Granite for Scary Sharp

[Shultzy]

Morrisons are selling granite place mats for <£5. They are A4 size and about 8-9mm thick. There's also a A3 size at >£8 that's about 12-13mm thick. These would make good bases for sharpening.

 

[WellsWood]

I saw those and had the same thought. I wonder just how flat they are though :-k

 

[woodsworth]

i'm all over that in the morning after the car boot

 

[wizer]

Apart from checking with a good straight edge, how can they be checked? or would a straight edge be sufficient for chisels and plane blades?

What size are they?

 

[woodsworth]

well i'll be getting one for pots on the table tomorrow so i'll check it with a flat rule and see before getting one for the chisels. mmmm which will be arriving on monday! can't wait

 

[wizer]

how easy will 8-9mm granite cut?

 

[woodsworth]

Quite easy with my wet saw.

If you even have a wet tile cutter you'd be able to do it with no problem. Thinking of cutting the A3 length wize? i was thinking of doing that as well.

 

[wizer]

What I've been thinking with my scary sharp stuff is that I'd prefer to have each grit on a separate flat surface, much like diamond/oil/water stones. This will enable me to work all around the 'stone' and off all edges. I was going to get a tuit to have some glass cut up for me. But this might be better/cheaper.

So I can't cut it on the tablesaw??? :lol:

 

[Lons]

I fit granite worktops occasionally and usually keep some of the offcuts for samples and possible bases for carvings.
Mostly 30mm so pretty thick though.
I have a nice 300 x 200 bit I use as a flat plate.

1). If you want to source granite, look in yellow pages and you will usually find a supplier no to far away. They will always have offcuts and usually quite happy to give some away FOC as they are of no use to them.
Alternatively just ask for a couple of samples and say the missus wants new worktops.

2). It can be cut quite easily dry (even 30mm thk) using a small angle grinder. Bit dusty so do it outside 'cause it gets everywhere.
Even easier if you buy a very thin (1 - 2mm) stone disk from one of the DIY sheds. I use this method for cutting the upstands which are supplied to me oversize.

It's normally flat enough, if not - get some more as it's not worth the effort trying to rectify it.

Incidently, There are suppliers of marble as well and most of them chuck it in a skip and will let you recover some largish bits if you ask (try fireplace manufacturers as well).

Happy hunting

 

[davebray]

Hi Shultzy,
You may want to try your local monumental mason (memorial headstones and the like).
About 9 months ago I got a rectangular offcut of polished black granite 600x200 and 30 mm thick for a fiver in the bloke's hand.
When I got it home it checked out flat in all directions with my expensive stainless steel Stanley 1 metre rule, but the rule is not a certified straight edge though.
Cheers
Dave

 

[Peter T]

Buy a granite surface plate off e bay.

I got one for about £35 that's about 4 inches thick and is flat to better than 1 micron.

Only downside is that they weigh a ton!!

 

[bugbear]

Unless the error is so great it induces a camber (or hollow!) in the width of the blade, most surfaces are "flat enough" for scary sharp use.

The requirments are far more stringent for back flattening, or plane sole flattening.

BugBear

 

[mike s]

sorry for the dumb question but what is a granite flat surface used for?

 

[jimi43]

If you are trying to make a metal surface flat you need to lap it against an abrasive substance that is fixed to a flat reference surface.

Huge lumps of granite can be made flat and stay flat (unlike some metals which may warp). Thick float glass is also dead flat because it is floated on molten metal and therefore gravity makes it flat...again, this is used as the substrate.

Abrasives can be carbide grits in a paste...affixed to a film (like 3M lapping films available from Workshop Heaven) or as a sheet of paper which is glued down with double-sided film or spray adhesive.

Some used thick MDF as the reference surface too.

You can then lap the sole of say a plane, flatten the back of a plane iron or chisel and also hone a bevel.

If you don't use a flat surface you will induce a curve into the item being lapped.

That's about it really.

Jim

 

[Scouse]

This may be a stupid question, but with a relatively thin piece of granite, such as the above placemats, if they are flat but placed and used on an uneven surface will the granite flex as I understand float glass is prone to do?

 

[John Brown]

"Thick float glass is also dead flat because it is floated on molten metal and therefore gravity makes it flat..."
You flat-earthers....

 

[Titus A Duxass]

"Thick float glass is also dead flat because it is floated on molten metal and therefore gravity makes it flat..."
You flat-earthers....

That's what I use, I got an offcut for a couple of quid.

 

[Jacob]

I saw those and had the same thought. I wonder just how flat they are though :-k

Well could could flatten them to make sure. With another bit of granite or something. You might have to flatten that one too!
Or just not bother at all with crazy sharpening practices! :lol: :lol:

 

[Kalimna]

Yehbut Jacob - if you ground a hollow in the surface, or a curved bit of glass, you could achieve a rounded bevel easily

Adam