DIY surface plate stand - please suggest how to make it rigid

Hi everyone,

I'm building a cart for my 24x36 surface plate. I took a standard "work smart" metal cart, that's rated for 1200 lbs of load, trimmed it down to lower the height, replaced wheels with heavier duty ones and added the rubber feet. The idea is to have wheels and feet at the same time. When the feet are up, I can move the cart around, but if I need extra stability - I can lower the feet. That should also allow for precision leveling.

It may not be obvious, how the feet work. They are Sunnex adjustable mounts. Rotating the bolt, I can adjust foot height within 1/2". In "default" state, feet are all the way up and there is a gap of 1" between the feet and floor. If I want to lower them down, I should insert spacers between bottom of the cart and the feet. Height of the spacer is a little bit less than 1", so it squeezes in there freely. When spacers are in place, I can start jacking up the cart by rotating the bolts. After a while, the wheels will lift up and the cart will stay explicitly on feet. Dismounting is the same sequence, but in reverse. It may sound complicated, but in reality it's just a couple of minutes to switch between wheels and feet.

Now the question: I suddenly realized, that top of the cart is to flimsily for holding the surface plate. Event though it's rated for 1200 lbs, it will sag by significant amount if I just press in the middle of the top with my finger. My surface plate came with 3 shims at the bottom from the factory. If I just put the plate on the cart as is, those shims will "sink" into the top of the cart because it will deflect. This will cause the plate to be supported mostly on edges rather than 3 points, where it's supposed to be supported. Not to mention complete lack of stability - the plate will go out of level under any load placed on top of it. How do I reinforce the top so it doesn't sag? I thought about putting 2 rectangular steel beams underneath the top, but it's not clear, how to properly attach them to the rest of the cart.

Thanks!

Here is the sag under 100 lbs of pressure

Frigzy said:

Hi everyone,

I'm building a cart for my 24x36 surface plate. I took a standard "work smart" metal cart, that's rated for 1200 lbs of load, trimmed it down to lower the height, replaced wheels with heavier duty ones and added the rubber feet. The idea is to have wheels and feet at the same time. When the feet are up, I can move the cart around, but if I need extra stability - I can lower the feet. That should also allow for precision leveling.

It may not be obvious, how the feet work. They are Sunnex adjustable mounts. Rotating the bolt, I can adjust foot height within 1/2". In "default" state, feet are all the way up and there is a gap of 1" between the feet and floor. If I want to lower them down, I should insert spacers between bottom of the cart and the feet. Height of the spacer is a little bit less than 1", so it squeezes in there freely. When spacers are in place, I can start jacking up the cart by rotating the bolts. After a while, the wheels will lift up and the cart will stay explicitly on feet. Dismounting is the same sequence, but in reverse. It may sound complicated, but in reality it's just a couple of minutes to switch between wheels and feet.

Now the question: I suddenly realized, that top of the cart is to flimsily for holding the surface plate. Event though it's rated for 1200 lbs, it will sag by significant amount if I just press in the middle of the top with my finger. My surface plate came with 3 shims at the bottom from the factory. If I just put the plate on the cart as is, those shims will "sink" into the top of the cart because it will deflect. This will cause the plate to be supported mostly on edges rather than 3 points, where it's supposed to be supported. Not to mention complete lack of stability - the plate will go out of level under any load placed on top of it. How do I reinforce the top so it doesn't sag? I thought about putting 2 rectangular steel beams underneath the top, but it's not clear, how to properly attach them to the rest of the cart.

Thanks!

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Hate to be the bearer of bad news, but you are heading down an expensive hole and need not keep on in that direction.

The key isn't thick metal sections. It is DEEP metal sections. Stiffness, y'see, increases exponentially with depth.

That cart should find some other use whilst you find a shop with a press brake.

The entire "factory OEM" wheeled table under my heavy Herman Grade A 30" X 48" is executed in... wait for it .. SHEET METAL!

The trick is a simple one.

The long axis side rails, the short-axis cross rails at each extreme end, and the TWO cross rails in-between, one under the two-disks, the other under the single-disc for 3-point plate support.... are simple "U" shapes formed from steel sheet, slightly rounded corners at the bends.

However.. that "U" shape is 8", each leg!

Basically square 8" tubing with one side missing.

Four vertical legs, the same again, AND they are set-in from the ends to midway between the end crossrails and the plate-support cross-rails, then also angle-gusseted back up to the end cross rails.

What are they are up to here? Simple. TALL sections and SHORT spans OF them.

Cross rails again, just above floor-level, short axis, one end carrying a "step-on" adjustable over-center jack right in the middle.

All four corners, leg bottoms fitted with welded-in plate, cast-Iron caster wheels, Bronze sleeve, greased, on hardened steel shaft.

Two of those Iron casters ALSO serve as the 2 of the three points, No rubber = no need of jack pads.

All that is needed to go from "use-me" to "move-me" or back is to set or release the step-jack at the third point.

Any heavy steel? About four inches of it.

An inch of "Ell" at each corner so the plate dasn't slide off, should someone tilt the Earth more than usual. They don't touch anything but air in normal use.

All this is executed in ignorant 10 or 11 gage sheet steel, all intersections welded rather nicely.

The steel for it is dirt-cheap. The bending work is straightforward. The welding can get tedious, expensive, or both.

I have a certain confidence that Herman got it right. He did INVENT the granite surface plate, after all.

Mind, certain Egyptians as built the temple of the Sphinx might have scoffed as they figured it was an idea so old already the origins of it were forgotten, even then.

But there you have it. Careless humans get to eating, drinking, shagging, sleeping, or such, they are forever misplacing all manner of s**t, knowledge first and foremost.

I welded a 2"× 3/16" wall, square tubing frame around/to a sheet metal cabinet for my 24" x 36" AA Starrett master surface plate. The stationary frame sits on 4 adjustable feet, the plate on 3. Seems to be sturdy enough and the tubing wasn't too expensive.

I would also add gusset plates to each corner.

Larry Dickman said:

I would also add gusset plates to each corner.

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The very sturdy cart, welded to the frame around it's top and bottom perimeter, is doing gusset duty

I put my 24 x 36 surface plate on top of a Lista cabinet that holds all of my measuring equipment. I move it with a forklift. Quick and simple.

I made a stand for a 4' x 6' granite plate.

Simply applied 6" x 1/4" wall thickness box tubing.

No mitering, no fancy joints, simply butted together.

Material is cheap, labor is not.

Obviously, you want to save what you have and make it work. If I were doing that, I would find a couple of 24" pieces of 1x2" steel tube with at least 1/8" wall (3/16 or 1/4 even better) and place them across the 24" dimension of the cart so that your plate "shims", which I assume are mounted at the support points used for lapping the plate, are sitting on the 2" face of the tube. They will act as load spreaders and help transfer the weight to the edges of the tray to some extent. I would probably add some diagonal bracing, or some flat panels across the open spaces, to help resist racking during movement. You can easily level using the feet anytime.

Nice cart, but the threaded feet should be on the top, not the bottom. Those feet support the bottom of the surface plate at the points defined for such support.

The feet should be pivoted (aka swiveled) such that tehy conform to the plate bottom surface when adjusted. That way the support point remains constant.

Suitable feet are on McMaster-Carr, here:
McMaster-Carr

- Leigh

morestainless said:

I welded a 2"× 3/16" wall, square tubing frame around/to a sheet metal cabinet for my 24" x 36" AA Starrett master surface plate. The stationary frame sits on 4 adjustable feet, the plate on 3. Seems to be sturdy enough and the tubing wasn't too expensive.

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Thank for sharing the design. The support base seems to be much narrower, than the plate. Is there any tendency for tipping over? Anyway, I absolutely need the cart to be on wheels, so I can slide it under the work bench when not in use.

digger doug said:

I made a stand for a 4' x 6' granite plate.

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Nice. Did you weld everything together or just used a bunch of bolts and nuts? I'm a terrible welder, it will break apart on me if I weld the frame. That's why I tried to use off-the-shelf components/fasteners as much as possible.

specfab said:

Obviously, you want to save what you have and make it work. If I were doing that, I would find a couple of 24" pieces of 1x2" steel tube with at least 1/8" wall (3/16 or 1/4 even better) and place them across the 24" dimension of the cart so that your plate "shims", which I assume are mounted at the support points used for lapping the plate, are sitting on the 2" face of the tube. They will act as load spreaders and help transfer the weight to the edges of the tray to some extent. I would probably add some diagonal bracing, or some flat panels across the open spaces, to help resist racking during movement. You can easily level using the feet anytime.

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Yes - I want to save, but not money. I'm short of space in my garage - I want to save that. That's why I need this very special design with wheels and feet at the same time - I can roll the cart under the table when it's not in use.

Thanks for the idea about steel tubes - that's what I'm thinking about. I've recently seen those electrical cable support C-channels at Home Depot. They look very sturdy and cheap as dirt. They're 1-5/8" x 1-5/8" and walls are pretty thick. What if I use bunch of those to reinforce the cart? I can connect all the beams together using their standard 1/2" fasteners. I attached a picture of what I'm talking about bellow.

The real Leigh said:

Nice cart, but the threaded feet should be on the top, not the bottom. Those feet support the bottom of the surface plate at the points defined for such support.

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That was my initial plan, but then I realized, that I really want the feet to be at the bottom, so the cart stays on feet and not on the wheels. I still can level the plate, adjusting the feet. What is the advantage of having the feet at the top versus at the bottom?

thermite said:

Careless humans get to eating, drinking, shagging, sleeping, or such, they are forever misplacing all manner of s**t, knowledge first and foremost.

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I really like the way you're writing. Please let me know if you ever write a book - I will definitely read it

It's not a question of "top vs bottom".

The plate is only flat when supported at the three points defined in the spec and used at the factory. If the plate is supported in any other way, the surface may not be flat.

- Leigh

Frigzy said:

That was my initial plan, but then I realized, that I really want the feet to be at the bottom, so the cart stays on feet and not on the wheels. I still can level the plate, adjusting the feet. What is the advantage of having the feet at the top versus at the bottom?

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Now I get it - sorry for the confusion. The plate will be supported at the 3 points - it sits on 3 plywood shims that were glued to the plate at the factory.

OK. That solves part of the problem, but not all. If the support structure is off-level, that changes the contact point for the support. By using swivel mounts under the plate itself, the support point remains the same.

- Leigh

Frigzy said:

Now I get it - sorry for the confusion. The plate will be supported at the 3 points - it sits on 3 plywood shims that were glued to the plate at the factory.

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Frigzy said:

Now I get it - sorry for the confusion. The plate will be supported at the 3 points - it sits on 3 plywood shims that were glued to the plate at the factory.

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Plywood? Or something that LOOKS like plywood?

Herman used disks that resemble partial-height hockey-pucks. Some sort of rubber or plastic - maybe even Old Skewl gutta-percha - but wotever it is - it won't absorb moisture, rot, get eaten by critters, collapse over time, etc.

If I had none, I might actually use real hockey-pucks.

Bought a box of a dozen "practice" ones used cheap enough. No logos or printing on a "practice" puck, so they can be right handy around the shop.

thermite said:

If I had none, I might actually use real hockey-pucks.

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That is a brilliant idea - thanks!

The plate is "ACE". The shims look very plywood to me, but it may also be MDF.

Frigzy said:

That is a brilliant idea - thanks!

The plate is "ACE". The shims look very plywood to me, but it may also be MDF.

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MDF is highly probable, and not the worst of all choices "terrible" as it is pretty stable in at least compression. Still - it is made from wood FIBER be it waste - or intentionally chosen as source wood not of much value intact.

A full-height hockey puck might have TOO much resilience for my 1100-1200 lb plate and slowly collapse. Maybe.

There are still only three points, no matter how large or heavy the plate. There should ALSO be an outer set of support pads near the rim, that never touch at all..

EXCEPT if/as/when some really heavy mass is placed off center and wants to tip the plate.

In that case, far better total tilt be limited right away, Bessel or Airy points second in importance to basic shop safety and not rolling heavy stuff off the plate at a rapid rate of knots.

thermite said:

EXCEPT if/as/when some really heavy mass is placed off center and wants to tip the plate.

In that case, far better total tilt be limited right away, Bessel or Airy points second in importance to basic shop safety and not rolling heavy stuff off the plate at a rapid rate of knots.

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The safety supports can be mounted on the supporting structue rather than on the surface plate itself. As long as there are lateral stops to prevent the plate from sliding off, either method works.

- Leigh

The real Leigh said:

The safety supports can be mounted on the supporting structue rather than on the surface plate itself. As long as there are lateral stops to prevent the plate from sliding off, either method works.

- Leigh

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Apologies, Leigh.

I should have made that clear. They SHOULD extend upward off the support, actually.

Much easier to get sight of whether there is still a gap - or NOT - atop each of them when so mounted and NO NEED to attach them to the plate in any way.

Similar concern may apply to any 3-point base - down at floor level - BTW.

Yes, 3-points define a stable plane. That can still be a long stretch from one that cannot be tipped-over. See children's high-wheel tricycles.

Make sure there are excursion limiters. Those need not touch the deck "in ordinary use", either but should be set damned close to it if they are to do any real good.

Long before an SP reaches point of no return tipping point itself, it can increase the speed of roll of finely finished goods or metrology gear towards a hard landing.

Leveled surfaces have more than one benefit.