Concrete counter tops??

[lazylathe]

Hi All,

In my quest to construct a good solid workbench and to provide a solid and stable
footing for my lathe i have been thinking about concrete.

I know that John Hills from madmodder had a whole concrete bench constructed for him and it is pretty awesome!
http://madmodder.net/index.php?topic=5847.0

I have been tossing the idea around of building the bench from doubled up 2X4's and then boxing in the area that the lathe is going to occupy.
Using rebar as the support structure internally and also placing the mounting bolts for the lathe so that they are
embedded into the concrete.

I was wondering if anyone had any insights into this idea?
I can work with concrete so that is not an issue.
What kind of concrete should i consider? regular, self leveling, hydraulic etc...
Also would i use just plain concrete or a mix with sand and or gravel?

I am thinking if this could be done it would be a neat solution as i could pour the slab to any thickness.
The thicker it is the stronger it will be and the more dampening it would give to vibrations.

Anyone ever done this before??

Andrew

 

[Jasonb]

Also would i use just plain concrete or a mix with sand and or gravel?

Surely all concrete contains sand & gravel along with cement. Its the size and proportion of the aggreregate that need thinking about, I would have thought to keep the coarse aggregate smaller than general construction say 10mm or 3/8 and go with a stronger mix (higher cement content) like 1:2:4

Make sure your formwork is completely flat as when you turn it over any twist in teh form will be in the concrete for good. Or are you going to shutter the bottom then float & polish the exposed top?

J

 

[Mainer]

Concrete is a mix of cement (the binding agent) and gravel (sand) and aggregate. For maximum strength you need the correct proportions of all three plus the correct amount of water. The less water you can use and still get a good mix, the better. A stiff mix will be stronger than a more soupy mix. For maximum strength let it cure in a humid environment for 28 days, although there are diminishing returns after about a week. And that's about all I remember about concrete from Engineering 232....

I think I would use regular cement and mix in the proper proportions of gravel and aggregate, or use bags of ready-mix, cement already mixed with gravel and aggregate -- just add water and stir! Arrange the form so you can strike off the surface by placing a 2x4 or similar across the form and pulling it across the surface. That will take care of the flatness. I would then trowel it after it has set up a bit to get a nice smooth surface. I see no need to use self-leveling, and isn't hydraulic cement a lot more expensive? You're not trying to plug a leak.

 

[Tin Falcon]

I too have thought about a concrete bench top.
If you pour in place the finishing to get a smooth surface is labor intensive.
for a small bench I would make a mold with a smooth flat bottom 2 x 3 sides. . Oiled Masonite should work you can still place anchors or studs in place. then when cured flip and mount IMHO this will save lot of finishing time.
I would probably put a few pieces of re bar in it or reinforcing wire. vibrate the mold to get the air out .

Also would i use just plain concrete or a mix with sand and or gravel?

HMM Portland cement =gray dry powder.
cement + sand and water = mortar
cement +sand + gravel + water = concrete
For a bench top a couple bags of quick-crete gravel mix should do the trick.
Here are links to the US Army Corp of Engineers concrete manuals probably more than you want or need to know but good references.
http://140.194.76.129/publications/eng-manuals/em1110-2-2000/entire.pdf

http://140.194.76.129/publications/eng-manuals/em1110-1-2009/toc.htm
Tin

 

[Mainer]

Keep in mind that concrete is very strong in compression, but weak in tension. Therefore, put your rebar toward what will be the bottom of the slab. When the slab tries to bend, above the neutral axis (the centerline) the concrete will be in compression, which is no problem. Below the neutral axis it's in tension, so it needs the strength of the rebar. Good support is also useful, of course.

Thickness depends on overall size, of course, but for what I would envision for a lathe bench top I'd use 2x4, for the sides of the form. That would give a 3 1/2" thick top, since a 2x4 is not 2"x4", etc. I like Tin's idea of casting the top upside down to get a smooth surface, but the "flip and mount" part might be a problem. That thing is going to be dern heavy. I would need about 3' x 5' x 3 1/2" for my long-bed South Bend bench lathe. That works out to 4 3/8 cubic feet of concrete, or around 350 pounds, I think. I guess that would be manageable.

Strips of cove molding along the inside edges of the form would give you a nicely rounded edge on the cast benchtop.

 

[Tin Falcon]

if You put pipe flanges and pipe at the ends of the mold then support the pipe on strong horses it should not be a problem. I have been involved in flipping 40 foot long yacht molds weighing several tons. it can be done safely
remember sliding heavy stuff is easier than lifting.
tin

 

[lazylathe]

Or are you going to shutter the bottom then float & polish the exposed top?

J

What does this mean?

I was planning on pouring the concrete mix into the hole i would prepare in the work bench.
The bottom would be a smooth flat board, supported from below by the main frame of the bench.
Same for the sides of the hole.
Smooth and float the top to get a level, flat surface that would be suitable for use as the top.
Otherwise it may be too heavy to flip and lift into position.

After it has cured i can always seal it and put a protective coat of top.
Or colour the mix and just seal it nicely.

Using some angle iron around the edges would also give a nice finished appearance and it would also
give me a nice flat surface to float to.
I can get it welded up to the correct dimensions and have some bolts welded onto the undersides
for retention in the concrete. Also gives you a super strong edge! ;D

Andrew

 

[Tin Falcon]

After it has cured i can always seal it and put a protective coat of top.
Or colour the mix and just seal it nicely.

you will probably want to polish it first!!! That my friend is the time consuming part

http://www.bargainblade.com/concrete-countertop-polishing-kit-p-135.html?cPath=268_270

Using some angle iron around the edges would also give a nice finished appearance and it would also
give me a nice flat surface to float to.
I can get it welded up to the correct dimensions and have some bolts welded onto the undersides
for retention in the concrete. Also gives you a super strong edge!

yes have the bolts or studs welded in so they are at a 45 degree angle.
tin

 

[Niels Abildgaard]

At the start of world war 2 the ministry of armament or something like that wanted that many south bend amateur lathes should be used for war effort.
They printed a leaflet with recommendations for how to cast a concrete foundation,wait a month,align lathe and start making precision optical parts.
I have read it myself on one of the many South Bend fora and that started me down the graveyard stone road but I have been unable to find it again.
Let us try and find it.Very clear with not a lot of formulas etc.
Well worth the effort finding it.

 

[lazylathe]

Hi Neils,

Your comment jogged something in my memory and i found this that i had read a long time ago!

http://www.practicalmachinist.com/vb/south-bend-lathes/concrete-lathe-bench-top-130222/

It is some excerpts from the pamphlet you mention.
The one member there, Paula actually has a whole write up about the bench she made from concrete!
I will find it and post a link!

Andrew

EDIT:
Here is the link to that post as well as a restoration of a South Bend lathe. Very long but a great read!!
http://www.practicalmachinist.com/vb/monarch-lathes/not-monarch-but-useful-info-just-same-166280/

 

[Niels Abildgaard]

Thank You Andrew

That was what I have read once.
Nobody seems to have noticed that Southbend and copies have another pair of flats on mid of underside of bed.
Probably from last machining process and if this is bolted down on concrete also we are in Hardinge stiffness country

Try and You will be amazed.
I made a post with photos 21 dec 2010 under Tools that show it but cannot link

Regards

 

[lazylathe]

Here is the link the Neils post mentioned above:

http://www.homemodelenginemachinist.com/index.php?topic=11934.msg129395#msg129395

Andrew

 

[Catminer]

Hi Andrew;
Check at Home Depot, they have a high strength concrete mix for just such things. I have seen it in London and found out it's not stocked at all stores. Rona lists the same mixture under Bomix brand.

Peter

 

[Mosey]

2 cents, and probably worth less, but here goes.
Concrete is a complex mixture, whose formula cannot be calculated. It is easy to make for guys that work with it regularly. Don't be fooled by the muddy boots and torn tee shirts, concrete masons really are crafts men. I suggest you find one around the neighborhood, buy some beer, and let them help you. The way to strength is to keep the water from evaporating from the fresh pour, buy wrapping it in plastic, or even putting in an admixture that helps the cure. Then soak it with more water to help the cure. Concrete can actually have its strength increased long after it is poured by adding water, but only a little.

Also, I seem to remember that my used tool dealer always had extra cast-iron lathe bases around, and usually cheap. Why not try to find one?

 

[ShedBoy]

I work in an underground environment and we make the strongest stuff you could imagine. It is used to hold in cable bolts which is a 13mm spring steel cable pushed into a hole drilled in the rock. A breather line is taped to the end which goes up to the top of the hole and hangs out the bottom then a fill pipe is pushed just inside the bottom of the hole (working above here) then the bottom sealed. We the half fill a mixing tub with water and start pouring low heat cement into it (low heat cement is needed to prevent cracking when curing. When the mix is like toothpaste (good rule of thumb is it needs to stick to your hand when upside down) it is pumped in through the fill pipe until it come out the breather pipe. After this has cured a plate and locking collet are put on and the plate is tighten against the rock with a hydraulic jack up to 15ton! It is nice and easy to work with as it is nearly self leveling. That is what I would use. I have seen rocks hanging of this stuff after blasting the size of a truck and the cable will snap before the grout lets go. I have mixed it at home in a bucket with a tile glue mixer. Good stuff. Once the surface is dry and you can't push a finger into it it doesn't hurt to spray more water on it. Concrete will set underwater and really hard.
Brock

 

[lazylathe]

Hi Brock,

What is the stuff you use called?
You just mention "low heat cement"

And the biggest question is: Can you buy it in a store?

Andrew

 

[ShedBoy]

Any cement supply place should be able to get some in if they don't already have it. Here is the brand we use
http://www.cockburncement.com.au/productinfo/range/brochures/Low Heat Brochure.pdf
Nothing fancy about it at all. If you use normal cement to make this style of mix it will get hot to the touch and then crack. I use to spray shotcrete and had to do a course on concrete and the most interesting thing was looking at cement under a microscope before and after adding water. Quite interesting when dry it looks like a smooth ball but when water is added it seems to grow spike all over it which lock in together with the others. I just quizzed an engineer here on the hardness of it and after 7 days it should be at 40mpa and after 28 days should be 50mpa. If you see the picture of Hiroshoma after being bombed the concrete arch thing still standing is set to 100mpa apparently and survived the bomb and earthquake. Cast iron is about 200mpa. All this is compression strength I think. No expert but it is dam strong stuff.
Brock

 

[lazylathe]

Thanks Brock, i will look into it!

I have also found this which is available locally and sets to 50mpa, so it should also work quite well!

http://www.quikrete.com/ProductLines/CountertopMix.asp

Andrew

 

[lazylathe]

Okay, here is a first rough draft of what i would like the bench to look like.
Any ideas or input appreciated!!!

The space between the legs will be turned into storage space, most likely shelves with doors on the front.

This is not to any sort of scale!! Just a quick sketch to see what it would look like!
I was also thinking of using some metal tubes instead of cementing the mounting bolts in, this would allow for some "wiggle" room!

Andrew

 

[Niels Abildgaard]

Hello Andrew

Looks rigth if You make the concrete 4 inch /100mm thick and put some pipes where bolts go in.