US2549254A - Vacuum hold-down for machines operating on flat stock - Google Patents

Description

H. A. SMYTH April 17, 1951 VACUUM HOLD-DOWN FOR MACHINES OPERATING 0N FLAT STOCK 3 Sheets-Sheet 1 Filed May 18, 1946 April 17, 1951 H. A. SMYTH 2,549,254

VACUUM HOLD-DOWN FOR MACHINES OPERATING ON FLAT STOCK Filed May 18, 1946 3 Sheets-Sheet 2 Fig. 2

HAQOLD A.5MYTH 7 T TERA/E V H. A. SMYTH 2,549,254

VACUUM HOLD-DOWN FOR MACHINES OPERATING 0N FLAT STOCK April 17, 1951 3 Sheets-Sheet 5 Filed May 18, 1946 2 AU; 3 J

M E rU HAROLD A- 5MYT A m/m fl TTU NEW Patented Apr. 17, 1951 VACUUM HOLD-DOWN FOR MACHINES OPERATING ON FLAT STOCK Harold A. Smyth, Olympia, Wash., assignor to Washington Veneer Company, Olympia, Wash., a corporation of Washington Application May 18, 1946, Serial No. 670,717

2 Claims. 1

This invention relates to a novel vacuum ,hold down for holding flat stock and the like firmly against atable top or other supporting surface, the principles of the invention being illustrated with particular reference to a bevel milling machine, although it is to be understood that this application of the invention is referred to for purposes of illustration only, as the invention may be applied to advantage in other machines and equipment.

The invention will, therefore, be described in connection with a bevelmilling machine for 'beveling the ends of wood veneer sheets and plywood panels. In the fabrication of large size plywood and veneer panels the expedient of scarf jointing of standard size sheets is utilized for making panels of, sizes far beyond the capacity of conventional plywood and veneer manufacturing equipment. Machines have been developed for making scarf joints in production quantities, but the trade acceptance of such large panels depends to a considerable extent upon the quality of the joint. In order to make satisfactory scarf joints certain requirements must be met. A perfectly fiat bevel is necessary to produce a scarf joint that will be adequately strong. Another requirem'entisthat the toe or the tip-of the scarf should be slightly blunt instead of thinning out toa ragged feather edge, so that the toe will ride slightly above the thick section of the scarf on the mating sheet'whenthe two pieces are brought together.' This is necessary in order to insure adequate pressure in the jointtoobtainthe close contact required for a successful 'bond between the bevel surfaces. The additional "thickness thus provided in *the joint compensates for the compression which "occurs under the combined heat and pressure of the-usual bonding'process and prevents the formation ota-depressed area at the joint. i

In the bowling operation, flat panel stock is clamped on a flat supporting surface in a'bevel milling machine. One or more end milling cutters are mounted on 'a'movablecarriage atthe proper angle to form the desired bevel onthe end of a toward the cutter head in certain regions causing an excessive depth of cut -to be made in those parts. When this condition exists to a slight degree the toe or tip of the scarf is out to a thin edge instead of abl'unt edge, and when this condition is aggravated, the bevel surface is found to have a concave out upon being flattened-out in a scarf joint press which concavity results in an imperfect glue line wherein the two mating beveled surfaces do not comein contact with each other in such regions. When this condition is severe the contour ofthe cut causes the bevel surface to intersect the opposite face of the sheet to form aragged edge instead of a straight, blunt toe line. Such bevels obviously produce a very poor quality of joint which --is not acceptable to the trade.

The general objcetof the present invention'is, therefore, to provide novel vacuum hold down means to hold flat panel stock and-the like firmly against a supporting surface.

A further object is to provide a novel vacuum hold down means in the stock supporting table of a bevel milling machine, directly under the cutter heads.

Another object is to provide a plurality of suction cavities in a table top, having a novel arrangement of passages, valves ;and piping for applying suction-to a certainnumber of. said cavities in accordance with the size of the stock being handled.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings illustrating a preferred embodiment of the invention, it being clearly understood that the same are by way of illustration and example only, and are not to be taken asin any way 1imiting the spirit or scope of the invention. The spirit and scope of the invention are to be limited onlyby the'terms of the appended claims.

In the drawings:

Figure 1 is a perspective ,view of a bevel milling machine incorporatingfi preferred embodiment of the novel vacuum hold down eans forming the subject matter of theinvention;

Figure 2 is a fragmentary cross sectional view through the machine shown inFigure 1 to illustrate the action of the cutter head in formin .a bevel on the end of a plywood panel, this ,view being taken on the linej2'2 ofFigure 3;

Figure 3 is a plan view showing certain parts in section on the 1ine 3- 3 of FigureZ;

Figure 4 is a sectional view taken onthe'line 4-4 of Figure 2;

7 going treatment by the machine.

Figure 5 is an enlarged sectional view showing the construction and arrangement of the vacuum cavities in the table;

Figure 6 shows a perfect bevel formed on a plywood panel by the machine illustrated in Figure 1; I

Figure 7 illustrates a scarf joint uniting two panels beveled as shown in Figure 6; and

Figure 8 is a plan view of a panel having an imperfect bevel resulting from failure to hold the stock flat against the table under the cutter heads.

In carrying out the principles of the present invention the table upon which the stock is clamped is provided with a series of cavities adapted to be covered by the stock to form vacuum chambers directly beneath the cutter heads, so as to act upon the stock in the area over which the bevel is formed. These cavities are I interconnected in groups by pipes leading to a suction line and valves are provided in these pipes for applying suction to those chambers which are covered by the stock. The suction line is connected through a control valve with a pump having sufficient capacity to quickly exhaust the air from those cavities which are covered by the stock so that atmospheric pressure is made effective over a considerable area of the pane1 directly on the surface to be beveled to make the panel lie true and fiat against the ,table top. By reason of the large area which may be utilized in this manner an enormous force may be brought to bear upon the stock to counteract any tendency to warp out of a plane surface to cause the cutter head to make an uneven cut. The suction force is controlled coordinately with the clamps ordinaril employed to hold the stock so that the panel may be instantly released at the end of the cut by a simple valve manipulation.

Referring now to the several figures of the drawing,rthe numeral In in Figure l designates the bed of the machine which comprises preferably a massive and rigid iron casting. A hardwood table top H is bolted to the bed, and on this table top is shown a plywood panel l2 under- On the rear side of the machine bed are upper and lower carriage slides 13 and I4 respectively, to provide for traverse of a carriage l5 carrying two bevel milling cutters I6. The upper slide 13 has'a sliding surface in a horizontal plane to act as a support or track to bear all of the weight of the carriage assembly. The lower slide [4 has a sliding surface in a vertical plane to act as a supportin maintaining the carriage assembly in its vertical position. These slides are machined to a high degree of precision, and the carriage base is provided with ways which are accurately machined andjprovided with adjustable gibs to insure precision movement of the carriage upon the bed in a straight line path of travel. Carriage travel is produced by an electric motor mounted on the carriage and operable through a variable speed drive and gear reduction assembly to effect driving engagement with a gear rack bolted to the machine'bed.

The upper part of the carriage comprises a pair of rigid cast iron overarms [1, each carry-.

ing a cutter motor assembly l8. Each motor assembly l8 carrying a cutter head 16 is mounted ve' ically on a bracket 20 on which it may be raised and lowered with micrometer adjustment, and tilted toward either the front or back of the machine to produce the desired angle of bevel.

The bracket 20 has accurately machined ways with adjustable gibs riding on slides 2| and 22' for movement along the over-arms for proper positioning over the work. These motor assemblies and their manner of mounting on the two over-arms [1' are substantially identical except that the parts are reversed by reason of the fact that these assemblies are mounted to faceeach other between the over-arms.

Certain of these parts are shown in greater detail in Figure 4. In this view is shown a vertical slide 23 on the motor for vertical adjustment in the way 24, which is in turn mounted on a rotatable plate 25 carried by a vertical portion 26 of the bracket 20. It is this vertical portion 26 of the bracket 20 which engages and slides upon the previously mentioned slides 22. By sliding the bracket 20 on the over-arm slides 2| and 22 the bevel may be cut at various distances from the end of the sheet. The angle of the bevel is controlled by the rotative position of the plate 25 on bracket member 26, and the thickness of the toe end of the bevel is controlled by the vertical adjustment of the omtor' assembly l8 in the way 24.

In the present machine the direction of carriage traverse is from right to left as viewed in Figures 1 and 3, and from left to rightin the rear view of Figure 4. The right over-arm is, therefore, in trailing position during traverse of the carriage, and the bracket 20 on this over-arm is provided with a disc cutter 3 0, as shown in Figure 4 to sever the toe thickness ofv veneer left at the tip of the bevel. This cutter is necessary since for the reason previously mentioned it is desirable to have a blunt toe end rather than a feather edge on the bevel to form agood scarf joint. The cutter disc 30 is journaled on a hori- Zontal pin 3| carried by a cutter bracket 32 mounted on the bracket 20. Thus, the cutter disc 30 is in a trailing position with respect to the milling cutter heads [6 to sever the end of the sheet after the bevel has been formed. 7

Along the rear side of the table top between the cutter heads l6 and the carriage slide I3 is mounted a pneumatically operated clamping bar 35 for gripping a marginal portion 36 along the end of the stock or panel [2. The bar 35 is attached to the upper ends of a plurality of vertical piston rods 31 associated with pneumatic operat ing means for exerting a substantial clamping effort upon the edge of the stock in response to valve control. The arrangementis'preferably such that when the air pressure'is released, the bar 35 will be raised by spring action to permit the removal of the severed end 36 afterthe traverse of the carriage, and: to permit the easy insertion of the next panel. The piston rods 3! may function as stops against which the panel may be abutted to hold it square with the machine for a beveling operation, or wood stops may be provided closer'to the cutter disc 30 to reduce waste. The milling heads If: and the disc cutter 30 may be moved back quite'close to the bar 35, as shown in Figure 2, to make the severed trol of a valve which also controls the action of clamping bar.

The motor switches and air valve required to produce the sav -arena eperations may be actuated by push button coritrolsoii a "co ntrol box mounted on theran as in hunt r the machine. Circuit connections are led from the control box through a stationary vertical conduit 46 and flexible conduit sections 41-. However, to avoid traveling wires the cutter motors 98 may be controlled by manualswitches directly on the fiiotdrs, and the air valve may also be shifted manually, without remotejcontrol.

The machine elements thus f-ar' described cons'titute the basic structure of one particular type of conventional bevel milling machine, there be ing many different types in, present day use. In these machines considerabie difiiculty has been experienced in obtaining a true and flat bevel' to 'ke high quality scarf joints between plywood panels. The present invention, therefore, relates to pneumatic lioldfdown'nieans to act iirConjunotidn with the reviousiy described clamps to maintain the stock absolutely true and fiat against the table top under the bevel. Whe'nthis is done the bevel will be true because the stock cannot warp or spring up into the milling cutters to produce an excessive depth of: out which will form concave areas when the sheets are flattened out in a scarf joint press. According to the present invention, the rear board of the table top H is replaced by a cast aluminum member 5!! of the same thickness and width as the original board. Provision is made in this member for securing bolts or cap screws 5i (Figs. 2 and 3) at closely spaced intervals to hold the member true and flat on top of the bed of the machine with its upper surface exactly in the plane of the table top I I. Openings 52 are provided for the piston rods 3'! associated With the clamping bar 35, and along the front edge of this clamping bar the member carries a dovetail groove '53 filled with babbitt material 54 forming a bas'eor track under the e cutterwlieel 30,'as shown in Figure 2.

Most of the remainder of the top surface of the member 50, not covered by the clamping bar 35 and the babbitt track 54, is formed into a series of cavities 55 of generally rectangular shape and having upstanding partition walls 56 therebetween. The sides of the walls 56 are inclined to produce thick sections for strength and rigidity in the member 50, leaving relatively narrow horizontal bridge surfaces 57 in the plane of the table top.

When a piece of stock such as the plywood panel I2 is placed in position on the table top I I it covers a certain number of these cavities to form closed chambers from which the air is evacuated by a suction pump. By reason of the narrowness of the bridges 51 the pressure differential thus established is caused to act over substantially the entire area across the sheet embraced by the continuous succession of cavities. The individual cavities are also relatively narrow to provide close spacing between the bridge sur faces to adequately support the stock under the weight of atmospheric pressure.

The cavities are interconnected in groups of three, as shown in Figure 5 so that suction may be applied along the length of the member 53 in accordance with the width of the stock being treated. The central cavity of each group is, therefore, tapped at 58 for connection with a suction pipe 59, and the walls of this cavity are apertured at 66 to evacuate the air from the adjacent cavities. The pipes 59 lead out to the front of the machine to valves 60 by which they are connected with a suction mainfold 6| whereby the Width of the table top to Which suction is appned ma be controlled in three cavity meremerits. It will be noted in the drawings that the central cavity of each group of three is made wider than the flanking cavities, but these rel-ative proportions and general pattern may be varied without departing from the spirit of the inverition. A suction pump is connected through a pipe '62 with the manifold 6|, this pump being of sufficient capacity to establish a relatively low pressure in thecavities which are covered by s'tockeven if valves are opened to pipes connected with several end cavities which may be uncovered. The capacity 'of the suction pump, the .size of manifold 65, and the size of pipes 59 may be chosen so that the uncovering of a few cavities will [not materially affect the degree of vacuum pr'foduced in the cavities covered by stock.

The suction or hold down effect produced by the cavities is controlled bya solenoidactuated valve 63 in the suction line 62 to operate simultaneously with the valves which control the air pressure supply for the clamping bar 35 and clamping feet till. These valves are preferably all solenoid actuated valves operated by a single push button control on the control box #5, al-

though of course. manual valves may be used. Witlrall of "the valves as closed, which are conriected with uncovered cavities, the suction limit of the ump is quickly established when the valve isopened in the line 62. Thus, a hold down ssure which may attain a possible maximum i 4.7 poundspersquare inch may be brought to bear over substantially the entire area of the betel, making it impossible for-the stock to rise into the cutter head to producea concave bevel surface.

Suitable means, such'as a pressure regulating valve, may be employed between the suction pump and the manifold St to reduce the degree of vacut um for holding more flexible stock. Where the cavities are large the degree of vacuum should be controlled to prevent the panel from being drawn into the cavities to form a concave surface instead of a flat surface on the top side. The defiection of the panels in this manner may be controlled both by varying the degree of vacuum and by varying the size of the cavities.

All. bevel milling machines are not provided with clamping means for the extreme end of the panel and in such machines the present hold down device is especially advantageous.

Figure 6 shows the panel I2 after it has been properly beveled for a scarf joint. This happens to be a three-ply panel wherein the individual veneer sheets are exposed on the bevel surface at in, ii and 12. When the bevel is fiat and true, the toe edge 13 is blunt, of uniform thickness, and forms a true straight line across the sheet. The glue lines l4 and 15 between the respective Veneers are likewise true and straight, and parallel with the edge it. The heel line 16 where the plane of the bevel intersects the top surface of the panel is also straight and parallel with the glue lines and the edge 13.

Figure 7 illustrates a scarf joint between two panels 12 and I 2 having beveled ends 11 overlapped and bonded together to form a long panel.

Figure 8 illustrates a poorly formed bevel which is frequently produced on the above described machine when the present vacuum hold down means is not employed. Here it will be observed that the clamping bar 35 and clamping feet 40 were ineffective to hold all parts of the panel [2a firmly and flatly against the table top. In. spite of the clamps a portion of the sheet buckled up slightly above the table top to cause the bevel milling cutter to take a deeper cut in that region. As a result the toe edge 13a is not straight and blunt, but runs into a feather edge at 1317 where excessive material has been removed. Likewise, the glue lines 14a and 15a and the heel line 16a trace contour lines on the bevel surface indicative of the bulge in the panel at the time of milling. This bevel surface is, of course, flat and true when formed, but when placed in a scarf joint press with the bevel surface on another panel the panels will be flattened out leaving a cavity between the juxtaposed bevel surfaces in the joint. Such a cavity interrupts the continuity of the glue line so as to make an imperfect bond and produces an irregular surface on the panel. By the use of the present vacuum hold down means these difliculties are overcome, whereby uniform high quality scarf joints may be produced consistently.

Various changes may be made in the construction and arrangement of parts in the present im- 7 provement, and all such modifications within the scope of the appended claims are included in the invention.

Having now described my invention and in what manner the same may .be used, what I claim as new and desire to protect by Letters Patent is:

1. In a wood working machine having a table top adapted to support stock thereon and having a wood treating mechanism mounted for traverse across said table top, a series of cavities in said table top extending throughout the length of said traverse and adapted to be covered by said stock to form closed chambers in a number of said cavities depending upon the width of said stock, a suction manifold, said cavities being arranged in a series of groups, the cavities in each group being communicatively connected with each other and out of communication with cavities in other groups, a pipe connecting each group of said cavities with said manifold, valves in said pipes to cut off the suction from those groups of cavities not covered by stock whereby the closed chambers under said stock may be evacuated to a relatively low pressure to hold stock of different widths firmly against said table top, and a valve for controlling the suction in said manifold.

2. In a wood working machine havin a table top adapted to support stock thereon and having means for engaging two edges of said stock in clamped relation thereto and having a wood treating mechanism mounted for traverse across said table top intermediate said two edges, a series of cavities disposed in said table top extending in the path and throughout the length 'with a source of suction, valve means to cut off the suction'fro m those groups of cavitie which do not contain any closed chambers, whereby condition of low pressure may be created in those cavities closed by the stock to effectively hold stock of different widths firmly against said table top in the path of said wood treating mechanism. s HAROLD A. SMYTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 477,306 Marsh, Jr June 21, 1892 1,683,250 Hitchcock Sept. 4, 1928' Stuart May 8, 1945

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