Just out of interest, what's the best/locost option for a flat surface reference? Various Youtube engineering videos shows the use of a big block of granite for measuring flat surfaces, blade sharpening surface, etc. Would a kitchen worktop piece work?

Just use a plate of glass. The thicker the better, less chance of you breaking it if something gets drop on it.
Davew823

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Originally posted by Slimy38
Various Youtube engineering videos shows the use of a big block of granite for measuring flat surfaces

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glass is quite flexible, it's smooth not flat

Ive got a bit of plate glass, 3/8 thick, and that seems to be flat,

might not be 100% flat, but near enough to get a straight edge, and check cylinder heads

It all comes down to the level of accuracy you require - a tool room would require a first-rate cast iron job that weighs a ton and costs a fortune.

If all you want to do is check the flatness of a piece of engine that usually seats against the block with a gasket then a good piece of new, thick float glass is more than sufficient. I use a chunk of marble hearth that is more than sufficient for my needs.

You could always buy 3 raw castings and make your own cast iron surface plate (3 plates, to be precise) if you have a lot of time, know how to use marking blue and know how to use a scraper! LINKY

The'old' standard cheap option for model engineers was the glass plate from a photocopier.