Originally Posted by lazylabs
Is it true that it's better to have them on an isolated piece of floor? I am going to be building a shop in the next few months so I could easily form and pour seperate sections for 2/3 machine pads. I was thinking about doing it anyway just to keep it from cracking all over the place.
let me take you from the day you order in the machine, to give you a rough idea what the steps are. Then maybe you can make the decision. Most lathes do not need an isolation pad, but they still have their own set of issues which we'll deal with later.
Lets say you buy a new machine center from XYZ Machine Tool company. When you get the order placed and after they receive their first deposit, they should send you a foundation print. Some will call out a spec on an isolation pad, while others will simply say something like 12" of re-enforced concrete with a density spec. I used the same grade of concrete they used in road building, no matter how thick they wanted it made. But there actually is a grade that's better, but not needed 90% of the time. In that drawing you'll see the actual layout of the machine including stand alone hydraulic tanks and the coolant system if it's also stand alone. You'll see how they prefer the CNC control to be placed and usually give you a couple of options as well. They will also give you the layout for the leveling pads and lag bolts (this must be done correctly!) I usually got this print about six to eight weeks before delivery.
In the above drawings you can start to lay out where you want to place the machine, and of course start to build an isolation pad if needed. By doing this ahead of schedule, you actually save a lot of time and money. But of course do it right. Otherwise you'll have to move the machine twice! I've poured isolation pads from 30" thick to 156" thick (beyond stupid!) Bought rebar by the flat bed truck loads (multi at that). I've done rebar by the old wire it together method, and the weld it all together method. That welded rebar is better. Don't skimp on the rebar, as it's important. If you have an existing floor, and have to install a pad, keep in mind that the pad is always one solid piece of concrete. Never set a machine on a pad that's less than two weeks old and really a month is a lot better. You want the surface finished as smooth and flat as possible, and this alone will help your installation. Doing the pad of course starts with a concrete cutting operation (I always do it with a saw). Kinda messy, but the nature of the job. Lets say you need a 10' square pad 36" deep. For starters it's best you find a concrete company that does road work or something that is critical by nature. You'll pay a little more, but save yourself a lot of grief 24 months later. You figure out you best location (remember there has to be access all the way around). I always went by the rule of the thumb that said to tale the axis travel and add two feet to it for added room. This will save you from cutting a hole in the wall, or even worse (and have I seen this one in person!) OK we have the 10' square laid out on the floor. Now add a minimum of one foot all the way around (I always recommend 18 inches or more). Have you guys cut the square out of the floor and pull it sections. Now we dig the soil and gravel out of the hole. Go about 48" deep (more is OK). I always put a layer of pea gravel under the pad, and tamped this down to where it's fairly solid. Limestone works well too (wet it down and tamp it a lot). Now we start to build the frame work for the outside ring around the pad. I will use a little bit of rebar with this part as well. Then pour the outside walls (you'll want them strait for a reason.). OK you got that part done and they've setup for a couple days. Now it's time to get serious. Pull the frame work. The next step is to install an anti vibration material that sorta looks like generic Cellotex, but it's not! You can install this all the way around with a Ramset. Put a layer on the floor if it makes you feel better (I never did). Now it's time to start welding rebar. If the machine will have a coolant flood system that goes in the floor you'll have to take care of this part as well. I always used a stainless steel trough, and poured up to it. You want several vibration devices to keep the air pockets out of the concrete. I always used a concrete pumper truck. Now comes the tricky and also a critical part. You need to install the lag screws. I like grade eight all thread. Some manufacturers will send in their own style of lags, others will tell you what they want. Most are simply L shaped threaded rod. Put them in the wet concrete as soon as possible. Four inches above the concrete is about right with at least eight inches in the concrete. Just make sure they are 90 degrees to the concrete, and are located right! After the pad is poured you just wait. I always covered mine with a roll of plastic, and hosed the pad down twice a day with water. After a week or ten days you don't need to be doing this anymore. Now you just wait a few more days. OK we've been a week now, and we're bored stiff. Pull the plastic, and clean the floor one more time (no acids please). Wrap every lag bolt with a couple layers of Ductape. In the drawings you'll see where all the leveling pads are placed (some use wedges and are far better) Lets make good leveling pads! I usually used 3/4" pads, but 1/2" thick pads are fine for light weight equipment. While your at it, cut between four and six 1" thick pads that are only spacers to help you position the 3/4" pads during installation. Take each pad and run a two flute end mill in them about 1/4" deep with about 1/8" clearance for the leveling bolts. This way the pads will stay in place. Roughly lay out your pads on the virgin concrete, and mark the new floor with a spray can of paint or even a magic marker. Buzz this area with a body grinder and sand paper to remover any bumps (there will be some).
Now we're ready to set the machine on the pad (finally!). I always recommend hiring riggers for this work, as they usually will set the base of the machine without tearing up the lag bolts. (I had a team of seriously good millwrongs out of a Michigan auto plant that wouldn't even scratch the paint on the machine!) Now some folks like to use anti vibration pads ontop their leveling pads. This is good, and this can cause grief. I've tried them under the pads, and it didn't work as well. Plan on cutting a hole in them, unless you buy them with the hole in them. No big deal. Wedges are the best thing for machine centers, and use a good anti vibration pad ontop them (I like Machinery Mounts). Have the guys set the machine on the thicker pads (1.25" is about right for a vibration pad and a 3/4" steel pad. It is critical about where you place the thicker pads (I've even used wood blocks) as the machine frame will flex a good bit.
With the machine set, your work is just beginning! You'll need at least two .0005" levels that are at least ten inches long. But if you have to you can get by with one. After you have the machine on the leveling pads, and the thicker ones removed rough level it to about .001". Now the electrician can do his conduit and you can start plumbing it in. I always lag down the hydraulic tank (s), and filter units
It is very important that the machine frame never sets over a crack in the concrete! Even more critical with a lathe or a grinder! Otherwise they just move all over the place. Most CNC lathes work well with 8" of re-enforced concrete, but some of the bigger ones want 12". They really don't need an isolation pad. But grinders like the isolation pad. I do recommend that you recheck the machine level daily till the frame quits moving. The level is not aligning the machine to make it cut strait and square, so don't get rooked into that though process! It's just the start of things to come. I used a 12"x12"x16" granite H block for most of the smaller machines. But I had a 48" long cylinder square for the bigger stuff. I liked using Federal electronic levels after the machine was running, but a good laser will do just fine. It's just easier with the electronic level. Plus you can work as close as your heart desires. For just about anything anybody here will buy, the two .0005" spirit levels will do nicely, but also will not help you square up the column if needed
I know this post is lengthy, but trust me I just glossed over it and told you the easy parts. You can have five machines that are identical, and all five will level and align differently. Once again the nature of the beast. I would not bother to pour a pad for a lathe. Just a nice thick floor with zero cracks will do fine. You can sink high grade lag bolt anchors in the concrete (they get expensive, and you'll need a good hammer drill). When you new machine is delivered, either leave it on the pallot, or set oak blocks where each leveling pad would be. A warped machine frame is not fun, and a warped cast iron one is a beast to deal with. (often takes months to get the warpage out). Lastly, be sure to use jam nuts on every lag bolt with a cad washer under them. Very important.