Twisted worktop?

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  • #698465
    Matt Cromwell
    Participant

    I’ve started making the workbench but have hit a snag rather quickly. I planed and glued the worktop and cut it to length, then very laboriously planed out all of the rounded edges on what i’d decided would be the top side. I set it aside for a weak or so stood on end as i was busy with other things. Now i’ve gotten it out and set it out across 2 benches to do the back and have realised it’s got a massive twist in it, it teeters back and forth between opposite corners when i lay it across my 2 benches. It does this on both sides. No idea how i could have missed that the first time round, or if it’s possible it developed a twist since the last time i touched it? Either way i’m wondering what to do now, to get it flat i feel like i’d need to plane 1/4″ (a guess) off each corner to get it flat on both sides, and with a hand plane that would take ages… Ideas?

    #698467
    Jonas Ericson
    Participant

    You’ve learned the hard way. Wood moves with changing humidity… Only way to get it decently stable is to drench it with epoxy and this is rarely a practical solution. Though thinner stripes glued together are normally relativaly stable.

    I recommend that you let the slab acklimatise for a while in the humidity you will mostly work in. It may reduce the twist a bit (or make it worse), then plane it again. Planing 1/4″ is quickly done with a scrub plane. If it keeps twisting I fear there is no other way than start over again nd be careful to choose stable wood (quarter-sawn)

    #698477
    neil grayson
    Participant

    Leave it flat for a few days and see what happens then do as needed.

    I made the same mistake but the twist was small maybe 3mm but I only realised when I lay it on the completed legs. I thought jee whizz the leg frames are heavy perhaps it will settle down and untwist again so I carried on. When I screwed the top to the frame the gap disappeared. Yay I thought!!

    Nope! What had happened was the leg had been lifted by the twist and because my garage floor concrete is crumbling and uneven I had not noticed.

    Worse is that although 3mm the gluelam is only half the width of the leg top so effectively the top magnified the error by around 2 (as a lever would) so now one leg sits around 6mm from the floor.

    It has moved slightly down over the last 6 months but definitely DO resolve the issue before carrying on.

    My only options are to make a new top and run a saw down the glue line between the old top and apron and do it properly or since it is too high and I need to lower it correct the wobble cutting the legs. The top side is flat and true so that is an option.

    Having said that given it’s the first thing I have made since leaving school 50 years ago its turned out pretty well. Standing on the shoulders of a giant like Paul has helped enormously and most people dont even see the issue currently fixed by a wedge but I will always know it’s there.

    #698480
    Darren
    Participant

    When you said “stood on end” do you mean vertical?

    When you are milling up boards it’s always best to leave flat on a side edge, and not up against anything. That maximises the surface area for even drying.

    You could try leaving the top like that for a while to see what happens.

    When I made my workbench I used reclaimed construction pipe, which was already pretty dry. Every time I’ve used new pine I’ve had a lot of trouble with movement of one form or another. Even so, my bench still expands and shrinks quite a bit with the seasons.

    If you have to remake it, leave a week between milling and glue up, and leave the boards flat and on a side edge, with good air gaps between them.

    Good luck.

    Darren.

    #698493
    Benoît Van Noten
    Participant

    1. To avoid board twisting, always plane the two sides the same day, if possible; otherwise the humidity will leave the board on the freshly planed side more than from the other side.
    Skim a layer from the underside. Then wait a week and see what happens before trying to correct the remaining twist.

    If you make a new bench-top, don’t try to directly flatten the top while leaving the underside untouched. Remove first a layer on each side, wait at least a week before the final flattening.
    This is a question of taste, but the workbench would perfectly be usable with the rounded edges still partly visible. I would have waited a year before eliminating them completely.

    2. The underside of my bench-top was apparently not perfectly out of wind (the two areas were it sits on the two leg-frames) and the workbench was rocking.
    – I have unscrewed the top from one leg-frame;
    – put a shim between the top and the leg-frame where appropriate;
    – screwed again the top to the said leg-frame.

    The workbench doesn’t rock anymore.
    No need to re-cut a leg. It could also be a solution for an uneven floor.
    A shim between the leg and the floor would probably not stay in place.

    #698514
    Cunha
    Participant

    You may want to find something to use for winding sticks before doing anything drastic. The two benches aren’t necessarily level or parallel. Also, if the heights are different but parallel the benchtop will rock if not perpendicular to the edges.

    Winding sticks will be the simplest method. If you have a precision machinist level you can test each end and try shimming a beam across the face to see what your difference is.

    Hopefully you are being misled by something that looks worse than it is.

    When you know more, post some info like how much twist, the thickness and width of the benchtop and the material. Your initial question asked if the top could have moved since you made it. If you aren’t using winding sticks you may have put the twist in when you planed the first side. The ability to rest on two benches is probably not the best gauge of flatness.

    #698758
    Benoît Van Noten
    Participant

    To flatten my workbench top, I had no reference flat surface available to test rocking and anyway it would give no other indication than twisting or bowing.

    I used winding sticks and a “straight edge”. (I used solely a “short” #4 plane.)
    The straight edge would “helicopter” on bumps.
    The center of the straight edge would not drag on hollows.
    Taking fine shavings on the high spots, finally the straight edge should drag everywhere (placed along, across or diagonally).

    The “straight edge” was just an inexpensive 1 m aluminium rule not a certified straight edge. Good enough for my 1.5m long workbench.

    #701363
    Debra J
    Participant

    I just glued my benchtop to the front apron and found a small gap between the bottom of the benchtop and the top of the leg frame. Best guess is I did not plane square the meeting faces between benchtop and apron. I had worked to get the twist out of the benchtop bottom and was pretty happy with it.

    After reading the comments above, I think I will squeeze a shim between the leg frame and benchtop. Seems like the least destructive option.

    Gap under benchtop

    - Debra J

    #701458
    Benoît Van Noten
    Participant

    Is the gap visible and the same above the two leg-frames?

    In addition to a twisted top, there are a few other causes possible:
    – the floor not being flat (then the two leg-frames bearers might not be parallel);
    – the two leg-frames not being identical (visible when placed against each other);
    – The apron not being square to the top;
    – the leg face not being square to the leg-frame bearer;
    – the housing in the apron not being of consistent depth;
    – the apron being cupped (convex on the inside face).

    The easiest thing is to place the workbench where you intend to use it and put a shim in the gap. It should cure any of these problems.

    #701574
    Debra J
    Participant

    That is exactly what I did. The workbench is set up where it will be used and now has a thin shim between the legframe bearer and the top.
    I cinched a long clamp across the aprons above the leg frames and then drove screws up into the bearers and through the benchtop. Nothing rocks and all four legs are square on the floor.
    Pretty happy so far.

    - Debra J

    #701594
    Roberto Fischer
    Participant

    Debra, that photo looks like it was taken if my workbench. Same exact thing happened to me. In my case, I can swear I checked for twist where the legs would rest but it’s like this nowadays.

    I’m actually considering planing the bearer itself. Haven’t done it. It doesn’t seem to be affecting anything and I haven’t needed my top to be an actually flat surface yet.

    #701695
    Debra J
    Participant

    Roberto, I checked for twist also and planed the underside until it was free of twist. I believe the meeting faces between the apron and the side edge of the benchtop were not square. I neglected to check before glue-up and it’s too late now!

    Fortunately the gap underneath wasn’t too huge. The shim was only needed on one leg frame. First, I did plane the tops of the leg frames (the bearers) and got them level with each other. They were both a bit twisty. If you do that, make sure your screws are well below the surface.

    I apologize to the OP for completely hijacking your discussion thread. We had the same problem with the worktop at the same time.

    - Debra J

    #701847
    Benoît Van Noten
    Participant

    Finally I don’t know for sure which was the cause of my workbench rocking. I did not thoroughly investigate.
    One can see the small shim on my workbench:

    DSC038512

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