No leaks - about vacuum suction cups and reference points

If you have missed the previous parts or want to re-read then click here for part 1. part 2. part 3. part 4. part 5. part 6. part 7.

CNC machine suction cup with nut clamp system

CNC machine suction cup with clamp system

As I have mentioned in the previous part CNC machines come with different types of vacuum suction pods and in different shapes like square, round, narrow and long and even curved. The pods which are getting bolted down may take a bit longer to setup but will hold a lot better. This system is very good if you have mass production opposed to single production as the longer setup time is less significant if you do more than just one countertop with the same setting.

Other suction cups come with double action which means they suck them self down to the table and hold the piece on top as well. That system is very flexible quick and easy. The disadvantage is that everything relies on suction and if you have a leak somewhere in the vacuum system then it's likely that your stone will not hold properly and may move during work.

Every CNC machine should have a vacuum pressure gauge which should stop the machine immediately when the pressure drops. Unfortunately that is not the case and I have seen some bad solutions which did not work or stopped the CNC machine only when it was already to late.

CNC machine tool cones with 2 profile wheels
CNC machine tool cones with 2 profile wheels

The important thing is how well this pods are designed. They need to have good rubber seal which will stay in place and not come off every time you move the stone on them.

Another important thing to watch out for is the suction cup height. If you are planing to have two profile wheels on one cone as in the picture then the height is crucial. There should be enough space left to the machine table so the tool will have enough clearance to pass over vacuum hoses and dropped offcuts.

Tip: When you are putting together your deal with the CNC machine salesman try to negotiate to include as many suction cups in various sizes as possible in your purchase price.

If you do have to buy extra vacuum pods later on they will charge you an arm and a leg for it in most cases. So think about how big stone pieces you are producing and how many suction cups you may need to hold your stone safely and get them included in your contract.

CNC machine suction cup setup ready for stone to go on

suction cup setup ready for stone to go on

The picture on the left shows a CNC machine with the suction cups and reference points already setup for the stone to be placed on. The stone will be put against the white PVC reference points so the machine will know exactly where the granite is located on the machine table.

This particular machine did not come with any reference points and required me to manually show the machine every time where the stone is located. That was much to time consuming.

I then designed the reference points which are made out of two parts. The bottom part is made out of high grade stainless steel which is connected to the vacuum system to hold the reference point in place once it is positioned. The top is made from PVC and is simply screwed onto the stainless part with a 3cm very course thread so it can be quickly and easily unscrewed to allow for the tool to pass.

This possibility is important if you have more than one stone countertop to do with the same setting. Simply screw the PVC back on to setup the next stone countertop or vanity or whatever you do.

Granite CNC machine reference point
Granite CNC machine reference point

I also added air pressure with a two way manual valve to this CNC machine to switch the airflow between air pressure and vacuum. That allows the stone to hover on the vacuum pods which makes it easier to push the stone to the right position without too much effort then switch to vacuum to hold the stone in place. Many CNC machines now offer a similar system which I think is worth getting especially if you do not have a crane to lift your pieces into position.

The vacuum pump should be able to produce 80m3/h and is ideally fitted with a tank. The tank will increase the vacuum volume and is beneficial when you have small leaks or porous marble or granite. The tank will also separate the air and the water provided it is big enough. I have seen machines(I won't name them here) which only have a small 3 liter tank which will fill up in 2 seconds when there is i.e. a crack in the stone. The bad thing was that there was no switch which would have stopped the machine. The pump just kept sucking water until the pumps oil reservoir filled up with water. You can imagine what mess that is to clean. That's just an example of a very bad design.

Hopefully I'll see you in the next part were I'd like to share my experiences with different CAD/CAM/ software.