Is granite countertop flat enough for flattening?

[Bill Bukovec]

Is granite counter top flat enough to use for flattening the backs of plane irons and such?

I know a lot of people use the precision ground blocks that machinists use.

I found a source for free granite. They are sink cutouts from a granite countertop company.

Bill

[Roderick Gentry]

Well who knows, it isn't graded, so it isn't graded, but if you can't measure the difference then how would it mater? If you had your best ruler and it couldn't show the difference, then the plane probably won't plane badly either. You could make a jig of three points that rest on the granite with a 10 buck dial indicator in the middle with it's point resting on the granite This could be three drywall screws in a piece of plywood. You move it around you can determine what variations are present. Basically if the points were a foot apart with the indicator somewhere in the middle, you would want the needle to not even move off one thou. This is an easy jig to use because it is just relative, no absolute measurements are being made. Most indicators have a barrel that is like 3/8", so you just need a snug hole for the indicator, and you would have to be careful to move the jig smoothly.

[Charles Bjorgen]

Been wondering the same thing because I'm hoping to create a sharpening station. Might be worth buying a straight edge to check the cutouts. Can you share what the cost of those cutouts might be?

[Matt Day]

Don't forget tempered glass is a good option too.

[David Hawxhurst]

i use a piece of 12" x 12" granite for sharping, use psa type paper to adhere to the granite. it is flatter than .001". my granite counter is not, when you put a quality straight edge you can easily see light and measure anywhere from .001" to .003" over three feet. you can get a reference granite plate if your that worried about it. i guess your not using stones of some sort to sharpen with.

[keith micinski]

.001-.003 over 3 feet surely is flat enough isn't it?

[Bill White]

I use a granite sink cutout. Its as flat as I'll ever need. My planes are within .002". My wood is happy with that and so am I.
Bill

[Ted Calver]

I purchased two 12 x 18" granite reference plates from Enco last year when they were on sale and had free shipping. Just got an e-mail talking about free shipping this week. You might check out their reference plates. Mine must have weighed 50 pounds, so free shipping was a good deal.

[Jeff Monson]

i use a piece of 12" x 12" granite for sharping, use psa type paper to adhere to the granite. it is flatter than .001". my granite counter is not, when you put a quality straight edge you can easily see light and measure anywhere from .001" to .003" over three feet. you can get a reference granite plate if your that worried about it. i guess your not using stones of some sort to sharpen with.

I do the exact same thing.

[Michael Horan]

The sink cutout I got was not flat when I put a straight edge to it. Like David said, you could see daylight under the straight edge. I ended up using glass shelves. Some were flat, others were not. My suggestion would be take a straight edge to your cut outs and see how flat they are. You might luck out. The cuts out are still useful even when not dead flat. I used mine to weigh down a Black & Decker Workmate so it would not move when I used it as an outfeed table. They are waterproof and easy to clean if you have some messy job. In addition to Enco as Ted mentioned, Woodcraft now sells a 6" X 18" Granite Surface Plate. If I was going to buy one, I would get that one since it is less to lug around.

[Kent A Bathurst]

Me got 2 pcs 1/2" x 5" x 24" glass. Me happy.

[Bob Falk]

I had been thinking of a dedicated sharpening station with a granite top and drawers to hold all the associated stuff (My Tormek, accessories,waterstones, etc.)...I figured I could just get a piece of scrap granite, but after reading this thread it sounds like a piece of thick glass would be a better choice.

[Jim Matthews]

I have a similar counter top cutoff - I can't get even a 10 thousandths feeler gauge under the straight edge.
That's better than the advertised accuracy of the straightedge I own.

These countertops are a smokin' bargain - like radial tires and lightbulbs, they punch above their weight class.