How to get a flat surface

[outofthefire]

I was told new mdf is flat, not sure how flat in the grand scheme of things, but definitely flatter than my or my lathes accuracy

 

[Screwdriver]

I was told new mdf is flat, not sure how flat in the grand scheme of things, but definitely flatter than my or my lathes accuracy

I doubt that. I'll be surprised if that lovely, shiny, "flat" MDF has a consistent, parallel plane within 10 thou. Plus it is a lot more flexible than any steel or aluminium workpiece you might be playing with so you'll be clamping it to something to stop it warping, twisting or bending. It will then conform to whatever you stick it to or built it on so that would need to be flat to your requirements. Then of course, the surface will wear out in no time...

You'll end up chasing your own tail.

 

[Brad93]

You want a surface plate

 

[Brad93]

My understanding is that you start with three flattish plates, cycle them appropriately as you lap them in sequence and by the magic of geometry, eventually, they all become perfectly flat.

There's a little more to it than that, but yes three square plates can be done that way.
They have to be square though.

 

[Seadog]

Do you mean that they have to be all the same size square, Brad?

Certainly round glass blanks for telescope mirrors would be the same diameter.

 

[Brad93]

Do you mean that they have to be all the same size square, Brad?

Certainly round glass blanks for telescope mirrors would be the same diameter.

Same size yes.

Round works too.

Rectangles don't work, because the overhang causes Issues

 

[Edward Teach]

Like Pete says it depends what you want to do. I have both granite (used in the kitchen as a trivet) and cast iron surface plate in the workshop. Neither are calibrated flat, even have a few dents n dings, both perfectly acceptable for the type of home Bodgery I do. At a push I guess a decent granite tile will be good enough for home bodgery

The only sensible answer by a long shot

 

[Parm]

The only sensible answer by a long shot

Steady old chap. Me and sensible very rarely go in the sane sentence

 

[fizzy]

I bought a small slab of marble from a salvage yard - old gravestone stuff. Incredible just how flat it is.
Not quite surface table league but not far off. Cost me £10!

 

[Screwdriver]

I bought a small slab of marble from a salvage yard - old gravestone stuff. Incredible just how flat it is.
Not quite surface table league but not far off. Cost me £10!

Should'a got two, then you could do the three card shuffle (flip one over).

 

[pressbrake1]

Same size yes.

Round works too.

Rectangles don't work, because the overhang causes Issues

Rectangle doesn’t work because you can’t spot corners when you turn the plates 90°

 

[Bornfree]

I had a lovely large piece of 3/4" float glass that I used to surface cylinder heads with, until I didn't notice a small screw on the bench top one day.

 

[Brad93]

Hi all, in various YouTube videos, people use flat stones as work surfaces. Does it need to be a special type of cut, or can I just buy a polished granite tile from a marble shop or stonecutter? Not sure what the trade is called in English. Thanks for your help!

Granite Surface Plate is the term you want to search fof