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10-14-2008, 12:28 PM #1
Minimum concrete thickness for 19,000lbs CNC
We just received our new Milltronics VM25 IL. The machine was received on Monday, and the technician couldn't get here till thursday. Anyways he leveled the machine that day, and we noticed on the following Monday that the machine was out at least .005 without having run it yet. There were some small cracks in the floor , but not on that pad.
Is my floor sinking?
What should the concrete thickness be for a machine that size?
We estimate that our floor is about 6" thick.
10-14-2008, 12:49 PM #2
It may just be some initial settling. re level and check again in a week or so.
10-14-2008, 12:58 PM #3
I've made a foundation drawing for a milltronics unit, you can call them up,
nice people, and ask them what they would like.
Now some foundation ramblings that probably don't apply
to your situation:
I'm seeing more and more the smaller machines like haas and milltronics
don't require a foundation, but they do have some minimum requirements.
I believe this no foundation trend is because of the smaller shops, stuffing
the machines in pole barns and the like. If the little guy's are your main
customer, you build your machines to accomodate them.
I had the requirement (from my employer) to anchor the machine down.
We like to use cast in place anchors, so I needed
a drawing showing those anchor points. When I inquire, I sometimes get a
Some haas machine's don't have any, and the kit they offer looks like strap clamps
that get epoxied in to a drilled hole after setting the machine. Purely an after thought,
probably caused by large companies requirements of bolting everything down (or up).
10-14-2008, 01:57 PM #4
How big are the pads the machine is sitting on? If the problem continues, set the machine on some 1/2" or 3/4" thick steel plates and epoxy the plates to the floor.
This will distriblute the load over a larger area and may help with settling.
10-14-2008, 03:43 PM #5
I hope this is just some initial settling. I was hoping it would settle in those first 4 days before he came to set it up. Evidently it is still going, so I will level it again in a little while and see what happens.
10-14-2008, 04:25 PM #6
Now on to some specifics..
If this is "settling", it looks to me like the concrete isn't doing it's job.
Just because it will stop settling by putting some plate's under it,
what's going to happen when you start shaking and vibrating it ?
You know, put power to it, and start making chips with it.
What are you trying to machine with it/ what do you expect the
machine to hold as far as tolerance ? and to add here, you may
not need a very tight tolerance on your machined parts,
but the machine may flex too much on your foundation, causing it to bind.
If your in a rented building and can't dig/pour, you could build a steel
framework underneath, but concrete is ussually cheaper.
10-14-2008, 05:25 PM #7
I found out that the space is an 1600 sq foot pole barn add on. Not too mention the problem of groundhogs that we had on that corner of the building.
What kind of framework are you talking about? Just connect the plates that I have under the footpads?
10-14-2008, 05:44 PM #8
If the concrete isnt thick enough you will have constant leveling problems.
10-14-2008, 05:47 PM #9
The floor could be shifting if you're having some seasonal changes right now. What do you know about what's under the concrete? (FWIW, I have a 34,000 lb machine on 6" minimum with a nice clay subgrade and everything is fine)
You may already know this, but I'll throw this out there since I'm seeing it mentioned...getting the machine level is not important...getting the machine square IS important. Getting it level is just a starting point for getting it square. After that, level doesn't matter.
However, if the level is changing, that means the squareness of the machine is likely changing as well, which is bad. Are you checking that the spindle is normal to the table? How is it doing with the change in level?
10-14-2008, 05:54 PM #10
A 19,000lb machine probably wants at least 2 feet of concrete under it.
A rule of thumb is the concrete foundation should be five times the machine's mass.
I make that about 40 tons of concrete; if you know the footprint of your machine then you can work out the thickness. Sure as hell it's more than 6 inches................
10-14-2008, 06:02 PM #11
From my limited experience with one 17,000# machine, and the civil engineers etc involved with it.
1. What is under the concrete matters as much or more than the concrete. This turns out to be a huge issue.
2. All concrete is not the same. Rebar is your friend.
So 6" of concrete with no reinforcement on soggy soil may not work out well at all. 6" of concrete with no reinforcement that happens to be directly on top of a very large granite rock will likely work out fine.
10-14-2008, 08:19 PM #12
Depending upon your desired results, it might be worthwhile to inquire to a small local Civil Engineering firm.
I've used Mike's rule of thumb before, but it is probably overkill. The only time I think I saw it in print it was for stamping presses.
The mentions of grade prep being as important as the concrete is absolutely true. You have no control over this factor. You must live with it as it now stands.
I'd probably just put in a foundation about 2' thick. I might go 3' thick and larger area if, upon excavation, I found the subgrade to be loose, soggy, rubble filled, or containing much organic material. I don't know anything about your soils, or the amount of fill or prep work that was done on your site before building. At my location, for an unprepaired grade, I would keep the soil loading less than 1000psf (machine, table load, and foundation).
Figure the weight of the concrete and use 2 percent of concrete weight as the amount of steel. I'd use 3/4 bar on 2' centers about 8" off the bottom for the bottom layer.
I am not a Civil Engineer, and the value of any comments does not exceed what you paid for them.
10-15-2008, 07:05 AM #13
From what I am told they used sand, some slag stone and plently of rebar when they poured the slabs on that half of the "barn". They poured it a little thicker there because the previous owner of this building had a yacht that he was refurbishing. That thing was 15,000lbs.
Well I may have some good news. One of the guys brought in another level and we checked the machine and everything looked good. The weird thing is that I checked that machine again with our level (this level is old but well taken care of and also Starett) and it is right according to that level. Now I cleaned everything very well before using so I know that can't be it.
I guess I will have to wait till tomorrow when the tech gets here and checks with his level to be sure.
10-15-2008, 09:22 AM #14
"What kind of framework are you talking about? Just connect the plates that I have under the footpads?"
I don't engineer this stuff, just lay it out for the engineer. But from what i've seen,
the framework would probably be 12" wide flange i-beams, in a rectangular weldment
to the extents of the machine. This would then be cross braced, and some concrete
added for dampening. Plus the operator would have to be 12" higher on a platform,
very inconveinent, and a constant trip hazard.
Like I said, if you own the building, cutting out the existing and pouring in what
you need is much cheaper. It would be like this, sawcut (use garden hose to keep
down the dust), jackhammer or backhoe to remove the concrete slab.
Dig hole to proper depth, going at least 6" deeper, good gravel fill to proper
height, plate compact to level. This should be in the first day.
Next day, tie re-bar, probably #5 (5/8 dia.)on a grid 12" c-c 3" off bottom
(use concrete bricks here, chairs sink), vertical bars every 3' c-c to support
top mat (same as bottom) keep it 4" from top, Add deco anchors to fit
machine builders drawing.
3rd day, pour in morning, add sealer, strip any forms in afternoon.
Give it at least 2 weeks before bringing in machine, should wait the full
28 days before applying loads. You can sneek this number (full loads in
2 weeks) by spec'ing higher strength (8-bag over 6-bag mix), but
the contractor may growl a bit, as the stuff is quite hot, and set's
up quite fast.
This machine looks like a simple pour, no pits, no gutters (unless
you want them for coolant splash, and hydraulic oil containment).
You could, at this point, run conduit in the pour to bring the electricity,
computor line, and compressed air under the floor. This nice little
feature is handy if you have a overhead crane, keeps operators from
removing them with the hook.
10-16-2008, 12:36 PM #15
Well I am glad to say for now that my master precision level isn't so precise. The tech is here today and everything is still dialed in a week later. Now lets see what happens when this baby is in full swing. Then I might have to take your advice digger.
10-16-2008, 12:53 PM #16
FWIW, I have 2 25Klb VMCs sitting on 6" concrete floors. The concrete was poured long ago on top of used foundry sand fill. They have been there a long time with no detectable shifting. Each one has 8 3" dia pads plus 4 more pads under the toolchanger, perhaps that helps distribute the weight.
10-16-2008, 10:56 PM #17
FYI This is what 2' of concrete looks like. When installing a foundation this thick you must add the weight of the concrete. In this case there was wet soil layer at about 6' and because of that the soil bearing dropped to low. The solution was at the critical load points there is a sub footing to a depth of about 8' where the bearing pressure increased. designs were through a few different engineering companies including a soils engineer -soil testing co.
the weight of the main piece of this machine is about 60.000#
10-17-2008, 01:48 AM #18
Well I am glad to say for now that my master precision level isn't so precise.
Sounds like you got caught out with a level that might have taken a bump. Old tricks for young players. Did the Tech take the time to show you how to check your level?
10-17-2008, 12:59 PM #19
10-27-2008, 08:30 PM #20
That means I would specify that they cut completely through it and saw up the slab.
The wrong guys with SkillSaw, jackhammer and backhoe.....goodbye floor.