Step 1 – 80 Grit Shaping Stage -Rock Tumbler Guide

This (step 1) assumes that you have a rock tumbler ready to go, all the correct grits, water and actual rocks.

On the right you can see an image of how rough rock will look before the process. The rocks are often full of sharp angular edges and there is little or no sheen showing – these are a little more rounded than usual. This is a typical image of the kind of rough rock you will find in lapidary stores / rock and mineral shops etc, dirty, chipped, unshaped and not very attractive to observe!

Take the rocks you have chosen and place them in the barrel. Remember to select a good range of sizes, with particular emphasis on those little bits and bobs which will do most of the hard work.

Fill the barrel until it is around three quarters to four fifths full – this applies to whatever sized barrel you are using.

Now pour cold water into the barrel until it just about covers the top of most of the top rocks. You can cover them (just about) totally if you need to, but I prefer to leave a little bit of rock showing because if I decide to take a look in the barrel at any time, I can just grab a rock which I can see – rather than messing around in the sludge!

Cold water is required because hot water can soften the materials (plastics) used to make the barrels, on certain models this could cause the lid to pop off whilst the water remains hot. Use cold water.

Now put in the grade 80 silicon carbide grit. Use around 1 heaped up table spoon of grit for every one pound of rock in the barrel. Don’t worry about exact amounts here, you really don’t need to. If you overdo it, then the tumble can go a little longer before all the grit is smashed up into inefective particles – thats all. If you don’t quite make up the full amount, don’t worry too much either – it simply means that this step of the batch may need to be repeated before you are satisfied with the shaping (more than one repeat of this (step 1) is often required anyway – so you will have plenty of time to buy more grit if you’ve run out).

On the right, you can see the blue line, this is the water line, the barrel is around four fifths full of rock, and the water level is covering most of the rocks, but leaving a few poking out of the top for me to grab hold of if I need to take a look inside during the run. You can see the silicon carbide grit floating on the surface tension of the water, and also resting on some of the stone. This is exactly what you want to be able to see in your project at this stage.

Now place the lid on the barrel and securely fix it into place. Double check it is tight – the last thing you want is for it to come off when you’re not around!

Before placing your barrel on the rails of the tumbler, power it up and let it warm up for a minute or two – just to get the motor going and bearings running smoothly. Follow any instructions on lubricating the machine over time, as this will add to its lifespan and ensire smooth running operation. Dry the outside of the barrel completely if it is wet.

Now turn off the machine after its warm up and position your barrel. Then turn it back on. Look over it to ensure everything is going well, check that the barrel is turning unhindered, sometimes they can slip if there is any damp on the rotating drive rail or outside of the barrel. If everything looks good, then it’s time to say goodbye to the setup for around 7 to 10 days. This length of time varies on the hardness of your rocks based on the Mohs scale of mineral hardness which is described as a qualitative ordinal scale which characterizes the scratch resistance of various minerals through the ability of a harder material to surface scratch a softer material – you don’t really need to go into all that – it will come with time though.

Time passes……….

When you next open up the barrel, you will see something which looks like the image on the right. The 80 grit (or most of it) will be have been broken down from shining black sand grain sized particles and converted into a grey sludge. The water will have turned a color which matches the rocks (often but not always) and there should be less volume of rock left over – the amount by which the volume depletes during a fixed timed stage depends on the quantity of 80 grit used, the hardness of the rocks and the balance of large : small rocks in the batch.

Remove the rocks from the barrel, and give them a good rinse in a bucket of water or under a hosepipe, don’t forget – never pour the slurry down the sink.

Having emptied the rocks from the barrel, give them a clean in water. If you think they are rounded and shaped enough for moving onto the next step, then give them the cleaning of their life – make sure that every single last particle of 80 grit is gone from any pits or cracks. You do not want any 80 grit in the next step – it can ruin the batch.

Whether now is the time to move onto the next step is totally your decision, study the pieces you have and look at the pitting, cracks, chipping, shape, size, exposed color, etc. How they look after an 80 grit tumbler session is how they will look at the very end after all steps are completed – except of course that they will be shiny. You can wet them now, and they will look similar to how they will when finished.

If you are content with the way they are, then move onto the next step. If not, go right back to the top of this page and repeat step 1 – keep repeating until the rocks look exactly right for your requirements – each repetition will grind them down and remove more and more flaws.

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