A new Diamond Cabochon machine – conclusion

The finished cabochon machine
The finished cabochon machine

Over the last two days I completed the build of this new machine. As it’s a clean machine as explained in my last post, it won’t need drip trays to collects water or anything like that, so it was decided that the machine would be mounted direct to the bench in a static position. This cut down on material costs as I didn’t have to construct a top, back and base for the machine as the bench top would be the base of the machine.

Note: in case you missed part 1 of this build you can find it here:


Bearing mounting blocks
Bearing mounting blocks

The first job was to cut two blocks to mount the bearings on which I got from my scrap wood pile which would otherwise have been destined for burning next winter in the fireplace.

The two blocks were positioned on the bench top and then wood glue was applied for extra strength and a couple of screws were put in from underneath the bench to pull the joint nice and tight and hold the blocks in place.

The next job was to place the bearings and shaft assembly on the blocks and position them, these were temporarily held in place with four long wood screws. Now I slackened off the grub screws in the bearings and the pulley, so I could get the shaft in the correct position, i.e. equal lengths on each side, once that was right the grub screws were clamped up.

Now I removed one of the four wood screws, leaving three in to hold everything in place while I drilled the first hole for the bolt that would go from underneath the bench top up to the top of the bearing, I did these one by one, fitting a bolt as soon as a hole had been drilled. By doing it this way everything stays in place and you can’t end up with a hole drilled in the wrong place. Yes it could be argued that by measuring everything accurately the same result could be achieved, but I believe by using the method I did then there is no chance of an error occurring.

Bearing mounting bolts
Bearing mounting bolts

So now we have the bearing and shaft assembly firmly secured to the blocks, at this point I realised my first mistake, I had forgotten to fit the V belt, but fortunately this was an easy omission to fix by simply unbolting it all, fitting the V belt and then bolting all back up again.

Aluminium shaft spacer tube
Aluminium shaft spacer tube

Next up was to make the spacers between the wheels, to do this I fitted all of the flanges and wheels and spaced them out how I wanted them, once I was happy with the spacing I marked the shaft against the edges of the flanges with a marker pen. Now all that remained was to remove all the wheels and flanges again and then take some measurements. The first measurement was between the face of the bearing and the first mark on the shaft, this would be the size of the first spacer.

Now I have got my spacer measurement, I went and cut the first two spacers, one for each side. I have used some aluminium tube for the spacers, it has an inside diameter of 26mm with a wall thickness of 3mm, so the dimension are pretty near perfect.

Aluminium end spacer tube
Aluminium end spacer tube

Right back to the shaft now and fitted the first two spacers, one each side butted up against the bearing face, then slid a flange on each side and then a wheel on each side, followed by a further flange. Now I took the next measurement for the next spacer which would go between the flanges. With next two spacers cut they were fitted onto the shaft on each side, followed by a flange each side then a wheel each side and then the final flange each side, and now it was time to measure the final two spacers. These I made a couple of mm longer than the measurement as I wanted to make sure everything gripped properly once tightened up.

Next I tightened the nuts at each end of the shaft and that was that stage of the job complete.

The next stage was to make the motor mount, this is just a lump of scrap wood again which the motor is bolted to.

Cabochon machine motor mount
Cabochon machine motor mount

When I built my first machine a few years ago I spent quite a while working out how I could make a motor mount that was adjustable to take account of any belt stretching that might occur and still be able to maintain a good belt tension. The result of deliberations again came from my scrap box which can be seen in the photo. I think this metal is called Dexion, but the fact that it has long slots in it gave me the answers to my initial problem.

So as you can see, the metal is screwed into the wooden block that the motor is mounted on. Then I placed the motor in position and put the V belt round the motor pulley and got everything lined up and then marked four holes in the bench top. These would be for the four blots that would go through the long slots in the metal. With the holes drilled, the bolts were glued in place from underneath and then the motor was put in place and wing nuts screwed onto the blots, and there you, my simple adjustable motor mount and it really works!

Now I took the time to check everything was secure and tight before firing the machine up for the first time. I almost forgot to mention that you must never run expanding drums without belts fitted.

So here we go, with on time and blast off, I was horrified to see that the whole thing vibrated like mad on initial power up.

I soon realised it wasn’t the machine that was at fault, it was the bench, it was too flimsy, the bench top was bending under the inertia of those wheels spinning up.

Bench stiffening blocks
Bench top stiffening blocks


So now the bench had to be stiffened up considerably, back to the scrap wood were I five lengths of wood, two of these would be screwed under the bench top as close the bearing bolts as possible, once theses were fitted the bench top was much less flimsy. But, and there always is a “but” isn’t there, I realised that the bench legs were not secured to the floor of the workshop and that this would allow some vibrating so that would need addressing too.


The bench legs
The bench leg modifications

So take a look at this photo to see what I did, the white bit of wood was screwed into the floor, and then the legs were cut to fit. The legs and the wood on the floor are screwed together from underneath and then more screws go into the legs from the top of the bench and now I happy to say that there is no vibration at all when the machine is started up.[benchlegs]

The four wheels are fitted with REZ belts, these are resin impregnated belts which have the diamond paste applied to them.

We will be using the following grades of diamond on the belts 28, 7, 2.5 and 0.5 micron which should give us a good coverage to follow on from the 600 grit silicon carbide belt on the other machine.

We got a very good result on a piece of lapis last year when we used the 0.5 paste, a result I couldn’t get with cerium oxide, so maybe we won’t be using cerium oxide very much in the future.

Our next job will to be to build a similar machine, but this will be a wet machine for the silicon carbide belts, but we will have to save up again to afford the expanding drums!

I hope you have enjoyed this

All the best