[pennlabs]

Here's a general question I just can't seem to answer easily by other means.
For the folks with a bridgeport- series 1 stlye for discussion purposes here - I know the weight is about 2200 pounds give or take a few. I plan on purchasing one down the road a bit and wondered about the possibility of my new garage floor cracking under the weight. The floor is 4 inch concrete over 3/4 crush stone (typical construction here in Pennsylvania) and settled for 3 years now. The garage is oversized a bunch which gives me room to have it either placed in a corner (that really scares me) or up against the side wall (much more room ) . Next to that would be a lathe in the near future as well - although spread out a bit. The last thing the wife would need to see is a section of floor cracked off the main slab! Boy would I have some explaining to do and be a tad upset myself. No sense ruining a good wife/machine shop relationship so far . I know many of you guys have similar setups at home. I just can't help wonder what that monster could do to a new floor!
Did you experience any problems with the weight issue or know anyone that did?


Thanks for any input,

Happy chip making

[Mcgyver]

i don't think you have to worry about the concrete if it really is a min of 4" throughout. 4" is as a standard light industrial floor, besides usually what you worry about with a floor is a high point load which the BP is not. in industry you'd be thinking thickness and compaction of the base, reinforcing etc, but 2200 / 4 corners is less load than each tire of a car.

[keebler303]

if you are worried you should put a piece of plate or wood to spread the load of the machine out. I personnally wouldn't worry about though.

Matt

[Geof]

I have 6000 lbs sitting on four 6" x 6" steel pads on a floor that is lucky if it is 3" thick and after 2 years there are no problems. I did put semi-rigid foam under the pads in an effort to avoid point loads because the floor was not really smooth.

[pennlabs]

Hey thanks guys! I guess I should have looked it it the way Mcgyver did with the weight related to a car tire over 4 corners. That actually makes a lot of sense. All those years as a mechanic - hmm I must be getting rusty - LOL. I think I'll sleep better now

I did think about the plate but decided to back off that because I know my dumb a$$ will trip over the edge of the plate and well.. you know the rest. I guess I just wanted to be a bit cautious but I'll more than likely just place the BP where I need it and not worry about it.

Thanks for the input folks!!

[pennlabs]

Thanks Geof, I just caught your reply as I was replying to the last two guys and didn't want to leave you out. But after reading your post I guess I really don't have a worry. All I want is a BP and floor lathe somewhat next to one another and it seems as though that will happen.

Thanks for the good news

[handlewanker]

Hi pennlabs, I've got a 4" floor in my garage too. I agonised a bit about putting a Bridgeport in the corner or along the wall.
The basis of the thought pattern is this:- garages can be built two ways, footings and walls and then pour a cement slab inside once the walls are up. Or pour the slab and build the walls up on the slab.
As I'm not familiar with your building regs. 'over there', I'll just give my reasons for what I think.
If the slab is poured inside the walls, normal practice, then putting the 'port in the corner puts a ton (2000lb) weight across two edges that join at the corner. No matter if the weight is spread across four points like car wheels, the total force is on the footprint of the mill, which is about 4ft X4ft out from the corner, and could lead to a crack across the corner.
In other words if the ground beneath the slab is not compacted enough it will not support the slab and it could crack.
Do the sums, draw the position to scale on paper of the 'port in the corner and then draw a line across the 'floor' in the corner to represent the hypothetical crack, (the hypotenuse of a right angle triangle.)
Whatever the length of the 'hypotenuse is, (about 5ft) then this length X the thickness of the concrete, 4", is the cross sectional area of floor that has to withstand 2000lb. The further out from the corner you come the better it gets.
The main weight of the 'port is centred about the round columnar body and this is towards the back.
If the walls had been built on the slab then it is better supported as it's further out.
Putting the 'port along the wall poses practically no weight problem at all, even adding a lathe next to it as the lathe would have to be 'down stream' from the table to clear it at it's maximum extension.
Unless you've got a hollow under the floor (unlikely) even then the floor as a whole spreads the weight.
The building regs in OZ have steel mesh in the floor, and I don't think you would have a problem even if the concrete was just down on the dirt.
I put the bridgeport in the corner facing out as this took up the least room and allowed the non-working bit, which is the back of the ram, to back into the corner and so save room.
The table traverse left to right is checked to make sure you can still get your hand round the handwheels at max traverse, and not hit the adjacent walls.
I think there is another factor in the equation too, and that is how reactive is the soil in your area? If it's clay then you may get seasonal movement due to drying and shrinkage or expansion and lifting.
My son is in the building trade and one of the most important factors of a site, affecting costs, is how the soil conditions are. It's the difference between old lake bottom silt or compacted clay.
Mine went in 10 years ago.
Ian.

[fpworks]

2200 lb machine will probably not be an issue for a 4" slab.

I have a 6000 lb VMC on a 4" concrete slab, standing on six 3" diameter cast iron pads. I was most afraid of the ~8000 lb forklift that carried the machine into place. (with hard rubber tires) I specified that the rigger had to use pneumatic tires, but he guaranteed me that the concrete wouldn't break, or he would pay. So I took the risk and he was right.

However, the subgrade is all clay, so we had good support underneath and that is very important. I recently talked to a dumptruck operator who told me that his 50,000 lb truck won't crack unreinforced 4" slabs in our area. You might want to talk to some construction contractors that work in your area.

The thing I don't like about the machine being on only 4" of concrete is that I can feel any medium axis acceleration in the floor. We're looking at some heavy, high G machines right now, and you better believe that we're cutting away the floor and adding a thicker, reinforced slab. (with studs!)

[Garage Shop]

This topic is right up my alley.

I have a 4" slab on I think 6" of 3/4 baserock.

I have a TRAK trm Prototrak bedmill (sits on 6 pads), and a standard bridgeport mill. I have a few cracks in the area where the machines used to be.

About a year ago I moved them to the other side of the garage BUT put rubber feet on them. And I have zero cracks near them now.

I also heard from a grage shop buddy of mine that if your mill rocks (it not being level) it will definatly assist in cracking concrete.

[widgitmaster]

Not a problem!

I have a 2300 lb Mill, 1500 lb Surface Grinder, & a 1200 lb 14x48 Gap Bed Lathe (and a hot water heater) all in a 6'x25' area in half of my garage!

Eric

[Chris64]

This topic is right up my alley.

I have a 4" slab on I think 6" of 3/4 baserock.

I have a TRAK trm Prototrak bedmill (sits on 6 pads), and a standard bridgeport mill. I have a few cracks in the area where the machines used to be.

About a year ago I moved them to the other side of the garage BUT put rubber feet on them. And I have zero cracks near them now.

I also heard from a grage shop buddy of mine that if your mill rocks (it not being level) it will definatly assist in cracking concrete.

hmmm...OK that's scary. Mine is about 3000 lbs. And it teeders in probably the worse direction...from the corner to the center. It just sits flat on the floor (no foot pads). My problem is that it just barely fits under the garage door so I can't lift it at all (a nice footing for example). I may try jacking it up with a car jack and put some type of wedge in the corner that is closest to the garage corner and level it out (part of me thought I should so that anyway).

I don't know how thick my footing is but it's a post-tension slab (with a small stem-wall) over granite back-fill. The ground is very stable...and after about 8 inches turns into rock. Anyone know if this is a better or worse scenario?

[handlewanker]

Hi FPworks, did I read your figures right, 50,000 lb? That's 25tons in round figures. I don't know how many wheels a dumptruck has but divide that by the number of wheels and it comes to one hell of a load per wheel.
The other thing about the guarantee not to crack the floor is only valid if it's in writing or witnessed verbally. I'd hate to go round to some guys house and tell him the floor's cracked and I want a new floor.
One thing a lot of people don't realise, it doesn't matter if you put a feather cushion under the mill it still presses down with 2000lb on its footprint area.
Using four pads under the corners for the 'port, the type that are round and have a rubber pad to sit on and are adjusted with a bolt through the machine base corners for levelling, you still get 2000lb on it's footprint. The individual load on each pad is 500lb and this is resisted by the 4" concrete. It would be practically impossible to punch a hole through 4" concrete with 500lb of static thrust, but a bit iffy if the machine is in a corner. It's like breaking the corner off of a biscuit.
The rubber pad type levellers are really meant to dampen out vibration and do a secondary job of leveling the machine. How many people just sit the machine down on the floor and away we go.
I see Garage Shop mentioned that "rocking" would cause damage. No levelling there.
The last firm I worked at bought in a couple of Nakamura Tome CNC lathes, not sure of the model number, but they were big mothers.
The first thing they did when most of the Herbert turret lathes were sold off was to dig a pit 5ft deep in the floor and pour a solid concrete block foundation. Then the block was allowed to cure for three weeks or so before the machine was brought in and installed.
Each machine had it's own foundation block.
I've seen some lathes with long beds just sitting on the floor with no attempt to level or bolt down. Bolting down onto an uneven floor will twist a lathe bed like a dogs back leg.
The mind boggles at the forces we subject concrete floors to. When I think of the fork lift weighing 8000lb (4tons) and the machine weighing 6000lb(3tons) moving into a garage with a 4" floor, then the combined load of 7tons on the forklifts footprint area is asking a bit much.
I suppose when the garage design computations were laid down before construction, it was envisage that the average family car or two would be sitting in the middle of it. Now we have a factory, and a different set of design rules.
Ian.

[handlewanker]

Hi all, before this becomes a scare excercise, think for a moment. What was the original design requirements that the planning permission was applied for?
I don't know what the building regulations are in USA but in OZ if you want a garage then the design computations are made to cater for the car or cars and nothing else.
The fact that some of us are making a garage into a factory with some seriously big equiptment is to say the least a bit haphazard.
Sure the machines go in and sit there, but is it safe? I bet a whole years pay against a pinch of dog poo that not one of us has had a design computation for a factory floor injected into the figures with the load figures we want to subject it to.
The other thing is how does the insurance policy see a garage as opposed to a factory?
Ian.

[scottmi]

This is all sitting on 4" concrete. Just my 2 cents.

[pennlabs]

First I have to say thanks to all for the responses made. You all have good and valid points. I understand where Ian is coming from being in the construction industry. I'm surrounded by new construction (homes and such) and really wanted to put a little thought behind the placement of large machines that would sit on a residential floor. My floor is the typical poured slab inside the foundation and block over 3/4 crush stone and thats over very large pieces of hammered rock that was removed to make my basement. (they had to dump it somewhere). There is a small hollow or void below the opposite end of the wall in interest (found that with a sledge bouncing on the floor lightly - you can really hear the difference). Must be due to settling. Soil is all clay and rock. The Pocono's is well known for it's lack of good soil. In fact it must be trucked on from out of state if you want anything worth growing in. I'll most likely park the BP and lathe along the wall as I was planning all along. If things get serious (and of course I hope they will ) I always have the "option" to build a shop in the rear of the property. Although that could be an interesting selling pitch to the wife -LMAO. Oh dear, by the way ...............

Thanks for all the good thoughts on this topic. This group seems like a fun bunch!

Eric

[pennlabs]

Not a problem!

I have a 2300 lb Mill, 1500 lb Surface Grinder, & a 1200 lb 14x48 Gap Bed Lathe (and a hot water heater) all in a 6'x25' area in half of my garage!

Eric

Eric is envious of Eric after seeing that pic

Nice and simple setup! Do you offer training as well? LOL I'll bring the beer
But I'll bet the commute would be a killer! Something tells me your MILES away from here of course LOL.

Nice shop ...........!

Eric

[jdelaney44]

'Nother data point for you.

No problem. Been running my BP for over a year on a 4 inch garage slab. No issues here at all.

[CoolHand]

The trick with keeping a slab on grade intact is to not exceed the bearing capacity of the subgrade that the slab is poured on.

If you don not exceed the bearing capacity of the subgrade, you get no deflection of the subgrade, which means no deflection of the concrete, which means no cracking.

Around here, we design to a subgrade bearing capacity of 1000 psf (lbs per square foot). With 4" of concrete and 6" of base rock under that, one square inch of floor area turns into 441 square inches of bearing area on the subgrade.

That means that at 3000 psi (the ultimate compressive strength of the concrete), the subgrade is only seeing ~7 psi (or about ~1000 psf). Meaning that when you are about to exceed the bearing capacity of the subgrade, you are about to crush the concrete.

Now, of course this assumes that you have 100% bearing of the slab on the base rock, which is where it "all falls down" so to speak. If you get voids between the concrete and the base rock, you generate bending moments in the concrete as it tries to bridge the gaps. That bending is what causes most cracked floors. The concrete can only bridge so much of a gap without some reinforcing steel in the right places.

If your contractor compacts the subgrade and base rock as they are supposed to, you won't get settlement after the slab is poured, so you won't have voids. Voids mean you didn't get satisfactory compaction, which means you need to be very careful how you load the slab (unless you happen to have a good bit of steel in the slab by chance). Check for voids (just like you have done) and avoid them at all costs. If you can't avoid them, you need to drill into the void and grout it full before you place the machine.

You'd be amazed what you can place on a 4" floor if your subgrade and base rock are properly prepared.