A Workshop Luxury- Build

[William Fretwell]

Decided to spoil myself and free my snack table of those lumps of stone. Managed to find an attractive granite off cut the right colour. Price was right until I was asked if I would like the edges finished, which I answered with a casual “yes”. Seems that doubled the price.
Well need some legs; lots of poplar lying around so after rough cutting and a good workout have some legs and stretchers.
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My plan was simple; top stretchers support the granite, bottom stretchers finish the structure.

After struggling with the 100lbs of granite I rested the top on the legs:

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Granite is supposed to be somewhat flat, so for fun I thought I would find out. Taking my good level out of it’s case I looked for light under the level. Sure enough there was light. My Lee Valley feeler gauges detected 10 thousands of an inch gap in the middle of the long dimension and oddly 12 thousands under the short dimension.

Well it was either not flat or drooping under it’s own weight, or both. Lugged it onto the bench and repeated the exercise, both droops were 2 thou less. As I wanted a flat table this meant regular stretchers would not stop the droop. They would sag over time and restore the droop. This meant I was going to have to use the Kruksfeld/Matagomi joint!

Before you rush to google, I made that up! Instead a 5th leg! Strong end grain to prop up a sagging middle.
Challenges:
Getting 5 legs sitting flush on the concrete floor.
Making the middle leg ‘adjustable’.
Pulling the edges down to the other 4 legs to achieve ‘flat’. Flat being a curve I could not detect.
My planned drawer now has a leg in the way.

Well another small workout and a fifth leg appears:
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Let the fun begin:
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To be continued......

[Greg Parrish]

Nice! Lie Nielsen sells one and they give accuracy specs. May be of interest for comparison. https://www.lie-nielsen.com/products/maine-gomni-holdingranite-sharpening-station?path=workbenches&node=4113

[Andrew Hughes]

You might want to check Craigslist for something more robust.
In my area granite surface plates are plentiful. I’ve even seen a few Craiglists post that were free if you can haul them away.
Anyways I picked up a 24x36x4 inches thick for 180 bucks. It’s very handy to have nice flat area that’s pretty indestructible.
Granite counter tops are not very flat.

[William Fretwell]

Yes Greg, I had looked at Lie Nielsen, their 2” top is flatter at the moment; also very heavy! On a flat surface mine is about 0.003” in 6”; but that is because of the ‘dip’ in the middle. Local flatness in 6” may well be similar if I can get rid of some or all of the ‘dip’. The fact that it droops 2 thou just under it’s own weight suggests I can get rid of at least 4 thou with persuasion. If that is the case then it will match Lie Nielsen.
Andrew we don’t have bargains like yours around here but that is a monster to handle! For the number of times I tape abrasive paper to the top to flatten the bottom of something I wanted to keep the cost down.
What I do like is the black as a sharpening background, with the right lighting it should make the bevels stand out.

[Kris Cook]

I have to ask the obvious question: why not build an apron with a center cross member and use four legs?

[William Fretwell]

Kris, I think the weight of the granite would sag the cross member in time. To flatten the top I may have to use anchors on the edges and use the middle leg as a fulcrum. The top stretchers will be used to anchor the edges. The only guarantee against sagging is end grain to the floor.

[Steven Mikes]

I have to ask the dumb question: Why do you need that tight tolerance of flatness in the first place, especially over the entire surface area of a table?

[William Fretwell]

Not a dumb question Steve, I’ve asked myself the same question! The only reason would be for trueing the bottom of longer planes. When doing the figure of 8 across the whole surface the ends would receive more pressure and curl up slightly, this effectively shortens the plane. For regular sharpening I’m sure it would make no difference at all.
The other reason is just for my sanity, knowing it is flat!

[Brian Holcombe]

Granite plates are often found inexpensively. That LN table looks awful thin to me. Granite surface plates are thick so that they have the structure needed to retain their flatness spec.

[William Fretwell]

Most around here are very small, larger ones are expensive. It seems 2” is a very common thickness for the small ones. Mine is 9/8”, as I’m not a machinist I hope to achieve enough accuracy to flatten the odd plane. I would like a sharpening jig that runs on the marble so I can use the whole length of the sharpening stone.

[Brian Holcombe]

It’s not flatness for flatness sake, basically you can’t lap something consistently unless your doing so on a surface that is truly flat. Lapping a plane on something with a curve to it is going to produce a curved surface.

[William Fretwell]

Very true Brian. An 8 thou dip in a 24” granite slab is disappointing. I wonder if anchoring the edges to the leg stretchers with the 5th leg as a pivot will work to straighten it or just want to lift the legs off the ground. As a place for sharpening stones it works well with a black background. The only flat guarantee is a thick plate ground flat. When flattening is a very occasional thing the expense of such a plate is prohibitive. I have doubts that I can get most of the dip out and must devise a test.

[Brian Holcombe]

I dont think you'll be able to get any of the dip out of it, it will just stand on that center leg.

I use a surface plate routinely in my shop, I have one small one basically for the odd chore then I have a nicer one for inspection. Most woodworkers aren't doing any inspection work, but I think they'd find a lot of use in the former. Sometimes have a perfectly flat surface is just exactly what is necessary when you need to double check something.

Worth hunting craigslist and facebook until you find something good.

[Tom Bender]

If you go ahead with your current piece of granite you might get it to flatten enough by pulling the corners down and supporting the center. But with your 5 legged design you are expecting your floor to be flat enough or you will have to shim.

Kris is on the right track with the x in the center but a cross would be as good and easier to make. Make it robust and it should not sag. But that misses another point. You may get better results if you plan to support the middle in several adjustable spots. You could make the adjustments with threads or with wedges. My preference would be wedges since they can be placed anywhere on the cross or around the perimeter apron.

You can delete the lower stretchers since the upper structure will be plenty for a sharpening bench. Now there is room for a drawer as well.

[Mark Hennebury]

You need three points arranged in a triangle to define a flat plane. Large granite surface plates rest on three points.
To make use of four or five legs complicates things... a lot.

[William Fretwell]

Mark, you need three points to level something; such as an accurate balance or my commercial laser level. All the commercial granite plates are flat by design but not necessarily level! They all have a metal frame with four legs, level is not a requirement. I do agree the fifth leg is a royal pain and agree with Brian it will just pull the other legs off the floor. I considered bolting it to a concrete plate with a spacer in the middle to provide leverage as an attempt to flatten it.

I may have solved my problem however. It may get sold to a local pharmacy as a balance table for their new compounding room. The mass of the granite counteracts room vibrations for accurate weighing. The fifth leg is gone and the drawer back! Money raised should cover a Kijiji listed commercial granite plate!

[Mark Hennebury]

You need three Points to support a Flat surface without distorting it. The three points of the triangle are placed to evenly distribute the weight. The base may have four legs. But the tops is supported on three points on the base. Four legs placed at the corners will not properly support the load, and would need to be individually adjusted to carry the same weight, and still won't properly support the weight.

[David Carroll]

You need three Points to support a Flat surface without distorting it. The three points of the triangle are placed to evenly distribute the weight. The base may have four legs. But the tops is supported on three points on the base. Four legs placed at the corners will not properly support the load, and would need to be individually adjusted to carry the same weight, and still won't properly support the weight.

We have a huge granite surface plate here in our machine shop. I think it's 2-feet x 3-feet x 4-inches thick and weighs a lot. It was purchased on a welded stand that I needed to cut down shorter so it wasn't taller than our benches. Just as you say when I took the stone off of the base (no easy task) it was supported by a triad of metal pads welded to the top of the stand. Very Cool.

DC

[William Fretwell]

Most interesting! It does make sense for such a weight. Have to calculate where the three supports would go.....
Even a small triangle would not solve my dip problem!

[Will Blick]

I too have a desire for a large FLAT surface.
for flattening long plane bottoms, wouldn't a long piece of float glass be more ideal? such as 14" x 36" ? not so heavy, maybe 1" thick I would guess.
Easier to store, so won't take up so much floor space.
Who makes this glass? Looked around for it once, but no luck... any ideas?

[William Fretwell]

Will, float glass will only be fairly flat but the sheet will bend also. I doubt very much it would be truly flat even on what you consider a flat surface (which won’t really be flat). The machined casting on one side of my table saw is probably the flattest surface in my shop but not even close to machine shop granite flat.

[William Fretwell]

Progress report:
Scribed the stretchers rotating them end over end so same side does not flip.
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Then used a large tenon saw to cut down. The right side cuts gave me more trouble than the left.
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Had to finish the cut with a bow saw:
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Clean up with a large chisel and/or Lee Valley large shoulder plane. Then the shoulder was tuned with the shoulder plane.
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Next step the mortices.
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Rotate! It will not!