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  1. #1
    Join Date
    Nov 2014
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    Istanbul
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    Default First Dinner Table Project - Guidance required please!

    Hi all,


    Very new to this website. I am no expert in woodworking, but I thoroughly enjoy it as a hobby which brought me to build a dinner table for my wife in time for xmas (as we have guests coming over!)

    I have made a plan to have a wooden tabletop, supported by metal legs.

    The wooden top consists of 3 planks of pine (W=350mm, H=80mm, L=2100mm) joined side by side on the length.

    The legs will consist of two square metal frames (section: W=40mm, H=100mm). It is quite a simple design I think but I have some doubts on the following:



    1) What is the best recommended way to join 3 large planks of pine wood along the length (I have read up on biscuit joining, tassels or just using glue based on the direction of the grain)?

    2) I plan to have a groove cut perpendicular to the pine planks of 40mm depth around 300mm from each end of the table so I can fit the top part of the metal frame that will serve as legs. The whole top section of the metal will then dissappear into the planks. Do you think this will be enough in terms or structural strength of the table?

    Any comments or recommendations most welcome at this stage. Thanks!

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  3. #2
    Join Date
    Nov 2007
    Location
    Albury Well Just Outside
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    Default

    Firstly welcome to the forum.

    Joining the planks of wood along their length is long grain to long grain and it produces a very strong bond.

    Recessing the square metal frame into the table top by 40mm leaving 40mm sounds adequate as you are leaving a lot of meat in the table top.

    One thing thou not knowing how the square frame is constructed I will mention that it might need bracing if the frame is made up from flat metal welded together.

  4. #3
    Join Date
    May 2003
    Location
    Central Coast, NSW
    Posts
    3,330

    Default

    Yep, only glue is needed for a join like that. Biscuits etc are more an alignment solution then a bonding/strength solution when joining longgrain.

    But, I do have some severe concerns about what you are planning to do.

    My main worry is that the table top will be massively heavy, and yet you haven't mentioned how you will prevent it racking. Imagine someone giving a shove to the top from one end - once that top gets started moving it will be very hard to stop and those legs may not do it. You almost couldn't have enough cross-bracing to keep that monster rigid.

    Another point to consider is expansion/contraction. The table top will expand and contract significantly (across the grain) as atmospheric conditions change. Usually, table tops are fixed to the legs or subframe in a manner that permits the top to expand across the grain. That's why they are seldom simply screwed on, its usually a matter of using fixing buttons or slotted holes etc. You will need to allow for this.

    Are you planning to simply screw through the steel frame into the table top. If you do, then remember that pine is soft so over time the screws will work loose. You may end up with slight play in the table after a few years.

    Finally, while I'm at it, I have some reservations on the design as well. Most of us would aspire to a 40mm top on 80mm legs. That looks right to most people - nicely balanced. I am concerned that a 80mm top on 40mm legs will look like a great heavy top perched precariously on spindly little legs. Of course you should ignore this if you have considered it already and found a design for which these sizes still work.

    Also, consider weight, and how it will be moved. I don't much like living in a house with lots of very heavy furniture. That's what we have and now I'm getting older its a pain - things like painting a room are suddenly twice the job they should be.

    cheers
    Arron
    Apologies for unnoticed autocomplete errors.

  5. #4
    Join Date
    Nov 2014
    Location
    Istanbul
    Posts
    4

    Default First Dinner Table Project - Guidance required please!

    Thanks Christos and Arron for the valuable and quick feedback.


    Let me try and answer / clarify some of the points you raised:

    1) About the bracing I did not plan to do one. The idea is to have the metal frames recess into the wood, then have perpendicular metal plates (which will be in the direction of the plank lengths) screwed into the wood for additional rigidity. That is the plan but at this stage I am unsure whether this will be rigid enough

    2) The metal frames are hollow and 100mm by 40mm. I calculate the weight of the tabletop to be about 80kgs (based on a pine density of 0.45g/cm3. This is quite heavy and the idea is that it ensures that it someone shoves it it will be difficult to topple or move something that heavy (unless done purposefully)

    3) I understand the point about aspiring to have 40mm top with 80mm legs. I have attached some drawings on sketchup and I like the idea that the focus is taken off the legs and more on the tabletop to have a 'float' feel. This is the idea, maybe the execution won't allow me!!

    4) I must admit I did not consider expansion/contraction in this design. I don't expect the table to move location, although the seasons here fluctuate quite a bit with humidity. Should I allow a little bit of clearance on the recess (The recess will be the width of the metal frame, 100mm plus a few mms either side).

    Here are the drawings (and a sketchup file) below to give you an idea. Thanks again for sharing your experience and expertise!

    Screen Shot 2014-11-24 at 5.11.00 pm.jpgScreen Shot 2014-11-24 at 5.11.27 pm.pngDinner Table Design v1.skp

  6. #5
    Join Date
    May 2003
    Location
    Central Coast, NSW
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    Ok, my mistake. When I read 'square' metal frames I thought you meant square section (ie 40 x 40mm). Now I realise they will be 40 x 100 mm then that nullifies my comments on design.

    Fixing the legs with metal plates changes things too. Whether it will make it rigid enough I cant say. At a minimum I would look for some type of inset that you can screw into, rather then screwing direct into the pine (pine being soft).

    Expansion and contraction is only significant across the grain. Expansion in the direction of the grain is usually so small as to be ignored for construction purposes. Hence you dont need to make the 100mm grooves wider. What you need to do is avoid binding the top rigidly to something which does not expand in a like manner (like steel). With components as large as your table the expansion is effectively an unstoppable force, so its effect over time will be that something has to give and it will probably be the tightness of the screws in the wood. A common strategy here is to use slotted screw holes in the steel. This allows the screw to slide across the steel as expansion/contraction occurs.

    All these comments assume you want the table to last forever. If you are just after something of a relatively short lifespan (a perfectly reasonable approach, especially with a first build) then they are not so important.

    Cheer
    Arron

    Cheers
    Arron
    Apologies for unnoticed autocomplete errors.

  7. #6
    Join Date
    Jun 2012
    Location
    Brisbane, Australia
    Posts
    142

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    G'day,

    I'd echo the concerns about the legs under racking force.

    I have just finished a 'similar' table: http://makimaki.com.au/gallery/lina-outdoor-table/

    A brace between the legs would be cheap, sufficient and not be seen. If you're worried about having it as one piece, make it separate and have some threaded holes tapped into the legs and brace piece and bolt them together (use 2 holes at each end to eliminate and swivel).

    Cam.

  8. #7
    Join Date
    Nov 2014
    Location
    Istanbul
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    Default

    I must admit, I am learning new things with every post.

    @ Arron you were right on my quote I had put a 'square' in the description. Sorry for the confusion, need to be more accurate so as not to create confusion. I am looking into raking but I am unsure what you mean by this (does it mean that the table may sag at the middle between the legs due to the weight of the tabletop?). I will take your idea about the slotted screw holes to allow for expansion perpendicular to the grain

    @ Cam I really like the design of your table, Haven't seen one with angled legs like this. Did you put a brace which fits in a recess under the tabletop in your design? Christos made the same comment about the brace. Could you share a picture of the underside of the design you shared to see how you allow for wood contraction / expansion?

    Thanks guys, this is really helping this eager newbie

  9. #8
    Join Date
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    Albury Well Just Outside
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    You are effectively making three pieces, the top and two legs. Let's say you are standing facing the table with it's longest edge in front of you. I would guess the racking would be more pronounced front to back then it would be left to right. Of course if you locate the legs closer together then left to right will come into greater effect.

    You could try testing what effects the legs have in different locations. On a flat level ground, set the legs down and then place the table top on them. Clamp the legs to the table top then push with one finger to see if this wobbles. You should be able to adjust accordingly. It would also give you a visual of what it would look like once put together.

    Another thing to note handling a table top on your own might not exactly the best thing to do and might require a second person to assist.

  10. #9
    Join Date
    Jan 2012
    Location
    Toowoomba QLD
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    62

    Default

    For fixing the table top cut slotted holes in the steel and use coach bolts with washers. This will allow expansion/contraction and the coach bolts have a course thread allowing them to hold better in pine. Might need a few though

  11. #10
    Join Date
    May 2003
    Location
    Central Coast, NSW
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    Racking is what happens to a square when you apply sideways force to one corner only. Imagine a square with one side flat on the ground, push it in the top left corner, and it wants to become a rhombus.

    Why would this happen to a table? Well, never underestimate the potential of children, visitors and removalists to do really stupid things to your furniture. In Turkey, you may need to think earthquake too.

    Really, though, its the tiny, everday movements that causes the problem, not the rare big ones.

    Racking is a very hard stress to resist. Its usually done by diagonal bracing.

    Because most of us are not engineers and dont know how to properly calculate racking forces the only thing we can do is overbuild things to make sure it not going to be a problem.

    Cam's table is interesting because it hybridises both the vertical leg and the diagonal brace into one component. Its still braced though, and intuitively it looks stable.

    Arron
    Apologies for unnoticed autocomplete errors.

  12. #11
    Join Date
    Nov 2014
    Location
    Istanbul
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    Default

    Guys,


    Thanks so much for your feedback. I am taking this all onboard and will look at adding an additional framing underneath the top to address the raking.

    Tomorrow I will have the tabletop delivered (with biscuit joints and the recesses for the legs done).

    I am quite excited to have a try with the metal frame legs to see how it holds up initially. I will ask some friends to help though as this tabletop is going to be heavy.

    Will keep you posted, and I really appreciate this community and the feedback/advice you are all sharing.

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