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Slab Saw Coolants

Posted November 23, 2014 By Admin

We are often asked what is the best coolant to use in a rock saw and given that there are lot of different “recipes” out there, we thought a more thorough look at this topic would be useful.

The job of the coolant is three-fold:

  • to cool both the blade and the material being cut
  • to flush out abrasive particles formed while cutting
  • and provide lubrication to keep the cutting edge clean.

It is vitally important that you use an appropriate coolant in your saw – this will extend blade life and improve cutting performance. Excess heat on any diamond tool (including saw blades) is the fastest way to damage the tool – using an inappropriate coolant will kill your blade quickly so choose carefully.

TRIM SAWS: for these smaller saws (up to 6″/6″ size), water is generally fine to use as the coolant. Some users choose to add a coolant additive to the water which has a rust inhibitor and surfactants to improve cutting performance. Please note that these additives will not completely prevent rust (you will still see rust forming at the water line if you leave the blade in water) – so we always recommend emptying out the saw reservoir after use. Examples of suitable coolant additives are Covington Koolerant #1 or Tool Cool – there are many others out there.

MEDIUM SIZE SAWS: for saws in the 8″ to 10″ range, we start to need a more efficient coolant such as oil. In a reservoir type saw, water usually does not pick up on the blade well enough to use as the coolant. For saws that use an overhead water supply via a pump, then water can be used as long as it is supplied freely at the point of the cut to provide maximum effect. Excess heat can cause blade glazing in sintered blades or remove diamond entirely for electroplated or cheap notched rim blades.

SLAB SAWS: Water should not be used in large power feed slab saws – water (alone or with an additive) is just not able to cool efficiently and can damage the power feed mechanism. We recommend a good quality cutting oil (light mineral oil) for best results in slab saws – for very heavy duty cutting, you may choose to use a cutting oil additive for better results on very hard stone. We recommend Covington Rockhound Oil but there are other similar products available.

What about the old diesel or kero/oil mix??  This is a traditional coolant and many still use it but there are a few good reasons NOT to use in your saw:

  • These mixes are very flammable with low flash point temperature – it is just not worth the risk of fire or explosion.
  • The unpleasant smell makes it annoying during the cutting and it is very difficult to wash off the slabs after cutting.
  • Dangerous to your health – even when used in an enclosed slab saw, the mist generated during cutting can be harmful. Can also cause skin irritations.


A light mineral oil has a much higher flash point (110°C or more) so are much safer to use – if you are cutting very hard rock. adding a bit of Covington Koolerant #2 will increase the flash point even more.  These oils have almost no smell at all, are easy to clean off the slabs after cutting and are much kinder to your body (hands, lungs, etc).  Play it safe – just use the right stuff.

If you are concerned about cost – note that these light oils can be filtered and cleaned for re-use. Low tech filtering can be done using layers of paper bag filters but Aussie Sapphire is now importing the EasyClean oil cleaning units to fit to your slab saw. These will conveniently clean your cutting oil and separate out the sludge for disposal – one initial investment means your oil will last longer, your blade will cut better and your saw will stay in good condition.

See this document from Barranca Diamond for more information on Slab Saw Coolants.

Also review this helpful document on Care and Feeding of Rock Saws (Richard Gindhart).



Classifier Mesh Sizes

Posted November 16, 2014 By Admin

Classifiers are used to size material accurately for classification – often used by gold prospectors who need to size concentrate for use in spiral wheels or the like.

  • 1/2 inch (the largest screen) is about 4 holes per square inch (use to remove worthless larger rocks)
  • 1/4 inch is about 16 holes per square inch (use to reduce size of gravel material for easier sluicing or panning)
  •  1/8 inch is about 64 holes per square inch (use for final clean up of gold concentrates from black sand or for recovery of small gem stones)
  •  1/12 inch mesh – good all around size.
  •  1/20 inch – FINE MESH is about equal to window screen (use for final clean up of FINER gold from your black sand or for recovery of very small garnets and gemstones, etc…)
  •  1/30 inch  – SUPER FINE MESH – a very tight weave
  •  1/50 inch – VERY FINE MESH – 2500 holes per square inch- OFTEN USED WITH #30 and #70 screen for BLUE BOWL CLEANUP
  •  1/70 inch – VERY FINE MESH – 4900 holes per square inch – use with the #6 (1/30″) and #7 (1/50″) screens for best blue bowl recovery.
  •  1/100 inch – the smallest screen – use for microscopic gold recovery and ultra fine gold dust and flakes.

Note that the standard pair of gemstone sieves will almost always be 1/4″ and 1/8″ – you can quickly go through the larger material on the top sieve and then anything that goes through the bottom sieve will usually be too small to worry about.

See the photo gallery below to get a feel for what these mesh sizes look like in reference to a metric/inch ruler.



Lapidary – where to start?

Posted October 16, 2014 By Admin

We often get calls from people who are interested in rocks and gems, would like to get started in the lapidary hobby but dont know where to start. It is a good question but a very BIG one that will need some research first.

First question is why type of work are you interested in?  Tumbling, Carving, Cabbing or Faceting?  Do you need a diamond saw to trim or slab your rock?  Depending on your interest and available budget, you will need to pick from one or more of these main categories to set up your lapidary workshop.

Selection of tumbled rocks ready for craft or jewellery making (photo from Aussie Sapphire)


  • TUMBLING – low entry cost and easy to learn.  Use your tumbler to turn rough rock into free form polished gemstones that can be used in various craft projects or drilled/strung or wire wrapped to make jewellery.

Tumblers are available in a range of sizes. You will need a starter kit of grit and polish plus time – it usually takes around 4 to 6 weeks to complete a batch of rock in a rotary tumbler.

More information:


Please read the FAQ ARTICLE HERE to learn more about the process or BROWSE OUR RANGE HERE.




Example of carving from http://www.daily-crystals.com/gemstone-carvings/

CARVING – low to medium entry cost although a little trickier to learn.  Carving is usually done using some type of rotary tool (dremel, micromotor, flex shaft or similar) fitted with appropriate carving burs and polishing bobs.

Create free form or carved shapes from rough stone – anything is possible here with the only limit being your imagination. Carve abstract or realistic shapes (animals, plants, religious motifs, etc). Pieces can be for display or drilled/set for jewellery.

Dremel kits can be purchased very cheaply at large hardware stores – all you will need to add are some diamond tools and polishing bobs/polish.  SOME SUITABLE ACCESSORIES ARE LISTED HERE.





A selection of cabochon gemstones from www.gemselect.com article.

CABBING – medium to high entry cost. Use a flat lap or cabbing arbor to create cabochon gems (usually flat bottom and domed top) – opals are the most well known cabochon gemstone but just about anything can be cabbed including gems that are more typically faceted. Can be regular shaped or free form – if you cut in a regular calibrated size, then your cabs can be set in a blank jewellery setting at very reasonable cost.

At the budget end of the range, we offer flat laps for cabbing – the machine will drive one horizontally mounted disc (6″ or 8″) and you will go through a series of steps to grind, sand and polish your cabs. A bit cheaper and more compact but not quite as convenient.  If you have a bit more money to spend, you may prefer a cabbing arbor which has a series of vertically mounted wheels in 6″ or 8″ diameter so you can move through the steps on the one machine. A 6 wheel arbor is most popular but if your budget is more limited, you may choose or 2 or 4 wheel arbor.

BROWSE SOME OF THE OPTIONS HERE – machines can be set up to suit your needs so contact if you have any queries.


Selection of faceted Blue Sapphire from Reddestone Creek mine (photo from Aussie Sapphire)

FACETING – high entry cost and more difficult to learn.

This is the top level of the lapidary hobby – faceting machines are a big investment but is the only way of creating a traditionally faceted gems that you would normally see in a piece of jewellery.  There are a number of different machines around so do your research thoroughly and choose carefully. We highly recommend doing a faceting course or having access to help at your gem club so that you have the help you need as you learn to use your machine. The basics of faceting is not difficult to learn – the process of becoming a master faceter able to create beautiful gems takes longer but is incredibly satisfying.

BROWSE OUR FACETING OPTIONS HERE – note that faceting machines are sold without laps so you will need to factor in the extra cost of the accessories – there are lots of options when choosing a lap kit.



Diamond saws to cut rock from 4″ trim saws up to 36″ slab saws.

CUTTING – most people will need some kind of diamond saw to cut their stone to size. Diamond saws are optional but very useful.

Generally you only need a trim saw around the 6″ to 8″ size but we have slab saws that can handle very large stone. The key thing to consider here is cutting depth – decide how large a stone you need to cut and choose the saw accordingly.

A more detailed discussion on saws is beyond the scope of this article but we suggest you REVIEW OUR COMPARISON VIDEOS ON YOUTUBE HERE to help you select the best option for you.




Once you have narrowed down which area of the hobby you want to focus on, then you can decide which package suits you best.  Buying second hand can help to cut down the cost of equipment – unfortunately, good quality used machinery can be difficult to find as it often changes hands privately within clubs. If you are keen on buying second hand, keep a close watch on Ebay, Gumtree and the classifieds  – good idea also to spread the word that you are looking so others can keep an eye out for you. Keep in mind that there will be no warranty support and sometimes spare parts are unavailable for older machines that are no longer in production.

There is a wealth of advice out there on the internet to help you get started in the lapidary hobby – we also suggest checking out the AUSSIE LAPIDARY FORUM and we are always available to answer any queries you might have.




Cleaning bolts in a tumbler – PART 2

Posted April 2, 2014 By Admin

Part 2 of this article covers use of a rotary tumbler for this job.
Barrel_1Barrel_A_Before2In this test, we have used both #80 and #46 silicon carbide grit as well as medium cut ceramic media (triangle shape) – a bit water is added for the rotary type tumblers – aim to fill the barrel up to about 2/3 full.

This photo shows the batch before it was tumbled – note some of the pieces were extremely rusty and others just greasy and dirty. Again, we would expect better results if parts were degreased before tumbling.

The 12 pound barrel can fit larger pieces in compared to the Gyroc tumbler (note the large cog which was too large for the Gyroc A) has cleaned up well in the larger 12 pound barrel.  As a size reference, the base of the purple sieve is about 10″ (250mm).

Compared to the Vibratory tumbler, the bolt threads did not clean up quite as well and it took a little longer to get this finish (about 2.5 hours). The Lortone tumbler runs quieter. We used the QT12 for this test but you can get a triple barrel tumbler (same 12 pound rubber barrels) for larger scale tumbling. 



Cleaning bolts in a tumbler – PART 1

Posted April 2, 2014 By Admin

Every now and then we get asked about cleaning bolts in a tumbler so we thought it was time to post a few pictures with extra information.  Tumblers are great for cleaning up all sorts of metal objects as it takes a lot of the tedious hand-work out of the job. There are a few different ways to do it – Part 1 of this article deals with tumbling in a Vibratory tumbler:


This test batch included a selection of old bolts and other items – some extremely rusty, others just very greasy and dirty.

The test machine is a Gyroc A tumbler (the medium size).  In this test, the tumbler was loaded with about 4kg of medium cut ceramic media (medium abrasiveness, triangle shape) – about 4 heaped tablespoons of #80 grit silicon carbide and a small amount of water was added along with the test parts.

The parts were tumbled for about 1.5 hours – just before removing and rinsing, additional water was added for about 10 minutes to make the clean-up easier.  Note that normally we would recommend degreasing parts before tumbling for better results – we did not bother with this small test batch.




After almost 2 hours of tumbling, the parts came out very clean (even better if degreased before tumbling).  However, there are a few things to consider with the Vibe Tumbling Method:

1) Using coarse abrasive grit in a vibratory tumbler will wear the barrel faster than in normal usage.  The tumbling is faster and more effective but you need to factor in more frequent replacements of bowls.

2) The donut shape of the tumbler bowl does restrict the size of piece that can be tumbled – they need to be small enough to move freely around the bowl.

3) Vibratory tumblers are more noisy than the rotary tumblers.


Vibe_B_AfterThese photos show a before and after shot of the pieces (note the large cog was too large to fit and was subsequently tumbled in the rotary batch instead).

There is a little rust remaining on the thread of the largest bolt – this would have been improved by degreasing prior to tumbling.