Remarks on the Cutting of Steel by Soft lron. 127 
Art. XV.—Remarks on the cutting of steel by soft iron, ina 
letter to the Editor, from Tuomas Kenpatu, Jr. 
As the subject of cutting steel by soft iron, has excited 
considerable attention, and seems not yet to be exhausted, 
I take the liberty to communicate such facts connected with 
the subject, as have come under my own observation, to- 
gether with some remarks, which are at your disposal. In 
the cutting of revolving tron by tempered steel, experiencc 
proves that there is a certain velocity beyond which it can- 
not be well and freely done. Much depends on the purity 
and state of the iron, much on the form, temper, and sharp- 
ness of the cutting instrument, much whether the work is 
performed dry or kept constantly wet with water or oil, and 
also much on the disposition of the particles of iron to chip, 
There is a great difference in different samples of iron in that 
respect, but much more difference in copper and its alloys, 
some of which, although sufficiently soft, can scarcely be 
wrought by turning, filing, drilling, or grinding. Whenever 
the steel or cutting tool, from any cause, ceases to act on 
the iron, and the heat is perhaps at the maximum, the iron 
if revolving will act on the steel; the greater the velocity 
the more freely it acts, and the progress is marked by differ- 
ent appearances corresponding with the different velocities. 
In the case of cutting a saw plate with soft iron, if moving 
with a velocity barely sufficient to act on the steel, this be- 
comes heated beyond the cutting tool to a blue colour; if 
moving with greater velocity, no change of colour is seen 
except on the burr raised by the tool; if with greater still, 
no change of colour is perceived, although the movement is 
attended by the combustion of most of the particles disen- 
gaged. These become ignited because, being connected 
with, and forming a part of the plate, they are by the motion 
disengaged with a velocity that does not admit of ‘the trans- 
mission of the heat to the other parts of the steel. Perhaps 
the ignition is commenced and earried to that degree de- 
nominated black heat, before the particles are separated, 
and is completed by the friction attending the separation. 
It is a fact, perhaps not generally known to those whe have 
written on the subject, that at the heat called black heat, 
(but which is in fact nearly or quite a red heat in the dark,) 
