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Has anyone used granite for an assembly table top?

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Forum topic by nkawtg posted 06-20-2016 04:11 PM 993 views 0 times favorited 9 replies Add to Favorites Watch
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nkawtg

204 posts in 718 days


06-20-2016 04:11 PM

I was considering making a torsion box top for an assembly table, when I got to thinking that a granite top would be pretty dead flat.

I would like your thoughts on the subject.

Thanks…


9 replies so far

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splintergroup

829 posts in 689 days


#1 posted 06-20-2016 04:19 PM

Not quite the size you are (probably) considering, but I regularly use a 24” granite surface plate for assembling boxes. The flat surface has the nice features of being both glue proof and flat with exceptional stiffness (helps with clamping).

I’d say go for it, especially if you have access to a proper sized piece of scrap and/or $$$.

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TheFridge

5765 posts in 952 days


#2 posted 06-20-2016 04:31 PM

It would be a great but expensive table

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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Loren

8313 posts in 3114 days


#3 posted 06-20-2016 04:38 PM

It will be nice for sure. Waxed MDF is just about as
glue-resistant though and you’ll need to make a really flat,
strong table to keep the granite stable as it will crack
under its own weight if not supported.

You could do a granite inset for a lapping plate as
a compromise.

View clin's profile

clin

514 posts in 463 days


#4 posted 06-20-2016 05:22 PM

Granite is used as counter tops all the time, and placed on commonly built base cabinets. So I would think any well built workbench base would be more than strong enough.

I also don’t know how truly flat granite tops are. I don’t know that they aren’t flat, but I wouldn’t assume it is flatter than a well built torsion box.

I’m actually just getting ready to skin a torsion box today. Typical 1/2” MDF using half-lap webs (full length webs cut half way through where they overlap). It’s coming out very well.

But, I did get an idea that I think has a lot of merit and would be much, much quicker to build. The idea is to laminate the 1/2” MDF skins to 2” thick construction foam board. I’d use a slow setting epoxy for this. However, I do not know how truly flat the foam is. I can cut webs within just a few thousands variation at most.

I’ve done much thinner construction for model airplane wings using foam core and composites like fiberglass skins. It really is surprising how stiff this is.

The only thing not obvious to me is a good way to cut the edges square after assembly. It would be too thick to cut with a typical circular saw, and awkward to handle on a table saw. Though with two people, and some infeed and outfeed support, I think a table saw could be used. Of course you could attempt to glue it up with everything cut to final size and aligned, but I find that seldom works out well.

Then of course add edging, well secured to the top and bottom skins. I think it might work very well.

-- Clin

View WillliamMSP's profile

WillliamMSP

757 posts in 1071 days


#5 posted 06-20-2016 05:35 PM

Someone in my neighborhood posted a free 4’ long countertop slab, so I picked it up. Still haven’t gotten it built in to a table, but hoping to in the next month or so. I have used it for sharpening/flattening, though, and it’s nice for that.

-- Practice makes less sucky. (Bill, Minneapolis, MN)

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JeffP

573 posts in 858 days


#6 posted 06-20-2016 11:12 PM

My joinery is not yet perfect. “sometimes”, my projects need some not so gentle persuasion to go together. I usually just tell myself that the glue has swelled up the mating parts. ;)

I’m not so sure I would be comfortable “persuading” my joints together on a granite counter top. I would be too afraid it would crack/break.

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.

View splatman's profile

splatman

563 posts in 865 days


#7 posted 06-20-2016 11:56 PM

Granite is not always the flattest thing. Some granite sheets cut for countertop usage sometimes has a slight bow, maybe as much as ΒΌ” over 10 feet. When laid on a support structure, it may flatten out some under its own weight (stone does have some elasticity. How much varies between types). Granite typically comes in 5’x10’ or 6’x10’ sheets, usually 3 cm thick. Most types are also available in 2cm thickness.

A better choice is quartz, made of ground-up quartz crystals glued together with resins. Comes in unusual colors and patterns and is much stronger than natural stone. Probably cheaper, too, though I never priced any. Look for sales or deals.

If you plan to build a stone-top table, build the base out of steel. Steel has the advantage of not reacting to humidity changes, neither will it “creep”. Now you’ll have a table that will be flat and will stay flat.

Whether you chose granite or quartz, the edges will be anything but straight. Unless you have the tools, you’ll need to have a countertop fabricator cut the edges straight. Speaking of fabricators, call around and find out if any have a partial sheet that they will be willing to sell cheap, especially if you do not need a table anywhere near 5’x10’. Smaller remnants can be epoxyed together to build a table top, and likely much cheaper on a per-area basis, too, so that’s another option to consider. Even find out if any C-top shops have any scrap granite/quartz that they will give away (think range cutouts and offcuts). Be aware that stone, both natural and man-made, is seldom the same thickness from sheet to sheet, so if gluing together offcuts, make sure their surfaces line up.

A stiffer table top can be built up by laminating together 2 or more layers of stone (another handy use for free offcuts/cutouts). Of course, you will end up with a table that is extremely heavy.

Bonus: You’ll have a pretty table to show off during your next wood shop party.

View Aj2's profile

Aj2

692 posts in 1264 days


#8 posted 06-21-2016 12:00 AM

Search your local Craig’s list for a granite surface plate.I have decent size one I got for cheap it does weigh about 400 pounds.But it’s indestructible.

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nkawtg

204 posts in 718 days


#9 posted 06-21-2016 09:06 PM

Thanks for all the great input.

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