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Comments and advice needed on table design...

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Digizz

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I just downloaded and got to grips with a bit of software someone else mentioned on here - Sketchup v4 - At first I thought it was a bit 'noddy' with only a few toolbars - but when you get into it - WOW! What a great (and simple to learn) drawing tool!!! I've used Autocad and others which all have a huge learning curve.

Anyway, these are the first ideas for a largish, simple, modern looking coffee table. I wanted others opinions on what joints I might use and especially how I might achieve the shelf in solid wood (would it be too unstable/problematic with shrinkage etc?) - should it be made out of a man made board veneered etc? I wanted to have it fixed into the legs.

What do you think?



 

johnelliott

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nice design work, I've heard others talking about Sketchup, must be really good.
Not sure about the mitres, unless the top was going to be veneered, should work well then.
The shelf will definitely need to be veneered board, probably MDF, unless maybe it was done as slats?
Don't know much about joints, so I will be interested to read what the others have to say
John
 

Midnight

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Digizz, that's a nice looking piece..

Personally, I'd hate to have to resort to veneered ply or MDF for the shelf, but you're right; seasonal movement is a prob. Personally, I'd resolve it with frame and panel construction, letting the panel float. If you made the frame from similar sized material to the frame surrounding the glass, the seasonal movement of each frame should be roughly equal, minimising any probs there.
 

Aragorn

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Nice design.
I prefer the mitred corners - I'd probably do that with loose tenons or even biscuits and a good glue. I'd mortise the legs into the completed top frame. Probably use short twin tenons on each leg.
I would also avoid using ply/mdf for the shelf. Bit of a shame. A simple frame and panel construction would solve the movement issue, although I like Johns idea of slats as this would reflect the lightness of the top's construction. The shelf will be very visible through the glass top and a solid board might appear too "heavy" and cumbersome.

Good luck with the design. Looks like useful software too.
 

Chris Knight

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Digizz,

You certainly seem to have mastered Sketchup - I have played with it but for some reason I can't get to grips with it - I am more used to a full blown solid modelling package and I think I am trying to use it like that (which it isn't designed for).

The intent for your table certainly comes across very well. For my money, I would prefer mitred corners to the top frame. The frame itself can be joined to the legs with mortise and tenon joints or dowels - I would use M/Ts because of the larger glue area they offer.

I have done lower shelves like you are proposing as in this nightstand


However, the size of this piece is only 18 inches square and the solid wood lower shelf will not move as much as your larger shelf. and in any case it should move in sympathy with the top and the lower case, the grain of which is all oriented the same way. you could leave gaps at the side of the lower shelf in the housing joint but these may be unsightly and I think I would either go for frame and panel to match the top or a veneered solution. My preference would be frame and panel but with no fielding of the panel which would be set to the same height as the frame. A narrowish border of say 1/4 inch all around will look crisp and match the clean appearance of the top.
 

Digizz

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Thanks for all the comments guys :)

I like the mitred top best too - no end grain then (I guess I could use some lipping around the edge but wanted to keep it simple).

As to the shelf and panneling - I guess the one downside is that the grooves (dunno what they're called?) would become a bit of a dust trap?

I might try a design with slats instead and see how that looks.

Oh - and I presume the main frame should be quite stable? Should I leave any gap between the glass and frame in the rebate or can it be flush (which from a design point of view I'd prefer)?

Thanks.
 

Digizz

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I've modified the design towards a more traditional leg and rail design as shown.

I was thinking about joining the table top mitres with a biscuit or two and joining the legs to the top with a double tenon. Is this OK and is it OK to cut a mortice through a set biscuit joint? I'll either join the rails to the legs with a standard mortice/tenon or a sliding dovetail (cut on the woodrat :) )

I was thinking of attaching the top to the rails with a button and groove or pocket screwed (might need thicker rails???) - which would you suggest?

As to the table top frame - the edges are currently 120mm wide by 25mm thick. Should I make this out of solid timber or a couple of pieces joined? Is a 120mm wide piece going to be stable enough?

Your thoughts most welcome :)



 

Digizz

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I'm having problems trying to find Maple thick enough for the 3" square legs - is it a good or bad idea to make them out of a laminated (2 pieces of 1 1/2" x 3") section?
 

ike

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Digizz,

I know I said I'd try and post pics of this design I mentioned and apologize for failing to do so yet. Seeing your designs, I'd like to offer my thoughts, and my efforts at a written description in lieu.

My eldest lad made a table for his GCSE. The design brief was for flat pack, so the leg to top joint is by a custom designed metal bracket rather than jointing but anyway the points I wanted to mention are:-

The top and legs are made from 30mm solid timber made with lamins (a la kitchen worktops) 25mm finished thickness in this case. It looks close to beech but I'm sure it's a tropical timber - maybe rubberwood or something like it.) The table size is 750mm x 750mm. The top consists of 4 pieces 160mm wide mitred and biscuited together with square 6mm 'antisun' (grey smoked) toughened glass inset. Using this timber material obviates any problem with movement as it is extremely stable and therefore mitred joints work very well. IMO the mitres are a significant design 'feature'.

The legs rather than solid square timber section, are also made from the worktop material i.e. two 100mm wide sections corner mitred and biscuited. The most difficult part of this project being acheiving a 'seamless' corner on the mitre joint, and he did commendably well given his lack of practical experience in woodworking.

The legs are flush to the edge of the tabletop aiming for a minimalist 'cubic' look. He found this to be quite tricky given the need for flat pack design as for it to look 'right', the joint needs to be dead flush and as seamless as possible. His answer was to route a 5mm wide x 3mm deep rebate around the outside edges of the leg top creating a 'feature groove'. The effect hides the joint seam and slightly 'disconnects' the legs yet retains the overall flush, 'cubic' look to the whole piece.

A lower glass shelf fits inside the 'L' profile legs supported on those acrylic shelf 'pins' (I'm not sure exactly what they're called). The support pins are not straighforwardly visible which contributes to the minimalist look.

The whole piece is chunky particularly with the 'L' legs, yet simple, much as I suspect you are looking for, after seeing your CAD models (he modelled his in 'Rhino' BTW).

I know this material is quite pricey. In this case however I'd been given a 6' x 3' slab for free (cosmetic damage - i.e. a few scratches to the pre-applied 2-pack varnish which was planed off anyway) from a source in the trade.

Postscript: He got an A*. His piece was shortlisted (8 out of 1200) for a national design award and received silver which he was really pleased with.

regards

ike.
 

ike

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Post postscript,

His is nearest in design to your first picture - (but wider top sections/smaller glass, 'L' section legs c/w feature groove and glass lower shelf).

Ike
 

Digizz

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Thanks Ike - I wonder if my top sections will be stable enough for the glass insert - how much will timber like this move I wonder?

And if it's in a centrally heated house, maybe only shrinkage is a problem rather than expansion?

Anyone know if a 1" thick, 5" wide board like this, mitred at the corners will be a problem? Would it affect the mitres or just the opening size for the glass insert? - don't want the glass falling through or cracking under the pressure of the contracting wood!
 

Chris Knight

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Digizz,

Buttons would work nicely - as would pocket screws. I have a preference for buttons but either works. Because the grain is running in the same direction as the rails, you do not actually need the sliding ability of buttons - heck, you could glue the top to the rails if you wanted.

120mm for the top rails is plenty wide, I don't think expansion should be a problem for the glass but you might reduce the width to say 4 inches. I would use bisucuits for strengthening the corners. No problems with putting tenions through them I think. If bothered, consider strengthening with externally visible mitre pieces (the decorative sort that are often made form veneer and seen in boxess and sometimes in picture frames)

You could make up legs in a few ways eg as mitred box sections of thinner wood, as two triangular sections glued together to make a square or as simple laminations. The first two methods allow you to manipulate the grain and figure that shows.
 

Digizz

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Thanks Chris,

The concern over stability of the table top sections is all to do with the glass insert - can i rebate the wood for a tight/flush fit of the glass or do I need to allow a small gap for movement of the wood? And if so, how much?

How much shrinkage can occur? Are there any rules of thumb for different woods and how they've been dried?
 

Chris Knight

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Digizz - sorry I just edited my post and it crossed with yours. Yes there are shrinkage tables for various woods I don't have a url to hand (gasp) but there are resources on the net. Oh, here is one http://home.flash.net/~ccwdwrks/tables.html

I think that in practice you will end up with a small gap anyway. The glass will have bevelled edges in all likelihood, may not be absolutely square and you don't want to be fitting the frame around a non-square piece for a flush fit.
 

ike

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Digizz

I think you'll be best off using toughened glass for safety (e.g if SWMBO slaps the freshly brewed teapot down on it!) which has a manufacturing tolerance of ±1mm on finished (polished edge) dimensions. My sons allowed an extra 1mm onto the upper limit of the glass size for his (6mm) rebate. A tight fit to the glass might be pushing your luck, although the glass won't crack - it'll 'explode' (as I recently observed with one of a set of new glass placemats I recently purr-chased :roll: ). I'm sure laminated timber is very stable compared to a similar natural section. So far his table looks fine, but I can still be proved wrong! :oops:

cheers

Ike
 

Digizz

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Ah just found some other links which explain it quite well - and has an EMC calculator.

How important is it to leave the wood in the workshop (or even in the house) for a while before machining? ... and how long does it need?

I'm keen to get on with it! :)
 

Digizz

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Yes - was definately going to get the glass toughened. I have a dining room table thats a simple beech frame (a friend made for me years ago) and a large sheet of toughened 5mm glass on top. Really thin but amazingly strong and flexible. Most visitors are scared of putting anything on it but it's taken a lot of bashing so far!
 

ike

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So, what do you think about laminating your boards?
 

Digizz

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I think I'm going to use solid timber - Timbmet have some 3" stock in and I'll try modifying the design to suit - if not, I might try a box section for the legs. 4" square is probably too thick anyway.

I'm sure by the time I'm finished, the original design for a coffee table will end up as a lamp base - the sort I made at school!!! ;)
 

ike

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I tried turning a lamp base once and ended up with a thimble! :cry:
 
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