Scientific American Volume Xxiv., No. 12, March 18, 1871 Part 4

This instrument will be found of great service in bringing together the ends of belts, the weight of which is so great that they cannot be held together by the hand while lacing. A strap engages with holes made in the belt, at the back of the holes punched for lacing, the tightening strap being provided with claws or hooks, as shown. A winch axle and ratchet, adjusted in a frame as shown, are then employed to pull the ends of the belt together and hold them firmly till the lacing is completed.

This is the invention of T. G. Stansberry, of Medora, Ill. Patented in September, 1867.

SOME THINGS I DON'T WANT IN THE BUILDING TRADES.

I don't want my house put in repair, or rather out of repair, by a master who employs "Jacks of all Trades."

I don't want my foreman to tell me too much at one time about the faults of the workmen under him, as I may forget asking him about himself.

I don't want a builder or carpenter to give a coat of paint to any joinery work he may be doing for me, until I have examined first the material and workmans.h.i.+p.

I don't want any jobbing carpenter or joiner, whom I may employ, to bring a lump of putty in his tool basket. I prefer leave the use of putty to the painters.

I don't want jobbing plumbers to spend three days upon the roof, soldering up a crack in the gutter, and, when done, leaving fresher cracks behind them. The practice is something akin to "cut and come again."

I don't want a contractor to undertake a job at a price that he knows will not pay, and then throw the fault of his bankruptcy on "that blackguard building."

I don't want any more hodmen to be carrying up the weight of themselves in their hod, as well as their bricks; I would much prefer seeing the poor human machines tempering the mortar or wheeling the barrow, while the donkey engine, the hydraulic lift, or the old gray horse, worked the pulley.

I don't want house doors to be made badly, hung badly, or composed of green and unseasoned timber.

I don't want houses built first and designed afterwards, or, rather, wedged into shape, and braced into form.

I don't want to be compelled to pay any workman a fair day's wages for a half day's work.

I don't want an employer to act towards his workmen as if he thought their sinews and thews were of iron, instead of flesh and blood.

I don't want any kind of old rubbish of brick and stone to be bundled into walls and part.i.tions, and then plastered over "hurry-skurry."

Trade infamy, like murder, will out, sooner or later.

I don't want men to wear flesh and bone, and waste sweat and blood, in forms of labor to which machinery can be applied, and by which valuable human life and labor can be better and more profitably utilized.

CORRESPONDENCE.

_The Editors are not responsible for the opinions expressed by their Correspondents._

ACTION OF THE RECIPROCATING PARTS OF STEAM ENGINES.

MESSRS. EDITORS:--I have hesitated about the propriety of replying to the criticisms of your correspondent, J. E. Hendricks, upon my paper, on the action of the reciprocating parts of steam engines. It is not to be expected that a truth so opposed to commonly received notions--the reception of which requires so much to be unlearned--should at once receive the a.s.sent of every one. Some odd fancies on the subject are likely to be ventilated first.

But your correspondent touches the root of the matter, and perhaps the fact questioned by him should be more clearly placed beyond dispute.

I will dismiss the introductory part of his letter, merely observing that his "logical inference" is quite gratuitous and unwarranted. He says himself that its absurdity is obvious, in which I quite agree with him.

The real question is this: What is the figure representing the acceleration of the motion of a piston, controlled by a crank which revolves with a uniform velocity? I stated it to be a right-angled triangle, and indicated, as I supposed, clearly enough, a simple method by which this could be shown. Your correspondent claims that the calculation, according to my own rule, gives a figure of a totally different form, and one that shows the acceleration, as well as the motion, to be reduced to zero at the commencement of the stroke. Let us see. Let the straight line, AJ, in the following figure, represent half the stroke of the piston, and let the distances, AB, AC, etc., on this line, represent the versed sines of 10, 20, etc., up to 90, or the motion of the piston while the crank is moving through these arcs.

At the points A, B, C, etc., erect the perpendiculars, Aa, Bb, Cc, etc., and let the length of each of these ordinates represent the acceleration imparted in a given time at that point of the stroke.

Then will AJ be to Aa as IJ is to Ii, as HJ is to Hh, etc., showing that the straight line, aJ, connects the extremities of all the ordinates, and that the triangle, AJa, represents the acceleration of the motion of the piston, from the commencement to the middle of the stroke.

[Ill.u.s.tration]

The following table will enable any one to make the calculations proving the truth of the above proposition:

Degrees. Versed sine. Motion for 10 Acceleration during 1.

0 .0000000 _Aa_ .0003046 10 _AB_ .0151922 _AB_ .0151922 _Bb_ .0003001 20 _AC_ .0603074 _BC_ .0451152 _Cc_ .0002862 30 _AD_ .1339746 _CD_ .0736672 _Dd_ .0002638 40 _AE_ .2339556 _DE_ .0999810 _Ee_ .0002332 50 _AF_ .3572124 _EF_ .1232568 _Ff_ .0001958 60 _AG_ .5000000 _FG_ .1427876 _Gg_ .0001523 70 _AH_ .6579799 _GH_ .1579799 _Hh_ .0001041 80 _AI_ .8263518 _HI_ .1683719 _Ii_ .0000529 90 _AJ_ 1.0000000 _IJ_ .1736482 _Jj_ .0000000

The method of obtaining the decimals representing the acceleration for 1, at any point, was fully explained in the paper, and compared with the similar method of showing the uniform acceleration of a body acted on by a constant force. The ordinary tables in the hand-books, going only to five places of decimals, are of no use for these computations.

I would suggest a practical experiment. Let any one having an engine running at a good speed, loosen the crank pin bra.s.ses a little, so that, at starting, it will thump heavily. Let the engine be lightly loaded, so that only a small portion of the boiler pressure will need to be admitted to the cylinder. As its speed increases, the thump will die away; and, if at its full speed, the pressure of the steam admitted is not so great as to overcome the centrifugal strain of the reciprocating parts on the crank, as it pa.s.ses the centers, the engine will revolve in silence. Any one can ascertain, by the rule given in the note to the paper, just what pressure can be admitted without causing a thump, or this can be found by a little experimenting. I am running an engine which does not thump with loose crank pin bra.s.ses, under eighty pounds pressure, admitted sharply on the centers.

Charles T. Porter.

ANSWER TO PRACTICAL PROBLEM.

MESSRS. EDITORS;--I submit the following solution of "Practical Problem" on page 147:

Given AB, arm, C, arm, D, chord of half angle of oscillation of arm, D, and angles of arms, with line AB.

To find angles, BAc', ABb, and length of link, E.

1. As the length of arm, D, is to the chord of arc, ab, divided by 2, so is the radius to the sine angle oscillation of arm, D, divided by 4.

2. 360 is to the whole circ.u.mference as the angle bBa is to the length of arc ab.

3. Now arc ab is equal to arc a'c'.

4. The whole circ.u.mference is to 360 as the length of arc a'e' is to the angle oscillation of C divided by 2.

5. Half angle oscillation, C, taken from angle BAa' is equal to angle BAc'.

6. Half angle oscillation, D, taken from angle ABa is equal to angle ABb.