The Hacker test Press, the Block Leveler, and the Plate Gauges
By H.W. Hacker. From a speech at the Second Conference of the Technical Experts in the Printing Industry, March 16-17, 1931, Washington, D.C. Published in Photo-Engravers Bulletin, June 1931. Present title by moderator.
The Hacker test press is a precision proof press of great strength and accuracy of impression. The printing distance, bed to cylinder , is guaranteed true within a half-thousandth under load. Bearer contact is assured for all normal printing loads. The impressional accuracy will hold indefinitely, baring injury to the bearers.
The bed and cylinder are held together during the printing stroke by powerful springs applying equal and measured loads to each side. In standard usage they carry 1,800 pounds on each bearer, 3,600 ponds total. This bearer load is adjustable, lighter or heavier, up to 4,000 pounds, total 8,000 pounds; but it is rarely necessary to change. The bed is 18 inches across. Printing load is 200 pounds per impressional inch.
By this construction an overload is taken by the springs. Overload and hard usage do not distort the press nor destroy accuracy of impression as occurs with rigid setting. Wear is automatically compensated.
It is to be noted that up to the rated load the setting is rigid and u yielding.
A thorough ink distribution for the full capacity, micrometer feed guides, and numerous devices and conveniences has equipped the press for a wide variety of uses; but the fundamental is accurate impression. Accurate impression is indispensable to inspection and premake-ready.
While measurements for dimension by gauges has important value, it is to be noted that inspection by a test press proof goes farther and gives added information, It is a printing test. It discloses the need of certain adjustments of dimension to the printing conditions.
For example, the finer sizes of brass rule will punch at 0.918 inch. A test proof shows that they run better at 0.915 inch. Again, heavy plates will print too light, and light plates will print too heavy if both are uniformly standard thickness. A test proof shows that a heavy plate runs better at 0.921 inch, or even higher, and that a light plate (small, lines, or vignettes) run better below type-high. Compensation for these differentials are made at the test press.
Premake-ready is done at the test press by underlay, both general and detailed. This operation corrects dimensional defects. The same operation also compensates for the variable densities of the printing surface and prepares each plate according to its printing characteristics.
Numerous other inspections to protect the production printing presses are done on the test press, such as ink, ink and paper combinations, register of color plates, color of color plates, etc.
By detecting and correcting errors of materials in printing forms before going to press there is achieved a saving of make-ready time and an increase of production press time.
The Hacker block leveler is a finishing planer for wood-mounted plates. In the average sizes, up to 8 to 12 inches, it is capable of leveling cuts within 0.001-inch accuracy. This degree of accuracy on wood is made possible by reason of two features of design:
(1) A small end mill revolving at high speed moves radially across the work, which rotates at slow speed. This method of removing stock puts a very light strain upon the machine as compared to slab milling. It makes possible the removal of 0.001 or one sixteenth inch with accuracy at the will of the operator, there being a quick up and down adjustment.
(2) The clamp jaws have two positions—the up or neutral for planning a warped board and the hold down for forcing the block and plate firm against the worktable to insure parallelism on final ct.
Dust and chips (over 95 percent) are vacuumed into a drawer inside the base. All important bearings are automatically lubricated from a 4-quart reservoir of oil. The 8-tooth 1-piece cutter is attachable and removable by a single nut. There is a quick micrometer up and down adjustment. Driving motor, one-half horsepower; vacuum motor, one half horsepower; maximum capacity, 12 by 18 inches.
Blocks are clamped by means of a smooth ring surrounding the worktable. The radial arm carrying the cutter is drawn by hand across the work to the center and back.
Old cuts can be reduced a measured amount and leveled on the bottom. The top side can not be leveled without removing the plate.
In an electrotype or photo-engraving plant the original height of the blocks is kept more accurate. In a printing plant inaccurate blocks are corrected.
An accurate block leveler is invaluable in a premake-ready department.
Hacker plate gauges apply printing pressure to plates and measure them with the load on. Measurement without full printing pressure means nothing, since blocked cuts yield and patent plates flatten down under printing load.
The pressure is 200 pounds, and there is patented device which prevents any possible damage to plates.
No. 8 gauge, floor type, is universal for all sizes of flat and curved plates. The lift is by foot lever, which leaves both hands free to handle the work, an invaluable feature in large heavy plates, especially curved ones.
No. 9 gauge, bench type, is for flat plates, with hand lift.
The head is quickly adjustable up and down for measurements of articles of different height, from 0.001 to 1 1/8 inches. All necessary standard setting gauges are provided.
A standard plug gauge of known height is placed under the pressure foot and the dial of the test indicator set at zero. The work is then measured in comparison with the setting gauge. The dial is graduated in thousandths.
Plates can be measured rapidly at any and all points, inside as well as edges.
When used only as a measuring device, the gauge instruments alone are all that is necessary. When used for rectifying the thickness of plates and the height of cuts, No. 9 gauge, the small one, is accompanied by a special worktable with facilities for proper underlay.
The worktable had compartments containing underlay paper in thicknesses from 0.001 to .010 inch. Thus the operator puts is hand at once on the thickness of paper indicated by his readings. The great majority of cuts and plates are below height and of uneven height. These can all be corrected by the plate gauge with rectifying equipment.
By correcting the average height of cuts and the thickness of patent plates there is a saving of press make-ready. The first pull will be level and ready for top make-ready. There is a 100 percent elimination of leveling underlay at the press.
The plate gauges are also useful for measuring paper, copper, cardboard. Bases, bearers, fabrics, or any material that will withstand pressure and is less than 1 1/8 high.
The Hacker type gauge is a little instrument for comparative readings by dial-test indicator of type, rule, lino slugs, etc. It measures both height and thickness. A special model measures mat depth. These models serve many useful purposes.