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Size of concrete pad for G4003g lathe?

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dsymes

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I took delivery of a G4003g last week and have realized that my existing concrete floor is not stable enough at the place I want to put the lathe. It was poured about 20 years ago as a series of slabs separated by 2x4 pressure treated lumber. Also, the floor slopes about 1" in 6 ft. Unfortunately, the place I want to put the lathe is at the joint between two floor sections, and when I step on floor on either side of where the stands will go, the floor moves about .004” or so (see photos). Since this is the best place to put the lathe in a crowded home shop, the obvious solution is to cut out a section of the existing slabs and to pour a 24sq ft x 4” or 5” pad, reinforced with rebar.

grizzly stand 1.jpg grizzly stand 2.jpg

My question is how large a pad will be adequate. My thought is to make the pad about 3.5 ft x 7.5 ft, or a little more than a foot larger than the footprint of the lathe in all directions. It would be nice to do the whole floor, but at this point, that isn’t practical.

The soil around here is clay, but I would not be surprised if I find the builder used sand to level this ground under the slab – I just don’t know what I’ll find. I plan to dig down a bit, add a layer of crushed rock, and tamp it down before pouring.

So, my question at this point is whether or not this slab is big enough not to move when I step on it while operating the lathe? Or should I pour a smaller pad, say 4” larger than the footprint?

Thanks in advance for all suggestions.
Douglas
 

Al 1

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Douglas, I would build my pad so it extends at least 3' in front of your machine area. That will give you room to walk on a level surface.
cut out old concrete and Dig down about 8 to 10", Fill with stable fill 4 to 5" and tamp well ( Clay is not stable. ). Try to have your finish concrete even as possible with your walking area. Install your re-bar and wire. make sure your wire and rebar are somewhat centered in depth of concrete.
If this concrete does move it will not flex so your machine will not flex. So you should be OK. Al.
 

Trip

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Dig a post hole at each end if the pad a couple of feet deep 8" to 12" diameter . The post holes will act like pilings it wont move
 

westerner

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I think I would remove sections, rather than cut them. Very, Very messy either way. Looks like 4 sections would give you a plenty big enough pad to hold the lathe.
 

dsymes

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Al 1 - I don't plan to make the pad level - it will have the same slope as the rest of the floor, so I don't have to consider having a level area to stand on, just whether or not stepping on the edge of the pad will tend to make it move.

Trip - I like it. I think it would work with a slab that was 2.5 ft x 6.5 ft (6" larger than footprint in all directions).

Westerner - your suggestion would make a better floor, but would involve way more concrete than I'm considering.
 

Al 1

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Douglas, Yes Trips idea is good. Al.
 

Radials

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#7
Not exactly along the same lines as your question but if I was in the same position I might consider making a leveling platform out of steel like the one shown with more points of contact than just the corners. This would allow you to straddle that crack and compensate for the slope in the floor as well.

Nick

1539136576416.png
 

dsymes

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Not exactly along the same lines as your question but if I was in the same position I might consider making a leveling platform out of steel like the one shown with more points of contact than just the corners. This would allow you to straddle that crack and compensate for the slope in the floor as well.

Nick
The problem isn't the crack, it is that the edges of each slab flex up and down when I put my weight on them. I'm resigned to going through the mess of cutting an inch or two down into the existing concrete with a skill saw at the edges of the new pad and then jack-hammering it out. Then pouring a new slab with rebar and probably some "pilings" as Trip suggested.

Thanks for the photo - I'm planning on welding some 1/2" x 2" steel onto the bottom of the stands and having it stick out 2" on each side so my leveling bolts will be outside the footprint of the stands. Haven't decided whether to have them run front to back like you have or side to side (to have less to trip on). In any case, I will anchor the threaded rod into the concrete with epoxy.
 

Eddyde

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I'm resigned to going through the mess of cutting an inch or two down into the existing concrete with a skill saw at the edges of the new pad and then jack-hammering it out. Then pouring a new slab with rebar and probably some "pilings" as Trip suggested.
Hi, Douglas,

I am a contractor and have a lot of experience with concrete remediation.

If your are pouring a new slab, I would skip the pilings. Unless you put them down 4' or so they probably won't add much support and are unnecessary. As suggested above, dig the soil out about 6" below the bottom of the slab, tamp it well, place a bed of gravel, tamp well and pour 4" of 5000# concrete mix. 4" or 6" wire mesh embedded about an inch from the bottom is all you really need but a couple of pieces of rebar wouldn't hurt.

Or, Instead of cutting out the old slab you could pour a new slab on top. Either just doing the lathe footprint, raising it up 3.5" (assuming a 2x4 form) or doing a larger area, to include adequate space to stand on. I personally find most lathes kind of low (and I'm only average height) so I would probably want to raise it a bit anyway. That avoids the hellacious job of cutting and jackhammering concrete indoors.

Eddy
 

Logan 400

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All good advice above. If it is movement between slabs that is the main concern use rebar or at least 1/2 slick rod and horizontally pin the new slab to the existing slabs about every 16" or so.
 

Cadillac

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Or just build a deck on top of floor. 2x4’s on edge double up where ever you like. Then 2 layers of plywood criss crossed. You can level platform so less leveling of lathe feet. Your just displacing the weigh over a larger area. Build platform large enough for you to operate machine. Easy, removable, less work and money.
 

rock_breaker

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#12
When you walk on one slab does the one next to it move? If it doesn't move build your pad to hold the lathe and walk on a separate pad otherrwise build the pad large enough so you and the lathe go together. As Eddyde said wire mesh and some rebar above the bottom high enough to let the largest rocks in the mix to pass under it. I would place some cross pieces of rebar in there too. Compaction of the earth under the new slab is critical, get it as hard as you can, water aids in compaction but don't make mud.
Have a good day
Ray
 

HarryJM

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#13
I have very little experience with concrete and at one time was thinking about cutting 4 holes in my wood shed to install Sonotube concrete forms for the base of my lathe. Never did pursue it though. As their web site states,
"Sonotube concrete forms stand strong as the most economical way to create round columns for buildings, entryways, structural columns, light posts and other commercial and residential structures. "
 

Cadillac

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Most garage pads just float on earth. Having sonotubes is good but if one heaves or drops with freeze- thaw than it become a problem.
For such a small area I think a slab would be the best option or deck it.
 

Mitch Alsup

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#15
I have watched this thread for a while. In my opinion there are more problems associated with making this base in concrete than by making a base in wood (and/or steel) that rests on top of the existing concrete with balanced wide load placement on both slabs. And like another reply, I would make the base wide enough that you feel comfortable at the controls while standing on the base (I consider 2 feet minimum). Finally, I put leveling screws/jacks on all of my tools.

I would probably make it out of 4x4s axially with the bed of the lathe held together with lag bolts or all thread.
 

P. Waller

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#16
10' wide X 4' deep X 3' thick, you can not have enough machine base in the hobby world, the bigger the better.
 
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