Poor man’s slab flattening

[Roger Feeley]

I’m going to be making a table that will be sort ov a giant cutting board. About 2.5’ x 5.5’ x about 2” thick. So I glue up all the strips and then I have to flatten it. I can get access to a wide belt sander for about $65/hr. Naturally I want to get as close as I can so it doesn’t take too long.

It occurs to me that my basement concrete floor is pretty flat. Is there any reason why I can’t build a plywood gantry on casters and flatten this thing. I’m thinking me on one side and the bride on the other and we pilot the router together. None of this two axis stuff. I’d make the gantry about a foot longer than the width of the table. We would do that strip and remount the router for the next strip.

if I was to get close enough, maybe I could avoid the big sander…

this thing is going to be a beast! I will be putting it on a custom steel frame that will look like I beams. Then I will add 4 cast iron swing out seats.

[Jamie Buxton]

Sure you can do that. The key issue is whether the floor is really flat enough. Most concrete floors are just eyeballed by the concrete guys, and aren't flat enough for furniture. Test it with a long straightedge. Put it down on the floor along the edges of the area where the gantry will roll, and running from corner to corner.

[Kurt Wyberanec]

The big question is how flat do you really need it? If it is going to be for a dining table or countertop I'm thinking flat enough to the eye and touch. If that's the case there's no reason you can rig up a very simply jig to get it flat. I would say if you can get 2 very flat 2x3s and tie them in around the top then 2 pieces of simple angle steel (or thicker aluminum) that are tied at each end will make a rudimentary but effective sled that you can guide on the edges of your 2x3 frame. Then of course you'll need a good spiral bit that's long enough to reach down and flatten. Get it darn close and then just finish up with RO sander.

Of course...that might all add up to $65 and a lot more time than the belt sander.....$65 really isn't bad unless you either a) have the materials to make the sled or b) plan on doing this again. In a good wide belt you'd probably flatten that thing in 15 min let alone an hour.....bring some more projects if you have an hour min fee!!!!

And BTW, don't worry too much about how flat the floor is....if it's close that'll probably work, but 2 things to note....1) the top probably won't flex at 2" thick and 2) if you're really worried about it being flat to the floor than you can use a level, shim it all out and use double stick tape to attach the frame I mentioned to the sides as your floating flat surface so to speak.

Good luck!

[Bradley Gray]

Rig a jig to hold it flat for the first pass and take it with you to the wide belt.

[Michael Schuch]

Make the top oversized by a couple inches in width and length so you can screw the rails the gantry is going to slide on directly to the slab. Then you can cut off the screw holes when you are done. The floor and the slab's orientation to the floor becomes irrelevant this way.

You could even just glue a couple of blocks to the side of the slab to screw the rails to and cut the blocks off after you are finished flattening. You wouldn't have to waste expensive wood this way.

I guess even bar clamping the rails to the slab would work if the rails were ridged enough.

Or use a couple of pipe clamps AS the rails the gantry slides on.

OR get the top close with a hand plane then finish it in the sander. One hour on a wide belt sander will clean up a LOT of irregularities on a 2 1/2' x 5 1/2' slab. You should be able to easily get a dozen passes in an hour. Starting with 40 grit the slab will flatten out pretty fast.

OR check craigslist for a piece of used bowling alley lane and forget about making the top yourself!

[Kevin Jenness]

Mill your stock accurately, glue it up in stages making sure to keep it flat, clean the glue off so the sanding belts don't get fouled and pay the man. $65 is cheap for a decent result and it shouldn't take more than 3 passes each side if you take care in assembly.

[John TenEyck]

What Michael said. You can use jointed wooden rails, nothing fancy required as long as they are straight and parallel to each other. Ride the gantry on those and have at it. Maybe this will be of help.

https://lh3.googleusercontent.com/pw/AM-JKLUYZFeSVyJgnaME5YchJvxsltFBe1r3-ZoEDupdVfhM09wx5qbR7ck5jRZJVqWg13bH-UGf4bhTD7OPfFWcTZ4jy7y8kowLeEO-ngiXUoiKXsLCYHFK0OJ5HzKuLMDR1beUxvNUG-aluiqfKfaPJvmGAg=w1190-h893-no?authuser=1


I use my bench as the rails and shim the slab lying on it as needed, but if you think of the bench as your slab then you should be able to see what I'm talking about. The gantry is a little more complicated because of the dust collection, but it's still nothing fancy, just a bridge with the router riding between the two cross rails.

I originally flattened the bench top exactly this way.

John

[Patrick Kane]

What size is your planer? I would glue up your 54” of width in multiple blanks. For me, I could do 3 blanks to get through my 20” machine. The next day, take a 1/16” off each face and then glue those three blanks together. The last step goes better if you have a biscuit joiner, domino, duo doweler etc. alternatively, you can use cauls. That is how I made many edge grain countertops years ago.

[Roger Feeley]

All great ideas. Thanks.
I like Patricks idea of making sub-assemblies. I have a 15” planer, so 4 planks. Glue the 4 into 2 then the two halves together.
for final flattening, just about everyone recommends some sort of rails so I’ll do that.

[Bill Dufour]

A hollow core door shimmed flat to the floor is a good first step. How about those power planes for door work instead of a router. Porter Cables version is called a "porta plane". used ones run around $125.
A chainsaw powered debarker comes to mind as well.
Bill D.

https://www.amazon.com/BotaBay-Debarker-Attachment-Debarking-Processing/dp/B09CV54MNL/ref=asc_df_B09CV54MNL/?tag=hyprod-20&linkCode=df0&hvadid=533224178111&hvpos=&hvnetw=g&hvrand=2160744794415788722&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9032277&hvtargid=pla-1471531399084&th=1
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[Bill Dufour]

Look into renting a floor sander.
Bill D

[Scott Winners]

Depends on your relationship with the guy that owns the sander. If you can get everything within 0.25" it should be less than 30 minutes on a big/good sander. 30x66 is enormous, but it would fit in the bed of my Tacoma. I would personally pay the $65 for an hour of shop time, though my local guy with whom I am careful to build a good relationship would probably only charge me for half an hour if I brought it to him within a quarter of an inch.

Besides relationship with the local commercial shop, it does also depend on how hard it is going to be for you transport that thing. My next door neighbor is about 30 years younger than me, his wife likes my brisket and I shovel a couple briskets a year over the fence for exactly this reason. I like the guy, but having a sinless 'in' with the wife is valuable as well. I can get it loaded and unloaded at my end; your next problem is finding a friend with a truck bed > 6 feet, but you live in Virginia.

What is your time worth to you?

[Kevin Jenness]

If you can get everything within 0.25" it should be less than 30 minutes on a big/good sander.

The decimal point is in the wrong place, If you need to remove any more than .025" on each side you need to re-evaluate your whole process. I would suggest that you glue up several sections, face and thickness and glue them up into halves of your finished dimension, run them through the sander, glue up the halves and Jack's your uncle. If you have a helper you could glue up the halves and run the whole thing through the sander, if not you should be able to slide the halves from a bench to a cart to a vehicle singlehanded.

When I do normal glueups and expect to run them through a sander, unless I'm getting tearout on figured wood I plan for removing .015" from each side - .010" at 100# and .005" at 150#. I often skip the widebelt as I have to use another shop's machine. I certainly don't plan on gluing up a non-flat assembly. It's reasonable to add a bit when using many small strips, but netting the variations by flattening subsections should minimize that before you get to the sander.. Accurate stock prep, concealed registration splines (biscuits, dominos, plain old splines) and balanced clamping on a flat surface should do the trick. Save the router sled for naturally occurring warped slabs, there's no reason to fabricate one.

[Patrick Varley]

Nick Offerman had a good setup which was detailed in FWW #222 (https://www.finewoodworking.com/issue/2011/09/issue-222) that I use. I don't have enough room to keep something up all the time, so I made the rails which can be setup on top of a bench (or even the ground) when needed. Unfortunately you do have to shim them level every time you break them out. I also don't have a long enough straight edge so I use the string trick (https://youtu.be/qtkBZHLJyD0?t=655) to level them. Throw the router sled on top and you're good to go.

[Dave VanDewerker]

When I made my counter tops I glued up the sections in manageable pieces first. I glued up each section in about 9" wide pieces, ran each of those thru my planer (DW 735) to get a nice flat top and all the sections the same thickness. I then glued up three section with lots of clamps and cauls. It came out plenty flat enough to do a final finish sanding with my 6" ROS.