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Floor bracing

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I've outgrown my midi-lathe and am looking forward to adding a second, larger machine. Unfortunately, my small shop just doesn't have room for it. So, to make this happen I will need to add a small "turning room" on the backside of my shop. I'm probably building something like 12' X 10' or so.

Here's my question for this group. How might I strengthen the floor? The add-on would be a wood stick-framed structure that sits upon some concrete piers. The height of the floor would be about 12-15 inches above ground level. The floor joists would be 2X8s and the floor would probably be 3/4" ply or 1-by planking. This would suffice for a work room, but I'm worried about the lathe. I'd probably be looking at a 16", 2hp, 110v, 500lb machine (or something in that class). Picture something more like a Nova Galaxi 1644, but less than a big Powermatic. I need to do something to the floor/joisting under that lathe.

I could pour a couple extra piers directly under the lathe spot. I could add bracing and even make a thicker floor there. I just can't picture how strong the flooring and bracing needs to be. I think about a big out-of-balance chunk on the lathe spinning and creating havoc. How would you approach this? I don't want to over-engineer this (too much), but I also don't want to see the lathe disappearing through the floor. Thoughts?

Thanks in advance.
 

Bill Boehme

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How about doubling each of the 2X8's, put more piers under the lathe location, and put two layers of 3/4" plywood on the floor? In this part of the country concrete is used almost exclusively because wood foundations just are too high maintenance (soil movement, moisture, decay, termites, snakes, skunks, armadillos, fire ants, etc.).
 
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Depends on what you turn as well. If you plan on doing out of balance natural edge work, then the 2x8's will act like springs. Extra piers, laminated veneer lumber joists, or wood I-beam joists will help. If you mostly turn vessels, ornaments, and round bowl blanks, your current plan will work.
 
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John, Kudos for thinking ahead! Bill is correct that a concrete slab would be preferred. If still framing in wood, I would consider putting blocking between all joists at least every 4' and gluing with construction adhesive. Glue the bejesus out of the plywood as well. You might consider bumping up to 2X12.

I live on the beach a quarter mile from the nearest road (and concrete truck), so I put in full width 2X14s and filled the bays between the joists where my lathe goes with rocks. The floor is full dimension 2X18-24"...I know, absurd dimensions, but I chainsaw milled rot resistant Alaska yellow cedar and it was easier to use larger dimensions that rip down to smaller. My floor is rock solid.

I've also seen where overbuilding carpenters put coil strapping down on top of the joists on diagonals from one corner of the joist framing to the other and then use construction adhesive with 1 1/8" ply. That seems to me like it wouldn't add that much, but some guys argue otherwise. Another thought would be to fasten some upside-down seismic brackets to the occasional doubled joists and tighter down to concrete piers with all thread.

It might also be a great time to hit up a structural engineer friend or even hire one for an hour to discuss best practices for a rock solid floor. I think you'll come up with simple and elegant solution with a little forethought.
 
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If your framing is going on a stem wall and footing, then fill it full of gravel and pour concrete. Much easier than bracing, and far more sturdy. No place for invading critters either...

robo hippy
 

RichColvin

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I have some family in construction. They tell me that engineered I-beams (like these https://www.apawood.org/i-joist) are significantly stronger & stiffer than 2x wood joists.

If I were doing anything, I would halve the distance between them. So, instead of (for example) 12" centers, I'd put them on 6" centers. But then again, I am NOT a structural engineer.

Rich
 
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John- I'm just getting a new shop setup and this comes at an interesting moment. the floor in the turning area (a section of the shop roughly 18' x 12' at the front of the shop has 2x12 joists on 12" centers with 1-1/4" plywood glued and screwed. The joists run perpendicular to the lathe bed. -All has gone well turning fairly well balanced blanks, but as soon as I took on a severly out of balance bowl blank I started feeling the floor move rhythmically under my feet. The lathe weighs in at over 800 pounds (Robust AB) and never had a problem on former concrete garage floor.

Planning to add two beams underneath spaced about the same as the lathe foot pads supported with floor jacks on poured footings. If that doesn't solve the problem the floor comes up and I'll build a box from ground level to floor height and pour a pad for the lathe.
 
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Jeff's idea is a good one I could just isolate the lathe floor from the room's floor. I could build an elevated 4' X 8' concrete pad for the lathe that is quite solid and then do normal framing around it. Sort of a slab foundation inside a pier foundation, with both floors at the same level. It seems like sending that vibration energy into the ground would be better than sending it into the adjoining wood framing. Still thinking.
 
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Hey John, I was a general contractor and home builder for 45 years, so I have some experience with framing and live loads. I assume that you need to dig footings to get below your frost line. I would use 8" sonotubes filled with concrete which you could mix yourself. You can get Tecko plates to secure the 2x10's to the concrete. I would use 9 tubes(3 each end , 1 middle row) Use 2x10"s, 16" On center and put 2x10 blocking between them running down the center. I would use an Avantek 1/1/2" t&g osb decking, glued to the floor joists. In the area where the lathe is going I wood put 2x10 blocking between the floor joists,laid flat and glued and screwed so that you can bolt the lathe down with lags. Hope this helps. Paul K.
 
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I have some family in construction. They tell me that engineered I-beams (like these https://www.apawood.org/i-joist) are significantly stronger & stiffer than 2x wood joists.

If I were doing anything, I would halve the distance between them. So, instead of (for example) 12" centers, I'd put them on 6" centers. But then again, I am NOT a structural engineer.

Rich

To first order, making assumptions about the span distance vs the thickness of the flooring, halving the distance will reduce deflections by 8, for the same amount of force (weight). Paul K's advice is sound; make sure your lathe is placed near one of the concrete piers.

Personally, I'm not a fan of bolting a lathe (or any equipment) onto the floor. If you're turning something so out-of-balance that you need to bolt the lathe, get a heavier lathe, or slow the speed down, or both (or use a chain saw as your cutting tool :eek:).
 
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If you have a specific location identified for your lathe you can run solid supports under the
floor joists down to the ground level. There are numerous solutions for a solid support under
the floor joists to support the lathe. You could stack several concrete blocks and glue a wood
block and secure that to the bottom of the joist. If you want to get creative you could make a
couple of jack posts with adjusting nuts accessible from above in your turning room. You could
turn a couple of round wood plugs that could be removed to access the jack post nut and tighten
them up if the foundation ever settles and you loose tension on the jack post supports. A jack post
can be made with a cut length of all-thread, a cut length of steel pipe and a threaded nut.
Another simple solution is a heavy threaded rod anchored in the foundation running up through the
floor or attached to the joists. A heavy washer or spacer supports the floor/joist with an adjusting nut
located below the washer/spacer that allows raising or lowering the floor. This arrangement would
allow you to level all four corners of the lathe location, but you would need to do this from below. Another
variation using the anchored all-thread through the floor is to actually mount the equipment to the all-thread
with heavy washers and adjusting nuts below, this allows you to level the equipment at each corner. This
is a commonly employed method of installing rotating equipment in the industrial sector.
 
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Just got done putting two 10' 4x8's under the floor joists in my shop. they're running directly under the legs of my lathe. Used two jack posts on concrete piers on each.
The difference is remarkable. I put an off-balance blank on to make sure I wasn't hallucinating. It's all good now...and it was a pretty easy fix - got it done before my son could arrive to help.
 
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After stewing over this for weeks, I've decided to pour a slab. Concrete guy is coming by this weekend to work up his estimate. I'm guessing that 6" of concrete will be sufficient.
 
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Of course it will crack, but

ACI 224R-01 “Control of Cracking of Concrete Structures” states:
“The minimum amount and spacing of reinforcement to be used in structural floors, roof slabs, and walls for control of temperature and shrinkage cracking is given in ACI 318 or in ACI 350. The minimum reinforcement percentage, which is between 0.18 and 0.20%, does not normally control cracks to within generally acceptable design limits. To control cracks to a more acceptable level, the percentage requirement needs to exceed about 0.60%.”

For a 4-inch slab, this amounts to about 0.3 sqin each way, e.g. #5 at 12" oc.
 
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John, Most garage floors are 4" thick and cars weigh 6x more than your lathe. You say 500 bouncing lb lathe. Your lathe should have rubber anti- vibration pads under the legs or base and be bolted into the concrete. More important than the thickness is the strenth of the concrete. If your concerned go to 3000PSI. I have a VB36 lathe, very heavy. I turn bowls that are 24" in diameter. The blanks weigh over 150#. My garage floor is 4" thick, 2500PSI and the lathe is bolted into the floor. 10 years and no problems.
 
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Okay, thanks everyone. That's just what I need to know.

Update: I just met with my concrete contractor and explained what would be sitting on his slab. He agreed that a 4" slab is sufficient, but he wants to use 3,500 psi mix. He gave me a good price, but wants a bowl for his wife. :)
 
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Won't the concrete slab quickly fracture around the hold-down bolts (red heads or whatever)? When I was 16 (a very long time ago) my father handed me a 20lb sledge and pointed me at a 3-1/2 inch (nominal 4") patio slab. 3 whacks with that sledge hammer in the same spot fractured the concrete. The patio slab was reinforced with 3/8 or 1/2 inch rebar so removal was a pain but at the end of the day no more patio slab and one worn out teenager.

Of course a vibrating lathe is not the same as a 20# sledge and a disgruntled teenager, but over time I still have to believe that the concrete will fatigue around the bolts. Then again, bolting the lathe to the slab appears to be a fairly common practice, so for those of you with bolted down lathes, do you see stress fractures around the hold down points?

-bruce
 
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My last word, 3500PSI is a waste of money for your purposes. 2500 or 3000PSI is more than enough. The way the concrete is handled is very importatnt. I see you are in OK. I assume it is hot there. Make sure the floor is poured in one continuous pour and the concrete is kept wet for 24 hours. If it dries too quickly it weakens it and may cause surface cracking. Either lightly spray the surface or cover it with wet burlap.
Answer to Bruce, Millions of machines in factories all over the world are bolted down into concrete. The holes are drilled not made with a sledge hammer. The floors don't fracture. I have bolted machines down for over 50 years. No problem.
 
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Where was it implied the holes would be created with a sledge? The point being, concrete easily fractures. An 800 or so pound lathe with a severely unbalanced log wants to jump around, over time it seems that the concrete surrounding the hold down bolts would want to fatigue. This is different than an industrial environment with finely tuned and balanced mill machinery, slabs poured for such a use and balanced stock.
 
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Bill Boehme

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Bruce, slabs are much more likely to crack from what's underneath than what's on top. If you have clay or gumbo without a sufficient sand blanket for the slab then it will be prone to develop flexure cracks. If the slab is for a structure then it also needs to have a perimeter beam and beams beneath load bearing walls is standard practice in this area. As Paul said, keep it wet. Concrete cures by chemical reaction, not by drying out. The longer it takes to cure, the stronger it will be.

Think about bolting the lathe down this way: when fastened to the floor, the lathe and floor become one. An untethered lathe dancing around isn't likely to cause the floor to crack and one that is anchored to the floor is even less likely to cause it to crack. The sharp impact caused by a sledgehammer isn't comparable to sinusoidal shaking from a lathe.
 
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That makes sense. My concern was four, relatively small, attachment points concentrating the movement. I can see where the sinusoidal nature of the motion could lessen the fatigue. I'll shut up now.
 

Bill Boehme

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Your best bet is doing this right the first time. You can get by without the concrete and re-bar using this method. ....

Now I feel like I have inadequate anchoring to terra firms. :D

You think that I might be able to get by with just one pile or should I go for one under each foot? Those big cylinders have to be filled with rebar and concrete so I might need to call for about a dozen 18 yard concrete trucks ... or maybe just set up a batching plant on site. :D
 
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When working on these types of projects it is difficult to determine where to start and stop.
Concrete has come a long ways over the years, as they can add fibers and polymers to
strengthen the concrete to prevent cracking. If you are bolting the lathe into the concrete
slab you can always use a nut and washer under the feet of the lathe which will allow you to
level the lathe and make any adjustments over time if there is any kind of settling of the soil
under the concrete slab being poured for the lathe.
 
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