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The Metal Polishing Process
Always
use a dust mask and wear eye protection to protect yourself from
debris from the grinding process. It is also recommended that gloves
be worn as polishing produces a lot of heat.
This applies to
all metals with slight variations to metal type or surface
condition. Various methods can be used to produce a fine or mirror
polished surface. When we polish to a mirror finish, what we are
really doing is making a series of finer and finer scratches, the
finer and closer they are together the brighter or more reflective
they appear.
Generally there are 4 stages, these are:-
Abrasive Finishing
This is often described as 'bobbing' or 'scurfing' and involves
the use of abrasives which, remove the surface irregularities or
imperfections. This is achieved with abrasive coated mops known as
'bobs' or 'scurfs' or with abrasive belts, cloths or papers.
Pre-Polishing
Pre-polishing or buffing involves the use of stitched polishing
mops such as sisal mops with a course cut polishing compound such as
Supercut (grey). This operation removes the scratches from the
previous abrasive stage and produces a brushed satin effect.
Bright Finishing
Here we use less aggressive stitched mops such as coloured or
white with a medium polishing compound such as pink or sovereign
(green), this will produce the bright finish of this stage.
Colouring
This final process involves the use of soft loose-leaf
unstitched G polishing mops with a blue
compound and produces the final mirror finish.
Stage 1: Abrasive Finishing
Abrasive finishing is done by coating 'coloured' stitched mops,
felt wheels or bobs with an abrasive compound to make a
'scurf mop'. These mops are then used to remove rough, pitted, or
irregular surfaces to produce a smooth surface prior to polishing.
This process can consist of one or several operations depending on
the surface condition therefore several mops should be coated in
intermediate grit sizes, i.e.,
80 grit: coarse
240 grit: medium
300 grit: fine
Abrasive Compound is available in
the following grit sizes: 80, 150, & 300
grit and is supplied in 430gm sealed tubes. It is
applied to the rotating mop as it is slowing down. To apply, start
up the machine and run up to speed, then switch machine off and
whilst it is slowing down gently apply the sateen to the periphery
of the mop causing the mop to stop, you should see a small amount of
the compound on the surface of the mop. Repeat this several times
until the mop is evenly coated all over, run the mop for approx 5-6
minutes when it should be set. It is then ready for use.
Depending on how rough the surface of the metal to be polished is
you may need to go through at least two or three grades finishing
off with fine 300 grit. The aim is to produce a fine, smooth,
even finish free from surface irregularities, ready for the
polishing process. As with abrasive grits you should always use a
different mop for each grade of abrasive compound.
Take care when polishing not to put a chamfer on sharp mating edges
of components where washers or gaskets may locate. The article to be
polished is held firmly against the rotating scurf applying a firm,
even pressure passing the work 'to and fro' across the scurf mop
crossing over at 90° where possible.
The mops have leather washers and screw onto the tapered spindles of
polishing machines, if you machine does not have one of these we can
supply one to suit your machine, just state the diameter of your
spindle and which side i.e., right or left hand.
Stage 2: Pre-polishing
In this stage the process is to remove the marks from the
previous abrasive finishing operation. This is done by using a hard,
very close stitched sisal mop and a coarse cut, aluminium oxide
'pre-polishing' compound, such as Supercut (Grey).
The mops is fixed to the spindle of the machine and started up, hold
the bar of polish against the rotating mop firmly but not too
heavily for approx 2 seconds, this should apply sufficient polish to
the mop. A new mop can be held against the mop a little longer. Too
much polish will cause the excess to be 'dumped' and will cause
streaking. The secret is 'little and often', conversely, if not
enough polish is applied the mop will break down. To remove the
excess, hold a stiff wire brush firmly against the mop whilst it is
rotating, this will remove the excess and return the mop to a usable
condition. This may need to be carried out frequently during the
polishing process as the mop will 'load up' after a period of
polishing and will also take up metal particles, particularly, when
polishing softer metals such as copper, brass and aluminium.
When polishing, move the article across the mop in different
directions and work 'to and fro' and from side to side, so that the
lines produced cross over, preferably at 90° to each other. If all
the polishing is done in the same direction the marks will just be
pushed further into the metal.
By changing direction you are cutting across the previous marks
thereby reducing them in depth, thus producing the smooth reflective
finish we are after.
Continue this process until you achieve a smooth brushed satin
finish. If this does not remove all the scratches from the previous
abrasive process, go back to that stage with fine grit scurf coated
with at least 240 or even 320 grit and use a small amount of grease
and lightly go over the area before returning to the pr-polishing
stage.
Stage 3: Bright Finishing
In this stage we use a less aggressive, softer white or coloured
stitched mops with a finer aluminium oxide polish such as Sovereign
(Green) to produce a bright finish. The primary function of this
process is to produce a smooth reflective surface with only a
minimal amount of material being removed.
As in the previous process the polish is applied in the same manner.
In this case we use either a coloured or white close stitched mop
(depending on the metal being polished) and Sovereign (a light
green) polishing compound. Again, follow the steps used in the
previous stage, remember
To apply the polish 'little and often' and keep changing direction,
cutting across the previous line of travel of the mop.
As you progress through the polishing process, you need to use less
and less pressure.
Stage 4: Final Colouring
In this final process we use the soft loose-leaf calico B or G
quality mops (again, depending on the metal being polished) with a
white or blue aluminium oxide polish.
Repeat the steps in the last process, this time using less pressure,
after this stage you should be looking into a mirror.
Finally, to remove all the grease marks left over from the polishing
process, wipe over the item with Vienna Lime Powder on a soft dry
rag, this will produce a highly reflective mirror finish.
To protect this mirror finish we recommend the application of
'Belgom Alu' polish. This is a wax-based product, which will protect
and seal your polished components for approx 6 to 8 weeks.
Polishing is a skill which has to be learned and only comes with
practice. However, by following these simple steps, anyone should be
able to produce a fairly professional finish.
We produce a wide range of DIY Polishing Kits suitable for use with
DIY pistol drills. We also produce 6" and 8" Bench grinder kits, all
our kits are supplied complete with the relevant adaptors and
instructions. |
