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Friday, 18 January 2013

Materials for Wooden Clocks

I have been wondering for a while now what wood to use for the next clock that I build. I used Oak for the Clock 14 and was really quite disappointed with the the quality of cut that I was getting even with new Carbide router cutters, and how difficult it was to get the teeth to clean up properly. The other thing with the Oak is that although it is very hard and stable it is liable to split and splinter so I kept losing bits from the gear teeth and other small detail places.
The problem is the very course open grain structure of the Oak, so this has led me to start looking for an alternative wood with a fine grain, but at the same time hard and strong  and capable of attaining a fine finish. I have visited a few websites in this quest and they are all listed at the bottom of this post if you want to undertake your own study.
I make no recommendations on what is going to be the best choice, mainly because there is no single best choice, but some woods are clearly more suitable than others.
The chart below lists some of the more common species that are available and one that isn't available any more (Lignum Vitae) for its historical use by John Harrison. 
The chart is self explanatory except to say that in the last two columns the lower the number the better.
Ash and Oak are the only ones listed that have a course grain, they are usable but the rest hopefully should be better.

Name  Density Texture Grain Ease of working Stability
Alder Medium Fine Straight 2 1
Apple Hard Fine Straight to Roey 2 1
Ash Medium Coarse Straight 2 1
Beech Medium Fine Straight 2 2
Birch Hard Medium Straight 2 2
Blackwood Hard Fine  Straight to Roey 1 2
Boxwood V Hard V fine Straight to Roey 2 2
Cherry Medium Fine Straight 2 1
Dogwood Hard V Fine Straight 1 2
Red Gum Medium Fine Irregular 2 2
Lignum Vitae V Hard Fine Straight 1 2
Lime Soft Fine Roey 3 1
Maple, Hard V Hard Fine Roey 3 2
Maple, Soft Medium Medium Straight 2 2
Oak Hard Coarse Straight to Roey 2 2
Pear Hard V Fine Straight 2 2
Satinwood Hard V Fine Roey 2 1
Walnut M Hard Medium Straight to Roey 2 1

From this list I will make a choice, I will give consideration to what is available locally, how much its going to cost , and more importantly its suitability to for the different clock parts, as the frames and the gears and the arbors all have slightly different requirements, so will probably finish up with different woods for different parts.

To help with the choice I have made a few notes on each of the different woods.

It is heavy, brittle and has a fine, dense, even texture, and bends easily, and resists splitting. Well suited for carving and turning, as it's extremely hard and limber.

 European Alder has closed pores, and a fine, even grain. The grain is usually straight, but can also be wild or irregular depending on the growth form of each individual tree.
European Alder is very easy to work with both hand and machine tools; it sands especially easy. The wood is rather soft, however, and care must be taken to avoid denting it in some applications, not suitable for gears but could be used for the clock frames.

Ash is a long-fibered, light-coloured, medium-density wood, hard, heavy and with a course ring porous grain. It has a prominent grain that resembles oak, will split and splinter easily.

Beech is a heavy, pale-coloured, medium-to-hard wood used widely for chairs and stools. It has a fine, tight grain and large medulla rays, similar in appearance to maple or birch woods. Beech wood has a high shock resistance and takes stains well. Humidity adversely affects the wood.

The sapwood is generally creamy-white, and the heartwood is a very pale brown. It has an even and straight grain, and has good strength and bending properties. It is stiff, very hard, and holds a clean edge. Suitable for frames, keels, and deck houses. Sharp tools are required. Should be selected carefully and cut to avoid grain patterns. Warps readily if not thoroughly seasoned

Australian Blackwood has small, open pores and a fine to medium texture. Grain is usually straight to slightly interlocked, and sometimes wavy. Colour can be highly variable, but tends to be medium golden or reddish brown, similar to Mahogany. It is easily worked with both hand and machine tools, though figured wood and pieces with interlocked grain can cause tear-out. Australian Blackwood turns, glues, stains, and finishes well. Responds well to steam bending.

A very fine textured hardwood with a strong distinctive tanish cream to yellow colour. Very dense with almost no grain or figure. It carves with great detail. Used for turned parts and small detailed components. Boxwood is relatively hard to cut, even with extremely sharp tools, but the effort is worth the labour. A superior wood for clock parts, as it retains sharp edges and details to the smallest dimensions. Care should be taken as in time it can warp and twist if not supported. 

Has a fine texture with close grain. The grain is usually straight and easy to work—with the exception of figured pieces with curly grain patterns. Cherry is known as being one of the best all-around woods for workability. It is stable, straight-grained, and machines and turns well. The only difficulties typically arise if the wood is being stained, as it can sometimes give blotchy results due to its fine, closed pores.

This is an extremely hard, dense wood with a close and very fine grain. A little hard to machine due to its toughness and hardness. Usually white to cream, but can be found in colours to pale yellow and pinkish-brown. Capable of an extremely smooth finish and can be turned to exacting dimensions. Doesn't take stain well and is difficult to work, but can be carved to delicate detail. Hardness will dull and burn saw.. A substitute for boxwood.

Similar to pear, but slightly darker. Has a close, fine, and even texture, irregular grain, and bright satiny sheen.. Red gum can be used as a substitute in appearance for walnut.

Lignum Vitae
Lignum Vitae has a fine texture and closed pores. Bare wood can be polished to a fine lustre due to its high natural oil content. The grain tends to be interlocked and tight. Lignum Vitae is regarded by most to be both the heaviest and hardest wood in the world. Its durability in submerged or ground-contact applications is also exceptional. Lignum Vitae has been used for propeller shaft bearings on ships, and its natural oils provide self-lubrication that gives the wood excellent wear resistance.
Unfortunately, Lignum Vitae has been exploited to the brink of extinction, and is now an endangered species.

Pale, almost white to pale creamy brown with a straight grain and fine uniform texture. Holds a fairly sharp edge, but frays when drilled and sawed. Bends relatively easy but has poor steam bending properties, and low strength. It finishes well but surface "fur" requires sealing.

Hard Maple
This is a heavy fine grained white wood, stable, and among the hardest of usable clock building materials. Although excellent for small parts, its extreme hardness and occasional irregular grain make work difficult. Grain varies from a bird's-eye figure to straight. Color can be pale yellow to deep honey, and can be dull looking. Has high density, a fine, even texture, and is strong and stable. An alternative to box. Easily worked with hand and power tools. Holds an edge well and takes a good finish. Suitable for turnings, gears and it will ability to take a smooth finish, and show a distinctive sheen.

Soft Maple
Soft maple, on the other hand, is relatively easy to work with. Because of their fine, straight grain, both varieties are more stable than many other woods. They also tend to be less expensive than other hardwoods

Oak is a hard, light to medium gray-brown, tough, short fibred wood with a distinctive grain structure. Like mahogany, because of its coarse grain structure is it not really all that suitable for model building.

 Pear is a fine, close grained wood with distinct pores. Can be worked to delicate detail, bends well, and takes an excellent finish. Selected pieces have a straight grain. Turns and cuts well with a clean sharp edge, and holds sharp detail, but has a slight dulling effect on tools. An excellent wood for clock making, but a little scarce. Domestic pear has a cream to pinkish brown to rose colour and the grain structure is excellent for clock making. Foreign pear is usually of better quality, but difficult to find.

Grain is interlocked, producing an attractive mottle figure, as well as striped or roey patterns on quarter sawn surfaces. Texture is fine and even, with a very high natural lustreDifficult to work on account of its high density and interlocked grain. Most surfacing and planing operations result in tear-out, especially on quarter-sawn surfaces. Pronounced blunting effect on cutters. Turns superbly. Glues and finishes well—able to take a high natural polish.

Walnut is a uniform dark purple brown. Even but coarse, open grain limits Clock making applications. Works easily, is hard, strong, and stiff. Free from warping or cracking. Sands to an excellent finish. Cuts and carves exceptionally well, but usually can't obtain fine detail.

For Turning: Apple, box, cherry, dogwood, holly, pear, maple, satinwood..

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