granite dresser tops for a surface plate or for lapping?

[strantor]

I found a great deal on some granite top furniture; $60 for dressers with smooth granite tops. Went and had a look. The granite is in superb condition but the wood part is mildewed. I don't care about the wood. I would cut it up for fire wood. But I'm wondering if these granite plates made for furniture are made flat enough and straight enough to be an acceptable surface plate. They are only 1/2" thick but at this price i could afford 4, stacked together gives me a plate 2" thick, 36"x48" for $240. That's less than half the price of a b-grade, bottom of the barrel shars 36x48 surface plate. But would i be making a $240 mistake and then spending an additional $500+ on a REAL surface plate?

If the answer is "yes, it should work fine", then could i get away with less than 4 plates? How many would it take to get something that won't flex or sag?

 

[Ebel440]

I started to measure a 12" granite floor tile and I stopped when I got around .015 out of flat I'm sure it was much worse but I didn't keep going. It looked flat though. So unless you can inspect it somewhere you will never know how flat it is. I wouldn't spend my money on it plus with that thin material you have the problem of mounting it so it won't sag or change with the surface under it.

 

[18w]

Save your money. Ask yourself what tolerances do I want to work to and how big of a surface plate do I need. A 3'x4' surface plate would be on my wish list if I had the room but a 18"x24" has served my needs. A lapping surface and a inspection surface are two different animals. If you are lapping something like the sole of a wood plane for example, get yourself a thick piece of glass. If you have the luxury of space often times you can find a good deal on the larger plates on craiglist or auctions as most hobbyists don't have the room or want to deal with the weight.


Regards
Darrell

 

[Uglydog]

Properly supported it would make a great bench and work space.
You aren't going to rebuild engines on her, but much of the work we do it'd be great.
Easy clean up. More durable than wood, and less expensive than steel.

Daryl
MN

I found a great deal on some granite top furniture; $60 for dressers with smooth granite tops. Went and had a look. The granite is in superb condition but the wood part is mildewed. I don't care about the wood. I would cut it up for fire wood. But I'm wondering if these granite plates made for furniture are made flat enough and straight enough to be an acceptable surface plate. They are only 1/2" thick but at this price i could afford 4, stacked together gives me a plate 2" thick, 36"x48" for $240. That's less than half the price of a b-grade, bottom of the barrel shars 36x48 surface plate. But would i be making a $240 mistake and then spending an additional $500+ on a REAL surface plate?

If the answer is "yes, it should work fine", then could i get away with less than 4 plates? How many would it take to get something that won't flex or sag?

 

[T Bredehoft]

Before you continue with the dresser tops, verify that they are granite, not marble, the usual stone for these. Granite's base mineral is quartz, as hard as glass, or harder, Marble's base mineral is calcite, softer than the dentine in teeth, another calcite mineral.

 

[f350ca]

I wouldn't expect the top of a dresser to be particularly flat, but on stacking them. 4 layers of 1/2 inch thick sheets is 4 times stiffer than one layer as expected but a 2 inch thick sheet is 64 times stiffer. For bending the moment of inertia increases with the cube of the thickness.

Greg

 

[Alan Douglas]

Even if the top is flat, the underside might not be. If the centers don't touch, there's no extra rigidity from having more than one piece. Or they might rock on each other.

 

[kd4gij]

I use a 2'x2'x1" granite counter top. it is the higher grade not home depot. It is as flat as I can check. For hobby work it is fine. If you can find some does high end homes and officees you can get drops cheap. Mine was free.

 

[yendor]

Check with a local Granite supplier of Kitchen Counters.

The cutouts from sinks can usually be had either very cheap or sometimes for free.

While they are clearly NOT surface plate grade material if you have nothing at the present they are great temporary solution until you can afford something better.

 

[Oversight13]

I found a great deal on some granite top furniture; $60 for dressers with smooth granite tops. Went and had a look. The granite is in superb condition but the wood part is mildewed. I don't care about the wood. I would cut it up for fire wood. But I'm wondering if these granite plates made for furniture are made flat enough and straight enough to be an acceptable surface plate. They are only 1/2" thick but at this price i could afford 4, stacked together gives me a plate 2" thick, 36"x48" for $240. That's less than half the price of a b-grade, bottom of the barrel shars 36x48 surface plate. But would i be making a $240 mistake and then spending an additional $500+ on a REAL surface plate?

If the answer is "yes, it should work fine", then could i get away with less than 4 plates? How many would it take to get something that won't flex or sag?

The answer is that granite made for furniture/kitchens isn't nearly flat enough for even toolroom work. If you're strapped for cash, but are willing to drive, check out CraigsList for surface plates. Try to get a mid-grade (A, inspection) plate and a decent stand, preferably something with a calibration sticker on it, even if the cal is 20 years old. Your work will never be better than your base inspection plate. I managed to buy a 48"x72" inspection-grade plate for $450, with a stand, from a flea market, of all places. The unit weighed 4500 pounds, but it cost me more to move it than I paid for the rock. If you're close to major cities, it helps a lot. (I'm not close.)