Very STURDY and Flat 4'x8' Workbench Table

[See the Time-lapse video of construction here: youtu.be/BSR1VasltE4 ]

I need a big flat workbench to be able to work with 4'x8' sheets of plywood stock using my Handibot CNC router and its indexing jig. Doing CNC carving and engraving is very sensitive to how flat and stable the surface is. No flexing, vibrating or wobbling allowed. I looked at many workbenches on Instructables and elsewhere, and was surprised to find very few used any diagonal members, instead relying on very thick legs for extra strength, and very good mortise and tenon joints or metal braces at the joints. Why are bridges and geodesic domes made of triangles, not rectangles? Because a rectangle can easily become a parallelogram if its joints are not really stiff and tight. So my design includes diagonal braces made from angle-iron bars, adding huge stiffness without much extra weight. The idea of a 4x8' (1220x2440mm) table is to be able to quickly attach (with 4 wood screws) a sheet of MDF to its top as a "spoil board" when the previous one gets too messed up by the Handibot or whatever abuse you may cause while doing your DIY stuff. Because 4x8 sheets of MDF, OSB, and plywood are used in the construction industry, they are everywhere and pretty inexpensive. Because I used entire 4x8 sheets, this design DOES NOT require a table saw or circular saw. (Or a welder; you could make a very sturdy table by welding it together from square metal tubing, but I did not want to go there.) This one is bolted together, with the top fixed to the legs by 8 hidden 14mm barrel-nut bolts, IKEA-style. My design is a weekend project requiring a minimum of tools and expertise; it's very forgiving of imperfect timber and inaccurate measurements. Best of all, it's relatively inexpensive, about €100 for the wood, and €50 for the hardware (in Ireland).

Most of the steps in this Instructable have several photos with notes, so if you are only seeing one photo per step, download the PDF of all steps, or use your smartphone and the Instructables app to look at it. If you see a little pencil to the upper right, I wrote a comment or note on the picture. Click on the pencil to see it.

One key design feature is a 15cm (6") overhang past the underframe on all 4 edges that allows easy clamping of material to its top using C-clamps or other clamps (see photo). The thickness of the 4-layer table is 61mm. Many workbench designs are really thick, or have a very wide edge or undershelf that makes clamping difficult. I also did not want any low shelf near the floor to knock my shins and ankles against, or prevent rolling a chair up very close. If you have enough room in your workshop, it is better to separate the functionality of a workbench and a storage unit.

Materials

• (1) 18 mm sheet of OSB/3 (oriented strand board) 4' x 8'
• (1) 18 mm sheet of plywood - choose a flat one 4' x 8' ideally, kiln dried and/or adapted to the humidity of your workshop
• (2) 12 mm flat sheets of MDF (medium-density fibreboard) 4' x 8'
• (3) 3-metre long 4x2s (the Irish name for 2x4s) dimensioned and sanded framing timbers - Choose straight ones. Ideally, kiln dried and/or adapted to the humidity of your workshop
• (3) 3-metre lengths of angle iron 25 mm x 25 mm wide x 3 mm thickness
• (8) BIG STRONG M14 x 150 mm hex-head bolts (see photo)
• (8) big washers ~40 mm for the big bolts
• (8) big nuts for the big bolts, with Nyloc inserts
• (6) Hex head wood screws, 10 mm diam by 10 cm long (see photo)
• (5) Hex head metal bolts, M10 by 60 mm long, with nuts, washers, and split-ring lock washers
• (12) 80 mm wood screws
• (12) 100 mm wood screws
• (16) 60 mm wood screws
• (2) "Kallax" casters from IKEA (see photo), article # 002.886.57, which have two wheels each, one with a nice brake, and strong metal base, for only €9!
• (4) stair step planks or equivalent (see photo) for the legs, 35 mm thick x 23 cm wide x ~1 m long, depending on how tall you want the table top to be. I wanted not to always be bending over a too-low workbench, so I made the top just below my elbow height when standing, when the casters are installed. They contribute about 115 mm to the height.
• Paint to rust-proof the angle-iron (optional)
• Sandpaper
• Parchment paper for tracing
• metal-drilling oil

Tools

• Hand drill
• Goggles or face shield
• Dust mask
• Earplugs
• Gloves
• 14 mm spade drill bit
• 10 mm wood/metal drill bit
• 2-3 mm bit with countersink attachment, or a separate countersink bit, for making pilot holes for wood screws
• Drill press (optional)
• Various clamps including a right-angle clamp
• 36 mm and 44 mm Forstner bits (or hole saws or auger bits)
• Chop saw or mitre saw, ideally, one that can do bevel cuts. You could use a hand saw (for the wood) and a hacksaw (for the angle irons) instead, but that is a lot of work! A battery-powered reciprocating "saws-all" saw would also work.
• Handheld belt sander
• 19 mm socket wrench and box wrench
• Hammer
• Centre punch
• Tape measure
• Square/straight edge
• Grinder and/or hand file
• Pencil or scribe
• Sharpie pen
• Paintbrush

I used stair steps for my workbench legs, and oriented the rear legs at right angles to the front legs so that neither one could flex much in its weak (thickness) direction because the other would have to flex in its strong (width) dimension. Any planks thick enough to accommodate your strong bolts and strong enough to support the table and what you plan to put on it should do fine. I think the workbench ended up well over 100 kg, maybe close to 200 kg.

Decide on the height you want the workbench top to be, taking into consideration things like: Who will be working at the table and how tall are they with their work shoes on? If it is just you, that is easier. Do you prefer to work standing or sitting? If sitting, how tall a chair do you like? If you will be using certain power tools, at what height are they the safest and most effective? I decided to have the top just below my elbow, 1m off the ground for standing mostly.

Cut the legs to the right height, which is the surface height minus the caster height (~11.5 cm) minus the thickness of the layers of 4x8 sheets you will use, ideally measured from a clamped stack that you will actually be using. These are the 1. plywood, 2. OSB, and 3,4. MDF layers, about 6 cm total (see photo, prev. step). So for example, I cut the legs to be 82.5 cm long, using a sliding mitre saw I carefully set to cut a right angle across the thickness and width directions. In retrospect, it probably does not matter much if the cut is not square, as the metal braces you will use can set them right, like 4 crooked teeth!

Sand off any splinters, sharp corners and edges. The stair lumber came already rounded on one edge, and well planed and sanded all over. You can see some practice engraving I was doing with them as they waited to become bench legs. It is much easier to sand them now than later when the bench is assembled. You might even paint or finish them now, too, though I did not bother with that.

In the second photo you see a test of the barrel nut ("IKEA-style" bolt) idea in some scrap wood. With a socket wrench and a box/crescent wrench you can really torque the bolt very tight so the nyloc nut digs into the wood. I stomped on this joint with my steel-toed boots and could not break or even budge it. Nyloc nuts are great because they don't need lock washers and will never unscrew themselves over time, even if the bolt were to loosen due, e.g., to wood shrinkage. Orwa's Instructable describes an even stronger version that uses a piece of iron pipe as the nut, distributing forces across more wood than a standard nut does. But drilling pipe and tapping threads is a lot of work. I think it is overkill for my needs but maybe not yours.

The long bolts will go through the plywood and OSB, so carefully measure their thickness, subtract that from the length of the bolt as measured from the underside of a big washer under its hex head to its tip. Mark the legs to cut two holes near the top of each leg through their thickness, centred at this distance from the end, and spaced about 1/3 and 2/3 of the way across the plank's width. The holes should be big enough to fit your box wrench around the nyloc nut. For me, a 36 mm Forstner bit worked well. I also tried a 38 mm hole saw, but that was a lot of extra work, because the hole saw's teeth kept clogging with sawdust, and the holes needed to be drilled from both sides to go all the way through the leg. There are other ways you could cut holes in the legs. But the drill press with a Forstner bit was quite easy.

To drill the holes that the bolts go down to meet these big holes, I used a long 14mm spade bit in a battery-powered hand drill. I set up layers of wood and cardboard on a seat so that the bit was just at the right height for the leg (clamped to a low table) when the drill's battery rested on the layers. The layers slid easily as the drill drilled. Try your best to have the hole emerge in the middle of the big hole, or else it may be difficult to get the wrench on the nut later. I drew lines on the legs leading to the middle of the holes as a guide. Using a long spade bit helped me sight along it and keep it going straight in. Ideally, choose a bit that exactly fits your bolt, so the bolt is pretty hard or impossible to insert without a hammer. Then it will not wiggle in its hole when the table is bolted together.

The casters IKEA sells for their modular Kallax bookcases are reasonably sturdy and cheap. When cut in half, the base happened to fit the planks I used for legs nearly perfectly. I used my new Evolution Fury3 saw to cut them, very easily. Unlike abrasive metal cutting wheels, this saw blade has big teeth (for wood and metal) that produce big hot chips of metal flying everywhere. If you use one, be sure to wear a hat, apron (or lab coat, in my case), face shield, and earplugs. Before cutting metal, I also vacuumed up the copious shavings produced by the Forstner bit so as not to set them on fire. After chopping the bases in half, I filed the sharp edges and corners down on a bench grinder.

I drilled an extra hole in the bases, so that I used three long wood screws to hold each one to the underside (bottom end) of each leg. I did not use the little right angle thingy (piece of metal) included with the caster set, for putting a screw in on the vertical edge of a leg, but you might want to. It causes the caster to protrude past the edge of the leg and I thought that would be weaker than having it below the leg.

I used 4x2 timbers (dimensioned framing lumber or 2x4s in the US) to brace the underside of the table from sagging and as a frame to hold the legs in the right place. Put the timbers on edge so they are less inclined to flex under the weight of the 4'x8' sheets or the stuff you put on the bench. You could even double up on the beams for extra stiffness if needed. I used two long 4x2 beams that were cut to be 15.25 cm (6") less than the width of the table top on both ends, or about 213 cm long. I cut three 4x2s to 86.4 cm, minus the thickness of the two long beams so the frame is about 15 cm from the front and back edges of the table top. I used the OSB sheet to do this measuring and assembling. Because the concrete under the carpet in my workshop is not very flat, I moved into the living room to do this step, where the floor is flat and level. Hopefully, your partner is as understanding and supportive as my wife is!

I used a right-angle clamp to hold the frame's corners while I drove two long woodscrews into each joint. I used a small drill bit with a countersink attachment to make pilot holes through the first piece of wood for each joint. That way, the screw's threads will grab the 2nd piece of wood and pull the two together more tightly than if no pilot hole is drilled. The countersink allows the screw head to be recessed into the wood where it won't scratch you later. A good battery-powered drill is your friend here. You may have to use it on the DRILL setting when screwing in the long screws, as the torque for the SCREW clutch setting may not go high enough. I used two hand drills, one for drilling pilot holes and one for screwing screws, just to avoid changing bits and settings a lot.

One of my 4x2s was twisted and the screws were only somewhat successful at unwarping it. So when getting wood, be picky and choose pieces that are straight.

Note that the final layering I used has the plywood as the bottom layer, NOT the OSB, because plywood is better for clamping to than rough OSB. I used the OSB to build the underframe on because it was quite flat and the plywood was still unwarping under the sofa (see below). You might save time in the next step if you build the underframe on the plywood instead and mark the plywood with the frame and legs' outline instead of marking the OSB.

Plywood flatness issues. I noticed that my 4'x8' plywood became quite concave soon after I got it. It would have been on the top of the stack at the lumber yard, so one side was getting different humidity than the other. I mopped the concave side with water and weighed it damp-side down against the flat living room floor with heavy sofas for a couple days. That helped a lot, but clamping it later between flat OSB and flat MDF really fixed it.

Once the underframe was assembled, I used a few diagonal wood screws to temporarily hold it to the OSB in just the right place and traced its outline on the OSB with a pencil. I clamped each leg to the frame, one at a time, being sure they were resting flat against the OSB before tightening the clamps. As noted above, the two front legs are oriented facing left and right, while the back two legs face front and back. This makes the whole thing much stronger than if they were all parallel to each other. I screwed each leg to the underframe with three long wood screws each, again using the countersink drill bit to put pilot holes in the legs first. I traced the outline of each leg on the OSB with a pencil

Then I took out the temporary screws holding underframe and legs down to the OSB, flipped the frame over onto its casters, and did the bolt-hole locating in the next step. Then, I rolled it back to the workshop for the rest of the assembly.

Using 4 big pieces of vellum or parchment paper and a Sharpie, trace each corner (each leg) of the marks you made on the OSB very carefully and note which corner and which side represents up (towards the ceiling) or down (floor) for the finished installed workbench. So the OSB, with its pencilled outlines is upside down during the first step of tracing, and the vellum is upside down.

The second step of tracing is to flip each vellum over (now right side up) and lay it on the top of the correct leg, carefully position it, and trace the bolt holes you drilled into the ends of each leg. Mark their centres and draw an outline of each of the 8 holes.

Next, carefully position the OSB right side up on top of the frame using the pencil lines you drew on its underside. Use a centre punch and hammer and your vellum tracings to mark where to drill the OSB on its top surface. Again, be careful you got the right corner and the right orientation for each component. Because oriented strands in OSB are chunky, the punch may not go exactly where your mark in the tracing paper was. You might use a narrow chisel or Dremel or something to create a pilot hole instead. Precision of better than one mm is important here.

Drill a 14mm hole through the OSB at the first location you punched, and hammer a bolt through it and partway into the leg, so as to hold the OSB in position for the rest of the process. Insert bolts (part way) as you go, to ensure they all can fit into the legs' holes at the same time.

If you got a nice flat plywood sheet, and used that to build your underframe, then you could be drilling both the OSB and plywood clamped together, in one go. Instead, I took out all the bolts, laid the plywood on a sheet of MDF to protect the floor and drill bit, laid the OSB on top of it top side up, clamped them together, and used the OSB as a stencil to drill all 8 holes through the plywood in the exact same location as the OSB. This was also useful to put 8 marks in the underlying MDF to locate where to drill big holes that will clear the washers.

As my Forstner bit was not quite big enough for my washers, I used a hole saw and hand drill to cut holes through one of the MDF sheets at the 8 bolt locations. Again, make a note on the MDF of which side is up and which way it faces. I had it wrong and had to flip the MDF over when I figured out why the washer holes did not meet up very well with the bolt holes.

Line up the plywood and OSB again on the underframe, and hammer the bolts all the way in with their washers. Tighten them with a ratcheting socket wrench on top and a box wrench (or non-adjustable crescent wrench) on the Nyloc barrel nut. Do one bolt for all 4 legs somewhat loosely before adding the second bolt for each leg and tightening them all really tightly. I learned by working on cars that you should always put all bolts into an assembly loosely first, then tighten them in a distributed or cyclic sequence.

Next lay the MDF sheet with washer holes onto the OSB, then the last MDF sheet on top of that. Line them all up perfectly, clamp, and drill 4 countersink/pilot holes (stop at the plywood top surface) near the centre of each benchtop edge. Screw all the sheets together with 4 long wood screws in those pilot holes, being sure the heads are below the surface.

Now that the table is assembled, it seems pretty sturdy. But by adding diagonal beams, it will be much less prone to wiggling, flexing, vibration, etc. Rember: Triangles=strong; rectangles=flexible. Also, putting the casters on and off one at a time is stressful to the geometry without the metal cross beams (more on that later). You may have noticed I had the beams on already in the last step. I thought that it might be easier to install them with no top on the table, but I don't think this is the case. I think instead that it is better for it to all be bolted together well with the top on before measuring the beam lengths.

Use measurements taken off the table itself (not your cool Sketchup or notebook drawing) to determine just how long to cut each piece of angle iron. This is in case the legs are not perfectly built and vertical after all the sawing, screwing and tightening. I used two long pieces to go diagonally in an X between the rearmost edges of the front legs.

On a previous workbench that I made years ago, I found this cross (with a pad on it) to be a handy foot rest when sitting. And the beams are back far enough that I won't be banging my ankles or shins against them when standing next to the table. I used one shorter piece on each side to go from the outside of the top of the front legs, down to the lower outer edge of each back leg (see photo).

Optional for rust-proofing/aesthetics: I painted my angle iron, after washing off oil and rust that was on it with soapy water. I used a water-based house paint, but you might want to choose something else. New rust came through the paint (see photo) when I left the angle iron outside overnight and the dew made the paint wet again after it had dried. So I did another coat of paint, this time on a warm sunny day.

I used the bevel and/or mitre features on the Fury3 saw to prevent having sharp 90° corners sticking out anywhere, and also ground down all the cut edges on the grinder. As with cutting the caster bases, be careful of flying metal chips when cutting and grinding the angle iron. Your eyes are precious! (We had a sign up in my lab near a powerful laser on our microscope: "Don't look into laser beam with remaining eye.")

I used a 10 mm Si-Nitride drill bit and lots of cutting oil on the drill press to drill a hole (or two, see photos) near each end of each bar, and in the middle of one of the long bars. Be sure to clamp the bars to the drill press table, and support them at their other end with something of the correct height. I drilled the middle hole in the second long bar using the other long bar's middle hole as a guide, using a hand drill. With a wood bit and a hand drill, drill 10 mm holes into the edges of the legs, or through their thickness, using the actual bars as measuring devices, and a centre punch and hammer to mark where to drill. Use a socket wrench to bolt the bars on, using regular M10 nuts and bolts (with washers and lock washers or Nyloc nuts) when going through the thickness of the legs, and using big 10 mm hex-head wood screws when going into the edges. Drill the wood and bolt one end of an agle iron on, then mark where to drill the wood at the other end of the brace, using its hole as a guide. This is your last chance to do any orthodontic work if needed, to straighten out something.

For the cross bolt in the middle of the long beams, I used some nuts, flat washers and lock washers as a spacer so I could make the bolt very tight without twisting the angle iron (see photo).

Should you even bother with casters? My lab had all its lab benches on casters and we found that to be very helpful when we needed to change to a new project, or got new equipment or personnel. Or if we just wanted to re-arrange things to keep it fresh and efficient. Since this workbench is so heavy, the casters really help when I want to work in the middle of the room, and can put the table back against the wall at the end of the day if I want to park the car in there. But for maximum sturdiness and stability, leave out the casters.

I walked the aisles of several hardware stores trying to find something inexpensive I could use to lift up the table legs enough to safely install or remove the casters. Otherwise, it would take two strong men to lift while a third brave person puts in the caster. I thought maybe a hoe or prybar would do, but could not find one that was sturdy and able to lift something up 12 cm. So I made a lever out of all-thread and leftover angle iron. Leverage works! As you can see in the photo, my first attempt, using only single angle iron, was not strong enough; it just bent. By doubling up the angle iron into a box girder, it was plenty strong enough to lift each leg. I would advise having a helper insert a big block of wood of the appropriate height under the leg and let it rest on that while installing a caster, rather than hoping the leg does not fall off the pry bar with your fingers under there.

I used a belt sander to round all the corners of the table to prevent bruises and scrapes. I chamfered the top edges that my forearms will be resting against at times, for comfort. MDF makes for easy sanding.

I did not apply any finish to the wood, though the stair step timbers were already weather-treated. I cut off excess bolts protruding from the legs using a reciprocating saw, and filed them a bit to get rid of any flash.

If you pay attention, you can see me in the video wiggling the frame and jumping on top of the table to test how sturdy it is. I was very happy with how this one came out, strong and flat to within a mm or two across the whole 4x8' top. I imagine I will have to add more beams or at least a few shims to the underframe for maximum flatness, as the wood dries and changes shape. The next version will probably be welded from metal....

Please post your comments and suggestions for improvements below, and if you make one, please post a photo of it here and create your own Instructable!