I'm looking at getting some sort of surface table for doing measurements and layout in my home hobby shop (so cost is an object and high precision is not).
I have a piece of scrap countertop granite (black) left over from a kitchen remodel, about 18x24 inches by 0.75 inch thick. How would this measure up to commercially available tables?
And how would one recommend mounting this thing? At least, I've got to think about attaching handles to the sides to make picking it up easier. But what about a base with some feet to keep it from rocking on uneven surfaces? Any examples out there to follow?
On Thu, 27 Nov 2008 11:31:01 -0800, the infamous "Paul Hovnanian P.E." scrawled the following:
Probably not too badly, given your requirements. Stone (fake or otherwise) is ground pretty darned flat. If it's good enough for plane iron sharpening the ScarySharp(tm) way, it's flat enough. ;)
I'd use a rubber-tipped adjustable bolt bedding on an angle iron table with adjustable rubber feet. Support it every 6 or 8 inches and it should remain pretty flat for you. Drill through the angle, tap, and bed it. Piece of cake.
Alternatively, Griz has nice cheap items.
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(Jayzuss, WTF happened to their shipping fees?!?) They show their stands there, too.
9x12" is under $30, delivered. The same size from Lee Valley is $51.
-- Our greatest glory is not in never falling, but in getting up every time we do. -- Confucius
You'd need something against which to measure it -- a precision straightedge, another big surface plate, or whatever. But those slabs can be surprisingly flat if they were ground on a table grinder. I have a large,
3/4"-thick piece of what was known as "Italian marble" back in the '60s. It was actually some kind of hard puddingstone. I measured it on a CMM when I had a better class of clients , and it was flat to just over 0.001" over
2-1/2 feet. That's my basic layout surface plate.
For smaller sizes, you can do very well with a thick piece of plate glass -- the real thing, not float glass. Plate glass is ground and you'll be amazed how flat it can be. You might get a cutoff from a commercial glazier.
I don't have any examples, but if you have uneven surfaces, think about three feet. My small Mitutoyo toolmaker's surface plate has four rubber feet, and they squish a little to accomodate my workbench top.
The 18x24x4 granite surface plates from China are pretty nice and quite inexpensive if you can avoid shipping. I picked one up at a Wholesale Tool branch when I was in the area.
I remember a loooooonnnnngggg time ago, a shop hint in Live Steam(???) magazine suggested a thick piece of glass would suit as a "surface plate" for most shop uses. The way it was put was that the glass was flat, but not flaaaaaaaatt Worked a treat for me for many years, back in the day before "less than a dollar a pound" surface tables became the norm.
I got a piece of float glass somewhere/somehow, about 1/2" thick and
24 X 18 or so. I made a 1X3 wood frame the ID the size of the OD of the glass plus 1/4" all-round and with two of the sides slanted slightly, and I tacked a "bottom" on it made out of a scrap of luan.. The frame was then 1/2 filled with damp plaster-of-paris, and then topped up with goopy wet plaster-of-paris, and the glass set on it while still very wet. The glass sort of "floats" on the goop, and when it is al set up it was good. The slant sides keep the plaster of pairs from wanting to fall out when the thing is moved later on.
Any of the counter-top stone I've seen has been fairly flat too. Not flaaaaaatttt, but pretty darn good.
Take care.
Brian Laws>I'm looking at getting some sort of surface table for doing measurements
if you can find yourself at a show like Westec where ENCO and that ilk show stuff, you can order from the catalog with free shipping and a 10% discount - that's how I got a 2 X3 ft surface plate delivered for $50.
On Sun, 30 Nov 2008 02:59:52 -0500, the infamous Wes scrawled the following:
It's likely a loss leader, Wes. They take a loss on the one product in hopes that you'll come in (or go online) and buy extra items (some of which are highly overpriced) at the same time you're buying that one item. I heard that at any one time, 1/3 of the items in the grocery store are loss leaders, 1/3 are normally priced, and 1/3 are exhorbitantly overpriced. They swap these around all the time so you don't catch on. ;) In the end, they get their margins.
-- In all affairs it's a healthy thing now and then to hang a question mark on the things you have long taken for granted. -- Bertrand Russell
I expect they make money on the item if you pay the shipping.. The free shipping is no doubt an oversight, since they have the truck symbol on the catalog page for surface plates. But the smaller sizes ship UPS.
Paul, I have an ENCO surface plate, a small one. I mounted a DTI (.0005"/ div) on a mag base, with about a 5" reach. And I cannot report any significant measurement when moving around the ENCO surface. However, on a 12"x12" marble square, it's all over the map. +-.005" to be optimistic, ignoring the holes. On a sink cutout, it's better, +-.002", again there are some significant holes in the surface..
I've tried various polished marble and granite floor tiles, and found them all similarly crude, despite their mirror-like looks. There is no reason to expect them to be precisely flat. A worked surface is at best a poorer copy of the precision of the tooling used to generate that surface, and these stone pieces are certainly not made on precision tools.
On Sun, 30 Nov 2008 18:52:01 -0800 (PST), the infamous Mechanical Magic scrawled the following:
Marble is a supersoft stone. I'm surprised it's sold for anything but wall surfaces, where it won't see any damage. The granite Paul said he had is likely a whole lot smoother.
-- The only difference between a rut and a grave...is in their dimensions. -- Ellen Glasglow
I just ordered the 12"x18" surface plate from Enco (free shipping) and I saw for $10 more I could get the Grade A instead of Grade B. What's the difference?
The Grade A also has two ledges. What are these used for?
Higher precision surface. If you're going to be using it for truly precision measurements, you'll want that -- and a matching set of gauge blocks, and a high precision indicator of some sort.
1) For lifting it to move it around,
2) For clamping measurement fixtures to, since these are stone not cast iron, so the magnetic bases won't do you any good.
As for what the benefits of a stone vs cast iron surface plate are, if you ding a cast iron one, you raise a circular ridge around the point of the ding, thus lifting whatever is resting on it. If you ding a stone one, you simply chip out a tiny amount of stone, and the surrounding area is still the original height.
If you're just going to be using it for layout work, go for the grade B -- that should be good enough. If serious metrology, go for grade A or AA or ...
Oh yes -- you can also use them for spotting when scraping a surface to flat. Probably the class-B will do for your first rounds, and then when you get to needing more accuracy (e.g. for making your own surface plate) you'll need a more accurate one, and if you had gotten the class-A at the beginning, it would be worn enough by now so it would no longer qualify anyway. :-) If you are serious about accuracy, you can get services to come certify (and improve) your surface plate, and certify your gauge block sets.
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