IMPROVEMENTS IN THE DAMPING TABLES OF LITHOGRAPHIC PRINTING MACHINES."
Year: 1880

page_text: LETTERS PATENT to John Harper, of Clerkenwell, in the County of
Middlesex, for an Invention of "IMPROVEMENTS IN THE DAMPING TABLES OF
LITHOGRAPHIC PRINTING MACHINES."
PROVISIONAL SPECIFICATION left by the said John Harper at the Office
of the Commissioners of Patents on the 23rd September 1880.
JOHN HARPER, of Clerkenwell, in the County of Middlesex.
IN THE DAMPING TABLES OF LITHOGRAPHIC PRINTING MACHINES."
"IMPROVEMENTS
The damping table of a lithographic printing machine is usually constructed of a
wooden bed covered with a pad formed of a layer of thick felt, with a covering of
moleskin nailed to the bed. The wooden bed absorbs the water, and is liable to
warp and become uneven, and the felt which absorbs color in working is difficult to
clean, as is required when changing colors since being permanently attached to the
bed, it can only be readily cleaned by scraping, which wears out the moleskin and
renders it uneven.
The object of my Invention is to obviate these defects, and the Invention
consists in substituting for the wooden bed a slab or bed of slate embedded or
otherwise mounted in a metal frame fitted in the travelling carriage of the machine.
In dispensing with the pad or under layer of felt, and in covering the slate bed
with a single layer of moleskin so attached as to be readily removable for cleaning.
The slate bed being less porous than the wood, does not abstract the moisture from
the covering, which therefore remains damp much longer, and the bed is not liable
to warp, and therefore retains the true surface necessary for the even distribution
of the water. The moleskin covering is attached to pins or other fastenings at the
underside of the table along one edge, and after passing across the table is attached
to a tension device consisting of a roller mounted at back of the table, around
which the edge of the covering is wrapped, said roller being provided with a ratchet
and pawl to retain the covering in tension.

page_text: SPECIFICATION in pursuance of the conditions of the Lotters Patent filed by
the said John Harper in the Great Seal Patent Office on the 23rd March
1881.
JOHN HARPER, of Clerkenwell, in the County of Middlesex. "IMPROVEMENTS
IN THE DAMPING TABLES OF LITHOGRAPHIC PRINTING MACHINES."
The damping table of a lithographic printing machine usually consists of a pad
formed of a layer of thick felt with a covering of moleskin, the pad being laid upon
a wooden bed, and the moleskin covering lapped round the edges and nailed to the
back of the bed. The wooden bed absorbs the water, and is consequently liable to
warp and become uneven, and the felt absorbs the turpentine commonly used to
remove the color which has become transferred to the moleskin in working. The
moleskin, requires to be cleaned each time the color is changed, and being
permanently attached to the bed, it can only be properly cleaned by scraping,
which wears out the moleskin and renders tho felt uneven, so that the surface of
the damping table being irregular, the stone is not evenly dainped, and the printing
becomes defective.
-The object-of-my Invention is-to-obviate-these imperfections, and the Invention
consists in substituting for the wooden bed a slab or bed of slate bedded or
otherwise fixed in a metal frame mounted on the travelling carriage of the machine
in the usual position of the damping table. In dispensing with the pad-or-under-
layer of felt, and in covering the-slate bed-with-a-single-layer_of_moleskin_so
attached as to be readily removable for cleaning. The slate bed does not abstract
the moisture from the covering, and not being liable to warp it retains the true
surface necessary for the even distribution of the water, which is very important.
The moleskin covering is attached to pins or other fastenings at the underside of
the table along one edge, and after passing across the table is attached to a tension
bar or roller mounted at back of the table, around which the edge of the covering
is wrapped, said roller being provided with a ratchet and pawl to retain the
covering in tension
Figure 1 is a view of that edge of the damping table at which the tension roller
is mounted; Figure 2 is an underside plan; Figure 3 is an end view; Figure 4 is
a section on line 1-1, Figure 2, drawn to a larger scale.
A is a cast iron frame bolted on bracket arms a on the end of the travelling
carriage of the machine in the usual way. B is a slab of slate planed perfectly
true and bedded in plaster or cement in a corresponding rebated opening in the
frame, and further secured by lead run into counter-sunk holes in the slab and
frame, as shown in section at x, Figure 4. O is the covering of moleskin or other
fabric usually employed stretched over the planed surface of the bed B. It is
attached by being hitched at one edge onto pins & fixed along the back of the
frame A, a rod e being first passed a number of times through the moleskin as
shown, in order to render the tension more uniform, and prevent the fabric tearing
on the hitch pins, this rod e taking a bearing against the hitch pins as shown. At
the opposite edge the moleskin is lapped round a roller extending the whole
width of the table, and mounted in cars f' cast on the back of the frame a at the
ends, said roller being provided with a loose nipping rod g, Figure 4, whose ends
are bent at right angles, and enter holes in the roller f. The edge of the moleskin
being laid under this rod g and then wrapped once round the roller f by turning
the latter, the tension of the fabric causes the rod g to nip it tightly, or the fabric
may be otherwise secured to the roller. h is a ratchet wheel on the end of the

page_text: roller f, and i is a pawl on the sido of the frame a, by which the roller is held to
keep the fabric tightly stretched, the roller being turned to apply the tension by
means of a key or spanner applied on the squared end h' of the roller f. By this
means a uniform tension is quickly applied, and the fabric is stretched smooth and
tight over the planed surface of the bed.
I would have it understood that I do not confine myself to the precise construction
of bed heroin shown and described, as the cast iron frame might be dispensed with,
and a slab of slate employed alone, but in that case it should be of greater
thickness for the sake of strength, and to enable it to be firmly secured to the
carriage, and for the attachment of the devices for stretching the covering upon it.
I would also observe that although I prefer the means of fastening and stretching
the covering which I have described, I do not limit myself thereto, as other means
may be used.
Having described the nature of my Invention, and the manner of performing the
same, I declare that what I claim as my Invention to be protected by the herein-
before in part recited Letters Patent is,―
1st. Constructing the damping table of a lithographic printing machine of a slab
of slate with a suitable covering, substantially as and for the purpose specified.
2nd. The combination of a slab of slate and a covering of moleskin stretched
over it without any pad or underlayer of felt, substantially as and for the purpose
specified.
3rd. The combination with the damping table of a lithographic printing machino
(whether such table be constructed of slate or other material, and whether an
underlayer or pad of felt be employed or not), of the means for stretching the
moleskin covering of the table, arranged and applied substantially as specified.
4th. The improved damping table for a lithographic printing machine, substan-
tially as herein shown and described.
In witness whereof, I, the said John Harper, have hereunto set my hand
and seal, this Twenty second day of March, A.D. 1881.
JOHN HARPER (s)