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edge of the cutter becomes dull; and the surface of the plate is

indented and burnished; instead of being turned。  Hence loss of time

on the part of the workman; and diminished work on the part of the

tool; results which; considering the wages of the one and the capital

expended on the construction of the other; are of no small

importance; for the prime objects of all improvement of tools are;

economy of time and economy of capitalto minimize labour and cost;

and maximize result。



The defect to which we have referred was almost the only remaining

imperfection in the lathe; and Mr。 Clement overcame it by making the

machine self…regulating; so that; whatever might be the situation of

the cutter; equal quantities of metal should pass over it in equal

times;the speed at the centre not exceeding that suited to the work

at the circumference;while the workman was enabled to convert the

varying rate of the mandrill into a uniform one whenever he chose。

Thus the expedients of wheels; riggers; and drums; of different

diameters; by which it had been endeavoured to alter the speed of the

lathe…mandrill; according to the hardness of the metal and the

diameter of the thing to be turned; were effectually disposed of。

These; though answering very well where cylinders of equal diameter

had to be bored; and a uniform motion was all that was required; were

found very inefficient where a Plane surface had to be turned; and it

was in such cases that Mr。 Clement's lathe was found so valuable。  By

its means surfaces of unrivalled correctness were produced; and the

slide…lathe; so improved; became recognised and adopted as the most

accurate and extensively applicable of all machine…tools。



The year after Mr。 Clement brought out his improved turning…lathe; he

added to it his self…adjusting double driving centre…chuck; for which

the Society of Arts awarded him their silver medal in 1828。  In

introducing this invention to the notice of the Society; Mr。 Clement

said; 〃Although I have been in the habit of turning and making

turning…lathes and other machinery for upwards of thirty…five years;

and have examined the best turning…lathes in the principal

manufactories throughout Great Britain; I find it universally

regretted by all practical men that they cannot turn anything

perfectly true between the centres of the lathe。〃  It was found by

experience; that there was a degree of eccentricity; and consequently

of imperfection; in the figure of any long cylinder turned while

suspended between the centres of the lathe; and made to revolve by

the action of a single driver。  Under such circumstances the pressure

of the tool tended to force the work out of the right line and to

distribute the strain between the driver and the adjacent centre; so

that one end of the cylinder became eccentric with respect to the

other。  By Mr。 Clement's invention of the two…armed driver; which was

self…adjusting; the strain was taken from the centre and divided

between the two arms; which being equidistant from the centre;

effectually corrected all eccentricity in the work。  This invention

was found of great importance in ensuring the true turning of large

machinery; which before had been found a matter of considerable

difficulty。



In the same year (1828) Mr。 Clement began the making of fluted taps

and dies; and he established a mechanical practice with reference to

the pitch of the screw; which proved of the greatest importance in

the economics of manufacture。  Before his time; each mechanical

engineer adopted a thread of his own; so that when a piece of work

came under repair; the screw…hob had usually to be drilled out; and a

new thread was introduced according to the usage which prevailed in

the shop in which the work was executed。  Mr。 Clement saw a great

waste of labour in this practice; and he promulgated the idea that

every screw of a particular length ought to be furnished with its

appointed number of threads of a settled pitch。  Taking the inch as

the basis of his calculations; he determined the number of threads in

each case; and the practice thus initiated by him; recommended as it

was by convenience and economy; was very shortly adopted throughout

the trade。  It may be mentioned that one of Clement's ablest

journeymen; Mr。 Whitworth; has; since his time; been mainly

instrumental in establishing the settled practice; and Whitworth's

thread (initiated by Clement) has become recognised throughout the

mechanical world。  To carry out his idea; Clement invented his

screw…engine lathe; with gearing; mandrill; and sliding…table

wheel…work; by means of which he first cut the inside screw…tools

from the left…handed hobsthe reverse mode having before been

adopted;while in shaping machines he was the first to use the

revolving cutter attached to the slide rest。  Then; in 1828; he fluted

the taps for the first time with a revolving cutter;other makers

having up to that time only notched them。  Among his other inventions

in screws may be mentioned his headless tap; which; according to Mr。

Nasmyth; is so valuable an invention; that; 〃if he had done nothing

else; it ought to immortalize him among mechanics。  It passed right

through the hole to be tapped; and was thus enabled to do the duty of

three ordinary screws。〃  By these improvements much greater precision

was secured in the manufacture of tools and machinery; accompanied by

a greatly reduced cost of production; the results of which are felt

to this day。



Another of Mr。 Clement's ingenious inventions was his Planing

Machine; by means of which metal plates of large dimensions were

planed with perfect truth and finished with beautiful accuracy。  There

is perhaps scarcely a machine about which there has been more

controversy than this; and we do not pretend to be able to determine

the respective merits of the many able mechanics who have had a hand

in its invention。  It is exceedingly probable that others besides

Clement worked out the problem in their own way; by independent

methods; and this is confirmed by the circumstance that though the

results achieved by the respective inventors were the same; the

methods employed by them were in many respects different。  As regards

Clement; we find that previous to the year 1820 he had a machine in

regular use for planing the triangular bars of lathes and the sides

of weaving…looms。  This instrument was found so useful and so

economical in its working; that Clement proceeded to elaborate a

planing machine of a more complete kind; which he finished and set to

work in the year 1825。  He prepared no model of it; but made it direct

from the working drawings; and it was so nicely constructed; that

when put together it went without a hitch; and has continued steadily

working for more than thirty years down to the present day。



Clement took out no patent for his invention; relying for protection

mainly on his own and his workmen's skill in using it。  We therefore

find no specification of his machine at the Patent Office; as in the

case of most other capital inventions; but a very complete account of

it is to be found in the Transactions of the Society of Arts for

1832; as described by Mr。 Varley。  The practical value of the Planing

Machine induced the Society to apply to Mr。 Clement for liberty to

publish a full description of it; and Mr。 Varley's paper was the

result。*

 'footnote。。。

Transactions of the Society for the Encouragement of Arts; vol。 xlix。

p。157。

 。。。'

It may be briefly stated that this engineer's plane differs greatly

from the carpenter's plane; the cutter of which is only allowed to

project so far as to admit of a thin shaving to be sliced off;the

plane working flat in proportion to the width of the tool; and its

length and straightness preventing the cutter from descending into

any hollows in the wood。  The engineer's plane more resembles the

turning…lathe; of which indeed it is but a modification; working up

on the same principle; on flat surfaces。  The tools or cutters in

Clement's machine were similar to those used in the lathe; varying in

like manner; but performing their work in right lines;the tool

being stationary and the work moving under it; the tool only

travelling when making lateral cuts。  To save time two cutters were

mounted; one to cut the work while going; the other while returning;

both being so arranged and held as to be presented to the work in the

firmest manner; and with the least possible friction。  The bed of the

machine; on which the work was laid; passed under the cutters on

perfectly true rollers or wheels; lodged and held in their bearings

as accurately as the best mandrill could be; and having set…screws

acting against their ends totally preventing all end…motion。  The

machine was bedded on a massive and solid foundation of masonry in

heavy blocks; the support at all points being so complete as

effectually to destroy all tendency to vibration; wi

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