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  • Torsion box workbench top

    Hey guys,

    I've built two workbenches already. The first one was for the basement and it was laminated 2x4's I got from a big box server which I then tried to flatten with a router sled. It's great, but it serves its purpose. I use it as a general purpose workbench in the basement. Right now it's mostly just collecting stuff. The other one I built was a combination outfeed table / work bench for my old table saw. The top was just a 3/4" aspen plywood on a crooked frame (again the frame was using big box 2x4's).

    Anyways, I got a new table saw this past Christmas and sold the other one and the bench I built for it. I'm looking to build a new one. I've come up with a torsion box design drawing on various sources on the internet. A nearby wood store (not a big box store), I grabbed 5 sheets of 3/4" baltic birch. The sheets were precut to 60"x30" which are the dimensions of the torsion box top (to keep things simple). I was planning on making the grid 3 inches thick sandwiched between two sheets of the baltic birch. I'm using baltic birch because it's basically a much better plywood then stuff at big box stores. I'm also using it because the workbench top is not just going to be an "assembly table" which is what I typically see torsion boxes being built for. I have half of a 2 car garage for my workshop so I don't have the luxury of lots of space. My workbench is going to be a multi-purpose bench - outfeed table, assembly table, etc. and I'm tired of using crappy wood to try and make something good so that's why I want to make something our this baltic birch and have it actually flat. It's been so frustrating not having something perfectly flat to work on.

    Anyways, quite a pre-amble. I saw the wood-whisperers torsion box build and planned on following a similar process in terms of using saw horses and shimming and across the saw horses and then shimming until level then a sheet of MDF on top check for level and then start with the grid assembly.

    I setup my saw horses and I have a bench jointer and a bench planer and I was looking at the 2x4's I have and they're all horrible. I hate big box 2x4's they're all twisted and warped in every possibly way. Anyways I decided to use one of the sheets of baltic birch to cut 3 inch strips on the table saw to lay across the saw horses on which I will be putting my 1/2 inch sheet of MDF ontop to serve as the perfectly flat assembly surface for the grid. By the way I cut and jointed and planed a 2x4 attached it on top of hte saw horse so these strips would have a flat surface to rest on.

    My problem is laying the 3 inch strips I cut on the table saw on their edges, across the saw horses they're not all the exact same. In the picture below I have them across the saw horses against each other. If I run my finger across them, in the middle they're roughly all the same, but towards the ends of these strips some of them are not in alignment with the others. Checking with a feeler gauge, it's like around 1/2 a mm in some places closer to a 1mm in the worst spot in terms of variation. So the next step is spread these out and lay the MDF ontop and then assemble the webbing. I'm concerned that these variations will translate up into the tabletop. Am I being anal? Should I be concerned? What should I do? I could try and shim the strips a bit and try and even it out more. Input welcome, Thanks!




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  • #2

    Re: Torsion box workbench top

    You might try to rip them down again, just taking enough off to remove the variations. This time, use a feather board to hold it against the fence. Also, try not to stop in the middle of the rip. Have your push stick in your hand while you feed it through, push with alternating hands to adjust your grip so that the piece is in constant motion.

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    • #3

      Re: Torsion box workbench top

      I can relate to much of the frustrations in your post and to your build... I watched and then built the same wood whisper torsion box table your talking about but my is 8’x30”.

      I’ll tell you what I did just because there’s a Lot in your post and I’m not sure I follow your whole build (sometimes you just gotta see it). I built mine with 3/4mdf sides and skins, 1/2 grid pieces, then wrapped all the sides in hardwood flooring (free in kijiji). To make all my sides and grid pieces exactly equal sizes (what you seem to be struggling with) I kept all the pieces as short as possible making them easier to work with and thus easier to maintain the same size. This meant I ran the grid pieces across the 30” span I think 12-13 times and then used 7” or so pieces to fill in the rest of the grid. This allowed me to work with no piece longer than about 34”. It wasn’t great for my planer but it’s not a great one anyway so after running everything through the table saw, I screwed bunches of them together on edge and ran them through the planer. Everything was bang on.

      I built it on top of the leg assembly and it came together perfectly flat! I throw my level on it from end to end and not a sliver of light comes through. Hopefully that helps.

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      • #4

        Re: Torsion box workbench top

        I thought about that, but that will only if the problem is only on one side of the strips, otherwise the strip will slide along the fence following the contour and just repeat the problem while creating a thinner strip ( something for a jointer to address) but I've read that jointing the edge of plywood will ruin the blades along the glue lines so I have a cheap ~ $500 porter cable 6" bench jointer but I dont' want to sacrifice the cutting blades on it. I guess what I'm wondering is should I try and fix it with handplanes? I could try a second table saw pass, see if that helps.... or are these differences negligible in the final product?

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        • #5

          Re: Torsion box workbench top

          Hi Pat, I'm not even at the webbing part yet. I'm at the putting these strips across spanning the saw horses upon which I will place a sheet of 1/2" MDF to serve as the "Flat surface" upon which to assemble the webbing. I'm going to take a stab at shimming the strips and putting the MDF on tonight. I have a 3 foot level, a 2 foot straight edge from veritas which I plan to use to check for flat. If it's not perfectly flat then I think I'll try another pass at the table saw... maybe handplane too.

          The problem I know came from trying to cut the 3 inch strips from 60"x30" sheet of baltic birch on my sawstop jobsite saw. Easier to handle as the sheet gets thinner but the first few cuts I think are where the problem came from

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          • #6

            Re: Torsion box workbench top

            Pat,

            I agree that it is challenging to rip 3" strips off a large, ungainly piece of plywood - even 30" X 60" ones. But if you follow the suggestion given you by Scott (post #2), and rip them again, I'm pretty sure you'll have much better luck. But, here's a few methods of work which I'd recommend you follow to get optimal results:

            1. Make sure your tablesaw is set up accurately: the blade is parallel to the slots in the top; the is parallel to those slots; and that the blade is tilted to 90 degrees.
            2. Orient all the strips so the concave edge (usually one of the edges will be more concave than the other) will be running against the fence.
            3. Set your fence so you'll be ripping approximately 1/8" off of the narrowest strip. then rip every one of the strips. Don't use a featherboard, but only hand pressure to keep the strips against the fence. The reason for this on the first rip pass, is that any concavity against the fence won't be passed along on the blade side, and it'll therefore result in a straighter ripped edge. Ensure you keep the strips as they come off the saw in the same orientation, as you'll be taking a second pass - this one on the opposite edge.
            4. Move your fence inward approximately 1/16".
            5. Turn all of your strips around so that the edge you just cut will be running against the fence.
            6. Perform the second rip, and again, ensure you keep them all in the same orientation as they came off the saw (as you may have to do a 3rd rip pass).
            7. Check each of the strips to see if you've trued all of them up and they're all the same width. If you feel you can do better doing a 3rd pass, then repeat from step 4, onward.

            I have also found that a longer fence will result in straighter rip cuts, so if the fence that came with your saw is relatively short, you can extend it by twinning a longer, and very straight board against it.

            Good luck with this and let us know how it works for you.
            Ken in Regina likes this.
            All the best,

            Marty

            - Instagram: @apexwoodworks
            - facebook: https://www.facebook.com/Apex-Woodwo...0243458908979/

            Secretary of Kingston Wood Artisans Inc. https://kwoodartca.wordpress.com/

            Master Mistake Fixer (because I've made them all... at least once)

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            • #7

              Re: Torsion box workbench top

              The problem with construction lumber is that a lot of the time it's green lumber meaning it's pretty damp and the boards get twisted pretty quickly when they are out of the bundle. If you get kiln dried lumber then that will be better and you can get kiln dried construction stock.

              An other issue is that construction lumber usually comes in a variety of species and are marked as SPF lumber. Spruce, Pine or Fir. And then there's sub species inside of those that make it harder to find good workable lumber for building a bench BUT if you go to a busy store you will see that the lumber on the rack will change every week. So you can go and find better lumber and when you see it you grab it.

              For me it took me a month to find the lumber for my workbench I was looking for lumber that didn't splinter on the rack. Saw mills usually have pretty dull blades on their planers so if a piece of wood comes out supper clean on the rack then it's probably going to work well for you in your shop. Again do not buy the green stuff buy the kiln dried stuff and go though the entire pile if you have too in order to get the straightest ones and when you get home pile them up with coles and let the air hit all the sides of the lumber for a week before doing anything.

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              • #8

                Re: Torsion box workbench top

                When I am doing strips with plywood I like using a straight 2x6 or 2x4 as a guide for my skill saw. I strip them thick by a quarter inch so I can finish it off on the table saw.

                Handling a big piece of plywood on a table saw can get dangerous. Not only because you might be handling a sheet by yourself which is super heavy and clumsy but if you do not have the riving knife on you are looking at a very serious knock back opportunity and it hurts because my table saw is just under my belt level... Don't ask me how I know that please... Just understand me when I say it hurts.

                If I had a track saw It would be used a lot in my shop to break down plywood especially.

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                • #9

                  Re: Torsion box workbench top

                  I have built a couple of torsion boxes over the years, the last one being the mattress base for the bed I sleep in. I watched enough of the WW video to see how he accomplishes level. His method is similar to mine except that he levels the sawhorses. I use BD Workmates and level the strips that I clamp into the jaws, not the sawhorse body. I think he adds a layer of complication by using those extra levelling boards. I didn't use them. Once my sawhorse boards were level (I made sure they were longer then the minimum required length), I laid my honeycomb rails across those sawhorse boards and glued/screwed the stiles into them. It has to be flat because the sawhorse boards were level in all directions and if you've cut your MDF rails/stiles properly they are all the same width and straight. I fastened the honeycomb to the sawhorse boards with temp screws, then glued and bradded the top onto the honeycomb. Once dry I remove the fasteners and flip it over, glue on the other face and clamp it all in place and leave it to dry.

                  If your sawhorse boards base is flat and level, if you saw your honeycomb parts all the same from stable material (MDF) and you fasten your glueup to the sawhorses until dry .... it has to be flat. There's no way around that.
                  Ken in Regina likes this.

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                  • #10

                    Re: Torsion box workbench top

                    So I re-ripped and did some shimming and got things close. Put the sheet of MDF ontop and proceeded to cut my pieces for the torsion box. My in-laws were here when the pandemic thing started so they've stayed with us. My wife and father inlaw decided to redo another room and borrowed a friend of mine's miter saw. I decided that would be a good way to cut the shorter grid pieces. Unfortunately something wasn't calibrated quite right so I had to re-cut all the edges which I did by making a simple cross cut sled (see pictures below)

                    Anyways Came across another issue using my sawstop. I got the sawstop at christmas so I'm kind of new to it. Already accidently set it off cutting pressure treated lumber. New break in it and as I was cutting the baltic birch a few times the saw would just shut off (not the break triggering) and the little light indicators would to solid red. According to their little chart it says replace the cartridge (this was newly replaced). Power cycling the saw made the problem go away, but it would happened a couple of times more. Anyone experience something like this before?

                    That was an aside.
                    Here is where things are at (see picture below).

                    To check for flat on the grid I used my 24" veritas straight edge and put my "tilt-box clone angle reader" ontop of it. It reads an angle to 2 decimal places. Going across the grid in checking in an x-y plane various places the range of variance was at most .05 degrees
                    I think that seems reasonable What do you guys think? I haven't assembled the grid, it's just dry fit right now. Click image for larger version

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                    • #11

                      Re: Torsion box workbench top

                      I don't want to sound like I'm suggesting not doing your best work, but I have a feeling that you have always been more than flat enough. The wood you are going to work with in the future will often move more than your variance as it's humidity levels change.

                      I do have a question..... your layout picture seems to show that your longest boards are the ones running side to side and the long runs are made up with short pieces? Is that correct?

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                      • #12

                        Re: Torsion box workbench top

                        Yes, that’s correct. That’s the way the wood whisperer did it I think? Except for outside part
                        Last edited by Windsurfer30; 05-11-2020, 11:09 AM.

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                        • #13

                          Re: Torsion box workbench top

                          It'll be interesting to see how well your benchtop works out over the years, as I most certainly wouldn't have oriented those long boards across the short span.

                          If I were you, then I would add two additonal pieces on each side, running the full length of the bench. Although that will add to the width of your benchtop, I believe it would result in a much stronger surface.

                          Originally posted by Windsurfer30 View Post
                          Yes, that’s correct. That’s the way the wood whisperer did it I think? Except for outside part
                          Last edited by MartyFromKingston; 05-13-2020, 06:13 AM.
                          All the best,

                          Marty

                          - Instagram: @apexwoodworks
                          - facebook: https://www.facebook.com/Apex-Woodwo...0243458908979/

                          Secretary of Kingston Wood Artisans Inc. https://kwoodartca.wordpress.com/

                          Master Mistake Fixer (because I've made them all... at least once)

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