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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； with the object of
securing full； round； and quiet cuts。 The rollers on which the
planing…machine travelled were so true； that Clement himself used to
say of them； 〃If you were to put but a paper shaving under one of the
rollers； it would at once stop all the rest。〃 Nor was this any
exaggerationthe entire mechanism； notwithstanding its great size；
being as true and accurate as that of a watch。
By an ingenious adaptation of the apparatus； which will also be found
described in the Society of Arts paper； the planing machine might be
fitted with a lathe…bed； either to hold two centres； or a head with a
suitable mandrill。 When so fitted； the machine was enabled to do the
work of a turning…lathe； though in a different way； cutting cylinders
or cones in their longitudinal direction perfectly straight； as well
as solids or prisms of any angle； either by the longitudinal or
lateral motion of the cutter； whilst by making the work revolve； it
might be turned as in any other lathe。 This ingenious machine； as
contrived by Mr。 Clement； therefore represented a complete union of
the turning…lathe with the planing machine and dividing engine； by
which turning of the most complicated kind might readily be executed。
For ten years after it was set in motion； Clement's was the only
machine of the sort available for planing large work； and being
consequently very much in request； it was often kept going night and
day；the earnings by the planing machine alone during that time
forming the principal income of its inventor。 As it took in a piece
of work six feet square； and as his charge for planing was
three…halfpence the square inch； or eighteen shillings the square
foot； he could thus earn by his machine alone some ten pounds for
every day's work of twelve hours。 We may add that since planing
machines in various forms have become common in mechanical workshops；
the cost of planing does not amount to mo