Through the agent for the wheel-cutter in England I communicated with the maker and inventor in America, and told him of our difficulties and perplexities over here, and chiefly with regard to two points. First, the awkwardness of the handle, which causes the glaziers here to use the tool bound round with wadding, or enclosed in a bit of india-rubber pipe; and, secondly, the bluntness of the "jaws" which hold the wheel, and which must be ground down (and are in universal practice ground down), before the tool can be sharpened.
His reply called attention to a number of different patterns of handle, the existence of which, I think, is not generally known, in England at any rate, and some of which seem to more or less meet the difficulties we experience, most of them also being made with malleable iron handles, so that fresh cutting-wheels can be inserted in the same handle. His letter also entered into the question of the actual dynamics of "cutting," maintaining, I think rightly, that a "cut" is made by the edge of the wheel (this
not being very sharp) forcing the particles of the glass down into the mass of it by pressure.
With regard to the old-fashioned pattern of tool which we chiefly use in this country, the very sufficient explanation is that they continue to make it because we continue to demand it, a circumstance which, as he declares, is a mystery to the inventor himself! Nevertheless, as we do so, and, in spite of the variety of newer tools on the market, still go on grinding down the jaws of our favourite, and wrapping round the handle with cotton-wool, let us try and put this matter straight, and compare our requirements with the advantages offered us.
There are three chief points to be cleared up. (1) The actual nature of a "cut" in glass; (2) the question of sharpening the tool and grinding down of the jaws to do so; and (3) the "mystery" of our preference for a particular tool, although we all confess its awkwardness by the means we take to modify it.
(1) With regard, then, to the nature of a "cut" in glass I am disposed entirely to agree with the theory put forward by the inventor of the wheel, which an
examination of the cuts under the microscope, or even a 6 diameter lens, certainly also tends to confirm.
What happens appears to my non-scientific eyes to be this.
Glass is one of the most fissile or "splittable" of all materials; but it is so just in the same way that ice is, and just in the opposite way to that in which slate or talc is.
Slate or talc splits easily into thin layers or laminæ, because it already lies in such layers, and these will come apart when the force is applied between them: but it will only split into the laminæ of which it already is composed, and along the line of the fissures which already exist between them.