Leadwood Desk

[OM99]

Custard, thanks for the thread really lovely slab of wood too.

You make it look very easy

Oli

 

[Woodmonkey]

Looking forward to the money shot of that oiled up slab...

 

[ColeyS1]

Top job Custard ! Enjoying seeing all the stages.

Coley

 

[Woody2Shoes]

Very fascinating. When my wife walked past me at the computer a moment ago I neglected to mention I was learning about 'bum-cheek' mouldings!

 

[galleywood]

As Woody2Shoes said - facinating thread.
Great tips re bumcheek moulding and merits of Dominoes.

 

[thetyreman]

looking really nice custard, the speed is impressive, and it's good to hear about the real world deadlines and problems as well as the good stuff.

 

[Phil Pascoe]

Custard, have you increased the price of this as it is now famous?

 

[whiskywill]

I Google "bumcheek moulding" and got this. https://www.etsy.com/listing/65277019/b ... jello-mold

 

[Phil Pascoe]

Whatever it was, someone bought it.

 

[Paul Chapman]

Great thread, Custard. Thanks for taking the trouble to post such a comprehensive description at what is clearly a busy time for you.

Cheers :ho2

Paul

 

[custard]

Second coat of Osmo, top fastened on, chamfers around the bottom of the legs.

All done.

Maybe not the most challenging piece, but one of the few furniture styles that consistently sell for a realistic price.

And if you want to have a go making something similar then you may find this useful,

http://www.nakashimawoodworker.com/inventory/

 

[custard]

If I understand the sequence of events correctly components are machined, joint positions marked up and then domino mortices are cut. You then mention cleaning off the pencil marks, etc. either by planing, sanding or both. I guess this is the point at which your 0.5mm allowance comes in? Having gone to such an effort to ensure the perfect alignment of the components with your shimming, etc. how do you deal with the risk that the planing / sanding doesn't introduce inaccuracy?

Fair question Terry.

If you're doing subcontracting work on cutting lists, components, or sub assemblies it's fairly common to be given a +/- 0.5mm tolerance. It makes sense to initially hit the upper limit and then have the maximum amount to play with if you have to correct any problems. I guess I've just carried over this practise, but you're right, 0.5mm is a generous allowance just for cleaning up.

As to introducing inaccuracies, as long as you sand or plane the entire surface evenly with overlapping strokes it's not a problem, a domino automatically plunges about a mill deeper than the length of the domino tenon, and all the joints still close up with airtight precision.

 

[custard]

does it's weight make it hard as well?
just wondering wether the 2 come hand in hand
also interested how you "clean" a waney edge

Steve

I think there's some relationship between hardness and weight, but I don't think it's totally linear. If I remember the list of the hardest woods they're not actually the same as the heaviest ones.

Cleaning up the wane is interesting. Leadwood is a dream because the sap is rock hard. At the other extreme you get timbers like Elm where the sap is quite soft and punky so that you end up taking most of it off.

I always remove all of the bark, usually with a drawknife, and I'll usually take off any soft sap with the same tool. After that it's down to steel and brass brushes to clean away anything too soft, and then a spokeshave and 80 grit to soften any sharp edges.

 

[custard]

Interesting indeed.
Do you allow for any 're-finishing' when pricing this sort of furniture (slabs) ? I've often wondered what happens if the slab behaves unexpectedly in its new environment and customer becomes unhappy with the overall flatness of the item.

I've done over twenty of these, and only had a problem with one. That was quite early on and it's when I discovered how fine the tolerance was for a computer keyboard to be free from rocking! No big deal, twenty minutes with a bench plane, refinished with Osmo, and it's been fine ever since.

I think a lot of furniture writing currently comes from the East Coast of the US, where they have one of the biggest humidity/moisture ranges in the world. Consequently they're extremely focussed on timber movement. By comparison our maritime climate is a relative doddle, we're mildly damp all year round without anything like as much seasonal variation.

I made a wide solid Oak table with breadboard ends for our house. By the end of the first year the breadboard ends were proud of the table by about 2.5mm at each side. But I monitor them every day and the subsequent movement is pretty negligible, maybe half a mill at each side over the course of a year due to seasonal fluctuations. That's not untypical, the big change is a one off when furniture first moves from the workshop into a domestic environment, once that transition is over as long as you've followed sensible construction principles you're usually okay...always assuming of course no one parks your furniture hard up against a radiator!

 

[Wizard9999]

If I understand the sequence of events correctly components are machined, joint positions marked up and then domino mortices are cut. You then mention cleaning off the pencil marks, etc. either by planing, sanding or both. I guess this is the point at which your 0.5mm allowance comes in? Having gone to such an effort to ensure the perfect alignment of the components with your shimming, etc. how do you deal with the risk that the planing / sanding doesn't introduce inaccuracy?

Fair question Terry.

If you're doing subcontracting work on cutting lists, components, or sub assemblies it's fairly common to be given a +/- 0.5mm tolerance. It makes sense to initially hit the upper limit and then have the maximum amount to play with if you have to correct any problems. I guess I've just carried over this practise, but you're right, 0.5mm is a generous allowance just for cleaning up.

As to introducing inaccuracies, as long as you sand or plane the entire surface evenly with overlapping strokes it's not a problem, a domino automatically plunges about a mill deeper than the length of the domino tenon, and all the joints still close up with airtight precision.

Thanks Custard, after I raised the question I did rather think that at a level of skill way above mine it would not be an issue as the ability to plane and / or sand consistently would be there. But, as I keep telling kids when they become disheartened about something, if it were easy there would be no achievement in mastering it!

Thanks again, this will be a reference post for me I suspect.

Merry Christmas,
Terry.

 

[Fitzroy]

Hi Custard.

Couple of questions if you don't mind.
1. Do you drill an oversize/elongated hole on the bearers to allow for movement in the top? If not how do you allow for movement in the top?

2. The thing that I find most interesting and hardest to grasp is timber proportions. The desk frame is, to my eye, very well balanced cf. the top. Any thicker and it would look to heavy and clumsy, any thinner and too light and insubstantial. How did you decide the thickness of the frame components?

Thanks

Fitz.

 

[JandK]

Thank you Custard for a very informative thread well worth reading, there is a lot to learn from this thread.

It has also brought back a lot of memories from my youth in South Africa. On the farm in the Limpopo province where I grew up this tree was mainly used for fencing posts because of its durability, the timber is resistant to termite attack. My grandfather planted a lot of the posts during the 1930's and they are still standing. People often said that if a termite bit into the heartwood it would need to see a dentist urgently
The wood is some of the best to use for a bbq.
It is also the choice wood for carvings and some excellent animal figures of buffalo and elephant can be bought for very little money in Zimbabwe.

 

[custard]

Good questions Fitz.

There are a few different ways of attaching a top while still allowing for timber movement. At one extreme here's a light and delicate occasional table,

For something like this I used traditional "buttons"

Buttons are the little Oak pegs that are screwed into the underside of the top and then seat into mortices in the apron rails, on this job I went a step further and shaped the buttons to add a bit more class. Buttons allow the top to move with the seasons.

But the waney edged Leadwood desk must weigh fifty times as much as the occasional table, so needs something a lot more robust. There are two stretcher rails immediately under the top, the rail at the front has 5 x 5mm/50mm long screws which fix the top at the front, the rail at the back has the same screw arrangement, but with deep countersinks top and bottom which will allow a few mill of play to take up timber movement. In addition there are two metal plates with slotted expansion holes that secure the top to the back legs.

In terms of proportions it's another good reason for doing a rod or full size set of plans. Once you've drawn them up it pays to just live with them for a few days and reflect if it all looks right to you. After all, it's a lot easier to rub out and move a line on paper than it is to plane away timber!

 

[custard]

Thank you Custard for a very informative thread well worth reading, there is a lot to learn from this thread.

It has also brought back a lot of memories from my youth in South Africa. On the farm in the Limpopo province where I grew up this tree was mainly used for fencing posts because of its durability, the timber is resistant to termite attack. My grandfather planted a lot of the posts during the 1930's and they are still standing. People often said that if a termite bit into the heartwood it would need to see a dentist urgently
The wood is some of the best to use for a bbq.
It is also the choice wood for carvings and some excellent animal figures of buffalo and elephant can be bought for very little money in Zimbabwe.

Very interesting. I believe Leadwood is now a protected timber in South Africa, but is still fairly abundant in some neighbouring countries. Incredible that it's used as fence posts, I've seen Kingwood used for fencing in Brazil and Rosewood used for railway sleepers in India!

 

[MusicMan]

I'd like to add my thanks, Custard, a remarkable piece of education, as well as of workmanship.

SteveF asked about the relationship between various properties. There is a strong relationship between density (specific gravity) and stiffness (elastic modulus). In fact the ratio of these two numbers, the 'specific stiffness' is very similar for most common constructional materials; wood, steel, aluminium, concrete ... only when you get on to exotic materials like kevlar, boron fibre and especially carbon fibre, does the ratio get much larger, hence the use of carbon fibre-reinforced plastics for extreme stiffness/weight ratio in much sports equipment. The stiffness of a structure depends on its design as well as the material stiffness of course (e.g. the torsion box).

The hardness and strength of a material, however, is very sensitive to its microscopic structure. Hence in heat treating tool steels, the strength and hardness varies enormously with heat treatment, which controls the microstructure, but the stiffness (elastic modulus) scarcely changes. So there is no necessary relationship between the density and the strength or the hardness (resistance to penetration). In wood, there is a very loose relationship, as woods have the broad features of the microstructure in common, but in general you just have to look up the numbers. As well as density, the rays and porosity and their distribution affect the properties.

If you are interested in following this up, there is a good Wiki article on "specific modulus". A most useful tabulation of wood properties is on The Wood Database (based on USDA information), http://www.wood-database.com. The properties are tabulated for a huge number of woods. Strength is given by "modulus of rupture", stiffness by "elastic modulus", hardness by "Janka hardness" and density by "specific gravity.

Keith (former materials science teacher)