Sunday, 12 May 2013

A Tale of Two Tables: 1. Grand Designs

There has been a large rectangular hole in our home ever since we got married. Our first flat was unfurnished so we begged, borrowed and freecycled the furniture we needed. The table is the only piece of furniture left that is on loan. More than a year ago we decided to start planning and, several design iterations and a house move later, construction is now under way. The biggest challenge to be faced in the design was meeting our own requirements! We want something that will suit the two of us eating breakfast, and something that will sit all our immediate family for an extravagant Christmas dinner. That meant an expanding table.

I should warn you now this post is long and features lots of numbers and theory - just wait for the later ones if you would like pictures!

Both of us had come from family homes with tables that could expand to some extent or another. Jenny's parents table slid apart and clipped an extra leaf in. My parents had an unusual antique design that expanded / contracted with a threaded rod up the centre of the table (like this one). The threaded rod meant it could properly clamp down on the extra leaves and expand a large amount without sacrificing too much strength. This is important but I shall come back to it later.

The first thing to do was work out table sizes. Based on our design criteria we decided we needed to sit 6 comfortably, 10 expanded but should be able to squeeze 12. This is where it is time to crack out some maths. We assumed that we would sit one person at the head / tail of the table and the rest along the side. Assuming the table is somewhere between 3 and 4 feet ( ' = feet, " = inches for those new to old units) wide the lengths are relatively simple. Allow 12" from each end for the end sittings. Along the sides each place needs 24 - 30 " for a generous sitting. We measured and decided that 24" seemed ample for us - our dinner setting with room either side fitted easily. This meant we needed a 6' table that could expand to around 10'. The width was an easier matter of measuring how far we could comfortable reach to pick up a plate from over a table. We settled on 42" (3'6" - for some reason table widths are normally defined in inches) as being big enough to get plenty of dishes in the middle but small enough to clear both sides at once.

Asking a table to stretch that far requires some careful consideration of the physics. There are three main methods of expanding a table, all boiling down to the frame beneath.

  1. Keep the legs in the same location and extend the overhang of the top.
  2. Stretch the frame and keep the legs at the corners of the table (inset or otherwise).
  3. Add extra legs to support an extended top.
These designs have some limitations for us. The first is typically limited to an extension of 24" or so (like this)- otherwise even with additional frame beneath you gain too large an overhang. This is a problem because people tend to lean on tables, even push against them when standing up. Imagine your largest friend (don't name them, just imagine them) pushing on a table top with a two foot overhang. Its going to need a lot of support! With normal table top thickness (3/4" to 1 1/2") an overhang of up to 12" is workable. This method isn't going to manage our 4' extension!

The second design allows a slightly larger extension than the first but still struggles with enough strength for large extensions. The frame needs to overlap sufficiently to still provide strength in the centre of the table when extended. This can be done - my parents table (mentioned earlier) manages it by using a threaded rod to clamp the two halves together. This keeps everything more rigid and stops it twisting, reducing the load on the centre of the frame when loaded. Still hard work on the wood and perhaps worth seating your largest friends nearer the legs (in the nicest possible way).

The third method does allow a large extension - almost any size imaginable but adds extra legs and is often done with drop leaf tables, blocking leg room when in the reduced size configuration.

Owing to the cumbersome nature of the drop leaves we decided to try and plan a table based on the second design. I found suppliers for a coarse threaded rod and worked out the combination of bolts to allow one end to rotate but not move and the other end to slide up and down the bar. Then we bought a house. This is the quickest way I have found yet to derail a project! By the time we got back round to the table it was winter and our loaned table was in the corner of the kitchen rather than the conservatory where it had been all summer. We had accepted this when we got the house and decided we would build our grand table in the conservatory and abandon it each winter for a second hand table that we would find for the kitchen. Then we realised we could kill two birds with one stone and settled upon our final plan - a variation of the add extra legs design.

We decided to build two tables. Both the same width, one 6' long and one square that when placed at the end of the other would extend it to our magical requirement of seating 10 people. A kitchen table and a dining table, which can be brought together to make a banqueting table.

The positioning of legs still required a little work - in order to be able to sit the full number comfortably when the two tables were together and not have someone banging their knees. We decided to make sure the two tables had a combined overhang at the head that when joined a person could sit exactly between the legs on the join. This would then leave two people between the legs on the larger table and one on the smaller (on one side, plus the head and tail of the table giving 10 total). From here on the design is relatively straight forwards. Build a top from planks joined together, make a box shaped frame underneath (with additional supports on the larger table) and join it all together in unison. Plan sorted! I will give the details at each stage of the build in later posts.

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