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I need to build a few workbenches for my office at work. They won't be used for true "shop" work but will need to be fairly strong, as there will be equipment and tools on them. I am planning on painting the top, so I don't care about the raw look of it.

To save time on the construction, I am planning on a tubular 3/4" galvanized frame like this: Img 1

For the tabletop itself, I am thinking of an IKEA solid oak 1 1/8" countertop

My worry is that since the tabletop will be around 8' long, and it won't be supported along the length like a standard wood frame, it will be prone to warping/bending/weakness along the unsupported areas.

The options I see are:

1) Add third set of tube supports in the center of the table, so it will now have 6 contact points. I think I should do this regardless of other measures I take.

2) Add an unsupported oak apron around the edge of the top.

3) Support the tabletop with some sort of metal structure.

4) (The option I am leaning toward) Fiberglass the top and bottom with some glass, like how a boat composite is made. This has the advantage of making a nice durable finish on the top that is easy to paint. Also strengthens the tabletop overall, and will solve any poor gluing issues by IKEA.

Let me know what your thoughts are!

Kyle Hunter
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  • It's right to be cautious, but this is oak and really quite thick (and made from glued up staves, so not really that similar to solid wood or a couple of planks glued along their edges). I plugged some numbers into the Sagulator to get a rough idea and it gave me a figure of Acceptable, with a 100lb central weight..... so I think you're good as-is! – Graphus Mar 24 '19 at 19:45
  • If you do decide to add an extra set of legs then you definitely don't need to do anything else as far as support for the top goes. There are some potential worries about racking forces which someone else might bring up, but I think you're fine there if these won't be used a true workbenches where you'll be pushing into them with tools sideways or inwards. If you do want to add some strength in this regard I'd add a second set of 30" connectors. – Graphus Mar 24 '19 at 20:15
  • The top will want to expand and contract in width during the seasons so it is good that the horizontal connecting pipes are 18" below the wood top. The pipe does not expand/contract and would not allow for movement if just below the top. Being down the wood movement should be absorbed by the pipe frame better. Any oversize of the holes (vs. screw width) in the pipe tops will also allow for the seasonal movement. As for any racking the pipe connections should easily resist that. – Ashlar Mar 25 '19 at 00:13
  • @Graphus Great that makes sense. Yeah I figured I was being overly careful. That's just because it's in a professional office and there will be expensive equipment on it. Yeah, there shouldn't be any lateral force, all should be straight vertical. – Kyle Hunter Mar 25 '19 at 00:38
  • Could you share how you did the sketch? It looks neat! As an aside about the construction: You have nothing dedicated to shearing forces (someone heavily bumping against the tabletop, worse if the feet happen to be unfree to skid) - as you seem to be using some sort of scaffolding parts (?) How about doing two diagonal struts (front left lower to right back upper and vice versa)? – loonquawl Mar 25 '19 at 09:07
  • Your table top will be fine, but I'd be concerned about racking of that pipe frame. – CoAstroGeek Mar 25 '19 at 15:29
  • @loonquawl I just found it on google actually! – Kyle Hunter Mar 25 '19 at 17:45

1 Answers1

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It's right to be cautious, but this is oak and over an inch in thickness which is really quite thick as far as tabletops go. The Ikea countertop material is also made from glued staves1, which isn't really that similar to a single wide board or 2-3 planks glued along their edges and is likely to be significantly stiffer than either.

But as it's best to err on the side of caution when I plugged some numbers into the Sagulator I ignored this likely advantage and basically did a worst-case scenario, assuming a very large central load and it gives the sag as Acceptable. Total sag was given as 0.13", which may be too small to see with the naked eye.

Even changing the width to the full 78" and the depth from 30" to only 25" sag is Acceptable, with a total of 0.19". Beyond this, using the original numbers but changing the material to numerous species of pine the sag is still acceptable because of the thickness of the material. So I think you're good as-is!

Other factors
There are some potential worries about racking forces with this design, but I think you're fine if these benches won't be used as true workbenches where you'll be pushing into them with tools sideways or inwards.

Wood movement is never something to ignore with a top made from solid wood and not a manmade board material like ply or MDF. For an 8% change in moisture content of the wood the calculated movement in flat-sawn oak 30" wide comes out to nearly 0.9", which is I think a little more than the flex in the structure would accommodate2. So some allowance for movement should be built in. This is easily done, e.g. by wallowing out the holes in the floor flanges which will be used to mount the wood top (ignore the ones that go on the floor). You could alternatively use screws that are a loose fits in the existing holes but in general it's better to use shorter, stouter screws than longer skinnier ones.

One last note, as you're working with hardwood you'd be advised to drill pilot holes for your screws. Be careful doing this so as not to drill through the top of the workbench! This is surprisingly easy to do and most woodworkers have made the mistake at least once LOL The small holes that result are patched easily enough (especially here since you plan to paint the tops) but obviously you want to avoid the extra work if you can. The old standby, the tape trick, is the easiest way to help prevent drilling too deeply.

1 A construction method these days often, but misleadingly, referred to as butcher block.

2 Your movement could well end up being less than this but it's best to account for maximum movement rather than undershoot and have things be put under stress (which can lead to stripped or broken screws and a wobbly table at the end of the day).

Graphus
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