I want some wooden panels, about the size of a typical large window. But I don't want to cut down a "standard" size panel myself. In the UK there were D.I.Y. shops that would cut MDF panels (medium density fibreboard) to whatever size the customer wanted.

Do such places exist on Phuket?

The machine used looks something like this:

Thanks for any suggestions.

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Haven't seen those here in Thailand, but, if you live anywhere near Nai Harn Beach, there is a cabinet shop that will cut what you need (for a fee).
It is between DILIGAF and Shipwreck bars on the Cheers road.