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  1. #1
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    How bad is worktop granite?

    Hi,

    I can't afford a surface plate the size I'd like for my projects.

    I wonder if anyone has experience of just how bad standard worktop granite is in terms of flatness? Is it just terrible, or maybe not that far from an entry level surface plate?

    Right now I just have a wooden table top made from flooring sheet... to give you a reference!

  2. #2

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    Re: How bad is worktop granite?

    Hi!
    Short answer is Not. You might make it flat... lap it . (time consuming)

    I don't think those are made with engineering in mind. Those are made only to look "nice".

    I'm attaching YT video with lad answering this question directly :

    https://www.youtube.com/watch?v=suTKWpwljTg

    Kind regards,
    Tom J

  3. #3
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    Quote Originally Posted by tom40 View Post
    Hi!
    Short answer is Not. You might make it flat... lap it . (time consuming)

    I don't think those are made with engineering in mind. Those are made only to look "nice".

    I'm attaching YT video with lad answering this question directly :

    https://www.youtube.com/watch?v=suTKWpwljTg

    Kind regards,
    Tom J
    Thanks!

    I did buy some man made 'quartz' worktop material but haven't picked it up yet. I also got a proper straight edge so I can see how it looks.

    My hope is that the quartz style material (about 90% ground quartz / 10% resin) will be flatter than cut granite and tougher than 'dupont corian' style which is more like 50% resin.

    I'm not expecting it to substitute a surface plate, but where that's not available I wo der if it might be the next best thing?

    I also have a thick slab of surface ground ali tooling plate which appears to be just as flat as my straight edge so it might be interesting to see how it laps with the quartz.

  4. #4
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    Re: How bad is worktop granite?

    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.

    Attachment 464546

    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.

    Attachment 464548


    Attachment 464550

    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?

    Click image for larger version. 

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  5. #5
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    Re: How bad is worktop granite?

    I have a feeling you are bout to become the expert on this particular topic.It may be quite easy or it may just snap.Alternatively,you may be able to eventually flatten it by abrasion and polishing-but it won't be quick or easy.A man with a large enough CNC router might be able to skim it flat for you,but then you might feel the need to polish it and that could swallow a few days with no guarantee that the flatness would endure.Would you be happy with the kind of flatness that suffices for kitchen worktops,or is utter perfection the goal?

  6. #6
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    Re: How bad is worktop granite?

    Hi sash - so by "quartz" you mean its artificial stone? cast from quartz aggregate and some resin? If so you can get the specs of it from the manufacturer. Small granite surface plates are 75mm thick, 600x600 are about 100mm thick and bigger ones are thicker. Granite has several 100,000 of years to stabilise. Resins take a long time to stabilise if they have not been post cured. I was involved in tracking print through and distortion of yacht hulls and some resins took 6 months or even a year to stabilise at ambient conditions. Peter

  7. #7
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    Re: How bad is worktop granite?

    Thanks for the replies. I don't know who the manufacturer of the worktop is, it was an offcut and the supplier is not great at communications so it's probably not even worth asking. All that's marked on it is a number.

    Yes it is artificial stone. Graded quartz aggregate with about 10% resin. I assume it has been cured at the factory.

    I do have a CNC router big enough to surface this smaller 1m piece but I somehow doubt my normal end mills are going to work on quartz, more likely just chip it? Are there diamond abrasive end mills or something? I wouldn't want to spend lots on special tooling for it. I think the usual method is water jet.

    I'm still hoping it can relax back to a flatter state. I think it is like this due to being stored on edge.

    Also FWIW this is the way it's supported.

    Click image for larger version. 

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  8. #8
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    Re: How bad is worktop granite?

    Hi Sash - A router won't cut a quartz plate unless you use diamond tooling. Also the plate should be supported inboard from the edge. See attachment. You could lap it flat with some more "quartz". The issue is once flat will it be stable and only time will answer that.

    https://en.wikipedia.org/wiki/Surface_plate

    Regards Peter

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