Floor for lathe

your garage really does not count. the length of your home machine and its weight is pretty minor. is your property built on built up shallows/swamps? i worked in both aerospace and shipyards..on the bay in san diego. very little solid rock base.

large measuring tables are zero'd every day, used only a short period during low tide. large machines on single thick pads...and not used at high tides. the changing water table allows machines to move!

his machine weighs enough...he needs to consider the slab and natural foundation it is on and the weather changes.

no i am not joking nor kiding.

mike in co
 
I am a structural engineer. The rule of thumb for vibrating machine bases is a concrete pad at least 3 times the mass of the machine and isolated from the floor slab. Unless your floor slab is floating (not attached to the wall footings, usually with tar paper isoloator) it will move vertically a little bit due to variations in soil moisture content throughout the year.

For a home lathe without other machinery running at the same time, there probably will not be a problem mounting it on the floor slab, but you never know. A separate pad will also allow for a level surface to mount the machine. You should also use 3/8" premolded expansion joint filler all around the machinery slab. I would also put #3 or #4 rebar at 12" on center each way at the top and bottom of the machinery slab to prevent cracking. If you decide to build a separate pad, concrete weighs 145 to 150 pounds per cubic foot.
 
Ok, I read back through the original post to make sure I wasn't missing anything.

I'll at least put it in simpler terms....it should not move any more that it did in the other shop, 15 miles away.
 
Jackson-in-GA: I was dealing in lathes, moving them in and out. Moving them around to make room, etc. I quit levelling them because of this. I came to find that they don't have to be level, just not torqued out of whack. Lathes set down on wood, weight evenly distributed, all feet landing flat, not level, worked just fine. My lathe at home slopes toward me a couple of degrees or more because it is against a garage wall and the floor is sloped for drainage. The lathe is dead-nut. the floor there is a plane surface so the lathe is not racked. I've had lathes so long that they had three bases. Care must be taken to set them down straight, but I still set them down on wood.
 
I've had a 2000+lbs. 13x40 lathe in my garage since Dec. '05. It took several months for it to settle in enough to remain level (as checked with a Stairett 98-8) for more than a couple of weeks. After that, I'd check it with the level mid-spring & mid-fall, and for the first couple of years, it'd require a little tweaking to get it level again. The last couple of years, it's been very stable - right up until last December, when I bought a 2500+lb. 14x40 lathe and moved it in to sit back-to-back within about 20" of the first lathe. Now I need to check them both on a daily basis - about what you'd expect when sitting machines with that mass on a 4" mesh reinforced slab. There was no room to put the new lathe anywhere else - it's a 3-car garage/shop with a sloped floor starting a few feet out from where I stand to operate the 2nd lathe; my vertical mill takes the space in front of the middle bay, and I didn't want to sit a machine right in front of the wall heater next to the 1st bay.

Lord only knows when or if the floor will finally stop settling with that much extra weight sitting so close to the 1st machine. I really wanted the 16x40 Grizzly gunsmithing lathe, and would have gone with one, but wasn't sure how to get one that heavy moved into the garage, nor whether the floor would support it. At some point - hopefully in the not-too-distant future - I'll build a new shop with isolated pads for all three machines. Question - would glass fiber reinforced concrete be suitable for such a pad, or should I stick with steel rebar?
 
flatlander said:
At some point - hopefully in the not-too-distant future - I'll build a new shop with isolated pads for all three machines. Question - would glass fiber reinforced concrete be suitable for such a pad, or should I stick with steel rebar?
Click to expand...

The thing that counts the most related to stability is what you do to prepare the area where you pour the machine pad. The pad is essentially floating on top of the place you pour it. If it is bed rock, which is the best, one can just pour the pad on top of it and not worry - it will move depending on how the bedrock is moving but that won't be a lot unless you are in an earthquake zone.

If it is undisturbed earth there are more things to worry about. One is whether or not it is subject to seasonal moisture infiltration which can be compensated for to some extent by making sure the area is well drained. The second is how well compacted it is.

In any event, the area where the shop floor will go should have a well compacted 4" (minimum) thick layer of crushed rock, no fines under the floor and any pads.

I have sandstone ridges and Hagerstown Clay under my shop. the ridges are, well, rigid. The clay is greasy when wet. Not the best situation by a long ways.

To compensate I dug it down 2' with my Nephew's CAT953C, had shale hauled in and compacted in 6" lifts with a 100" vibrating roller to bring it back up to 10" below the designed floor, then compacted crushed rock over that to build up a 4" layer. When I was done it felt like walking on an airport runway.

Then I had a 6" thick reinforced floor poured over that. No seperate machine pads.

I moved the 2 lathes and mills in about two years ago. I didn't get them set up and leveled for about a year with all the other things I had to get done. I check the two lathes now and then with my precision level (.0005" in 12" sensitivity or something extreme like that), but they don't move much. It if stays within one mark on the level, I leave it alone.

The home made lathe benches have jacking screws in the bottom of each leg. The jacking screws were machined to a point and rest in counter sunk holes in steel floor pads.

Fitch
 
I don't think you will have any problems with the machine busting your floor, but it WILL move. A standard floor will be made as cheaply as the code will allow-typically, this is 4" nominal which means using a 2x4 as a form which is really only 3 1/2" thick. Concrete has almost no tensile strength-that's why reinforcing bars are added in areas with a surcharge. I won't cost you too much to do it right. saw a hole, dig it out a couple of feet deep, place a crushed rock/sand mixture back in for at least 6" and pour it full. The expansion joint around the perimeter is good advice too.

There are thousands of 2000# lathes sitting on garage floors all around the world and they still turn on when you flip the switch and don't bind up. I'll bet very few of these guys have a QA plan in place and don't check for flatness or level. We are talking constantly about working to tenths here and you can't do best work with a machine that is moving around.

When I built my shop, I let the concrete guys do their final grading. I then went over the whole thing with a compactor myself and got another inch out of it. I then placed #6 rebar at 24" O/C and #4 at 12" both directions. I then placed 1/2" PEX lines at 12" O/C for heat. I then poured 7 1/2" of concrete over this (4000 psi mix). This was about the best I could do considering that I didn't know exactly where machines would go and I had the tubing to deal with. I isolated the slab the best I could and built the whole thing on top of 3' of engineered pad (mostly ABC). I made control cuts in it about 2" deep and I haven't got a single crack running out of them yet.

I am hoping that this will be stable enough to keep them from moving. I know my jig borer would move a little on my last garage floor and it was 5" with very little rebar.
 
If it's going

to cause a loss of sleep, give your local civil engineer a call and tell him/her what your plans are. Best information you'll get.
 
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