Concrete for table bed & sizing?

[Johnuk]

How about using reinforced concrete for a table's frame?

I've seen welded square section pipe and aluminium extrusion being used so far.

Reinforced concrete would be very cheap and very strong. The mold could be made with MDF boards and the whole thing could be designed to bolt together using studs burried in the concrete.

The automation would could be supported by studding burried in the concrete, so that it could be leveled and locked in place once fitted.

I would also be interested to hear what size tables everyone is using, what form of automation & guide ways and what they think of the combination.

Best wishes,
John

[frinkdaddy]

Sounds like a pretty good idea, especially in terms of pure mass and solidity.
This might provide one with a very stable work surface, if properly supported and reinforced. The problem with concrete, is weight.

Your formwork would have to be quite accurate, and stable to allow the concrete to cure for at least 21-28 days. I would use a 5000 PSI mix design, and an intermediate size aggregate, 1" and smaller. Perhaps 1 or 2 layers of (4x4 to 6x6) x .25 in. WWF could be emdedded therein, depending upon total slab thickness.

1- Don't forget to vibrate as you pour, to remove voids. ( Caveat: too much vibration leads to segregation, and loss of ultimate design strength.)

2- Do not make your mix too wet. ( Caveat: too much water in the mix increases the water to cement ratio, thereby reducing ultimate design strength.)

3- Once your concrete has set, ( usually 24 hrs.) cover it with plastic, and mist with water once a day.

4- Protect the young concrete from freezing for at least 7 days after initial set.

You could probably make a template to hold a series of threaded rods/studs, and mount them in the freshly poured concrete. Aluminum, is a bad choice for this because it reacts with cement paste. Concrete and aluminum, just don't get along. Steel would be a better choice, stainless even more preferrable.

All of this information can be found in your CRSI ( Concrete Reinforcing Steel Institute) manual. Probably available at the library, or at the home of an engineering friend.

As for table size, 4'x8' would lend itself to utility of materials. One might also consider putting a very small arch in the formwork to allow for deflection when placed into operating position.

I would probably try something like this, but I have lathes, drills, mills, welders, plasma torches, grinders, and a plethora of other tools with which to work. As a bridge engineer, I've seen concrete, both good and bad.

Good luck !!

[svenakela]

I know a guy who has made his own lathe, a uge piece running in a production environment, and that machine is based on a steel framework filled with concrete. I can tell you, it's not moving at all. ;-)

Cheers,
Sven

[Johnuk]

Thanks for the replies!

I was reminded of the idea when I was looking at 5-axis portal mills. The walls of the machine are sometimes hollow. When they're delivered to their user, they're bolted to the floor and filled with concrete during installation.

I like the idea of misting the concrete every day - It's kind of like growing a machine!

[Johnuk]

I generated a quick render of an idea for how the table might be constructed.

This is very rough, I wanted to gather some opinions on what to do with it before I went any futher. Please excuse all the arrows and notes, I drew this diagram to explain the principle to a group not involved in CNC.

In the picture, the wide parts of the cast concrete are about 150mm and the thinner sections 100mm. So it's 150 by 100mm box in effect.

Best wishes,
John

[frinkdaddy]

Johnuk,

Very nice design. and rendering. I think that your side pieces might not need the top flange. Certainly easier to form up and pour.

Instead of buried studs, one could also employ embedded weld plates and corners. This is used by builders of tilt panel buildings to join adjacent panels. Needless to say, this method results in a permanent installation.

These simply amount to a flat plate of steel, or angle iron, with a couple of studs or anchors welded to the back. They must be attached to the formwork such that the weld surfaces will be flush with the finished concrete surface.

Needless to say, weld embeddments must be properly aligned prior to casting the concrete. Once cured, your pieces could be positioned, squared, and tacked together.

I also liked the shape of your pieces, in that they might be duplicated easily by reusing the concrete forms. Lots of non-stick form material is currently available on the market. If you apply a very slight taper to your forms, your finished piece should pop right out, allowing you to re-use the same forms multiple times. Release agents also assist one in this endeavor.

I can see that you have given your design much consideration, and can only say, keep on dude. Anything is do-able in concrete (( is "do-able" a real word?)).

Well anyway, I applaud you. I can send you some ideas for embeddments, and reinforcement, if needed.

Keep in touch.

frinkdaddy

[Johnuk]

Thanks for the positive notes!

I posted the rendering on a forum to do with tiling and concrete also. A lot of people thought it might be easier to just make it out of steel, and that the molding for the design would take too long.

I decided that perhaps there is a mid point. Breeze blocks, or cinder blocks in the US.

These are very easy to get hold of, strong compression wise, very cheap, not too difficult to work with and not too heavy.

I thought that by they could be arranged into supports ~70cm high and placed with three either side of the table - one at the back, middle and end. More piles could built lower down within the work area to support a water tank.

I think breeze blocks are about 10 - 30p each or something like that, so the entire support should come out very cheap using this method.

My aim with this table is to make it as cheaply as I possibly can, whilst, if anything, making it work more effectively than it would otherwise. Kind of like the way there's no point machining the casting of an already expensive machine tool unless it's actually going to make a real difference. The only problem at the moment will be convincing my family I really need a table that big in the new garage!

[frinkdaddy]

Cinder blocks, are a good alternative. They can be filled with Sackrete, or motar, and with the addition of a couple of pieces of rebar, you should have a very stable work base. Mounting points, and other attachment points can be inserted into the fresh mud
for the final assembly.

Really innovative design. Let us know how it turns out.

frinkdaddy

[CNC Pro]

I recall seeing a wood lathe that was poured concrete, the spindle was a Ford 9" rear-end, and was set in the mold as they poured the headstock(one solid block)! It was being used for turning tree stumps screwed to a huge face plate. The owner said "it was as smooth as silk"!

[freak_brain]

here is a link that was posted a few weeks back by cncadmin. I remembered this as concrete construction but I think now that it is weldments. However, it could easily be concrete.

http://www.scaled.com/services/cms_mill.html


by the way, 50ft of "X" travel, imagine what you could make with that!!

-Allen

[Johnuk]

Thanks for the link Allen,

I've seen that page a few times recently.

One thing that concerns me is the subtitle under the picture that say 'The 5-Axis CMS Lathe'. If they can afford to buy something that expensive, you'd have thought they'd know what it was that they'd bought.

Kind regards,
John

[freak_brain]

that's funny.....I noticed that too. Probably some puter geek did that, lol...


-Allen