Auxiliary floor suitable for Bridgeport?

jellywerker · Jan 23, 2022

I am looking to move into a new shop. It is the second floor of an old industrial building, with wooden floors. Heavy beams, adequate floor ratings for machinery, etc...

However, the building has shifted substantially over time and the space I am looking at has about 6in of slope over 20ft.

What I would like to do is run scribed/levelled sleepers on top of the floor, and then put down a new floor directly on top. Screws for everything as it will potentially need to be removed after a few years.

I am planning on 12in spacing.

That's the background, the question is what kind of floor material should I put on top of the sleepers that can support a basic knee mill? That's the heaviest thing I'd want to put in there, and that's about 500 pounds per square foot over around 6 square feet, once I account for the biggest work I might get up there. My understanding is a 9x42 bridgeport is about 2,400 lbs and the base is 24x36.

I assume 3/4 plywood is going to get crushed. Is the beefier 1-1/8 or so subfloor material adequate for this? I'd plan on putting a thin steel plate under the machine itself, probably 1/4in just to keep any feet or levelling shims from sinking.

partsproduction · Jan 23, 2022

I think if you level it with a precision level, .0002" per foot, that experience will answer your question in a way you remember for life. I may be wrong but I think you'll have to level it every week.

EPAIII · Jan 23, 2022

Six inches of slope in 20 feet and you are asking about it.

FIND ANOTHER PLACE! The weight of your shop may entirely collapse that building. That place scares the heck out of me.

jellywerker · Jan 24, 2022

I appreciate the concern, but there is plenty of other industry in the building and it's a worthwhile move for additional reasons. I'm having their engineer/architect look into it.

The rest of my shop combined weighs as much as a Bridgeport. I do lightweight ornamental work.

Honestly it sounds like maybe a smaller mill is the way to go. I don't really need the full capacity, but everything smaller that I've used feels kind of chintzy, and even a Bridgeport starts to feel kind of small on Z height once you get a long reamer and a tall piece on the table.

GregSY · Jan 24, 2022

You won't 'crush' 3/4" plywood. It would work if you support it well enough, like using oak beams every 6". But as others note, this whole thing sounds shaky.

Tony Quiring · Jan 24, 2022

1.125 plytainium floor is APA rated 48 inch span.

This stuff is very strong stuff and just place it over existing floor then securing through existing into supporting beams with long screws (many) would greatly help.

Or you could make a box with this on bottom with dimensional lumber frame and another sheet on top, screwedto floor then top plate attached.

We did this year's ago to place a cell site inside an office, weight same as bridgeport and structual engineer approved it.

It spreads the load out to wider area reducing the per Sq ft loading on floor.

This used 2x10 spaced maybe 12 inch centers.

Glued and screwed with 3 inch large drywall type screws made for framing.

Made frame directly on bottom then found out floor was not as flat as the unit so screwed down to floor.

Then glued and screwed top on.

This was a Sprint site...T-Mobile will need to cut it apart to get it out...

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deltap · Jan 24, 2022

Making a raised floor is creating a hazzard. Shim one side 5/8 " and call it good.

ArmchairEngineer · Jan 24, 2022

jellywerker said:
I am looking to move into a new shop. It is the second floor of an old industrial building, with wooden floors. Heavy beams, adequate floor ratings for machinery, etc...

However, the building has shifted substantially over time and the space I am looking at has about 6in of slope over 20ft.

I have to ask --- is this 106 Ferris? That's the only address I've ever been in with a slope that matches what you're describing.
My former employer has a furniture shop there, including some metalworking machines like a Bridgeport and South Bend lathe. For the work we did (do) there, shimming did the job.

gustafson · Jan 24, 2022

You can find that much local variation in a concrete floor. Shim it and think about it no more

Hell, Bridgeports were made for short people, you need to jack it up a couple inches anyway

Newman109 · Jan 24, 2022

EPAIII said:
Six inches of slope in 20 feet and you are asking about it.

FIND ANOTHER PLACE! The weight of your shop may entirely collapse that building. That place scares the heck out of me.

Oh man! I coudn't agree more. I once lived in a tract house in L.A. where the living room had sunk 3/4" in 15 feet!. I could tell because a kid's beach ball would roll to the corner when set on the floor.

My Dad and I pulled up the rug and we made a matrix of wire and concrete nails in the deepest spot. We then filled the whole tapered portion of the floor with concrete until it was level. Once it set and the rug replaced you couldn't tell it

We even had to patch the dry wall where it had split in long cracks.

Six inches of slope in 20 feet? Forget that for a machine shop!

adammil1 · Jan 24, 2022

Not really practical for your needs but, interesting story about a Bridgeport in an old building. My dad's a mentor on a robotics team. They were able to find a town who had a historic 1 room school house dating to the very early 1800's. The town wanted to find a use for the school house and was delighted to rent it for $1/yr to the team. Well they needed to put their Bridgeport in there and the structural engineer was concerned about the floor. So the town had the engineer design up a concrete pedestal which they put in the dirt floor of the basement and the thing stretches all the way up to the first floor. When they moved the Bridgeport in the rigger put down steel sheets to spread the load and moved it with a pallet jack and it all worked well. But you're on the 2nd floor so probably not an option.

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CalG · Jan 24, 2022

I spent some time in a place that had three BPs on castors. Roll around to where they were needed. Never a problem with meeting typical specs.

The machines went up on wood blocks while in use. Just pinch bar work for one man.

richard newman · Jan 24, 2022

Sounds like you're trying to solve 2 problems: leveling the floor and supporting a B'port. If as you say the beams and floor ratings are adequate, then shimming the mill should do, or creating a heavy duty pedestal like Tony describes.

How large is the shop? Leveling the floor so all of it can support the mill will be way more expensive than just a small local area. If you're expecting to only be there a few years, can you get by as is?

jellywerker · Jan 26, 2022

Not 106 Ferris, but I know that building! Brooklyn and Queens have a lot of old, well settled industrial buildings!

I appreciate all the additional responses, still waiting to hear from the building engineer.

The goal is to have a fairly level floor as a base for the shop. I don't like having fasteners
or carts roll away, and the rest of the shop is on casters since I've always worked in compact spaces.

The shop is about 500 square feet, so levelling won't be cheap if I do the whole space, but not astronomical either. A bit under $3k I'm estimating with current lumber prices.

As mentioned, the current floor will support the weight, it's more that if I build an auxiliary floor, I'd like to have the freedom to scoot it to a new place if I need to adjust the layout.

Seems like one of those things where if I don't do it on move in, it will never happen, and I may or may not curse myself for not doing it.

ArmchairEngineer · Jan 26, 2022

jellywerker said:
Not 106 Ferris, but I know that building! Brooklyn and Queens have a lot of old, well settled industrial buildings!

Ah, ok! To all the naysayers, I'd add: At 106 Ferris, maybe the same as your prospective shop, we came to the conclusion that the extreme slope was not due to settling, but that the building must have been constructed that way (built as a warehouse in the 1800s, could have been for drainage, etc., who knows?). The building also conveniently had PSF ratings for each floor listed in the stairwells. I don't know if those were original, or reviewed regularly -- but at any rate we got along fine with the heavy machinery.

In that space, the floorboards were exceptionally thick (no subfloor) and outrageously worn and weathered. So much so, that small screws and pins would always be getting lost amongst the gaps, splinters and splits. And virtually every time I'd reach down to pick something small off the floor, I'd graze the surface and get a splinter under my nail. For that reason alone, I'd look into your subfloor idea if the space is 500 SF only.

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