Pedestal table design question.

[Bremner]

Hello,

I've been commissioned to make a solid Oak pedestal table for a customer of mine but I have a few things I'm not sure of. My usual line of work usually involves man made boards and the odd bit of softwood so a solid oak table is a bit out of my comfort zone and also my work normally revolves around built in furniture not freestanding.

The customer has stated the table must be 1800mm diameter - I have never seen a pedestal table that big and wondered if there is a reason behind it? On my initial design below I have drawn in 5 legs rather than 4 in an attempt to stop it tipping? Do you think this will stop that?

I am a bit worried about the expansion of the top and keeping it flat. When I make it I plan to domino the boards together with alternating growth rings and when fixing down to the pedestal legs use screws through elongated holes orientated across the grain. I will be using kiln dried white oak.

I think they are the only worries I have but any other advice or criticism is welcome, please see the below Sketchup drawings of the proposed design.

Cheers, Andy

 

[MikeG.]

Without having any access to your dimensions, it looks to me that you're overly worried about tipping this table over. This has produced feet which are longer than necessary (my view from eyeballing it). If your chairs are accurately modeled then there will be some clashes between the feet and the chair legs. If you had 4 feet rather than 5 you would probably resolve those clashes, as the relationship between 8 chairs and 4 feet would be predictable and controllable. I'm guessing the diameter has been chosen to enable 8 people to fit around the table.

The table top is not straightforward, and you may even need to get a handtool out..........but the pentagonal pedestal is going to be even more fun. Personally, I think I'd be looking to make a bit more of a show of that element. Also, 'twere it me I'd definitely be going for buttons to hold the top in place.

Edit: I've just drawn this quickly, and I can tell you that this size is only just big enough for 8 people. The chairs won't go fully under the table when they're away, as they'll bang into each other.

 

[Bremner]

Thanks for the reply Mike, much appreciated!

You're correct the idea behind the 6' diameter is to seat 8 people, I was worried about warping, tipping etc etc on 6' so I'm hesitant to make it any bigger. Would you think it needs to be vastly bigger to get the chairs under fully or will another 6" on the diameter make a big difference?

I was fully prepared to get out a plane or two to flatten/smooth the top and don't tell anybody but quite looking forward to it! I might even buy a nice low angle jack plane!

The pentagonal base is going to be all track saw on the bevel with dominoes for strength and "plugs" top and bottom. I plan to make a MDF mock up first to get all the angles and dimensions dialled in before I turn the lovely expensive oak in firewood!

Buttons might be a better idea as you suggested, I was thinking screws for a cleaner look but at the end of the day it is under a table and who looks under tables........well except wood workers.

 

[MikeG.]

Yeah, they're pretty much fully under if you add 150 to the diameter. You need to be careful that the room is big enough, though. I wouldn't put that table (at 1950 diameter) in a room under 3.6m wide and long, otherwise people are going to struggle to get to their places behind others already seated.

Your table, your client, your call, but I'd seriously look at reducing the length of each of those feet. No-one is going to be tipping that table.

 

[custard]

Interesting question.

I've made a 1.85m diameter circular table to seat eight people. It worked okay, but no better than okay.

The problems were two fold. Firstly the minimum place setting zone is around 600mm wide, you just get there with this table, but only just. That's fine for casual family dining, but it becomes a bit cramped for more formal dining. Ideally you want to aim for 750mm, which if you increase the diameter then takes us to the second problem; the "shared access zone" in the centre of the table. Circular tables work great for four or six people, but once you get above 1.8m diameter the problem is reaching to the centre. In China, where large circular tables are very popular, they engineer some amazing, electrically powered lazy susans in order to make the whole thing function properly!

Regarding the relationship between room size and table size, the bible for furniture design is "Human Dimension & Interior Space" by Panero and Zelnik . They recommend a minimum clearance of 1200mm between the edge of the table and the nearest physical obstruction such as a wall. That may be sensible for say a restaurant where serving staff may need access, but in a domestic environment you can shrink this considerably. Personally I find 700mm is adequate and 600mm is do-able at a pinch.

 

[MikeG.]

......... the minimum place setting zone is around 600mm wide, you just get there with this table, but only just. ...........

And furthermore, that 600mm width is only at the table edge with this round table. It tapers in from that, so arguably the diners will have adequate space for themselves, but the table itself will be cramped, with side plates overlapping adjacent cutlery and so on.

 

[Jacob]

Large circular table no prob if you just follow the common (and very elegant) Georgian/Victorian pattern.
The top would consist of an apron ring say 2" smaller diameter than the top, about 2" vertical and 1" horizontal section, made of 2 layers of staggered segments solid wood, then veneered. I've got one downstairs I'll do a photo later. I made it for an unfinished project, copying an old one.
The ring would then be spanned by 4 bearers crossing off centre to leave a square in the middle, say 12 to 18", into which the top of the pedestal would fit - fixed or hinged.
Pedestal design commonly 3 legged but you could do what you like.
The actual top would be edge joined ex 1" hardwood, extending 1" or more past the apron and fixed with buttons to allow for movement. The circular apron would be slightly flexible too and would take up s bit of movement. A thumbnail moulding around the edge , or whatever.
PS no come to think the four bearers didn't reach all the way the apron they just supported most of the top, with the edge held in place by the apron, also fixed only to the top boards.
Sounds complicated but actually very simple, practicable, neat design to accommodate movement in a 4ft diameter table.
Should scale up to 6'.
PS this is a fancy version of the sort of table I had in mind
http://www.wickersleyantiques.co.uk/sol ... ing-table/
Three legs. You can see the veneered apron, the top boards would be less than 1" thick, the whole fairly light construction, unlike our OP's bomb shelter design!
The central frame around the pedestal would support the boards. The boards support the apron. The whole being flexible enough to allow for differential movement.
6' (1800mm) diameter is pretty big - you wouldn't be able to reach the middle very easily, what about having a large hole there instead? Stand a plant in it, or statue, female form?
PPS 6' is big and difficult. I know another huge table where they have made it into a slender oval shaped, about 12' long and 4' wide. I'll measure it next time I'm there.

 

[Bremner]

Thanks for all the replies, I've been trying to find the original sketchup file from when I first drew it out but no luck, would have been nice to refer to all the dimensions.

I did talk to the customer briefly about the size of the table for 8 people and they basically said it would be once in a blue moon when it seats 8 and could live with it as long as all the chairs fit underneath. I've decided to add on the extra 6" we discussed to make sure.

I did suggest an apron, I thought it would help to keep the table flat but the customer insisted to have a simple look of just the thickness of the table top. A simple pedestal table was the brief so that's what I hope to deliver.

I also wanted to ask you guys opinion on the final thickness of the table top, I had about 35 - 38mm final thickness in mind does this sound substantial enough for this design?

 

[MikeG.]

From a design perspective, I think that if you don't have a skirt you need a rather substantial edge on a table this size, so 35-38mm sounds fine to me. This isn't going to be a subtle piece of furniture! I have to say that I do worry a bit about such a large area of edge-joined timber not being tied down to a frame of any sort. It could easily end up going a bit wavy on the top, in my view. A circular band of timber, acting like a continuous breadboard end, would be a hell of a joinery test, though, and that seems the only option if a skirt isn't to be used. Mind you, if you were to do that your top timbers could be very much thinner.

 

[Jacob]

...
I did suggest an apron, I thought it would help to keep the table flat but the customer insisted to have a simple look of just the thickness of the table top. A simple pedestal table was the brief so that's what I hope to deliver.

Remember rule 1 - the customer is always wrong.
If you don't like it they probably won't either, but you get the blame!

 

[St.J]

Do you have access to a copy of “Human dimension & Interior space” by Panero and Zelnik?
Pages 144 and 145 would be worth a read.
St.John

 

[rafezetter]

My only possible suggestion to this task is a tip learned from Norm Abram - rather than cut the pedastal column sections at the angle required, cut them at 90deg, and use slim angle cut strips between each - less wastage and easy to replace if it goes awry, they could be set slightly proud of the faces as a feature so the join and grain 'tween the faces and the strips matters less.

Otherwise a request for a WIP with pics please!

Oh errm would it be feasable to make MDF feet first smaller than required and see how the table reacts vis a vis tipping - assuming a possible scenario of 3 people sitting all on one side adjacent to each other, with plates of food etc. 2 bricks per place setting ought to be enough.

Or better yet as large as first thought and cut bits off (making a note) until it gets beyond safe stability, this way you could keep them as small as feasable to reduce the chairleg / human feet issue which speaking as a person with long legs can be a real problem, painfully so.

No idea if extra weight at the base of the column will help with this.

Just a thought.

 

[Yojevol]

My only possible suggestion to this task is a tip learned from Norm Abram - rather than cut the pedastal column sections at the angle required, cut them at 90deg, and use slim angle cut strips between each - less wastage and easy to replace if it goes awry, they could be set slightly proud of the faces as a feature so the join and grain 'tween the faces and the strips matters less.

That's similar to what I did with this octagonal column although the veneered MDF panels were angle cut to allow thin, raised joining strips to accentuate the veneer:-

Brian

 

[Sheffield Tony]

Oh errm would it be feasable to make MDF feet first smaller than required and see how the table reacts vis a vis tipping - assuming a possible scenario of 3 people sitting all on one side adjacent to each other, with plates of food etc. 2 bricks per place setting ought to be enough.

Can I chip in as an engineer ? If you look at the picture, 5th one down I think, underside view. Draw a line between the outer tips of an adjacent pair of feet. This is the line the table must pivot around to topple over. To topple right over, it would need the centre of gravity of the table - somewhere within the centre pedestal - to pass over that line.

If you work out the weight of the table, it's a fairly straightforward bit of mechanics to figure how much weight you'd have to lean on the edge to lift the opposite feet off the floor, I think ... Assuming you lean on the very edge, in the worst place - between two feet. Your applied weight effectively balances the weight of the table (modeled as a point mas at the C of G) with the line through the two feet as the fulcrum.

So the weight with which you'd need to lean needed to lift the feet off the ground is

W = M * l * cos(36) / (r - l* cos(36))

Where M is the mass of the table, r the radius of the top, and l the length of the leg. The l*cos(36) is the perpendicular distance of the line drawn between the two adjacent feet, and the centre of the table assuming 5 feet. If the top is 35-38 mm of solid oak, the top alone will be ~70kg, so the weight of the table will be about the same as a moderate person. A foot length of ~0.55m would mean a person of about the same weight as the table itself sitting on the edge would just about be the limit of stability. You might add a bit of margin.

 

[Jacob]

Or just do 3 feet in the trad way. Innately self levelling, simpler. There's nothing about a big table which demands more feet. Just more stuff getting under the feet of those sitting around it.
As drawn it looks like a heavy engineered bomb-proof shelter. I think it could be lightened up and much simpler!

 

[Sheffield Tony]

Or just do 3 feet in the trad way. Innately self levelling, simpler. There's nothing about a big table which demands more feet. Just more stuff getting under the feet of those sitting around it.

Just to mildly disagree, if you went for 3 feet, that equation above would need the cos(36) replaced by cos(60). Where 5 feet at 550 mm long would be fairly stable, you'd need 3 at 900mm long for the same stability - i.e, right to the edge of the top. Or educate people not lean their butt on the edge of the dining table !

 

[MikeG.]

Or just do 3 feet in the trad way. Innately self levelling, simpler. There's nothing about a big table which demands more feet. Just more stuff getting under the feet of those sitting around it.

Just to mildly disagree, if you went for 3 feet, that equation above would need the cos(36) replaced by cos(60). Where 5 feet at 550 mm long would be fairly stable, you'd need 3 at 900mm long for the same stability - i.e, right to the edge of the top. Or educate people not lean their butt on the edge of the dining table !

Four feet, then, would need to be of the order of 720 long, and would work perfectly with the 8 chairs proposed for this table (which don't work at all with the currently proposed arrangement). I think we can assume the floor will be flat enough to eliminate the need for Jacob's (perfectly valid) point about 3 being un-rockable. Four feet also leads to an obvious octagonal central piece, which would be so much easier than the 5 sided thing to make.

 

[Jacob]

Or just do 3 feet in the trad way. Innately self levelling, simpler. There's nothing about a big table which demands more feet. Just more stuff getting under the feet of those sitting around it.

Just to mildly disagree, if you went for 3 feet, that equation above would need the cos(36) replaced by cos(60). Where 5 feet at 550 mm long would be fairly stable, you'd need 3 at 900mm long for the same stability - i.e, right to the edge of the top. Or educate people not lean their butt on the edge of the dining table !

In that case there are a huge number of unstable tables in the world! I wonder how often they fall over?
I suppose the fault in the maths is in assuming that someone would put their whole weight on the very edge of a table to start with. This would be difficult to do in practice, whilst your feet were still on the ground. Even if they wanted to climb up stand on the edge they would be cautious about it and not be caught out, unless very drunk. :shock:

 

[Sheffield Tony]

I was working on a worst case of someone sitting on the edge of the table. If you have better behaved dinner guests, then I guess shorter feet would suffice

 

[MikeG.]

I think the worst case is when everyone is seated and one or two on the same side of the table lean on it at the same time. The chairs would ordinarily protect the table from anyone who felt like perching their bum on it. I've certainly had pub tables tip slightly with people leaning on them. The other classic is when people on opposite sides of the table lean on it at the same time, cancelling each other out.............and then one of them sits back before the other. Whoopsy......