks
are often made from titanium or aluminum and can damage. Aluminum
racks have to be stripped on a regular basis due to anodize buildup.
Typically I have used a total coating thickness of .0002" to .0005" for clear
anodize. If this type of thickness is specified, oversize threads are
not typically required. Even with thicker Type II dyed anodize we
typically do not oversize threads. Small diameter and fine pitch threads
would probably be oversized but we just don't do that very often. One
of the critical things, especially for Type III (hard anodize) is to
make sure the anodizer knows the alloy. The tank setup for 6061 is quite
different that for 2024 or 7075, etc. Alloys with high copper
contents are more difficult to hard anodize and can burn easily. Typically
2024 is limited to around .0017" total coating thickness for normal
production. With special setup and electrolyte chemistry greater
thicknesses can be generated but it is very uncommon in my experience. Hope this
is helpful, Regards, Matt"
Plating:
These processes deposit a layer of harder, more corrosion resistant
metal on the surface of your part. In firearm applications thicknesses
vary from 0.0002" to 0.0006". Depending on design specs, most of these
finishes can be applied to just about any metal surface. One problem
with any plating is that it retains a very high surface tension and tends
to peel away from the part when scratched through. Thorough surface
prep is key in any plating process. Also to reduce this tendency a
thorough plating process will include post-plating heat treatment to relax
the plating and improve its bond with the part. The heat treating may
also be used to harden the finish but, of course, that may also affect
any cold-worked properties of flexible parts like springs and parts made
of nonferrous alloys. There are 2 general categories, Electroplating
and Electroless plating. Basically, in electroplating one wire is
connected to the part and one to a plating metal source. The 2 are
submerged in an acid-ion solution and DC current is run through the wires. The
plating metal atoms (ions) then dissolve in the acid and those in the
solution deposit on the metal part. One of the disadvantages of this
finish group is that the thickness of the plating depends on the
electromagnetic field distribution on the surface of the part. It works fine
for tubes, bars and other simple parts, but on every edge, step, or
other change in geometry, electromagnetic field concentrations create a
thicker finish deposition. Small holes may bridge off at the surface
because of this issue. Also, Matt suggested I look into hydrogen
embrittlement from electroplating. It turns out that the electrical current
also breaks down the water molecules of the solution into oxygen and
hydrogen. The free hydrogen penetrates the surface of the part, and acts
like little microscopic wedges between the metal's grain boundaries. The
surface of the part then becomes brittle. It is another problem that
can be cured by heat treating the plated parts around 300 deg. F, which
drives out the hydrogen atoms. Electroless plating eliminates the
electrical current and deposits the finish through a chemical reaction
between the plating ion solution and the part. The only commercial
electroless finishes I am familiar with are nickel based. This family of
finishes is not as resilient as some of the tougher electroplated
finishes, however the depostition process results in a much more consistent
plating layer, which allows for more precision. When purchasing a gun
that has been finished at the factory it's important to make an effort to
recognize what finish type is hiding behind a manufacturer's fancy
"Super-Duper-Norust TM" brand name, because it will let you know what to
expect. One of the advantages of choosing your own finish is QC under
your control.
Electoplated Nickel (aka Nickel plating)
This is the oldest firearm bluing alternative - available on guns like
S&W revolvers during the early 1900's (earliest that I know of). It is
reasonably effective, and of course, very decorative. The problem is
that when a scratch or wear expose the steel underneath, which is then
exposed to sweat or other moisture, the electro-chemical interaction
between the nickel and the steel accelerates the corrosion of the part.
An airgun example of electroplated nickel is a Sheridan Silverstreak.
Hard Chrome Electroplating (aka hard chrome finish, matte chrome
finish, or dense chrome)
This is great stuff, but it is getting harder and harder to find
vendors, because of the very environmentally unfriendly chemicals involved.
It's really too bad because hard chrome is probably the toughest
plating for firearm applications. The most common place you'll find it is
inside an AK-47 barrel. Need I say more? Well I suppose there is one
more thing. When scratched or worn through the finish offers sacrificial
anode protection to the exposed steel. Basically when exposed to
moisture the chromium is more prone to corrode, which significantly cuts
down on the corrosion of the exposed steel. Of course, as with aluminum,
chromium corrosion practically stops after forming a thin layer of
oxide on the surface, so until that protective oxide layer is removed
virtually no more corrosion takes place. This chemical interaction
between chromium and iron is what makes stainless steel stainless, except the
chromium is part of the alloy instead of just being on the surface.
Matt also reminded me to mention the adhesion issues with plated
finishes. Hard chrome has the strongest adhesion of all the finishes here.
Basically, with proper prep and plating practices about the only way to
separate the part and the hard chrome plating is to corrode away metal
from under the chromium layer, or if it is mechanically sheared this
finish will fail at the substrate metal not at the plating-substrate
interface.
Electroless Nickel (aka E-Nickel)
This is a base for a range of finishes. Basic electroless nickel
finishes are commonly found on lower end "all weather" muzzle-loaders. You
can distinguish hard chrome from e-nickel in a side-by-side comparison
by color. Chrome has a grey-silver color and e-nickel has a
yellowish-silver color. They are quite effective and, unlike the electroplated
nickel do not have the tendency to accelerate scratch corrosion. I'm
really not sure why that is, because the nickel-steel cathode-anode
couple still exists but somehow it is a more passive finish. Electroless
finishes do not adhere as well as electroplated finishes, and surface
prep will make or break their longevity. Because, unlike hard chrome,
these finishes will fail at the finish-substrate interface, they are not
used inside rifled firearms barrels. Airgun barrels are not subjected
to the same stress levels, but you have to communicate with the vendor,
as they will be inclined to mask the bore if they think it's for a
firearm. The finish thickness is more uniform than with electroplated
finishes, but whereas electroplating deposits more finish on sharp corners,
electroless finishes deposit less, so again sharp corners should be
eliminated whenever possible from your design - which is part of good
fabrication practices anyway. Again blind and small holes will not plate
well, so avoid them whenever possible. If you must have a blind hole,
try to drill a small relief hole, if you can, to establish solution
circulation through the cavity. The basic E-Nickel plating is relatively
inexpensive too. The aforementioned and now defunct local vendor in
Fort Collins plated a mixed 103 small parts batch for me for $150. There
are some fancier upgrades in this finish group. One I'm fond of is
brand named NP3. This is a mixture of Nickel and Teflon. While softer
than straight E-Nickel, the Teflon reduces this finishe's friction
coefficient and improves its corrosion resistance. It is probably only an
attractive alternative to folks as crazy as me, because a batch of 62 (a
couple of complete airguns' worth) mixed parts cost me around $300.
If there is a gun you plan to keep for the rest of your life (like an R1
he he he) that sort of an investment is negligible. Esthetically I
find this the most attractive finish. Its dark grey color very much
resembles Ruger's "target grey" nickel plated (don't know what process)
stainless guns. The first picture below is of a couple of 22XX guns I put
together with E-Nickel plating. Next one down is an NP3 plated CZ634,
R1, and the bottom picture is an NP3 plated AL Logun Axsor breech.
src="http://i56.photobucket.com/albums/g191/dsmush/Crosman_22XX.jpg">
src="http://i56.photobucket.com/albums/g191/dsmush/CZ-634_super-1.jpg">
http://i56.photobucket.com/albums/g191/dsmush/BeemanR1.jpg">
http://i56.photobucket.com/albums/g191/dsmush/AxcorR.jpg">
Here Matt has some good info on metal plating:
"As for adhesion issues with electroless coatings...you are correct,
surface prep is critical to good adhesion but even with good surface prep
they will not adhere as well as an electroplated equivalent. Hard
chrome has very good adhesion when compared to electroless nickel, and
thin dense chrome has excellent adhesion. With thin dense chrome, the
substrate often has to fail for the coating to come off. There is some
good info at
http://www.nimet.com/engineering.php
(you have to register) that talks about electroles nickel buildup
around edges and into holes. Another issue for electroplating is the
possibility of hydrogen embrittlement. During the electroplating process
hydrogen is generated and can be absorbed by the steel. Basically the
hydrogen starts to collect in tiny voids along grain boundaries. As it
collects in the void and creates internal pressure. This can lead to
reduced ductility and can cause failure under very low loads. High
strength steel alloys are the most sensitive to hydrogen embrittlement but
it is possible with many materials. A post plating bake is normally
used to drive the hydrogen out, thereby restoring the tensile properties.
The bake temperature has to be lower than the tempering temperature
so that the hardness and therefore strength is not changed. 375 to 400F
is fairly common. Fasteners are common victims of hydrogen
embrittlement."
Epoxy/molybdenum based finishes
These are epoxy based finishes that are sprayed on and baked at around
300 F to cure. What makes them neat is that the molybdenum particles
suspended in the finish make it very tough, so you can make it thin - I
think as thin as 0.00025" to 0.00015". Because the epoxy has a lower
modulus of elasticity (more flexible) than the metal part it will not
crack if the metal flexes. It is a less resilient finish than plating or
type 3 anodizing, but it is very corrosion resistant and not terribly
expensive. Also some less desirable alloys, like zinc and 3000 series
extruded AL alloys used in trigger guards and other airgun components
do best with this finish, because they are so soft that they don't hold
on to the harder less flexible finishes very well. Also, these
finishes have a range of colors to choose from for the fashionably inclined.
I have had some R1 trigger guards refinished in black "Roguard", which
is Robar's version of this finish type.
Phosphate
I don't know much about this finish except that it's reasonably tough,
retains oil quite well, but doesen't work great between moving surfaces
because it results in a higher friction level between parts (my
practical personal experience with this finish was on a post-war P38 and an
A1 M16), and, like epoxy based finishes, is not applied inside barrel
bores. I suspect this finish may soon be replaced with the epoxy
finishes in firearm applications. I know that many grade 8 bolts are
phosphate coated, and I don't know if there is any difference between that
finish and what I have seen on the guns. It does form a stronger bond with
metal, so some military weapons use a phosphate base, and an epoxy or
epoxy/moly topcoat for a very robust combination finish. I've looked
into that combination, but my favorite NP3 finish still turns out
cheaper, so I'm sticking with it.
Some helpful hints:
1. Find out and/or specify your finish thickness.
2. Do not plate pins if you plate the parts (ie trigger housing pins
break-barrel pivot bolts etc.) they go into.
3. Make sure you do not have any tight threads (mostly an issue with
type 3 anodizing)
4. Now, lets do some quick math: Let's say you want to plate a barrel
band and a barrel for a gun. The clearance between these parts is
0.002". Finish thickness is 0.0004" to 0.0006" per surface. Will the
finished barrel fit through the finished barrel band? Not likely. With a
finish thickness of 0.0006" the ID of the band will decrease by 0.0012"
- say from 0.438" to 0.4368", and the barrel OD will grow by 0.0012" -
say from 0.436" to 0.4372". See the problem? Tiny numbers are a huge
pain in my butt. Don't worry though, it only takes a couple times of
paying a couple of bills for a strip and refinish to never make that
mistake again.
5. Make sure everything is deburred, bead blasted, honed etc. before
you send off your parts. If you miss something you wanted to do
beforehand you will definitely find it after the fact.
6. If you want barrel bores plated make sure you discuss it with the
vendor first and note it on your order.
7. Lots of things, like muzzle brakes, on airguns are attached with
lock-tite - make sure to take these apart and clean out the locktite
before sending your gun parts off.
8. You probably will not be able to find a vendor for anodizing
aluminum parts with permanently attached steel components, because the steel
will contaminate their anodizing tanks.
9. Some things that Matt reminded me to emphasize: Remember sharp
corners and blind or small holes will not have the finish consistency of the
rest of the part, (As you have read the reasons differ, but the result
is always inconsistency) so try to reduce them in your design.
10. Sending parts instead of an assembled gun puts QC into your hands.
This is YOUR gun so YOU should be the best and toughest QC inspector
of the work performed on it. That's the whole point of this
exercise.
11. Reading this post will not make you refinishing guru, so do some
research on your own after you read it and then learn the best way -
practice.
Placing your order:
Make sure you package everything thoroughly. There's nothing worse
than getting back parts that got scratched by each other during shipping
and were subsequently plated. It really hurts. Usually, I call ahead
and discuss with the vendor what I'd like to accomplish, get input from
him, and get ready to ship. Then I take a picture of all the parts I'm
sending, number them, and write up a brief description of what I'd
like. Mr. FedEx then speeds of, and in 1 to 2 months I get a healthy bill
and once I pay it I get my parts back. Here is an example:
src="http://i56.photobucket.com/albums/g191/dsmush/Picture022.jpg">
To:
The Robar Companies, Inc.
21438 North 7th Ave,Suite B
Phoenix, Arizona 85027
(623) 581-2648
From:
Dmitry Smushkov
Dair Designs
XXXX Yxyyx St.
Fort Collins, CO 805XX
Phone: (XYX) XYZ-3851
Dear Robar Representative,
First of all thanks for the good job on plating the last batch of
parts. This is another batch (batch #4) for NP3 plating. As usual I have
included a picture of all parts for your reference. OK, so here is the
rundown of special requests/instructions:
X This batch has no firearm receivers, so I wonder if you could save me
on shipping and not ship it back by 2nd day shipment.
X There are no critical tolerances, so please plate on the heavy side:
0.0005" to 0.0006".
X All barrels are airgun barrels, so please do not plug the bores for
plating. The plated bores turned out quite well last time, and I would
like the corrosion resistance this finish offers in the bore.
X Parts 1 and 2
o Parts 1 and 2 are rework from last shipment. It turns out they were
locktighed or epoxied together and came apart as soon as I took them
out of the box.
X Parts 3 - 7
o Parts 3 - 7 are Aluminum and will need to be stripped of their
anodized finish.
o I spoke with Karl before sending them and he said there shouldn't be
any problems NP3 plating them.
o Part 3 has a steel part peened in, which, according to Karl should be
OK.
X Parts 8 and 9 are Zinc die cast trigger guards. I hope you'll be
able to NP3 plate them.
o If you cannot NP3 plate these 2 and it would be the same price or
cheaper to coat them with dark green or black Rogard go ahead and apply
the Rogard finish at this time.
X Part 10 is not a spring, so the plating process should not cause
problems.
o It attaches in the back of the magazine well on a CZ 75 and protects
the hammer spring from dirt etc.
X Part 11 is a hammer assembly with pins peened in place.
o If you can disassemble and reassemble it please do so, otherwise
plating it as an assembly is fine by me.
X Part 12 is a riveted barrel assembly. Plate as an assembly.
o I understand that the internal surfaces of the riveted joint will not
get plated.
Thanks for your help, and I'm looking forward to sending you a bunch
more work in the future.
Dmitry Smushkov
Websites for finish vendors
The one I have used extensively is Robar. They do a great job prepping
parts and I really enjoy signing over my paychecks to them. I'm going
to have to try an anodizing outfit as well though, because my local
guys are, sadly, out of business. Some of these vendors I have stumbled
upon myself and some, including Robar, were recommended by other forum
folk.
http://www.mrarms.com/index.html
http://www.eabco.com/cssfg.html
http://www.shootersolutions.com/allproducts.html
http://www.hotflashrefinishing.com
http://www.originalmetaloy.com
http://www.robarguns.com/DesktopDefault.aspx?tabid=4&tabindex=2
http://www.techplate.com
The website Matt recommended, which has awesome info but you have to
register:
http://www.nimet.com/engineering.php?action=signup
I hope this helps you guys. I'll be happy to help you in any way I can
if you decide to attempt this. Just shoot me an e-mail and I'll be
happy to give you my number, so we can chat about all this stuff. Good
luck and remember a hungry airgun is a sad airgun, so be sure to feed
yours regularly. Later, D 