Suction cup beneat your cutout or not?

[Stonecutter]

Hey guys,

At work we usually place a suction cup beneat a cutout in a granite slab. But today I saw a youtube movie where the cutout just falls on the working table after the finger bit has done it's work, and the CNC can continue it's work right away.

Now, I'm new to CNC-ing things, so I am a little scared about just letting that piece fall through. But maybe the more experienced one here can enlighten me about why you should or should not place a suction cup beneat a cutout in a granite slab

I'm thinking:
* When placing a suction cup, you must be very quick to remove the leftover piece, because your suction cup will suck up water, and let your vacuum reservoir fill up.
* It prevents the falling piece to damage your table
* Not placing your suction cup speeds up your work, as you do not have to remove the piece to finish your edges (i case of an undermount sink)

[shrew]

I always place a suction cup below the cutout on undermount sinks. This is just to make sure that when the router gets to the last bit and the stock granite falls it doesn't chip the soon to be polished face of the cutout.
As for overmount sinks if using 30mm granite i rout down 27mm leaving the rest in just for strength when transporting/fitting. The fitters just chisel it out on site once fitted.

[T_Kiwi]

Being in the stone machining industry for 10 years as an operator and technician i will give you my advice.

Firstly you will need to make a judgment based on type of material used.

Basically as a rule you do not need to place suction cups under a cutout for granite or engineered stone. Start your cutout to the back of the piece, not the front, that way there is plenty of meat on the work piece to handle the weight of the offcut. make sure you have clamps or the 60mm suction cups in the front of workpeice (presuming your front is 80+mm to the sink).

Some marble is quite strong and do not need support under the cut out either so its really a judgement call based on experience.

I only ever place support under the cutout on veiny marble ands some soft granites but i do not connect the suction cups to the vacuum pump.

Any other questions then dont hesitate to ask

Anthony

[jonnie]

As i stop the machine and re-measure the thickness of the stone around the area where the bowl is it is no problem removing the cups i have placed under the bowl cut out.I have run the machine with out those cups under the bowl with only one problem with the edge chipping but like i said i did run the machine by measuring all four corners but found that the stone varied in some cases around the cut out area which resulted in the grinding heads touching the face of the stone as i was using a double pencil round profile

[T_Kiwi]

Originally Posted by jonnie As i stop the machine and re-measure the thickness of the stone around the area where the bowl is it is no problem removing the cups i have placed under the bowl cut out.I have run the machine with out those cups under the bowl with only one problem with the edge chipping but like i said i did run the machine by measuring all four corners but found that the stone varied in some cases around the cut out area which resulted in the grinding heads touching the face of the stone as i was using a double pencil round profile

It is advisable to always work with face down when possible, this eliminates lipping on the face when the thickness varies

[jonnie]

I know in the ideal world it is good practice to work the job upside down because of what you have said but most of the bowls we do have a set of drainer grooves on either the left or right side or both ,and as this process has to be done face up it makes sence to do the bowl face up as well.

[T_Kiwi]

In that case its perserverance all the way. the joys of stone.