How flat is a granite worktop?

[AT Laser]

I have 6 Compositor stones (two together attached) which, in my humble opinion, are about as good a surface as you can get, my company used them for die making, where flatness and consistency of height is required for making the best tools

[Voicecoil]

About as straight as Philip Schofield....

.....or the people in the government doing the procurement during the pandemic

[Tenson]

Update!

I got 30mm thick quartz, 1m x 0.6m and 2m x 0.6m

I created a steel support frame with screws around the top that I can adjust to support the quartz nicely.



I got myself a nice straight edge and I'm glad I did!

So far I only mounted the 1m piece, but the results are that it is pretty flat on the longer axis but cupped on the shorter axis. Damn, it's almost 1mm!

I expect it was flat when created as it comes in a far larger sheet, but I'm not sure if this cupping is due to storage or internal stress released when cut. Being cast, I expect the former.





Now I'm wondering how much I can help the situation by supporting it only at the middle points and clamping down on the outside edges. It has helped flatten it while the clamps are there.

I know quartz can sag if not well supported, but I don't know how long this might take?? Days, months? Any ideas?

[JAZZCNC]

If that slab is only supported at the outer edges I would be very careful what you put on the top as it won't take much of a knock for it to crack.!

[Tenson]

If that slab is only supported at the outer edges I would be very careful what you put on the top as it won't take much of a knock for it to crack.!

Its supported around the perimeter, but inset about 10cm.

[routerdriver]

When I worked with Corian,and similar, worktops we dreaded having to lift them once a sink cutout was in place.They were prone to cracking or even breaking from the corners of the cutout to the edges.We made a point of carefully sliding a similarly sized piece of plywood or MDF under them.I would think you ought to be providing a lot of support to a sheet of that size as objects of any significant weight may cause deflection.For aeromodelling,it may not be a consideration.

[phill05]

Its supported around the perimeter, but inset about 10cm.

No where near mate,you need to fully support it no matter what you will use on it.

Phill

[JAZZCNC]

Its supported around the perimeter, but inset about 10cm.

I asked my mate who makes counters from Granite and quartz about using quartz unsupported and said wouldn't recommend it, just one tap in right place and it could shatter like glass. Apparently, it can crack under its own weight if wide enough and not supported well enough.

[Tenson]

It's supported as below. Top is 1m x 0.56m and 30mm thick. Most quartz worktops are 20mm as it is stronger than pure granite or corian.