160 MODEL AVIATION
I THOUGHT I would take a break from
traditional Racing information this month
and share some basic facts about chrome.
This column is intended as a general
overview of chrome and not a how-to-do-it.
I may write some more-detailed information
in the future.
Last May I took a position as a
production manager with a chroming and
grinding company. We do “hard,” or
industrial, chrome and grind work on
everything from tiny pins to parts that are 14
inches in diameter and in excess of 100
inches long. Shaft work is our main area of
production, but we do approximately 40%
of our business chroming and grinding
cylinders.
Again, this column is not intended for
you to be able to go out and chrome after
you read it. If you decide you would like to
do it on your own, follow the proper safety
precautions. This column will not address
the plating of aluminum; that requires
different procedures beforehand.
Some people think chrome is a trick that, in
itself, makes engines run faster. It probably
helps in some applications; however, some
of the fastest engines in Quickie Rat are not
chromed. The chrome has allowed different
materials to be utilized for pistons and
liners, but in most applications it provides
the equipment with longevity.
Chrome is much harder than casehardened
steel, which provides better wear
and lower friction properties. When chrome
is used as a bearing surface, it must be
micro-finished; that will provide a lower
coefficient of friction than any other metal
when used against steel, iron, brass, bronze,
or aluminum alloys. Chrome should not be
used against chrome because it is poor at
wetting out.
Although people will say you can put X
or Y amount of chrome on a surface, you
can put on as much as time and your
technique will allow. Chrome will build up a
resistance in time and actually stop plating.
In that case you need to grind or hone the
part to a point where the chrome is smooth,
as if it were finished, and continue with the
plating.
We regularly apply between .0002 and
.0600 of chrome to surfaces. In our
applications we apply additional chrome for
grinding. Depending on the part, anywhere
from .005 to .010 of additional chrome is
added to allow for setup during the grinding
operations. The typical model liner would
have what we would call “flash chrome,”
meaning .001 of deposit or less.
The chrome you
add to a part will
only be as good as
the piece was before
plating. If the part is
dirty, has large
indentations in it,
etc., then the chrome
will have that in the
finished product. A
dirty part can cause
the chrome to not
adhere and not plate
at all, or it can cause
peeling during the
grinding operation. That is not the only
reason for peeling, but it is a major one.
How do you clean a part? If you have a
typical piece that requires no grinding
before plating, it is first bead blasted,
depending on the surface. If no bead
blasting is required, determine the area to be
plated and how to hold the part.
After the part is racked up (held on a
copper hook), dip the entire thing in hot
beeswax. After you remove the part from
the wax and it starts to cool, wipe down with
gasoline and/or alcohol the area to be plated.
Redip the part in the wax and repeat the
procedure until it has sufficient wax to
prevent chrome deposits in any unwanted
areas. Wax is not the only way to keep
chrome off of an area; a stop-off lacquer
and/or plastic material and electrical tape are
also used.
Once the part is clean, do not touch the
surface to be plated. The oils in your skin
can cause problems if you do not give the
part sufficient reverse.
Do not use electrical tape as a parting
line because you really want the chrome to
flow up and over any parting lines. The
preferred method is to use aluminum tape,
which will draw the chrome up over it,
giving you a nice edge when you remove the
tape for grinding or finishing.
If you use the electrical-tape method, the
chrome will come to the tape line and stop.
This can cause an irregularity which is
known as a stop-off ring; it’s an area with
the improper amount of chrome deposit that
will not clean up during finishing.
On a model engine liner, for instance, a
layer of brass shim or aluminum tape should
be wrapped on the outside of the windows,
allowing the chrome to be drawn into the
window and giving good adhesion. Also, the
sharp corners of the windows should be
broken because the chrome will not adhere
to a 90° corner over time. It will be knocked
off during finishing, by the piston, or simply
wear faster because you will have little
chrome in that area.
An often-asked question is whether or
not you can put chrome over chrome. Yes,
with great success, but only if the chrome
layer you are plating over has good adhesion
(no bubbles or peeling). The problem arises
if you have an area that is chrome and steel.
For instance, a cylinder that has chrome
on one side and none on the other should be
completely stripped. If it is a shaft, simply
plunge down until the area has no chrome,
CONTROL LINE RACING
Dave McDonald, Box 384, Daleville IN 47334; E-mail: [email protected]
A close-up view of a fixture to hold a liner
for plating. Notice that the anode location
is on center.
Shown is one of Henry Nelson’s liners.
Henry has some of the finest chromed
aluminum liners in the world.
Wayne Trivin’s fixture to hold cylinder for chroming and John
McCollum’s design. It allows for proper location of anode.
April 2004 161
and bleed the new chrome up over any areas
to either side that have chrome. You are
looking for straight lines.
A cylinder will need an anode dropped
in it to make the current correct for the
chrome to be attracted to the surface to be
plated. Take great care in the location of the
anode; with an anode that is off-center, you
will grow more chrome to one side than the
other. This will result in an out-of-round
part, causing great problems during the
finish stage. After you have determined that
the part is clean and the anode is correct, it
is time to plate.
The plating bath is approximately 130°, so
be careful. Plating baths emit a hazardous
gas; exercise great care around them. Allow
the part to sit in the bath for a short time to
begin to warm up. After sufficient time, a
sufficient reverse is done to get the part
gassed out.
“Reversing” is actually turning around
the current in the part. Chrome is done
using direct current. A rule of thumb is 2
amps per square inch of material. In our
shop, with the tanks loaded we will be
pumping approximately 700 to 1,700 amps.
Your current use will be much smaller for
modeling projects.
After the part has had a sufficient
reverse, and you can actually pull the part
out, it should have a gold appearance. Place
it back in the chrome bath, and start
working your current up to the appropriate
level. You do not just want to crank the
current up; turn it up slowly in time.
Generally, you will add (or we do)
approximately .002 of chrome per hour to a
part. You will have to determine your
settings, and that will give you an
approximated time to leave the part in the
bath.
After you have removed the part from
the chrome bath, wash it off with water,
and, in our case, dip it in a vat of hot wax to
remove the wax from the setup stage. Then
clean the part and prepare it for grinding.
As I mentioned, the finished product will
only be as good as the product you started
with. If you have to put, say, more than .020
of chrome deposits on something, pinholing
becomes an issue. For the average model
project, you are probably going to put less
than .002 of chrome on.
If you are chroming and are having
troubles, remember the following situations
and causes.
• Milky-deposit-looking chrome is usually
caused by high chromic acid/sulfuric ratio,
chloride contamination, iron contamination,
and excess trivalent chrome.
• Hazy deposits: High chromic acid/sulfate
ratio, high chloride contamination, iron
contamination, excess trivalent chrome, low
temperature, too-high current density,
intermittent current flow.
• Rough deposits: Low sulfate, low
temperature, poor surface preparation,
suspended particles in bath.
• Burned deposits: High chromic acid/sulfate
ratio, low chromic acid, excess trivalent
chromium, too-high current density, low
temperature.
• Poor adhesion: Insufficient etch, surface
contamination, intermittent contact.
• Poor coverage: Low chromic-acid content,
low chromic acid/sulfate ratio, too-low
plating current, oxidized contacts, scaled
anodes, high temperature.
• Pitted deposits: Pitting in base metal,
solution contamination from magnetic
particles, gas pitting.
I don’t believe that any one person knows
everything about chroming, but I hope this
column will provide some insight. If you
would like more information about plating,
visit www.caswellplating.com or
http://homepages.pavilion.co.uk/nickfull/.
As always, your comments are solicited and
appreciated. MA
Sources:
Caswell Plating
7696 Route 31
Lyons NY 14489
(315) 946-1213
Edition: Model Aviation - 2004/04
Page Numbers: 160,161
Edition: Model Aviation - 2004/04
Page Numbers: 160,161
160 MODEL AVIATION
I THOUGHT I would take a break from
traditional Racing information this month
and share some basic facts about chrome.
This column is intended as a general
overview of chrome and not a how-to-do-it.
I may write some more-detailed information
in the future.
Last May I took a position as a
production manager with a chroming and
grinding company. We do “hard,” or
industrial, chrome and grind work on
everything from tiny pins to parts that are 14
inches in diameter and in excess of 100
inches long. Shaft work is our main area of
production, but we do approximately 40%
of our business chroming and grinding
cylinders.
Again, this column is not intended for
you to be able to go out and chrome after
you read it. If you decide you would like to
do it on your own, follow the proper safety
precautions. This column will not address
the plating of aluminum; that requires
different procedures beforehand.
Some people think chrome is a trick that, in
itself, makes engines run faster. It probably
helps in some applications; however, some
of the fastest engines in Quickie Rat are not
chromed. The chrome has allowed different
materials to be utilized for pistons and
liners, but in most applications it provides
the equipment with longevity.
Chrome is much harder than casehardened
steel, which provides better wear
and lower friction properties. When chrome
is used as a bearing surface, it must be
micro-finished; that will provide a lower
coefficient of friction than any other metal
when used against steel, iron, brass, bronze,
or aluminum alloys. Chrome should not be
used against chrome because it is poor at
wetting out.
Although people will say you can put X
or Y amount of chrome on a surface, you
can put on as much as time and your
technique will allow. Chrome will build up a
resistance in time and actually stop plating.
In that case you need to grind or hone the
part to a point where the chrome is smooth,
as if it were finished, and continue with the
plating.
We regularly apply between .0002 and
.0600 of chrome to surfaces. In our
applications we apply additional chrome for
grinding. Depending on the part, anywhere
from .005 to .010 of additional chrome is
added to allow for setup during the grinding
operations. The typical model liner would
have what we would call “flash chrome,”
meaning .001 of deposit or less.
The chrome you
add to a part will
only be as good as
the piece was before
plating. If the part is
dirty, has large
indentations in it,
etc., then the chrome
will have that in the
finished product. A
dirty part can cause
the chrome to not
adhere and not plate
at all, or it can cause
peeling during the
grinding operation. That is not the only
reason for peeling, but it is a major one.
How do you clean a part? If you have a
typical piece that requires no grinding
before plating, it is first bead blasted,
depending on the surface. If no bead
blasting is required, determine the area to be
plated and how to hold the part.
After the part is racked up (held on a
copper hook), dip the entire thing in hot
beeswax. After you remove the part from
the wax and it starts to cool, wipe down with
gasoline and/or alcohol the area to be plated.
Redip the part in the wax and repeat the
procedure until it has sufficient wax to
prevent chrome deposits in any unwanted
areas. Wax is not the only way to keep
chrome off of an area; a stop-off lacquer
and/or plastic material and electrical tape are
also used.
Once the part is clean, do not touch the
surface to be plated. The oils in your skin
can cause problems if you do not give the
part sufficient reverse.
Do not use electrical tape as a parting
line because you really want the chrome to
flow up and over any parting lines. The
preferred method is to use aluminum tape,
which will draw the chrome up over it,
giving you a nice edge when you remove the
tape for grinding or finishing.
If you use the electrical-tape method, the
chrome will come to the tape line and stop.
This can cause an irregularity which is
known as a stop-off ring; it’s an area with
the improper amount of chrome deposit that
will not clean up during finishing.
On a model engine liner, for instance, a
layer of brass shim or aluminum tape should
be wrapped on the outside of the windows,
allowing the chrome to be drawn into the
window and giving good adhesion. Also, the
sharp corners of the windows should be
broken because the chrome will not adhere
to a 90° corner over time. It will be knocked
off during finishing, by the piston, or simply
wear faster because you will have little
chrome in that area.
An often-asked question is whether or
not you can put chrome over chrome. Yes,
with great success, but only if the chrome
layer you are plating over has good adhesion
(no bubbles or peeling). The problem arises
if you have an area that is chrome and steel.
For instance, a cylinder that has chrome
on one side and none on the other should be
completely stripped. If it is a shaft, simply
plunge down until the area has no chrome,
CONTROL LINE RACING
Dave McDonald, Box 384, Daleville IN 47334; E-mail: [email protected]
A close-up view of a fixture to hold a liner
for plating. Notice that the anode location
is on center.
Shown is one of Henry Nelson’s liners.
Henry has some of the finest chromed
aluminum liners in the world.
Wayne Trivin’s fixture to hold cylinder for chroming and John
McCollum’s design. It allows for proper location of anode.
April 2004 161
and bleed the new chrome up over any areas
to either side that have chrome. You are
looking for straight lines.
A cylinder will need an anode dropped
in it to make the current correct for the
chrome to be attracted to the surface to be
plated. Take great care in the location of the
anode; with an anode that is off-center, you
will grow more chrome to one side than the
other. This will result in an out-of-round
part, causing great problems during the
finish stage. After you have determined that
the part is clean and the anode is correct, it
is time to plate.
The plating bath is approximately 130°, so
be careful. Plating baths emit a hazardous
gas; exercise great care around them. Allow
the part to sit in the bath for a short time to
begin to warm up. After sufficient time, a
sufficient reverse is done to get the part
gassed out.
“Reversing” is actually turning around
the current in the part. Chrome is done
using direct current. A rule of thumb is 2
amps per square inch of material. In our
shop, with the tanks loaded we will be
pumping approximately 700 to 1,700 amps.
Your current use will be much smaller for
modeling projects.
After the part has had a sufficient
reverse, and you can actually pull the part
out, it should have a gold appearance. Place
it back in the chrome bath, and start
working your current up to the appropriate
level. You do not just want to crank the
current up; turn it up slowly in time.
Generally, you will add (or we do)
approximately .002 of chrome per hour to a
part. You will have to determine your
settings, and that will give you an
approximated time to leave the part in the
bath.
After you have removed the part from
the chrome bath, wash it off with water,
and, in our case, dip it in a vat of hot wax to
remove the wax from the setup stage. Then
clean the part and prepare it for grinding.
As I mentioned, the finished product will
only be as good as the product you started
with. If you have to put, say, more than .020
of chrome deposits on something, pinholing
becomes an issue. For the average model
project, you are probably going to put less
than .002 of chrome on.
If you are chroming and are having
troubles, remember the following situations
and causes.
• Milky-deposit-looking chrome is usually
caused by high chromic acid/sulfuric ratio,
chloride contamination, iron contamination,
and excess trivalent chrome.
• Hazy deposits: High chromic acid/sulfate
ratio, high chloride contamination, iron
contamination, excess trivalent chrome, low
temperature, too-high current density,
intermittent current flow.
• Rough deposits: Low sulfate, low
temperature, poor surface preparation,
suspended particles in bath.
• Burned deposits: High chromic acid/sulfate
ratio, low chromic acid, excess trivalent
chromium, too-high current density, low
temperature.
• Poor adhesion: Insufficient etch, surface
contamination, intermittent contact.
• Poor coverage: Low chromic-acid content,
low chromic acid/sulfate ratio, too-low
plating current, oxidized contacts, scaled
anodes, high temperature.
• Pitted deposits: Pitting in base metal,
solution contamination from magnetic
particles, gas pitting.
I don’t believe that any one person knows
everything about chroming, but I hope this
column will provide some insight. If you
would like more information about plating,
visit www.caswellplating.com or
http://homepages.pavilion.co.uk/nickfull/.
As always, your comments are solicited and
appreciated. MA
Sources:
Caswell Plating
7696 Route 31
Lyons NY 14489
(315) 946-1213
