An Account of the Manner of bending Planks in His Majeſty’s Yards at Deptford, &c. by a Sand-heat, invented by Captain Cumberland. By Robert Cay, Eſq;
The place, where the Planks lie to be ſoftened in the Stove, is between two Brick-Walls; of ſuch a length, height, and diſtance from each other, as ſuffice to admit the largeſt, or to hold a good number of the ſmaller Sort: the bottom is of thick Iron Plates, ſupported by ſtrong Bars; under the middle of which, are two Fire-places, whoſe Flews carry the Flame towards the Ends.
The Planks are laid in Sand; the loweſt about ſix or eight Inches above the Iron-Plates, they are well cover’d with the Sand, and Boards laid over all, to keep in the Heat. The Sand is moiſtened with warm Water, (for which purpoſe they have a Cauldron adjoyning to the Stove) and if the Timber be large, and intended to be very much bent, ſo that it muſt lie long in the Stove, they water the Sand again, once in 8 or 10 Hours. (more…)
The paper is to be very plain, sufficiently brief, and is intended to lead to practical results; but whether such intention succeeds will, as usual, depend on the obedience and sympathy of those to whom it is addressed.
I was asked the other day to make a set of shelves to hold a few books, and while engaged in the work I determined to jot down a few notes upon those pitfalls which would beset an amateur not quite up to the mark who might undertake a similar job. To an onlooker nothing can be more simple and apparently easy than to cut out and put together a plain set of shelves, especially if they are to be nailed together; yet not a few make a terrible mess of it. (more…)
The frequent inquiries in the Correspondence columns of Carpentry and Building indicate that there is a dearth of knowledge as to the proper method of sharpening a scraper. Without any disposition to assume superior knowledge in this connection I am constrained to remember that we cannot clean our floor without sharp tools, and will give your readers the benefit of my experience along this line.
I presume that every reader understands that the cutting edge of the scraper is formed by turning over a “burr” or wire edge, which does the cutting when applied to the wood. This burr is made by rubbing against the edge of the scraper with a tool called a burnisher, which may be made of any piece of steel of convenient form but which must be harder than the scraper. (more…)
The general demand for finely finished floors of hard or soft wood in modern residences has given rise to such a variety of tools and finishes designed for this special purpose that natural confusion arises as to the best tools, finishes or methods to employ in this highly important branch of the trade.
The growing demand for the conveniences of the city residence in the homes of the smaller towns and the rural districts often brings the carpenter and the painter up against this sort of work, demanding methods of treatment with which they are unfamiliar, and many a good job of floor has been spoiled or indifferently treated by otherwise good mechanics, simply because they lacked the knowledge or experience so essential to success.
It has been the fortune of the writer to have a somewhat extended experience in the better grades of modern floor finishing, and it is with the hope of affording some degree of general information to the craft that this discussion of the topic is undertaken. For convenience in treatment the subject will be considered with reference to the following elements:
1. The carpenter.
2. The tools required.
3. The laying of the floor.
4. Preparation of the surface.
5. The painter’s work.
6. Different varieties of finish.
7. Relative cost of floors and finishes.
8. Suggestions as to estimating. (more…)
Freshly-cut red oak, destined to become Roubo workbench legs
A few days ago, Chris broke one of the cardinal rules of this blog: he began a sentence with, “You should…” He said to me, “You should be writing about this stuff…as a full-on blogger.” I agreed, then explained that the reason I don’t is that I find writing to be painful. So what does he do? He offers to let me write on his blog. I suppose I should be thankful that he didn’t kill me outright, like poor Raney. On the other hand, Raney’s death was quick and presumably fairly painless. Mine will more likely be slow and lingering.
Wood and water. From the woodworker’s point of view, not exactly a match made in heaven. Why is it that thick slabs of wood take so %$#@! long to dry? You may have heard the old air-drying rule of thumb, “one year per inch of thickness.” I remember reading it for the first time many years ago and thinking, That can’t be right. From basic geometry, doubling the thickness of a piece of wood should quadruple, not double, the drying time, and my own experience with drying wood since then has at least approximately confirmed that. There are two factors that cause thicker pieces of wood to dry more slowly: one, there is simply more water to remove through the same amount of surface area, and two, the water has to travel further, on average. Both of these factors are proportional to the wood’s thickness, and they’re multiplicative, so in the simplest approximation the drying time goes as the square of the thickness.
I’ll skip the physics lecture (for now, but there might be an exam later) and show the results of some computer simulations that I ran for water loss in wood, from fully saturated to near equilibrium, using a few assumptions (physicists are all about making simplifying assumptions). The assumptions I made are:
the board is wide and very long compared to its thickness, so I only have to worry about water movement through the faces of the board, and not the edges or ends,
the temperature is a constant 52°F (the year-round average for southeastern Ohio, where I live), and
the equilibrium moisture content is 12% (a typical outdoor value for this climate).
Here are two graphs (click to enlarge), showing the computed change in moisture content over time in red oak, in a 1″-thick board (left) and 6″-thick board (right), subject to the above assumptions and using published data for the various water transport parameters:
As the graphs show, the 1″-thick board settles down in a couple of years, while the 6″-thick board takes over 70 years to equilibrate to the same degree. Apart from the 36-fold difference in time scales, the graphs are nearly indistinguishable. In other words, there’s no significant qualitative difference between thin and thick boards; they both behave more or less the same, just on very different time scales.
So that’s at least a partial answer to the puzzle. In part 2, we’ll look at the role that end grain plays in drying (there’s good news, and there’s bad news), and examine Chris’s hypothesis about how “being surrounded by so much dry wood keeps the moisture in” (hint: he’s at least partly correct).
These first two are fairly non-technical, but they focus on the what and have little to say about the how and why.
Baronas R et al. (2001) Modelling of Moisture Movement in Wood during Outdoor Storage, Nonlinear Anal. Modell. Control6:3-14.
Includes an excellent comprehensive overview of the theory of moisture movement in wood; requires a working understanding of partial differential equations.
Simpson WT (1993) Determination and use of moisture diffusion coefficient to characterize drying of northern red oak (Quercus rubra), Wood Sci. Technol.27:409-420.
Source for the data used in the computer simulations.
