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The Basics of Polishing Mops & Compounds
What is Polishing?
When polishing the operator will use a polishing mop in conjunction with a bar of compound. Mops usually have a leather washer and are screwed on to a tapered spindle for use on a hand held polisher, bench-mounted grinder or polishing machine. These should not run any faster than around 3,000 – 4,000 RPM, otherwise there will be excess heat generated which could risk melting the mop and damaging the workpiece, particularly on softer metals and plastics/composites. In turn the slower speed will allow greater control over the finish.
The bar of compound is pressed against the edge of the mop as it is spinning, with the heat generated melting the compound on to the mop. The mop itself acts as a medium for the compound, with the mop type and density helping the compound to do its work. Over time this will build up as a hard residue on the mop and so will periodically need cleaning; this can be done with a mop rake which is essentially a wire brush that is pressed against the edge of the mop while it rotates.
Types of Polishing Mops
Mops are available in various materials but they will usually be either stitched or loose fold. A stitched mop has concentric rows of stitching which make these harder than loose fold mops and so they are often used for first or second stage polishing, with the closer the rows the stiffer and harder the mop. There are 3 sizes of stitching: 1/4″ (close stitch, most stiff), 3/16″ (middle ground and also the most common) and 3/8″ (open stitch, least stiff.) The thickness of a stitched mop is measured in sections, with each section usually approximately 1/2″ thick, e.g. 2 sections would be 1″ thick.
Sisals and white stitched mops are the most common types available. Sisal mops are hard and cut very quickly, and are available either dry or with an impregnation, which makes the mop even harder and longer lasting. As such they are ideal for harder metals that require a more aggressive cut rate. White stitched mops are not quite as firm and so are a popular general purpose mop for either the first cut or after using dry sisals.
A loose fold mop does not have any stitching and as such is very flexible and soft, so often used in the latter finishing stages. The thickness is measured by the inch, e.g. 1/2″, 1″, 1-1/2″ etc. The most common are G Mops, which are soft and a popular general purpose option for most substrates; B Mops, these are semi-stiff and for light cutting on softer substrates or finishing on hard materials, and WDR Mops (similar to Swansdown Mops), which are very soft and used for final finishing on precious and non-ferrous metals.
A less common type is a coolair mop; these have gaps between the folds which increase air flow circulation and therefore offer a natural cooling effect. This is beneficial for heat-sensitive substrates such as plastics and composites.
Types of Polishing Compounds
There are different types of compounds for various substrates as well as for the individual stages of the polishing process. When considering which to use and when, the most important factors are the coarseness of the cut and whether it has a dry, powdery consistency or if it is more greasy. A dry compound does not leave a greasy layer on the finish and so is useful when looking to achieve a very high quality polish, however it will be harder to apply to the mop as it can tend to crumble. Conversely a greasy compound will take much more easily but it will leave a layer of grease on the workpiece which can be difficult to remove.
Fused-Alumina
Black VCGM – Very coarse greasy compound for sisals.
Black CGM – Very coarse medium greasy compound, with more cut than Carbrax SMG.
Grey MGM – Good cut and colour bar for polishing prior to plating, good mop retention but not too greasy. Equivalent to LEA 2464 / 2464D.
Light Grey DMG – Dry cut and colour on stainless steel, good mop retention and not so dry that the mop will overheat. Equivalent to ULTRAPOL 70.
Carbrax SMG – Popular heavy cutting compound for carbon steel, stainless, iron and titanium.
Cut & Colour
Green BG – Very high quality cut & colour compound, with high cut rate and also leaves a bright finish.
Tripoli
Saictrip HC Tripoli – Slightly greasy compound, good mop retention. Equivalent to Lustre and LEA 2640.
Saictrip Superior – Clean cut and colour, best all rounder. Equivalent to LEA 2468.
Lustre – Highest grade tripoli, very popular in jewellery polishing.
Calcined-Alumina
Hi-Brite White – Common finishing compound, slightly greasy with good colour. Can be used as cut & colour on precious metals. Equivalent to Hyfin and LEA 312.
Hi-Brite Green – Drier compound than Hi-Brite White, gives very good depth of colour especially on aluminium and brass. Equivalent to Ultrapol Finishing Green.
921 White – Very good colouring off bar, when used with very soft loosefold mop leaves clean scratch-free finish. Equivalent to LEA FF9 and FF11.
Hyfin – A very popular high finish compound which performs particularly well on silver.
Bluepol – Popular finishing bar for all substrates.
Vonax – Primarily used for achieving high gloss finish on plastics/lacquers.
Ferrous Metals / Nimonics | Non-Ferrous / Precious Metals | Plastics / Composites |
| First Stage (Cutting): Mops: Compounds: | First Stage (Cutting): Mops: Compounds: | First Stage (Cutting): Mops: Compounds: |
| Second Stage (Finishing): Mops: Compounds: | Second Stage (Finishing): Mops: Compounds: | Second Stage (Finishing): Mops: Compounds: |
| Third Stage (Very Fine Finishing): Mops: Compounds: | Third Stage (Very Fine Finishing): Mops: Compounds: | Third Stage (Very Fine Finishing): Not Applicable |
