Duct joint layout tool

A layout tool and a means for using the tool to fabricate multi-segment elbows and offset joints from rectangular cross-section fibrous air ductboard material. The tool has a triangular main body having at least one structural feature that defines a plane. At least one flange is connected to the main body, is oriented substantially perpendicular to the main body plane, and forms the first side of the triangle. The main body includes a first outer straight edge extending at an angle of 67.50 degrees from the flange forming the second side of the triangle. A second outer straight edge extending at an angle of 78.75 degrees from the flange forms the third side of the triangle. An inner structure of the main body forms a straight edge perpendicular to the plane of the flange. The outer angled and interior straight edges enable 22.5- and 45-degree miter joints to be easily marked and cut in pre-formed fibrous air duct. Markings on the main body indicate required distances between cuts to accomplish desired offset rises.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of measuring and marking tools having a generally triangular configuration and a flange, perpendicular to one side, projecting above and below the upper and lower surfaces of the triangle, and upon which linear measurement markings are provided on the surfaces of the triangle along the respective edge portions. In particular, this invention relates to tools having a scalene triangular configuration in which the angular orientation of the sides relative to the flange are common angles used in mitered construction and markings on a surface of the triangle providing commonly used mitered air duct joint fabrication measurements.

The use of fibrous ductboard material for heating and air conditioning ducts is well known. Such ductboard typically includes a layer of fiberglass attached to a composite outer covering. The outer covering is typically made up of a layer Kraft paper, a layer of scrim-like material, and a foil-like layer, the composition providing stiffness and forming an air-impervious outer layer for the duct. Fibrous ductboard material is commonly available in flat-sheet form or pre-formed into rectangular cross-section ducts in a variety of sizes. When flat-sheet material is used, it is conventional to cut, either by machine or the installer, a set of laterally-spaced-apart, longitudinal grooves in the fiberglass side of flat-sheet ductboard to form rectangular cross-section duct sections.

It is also well known in the duct construction field that fittings, such as elbows and offsets, may be fabricated from the ductboard material using mitered cuts on the duct. For example, a simple 90-degree elbow can be formed by cutting the duct along a plane oriented 45 degrees to the longitudinal duct axis, rotating one segment one-half turn about its longitudinal axis, and connecting the two sections at the cut plane to form a 90-degree mitered elbow. Fittings having more gradual transitions, thereby imposing less resistance on air flow, are commonly formed by reducing the miter angle and increasing the number of duct segments comprising the fitting.

In preparation for making a duct fitting, the user assembles tools including a marking pencil, an incrementally marked straight edge, a protractor, and a cutting knife and determines the dimensions of the desired fitting. The user then makes a series of cutting marks, or layout lines, on the ductboard material to define a cutting plane. Conventional flaming squares or carpenter's triangles are typically employed to make layout lines oriented perpendicular to the longitudinal axis of the duct. Non-perpendicular layout lines require the user to establish two points along the desired line with a protractor or other similar tool and then make a line using a straight edge. The duct can then be cut by drawing a cutting knife along the layout line, optionally using a straight edge as a guide, and cutting all the way thorough the ductboard material. Finally, the user aligns the resulting duct segments to form the desired fitting, reconnects the segments with adhesive, and seals the connection with duct tape. Drawbacks in using the above-described tools and method for making mitered elbows and offsets are the considerable length of time involved and the limited quality and accuracy of the resulting joint due to variations in measuring and cutting.

It is therefore the principle objective of the present invention to provide a tool and a method for selecting and making a series of quick layout lines for the most common miter angles used in air duct fitting fabrication and for aligning the edge of a cutting tool in making the cuts. It is another objective of the present invention to provide a tool and a method for controlling the accuracy and quality of miter joint cuts.

2. Description of Related Art

Numerous measuring and marking tools of the right-triangular type are known in the prior art. U.S. Pat. No. 4,513,510, by Swanson, discloses a right-triangular-shaped layout tool with a T-flange base on one side, and which is adaptable with a layout bar to provide a means for repeated marking of predetermined angles as are common in marking of stair stringer boards. U.S. Pat. No. 5,727,325, by Mussell, discloses a right-triangular-shaped tool with a T-flange on one side and markings to facilitate aligning the tool on workpieces at selected angles commonly used in rafter and stair stringer framing. U.S. Pat. No. 6,622,394, by Werner, discloses a right-triangular-shaped measuring tool with a T-flange for aligning the tool base to the workpiece. Indicia along the hypotenuse in conjunction with a defined origin allow marking of acute angles commonly used in deck construction. U.S. Pat. No. 6,688,014, by Allemand, discloses a right-triangular-shaped measuring and marking tool that includes internal structures for marking frequently used wood frame construction dimensions and a method of using the tool to mark layout lines common in wood frame construction.

These measuring and marking tools have limited efficacy compared with the present invention. All are based on a right triangle having a flange perpendicular to one leg of the triangle useful for rapidly aligning the tool with an edge of the workpiece. The limitation with this right-triangular design is that the second leg of the right triangle is always perpendicular to the flange, leaving only the hypotenuse available for non-perpendicular layout lines. To overcome this limitation, each tool includes structures for marking other common framing angles. However, using these features is a multi-step operation. One method requires making a pair of marks to define a line, moving the tool, and using a straight edge to draw the desired line. Another method requires visually aligning two or more points on the tool with a reference edge of the workpiece to establish the desired angle and then drawing the desired line. In the former method, making a layout line is a three-step process; the second method requires two steps and fails to take advantage of the T-flange for quick and accurate tool alignment with the workpiece.

In addition to framing tools, drawing instruments are known in the prior art. U.S. Pat. No. 2,610,407, by McQuaid, discloses a drafting instrument incorporating straight edges inclined at angles commonly used in making axonometric projection drawings. U.S. Pat. No. 4,455,760, by Arceneaux, discloses a drafting instrument incorporating straight edges inclined at angles commonly used in making isometric projection drawings. These instruments depart from a standard right-triangular-shaped design and incorporate interior structures thereby increasing the number of straight edges offered in a single instrument. As drafting instruments, these instruments do not incorporate a T-flange to align the instrument against a workpiece corner. Alignment to a reference line is commonly performed using a T-square or similar drafting apparatus.

Layout and fabrication tools specifically useful for working with fibrous ductboard material are also well known in the prior art. U.S. Pat. No. 4,179,808, by Smith, discloses a movable tool guide for cutting and removing wedge-shaped pieces from sheet-form fibrous ductboard material enabling air duct transition pieces of a range of sizes to be formed. U.S. Pat. No. 4,608,902, by Ivey, discloses a portable measuring and cutting tool guide for cutting parallel V-grooves in fibrous ductboard material enabling rectangular air duct to be formed from flat-sheet material. These tools are designed to make layout lines and cuts on ductboard material in sheet form needed to form rectangular cross-section ducts, but they are not suited to working with pre-formed rectangular cross-section ducts.

SUMMARY OF THE INVENTION

The present invention is a measuring and layout tool providing straight edges oriented such that layout marks and cuts commonly used in fabricating elbows and offsets in rectangular cross-section duct can be made more easily. The invention essentially comprises a main body structure having a triangular outer perimeter with a flange affixed perpendicular to a base edge of the main body structure. The base-edge flange allows quick and consistent alignment of the tool with a corner edge of a rectangular cross-section duct workpiece so that the main body structure lies across a face of the workpiece.

One of the remaining two outer edges of the main body structure is offset 22.5 degrees from a line perpendicular to the base-edge flange. Miter cuts of 22.5 degrees are used to form 45-degree miter joints in ducts. Two 45-degree miter joints may be combined to form a three-segment, 90-degree elbow fitting. Forty-five-degree miter joints may also be use to fabricate sharp transition offset fittings useful for making parallel shifts, or offsets, of the longitudinal duct axis.

The remaining outer edge of the main body structure is offset 11.25 degrees from a line perpendicular to the base-edge flange. Miter cuts of 11.25 degrees are used to form 22.5-degree miterjoints in ducts. Four 22.5-degree miter joints may be combined to form a 90-degree elbow fitting having a smoother transition than the elbow fitting made using 45-degree miter joints. Smooth transition offset fittings using 22.5-degree miter joints may also be fabricated using the 11.25-degree outer edge of the layout tool.

A portion of the main body structure is removed to form an interior structure having a straight edge oriented perpendicular to the base-edge flange. The perpendicular straight edge aids in layout and cutting of duct faces that must be cut perpendicular to the longitudinal duct axis to form a mitered duct joint.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiment shown inFIG. 1is a layout tool10consisting of a main body structure12having a generally triangular periphery and a substantially planar surface. The periphery of main body structure12is formed by base edge14, 22.5-degree straight edge16, and 11.25-degree straight edge18. In the preferred embodiment, base edge14measures approximately 14⅝ inches long, 22.5-degree straight edge16is approximately 25⅝ inches long, and 11.25-degree straight edge is approximately 24⅛ inches long. A portion of main body structure12is removed to form an interior opening that includes 90-degree straight edge20. The layout tool10has a first planer surface24facing in one direction and a second planar surface26facing in the opposite direction, said surfaces being parallel and separated by a short distance ranging from about ⅛ inch to ¼ inch. Though the invention may be made of any suitably rigid material, such as steel, aluminum, or plastic, the preferred embodiment is made of plastic.

Linear measure markings28located on first planar surface24along 22.5-degree straight edge16and along 11.25-degree straight edge may be used to define distances in the manner as a ruler.

A first data table30is marked on first planar surface24and provides information useful for elbow-fitting layout. First data table30is shown inFIG. 3. A second data table32is also marked on first planar surface24and provides information useful for offset fitting layout. Second data table32is shown inFIG. 4. Use of first data table30and second data table32is described later in this specification.

Referring toFIG. 2, base flange22is shown affixed to main body structure12. Base flange22is oriented perpendicularly to main body structure12such that a first portion of base flange22extends outwardly from first planar surface24approximately ⅝ inch and a second portion of base flange22extends outwardly from second planar surface26approximately ⅝ inch. The length of base flange22is approximately equal to the length of base edge14.

Fabricating rectangular cross-section duct fittings requires the user to make at least one miter cut of the duct. Using layout tool10improves the efficiency of the layout and cutting steps. Forming a miter cut of a rectangular cross-section duct requires the user to cut each of the four faces of the duct. The user must cut two faces opposite of each other at an acute angle measured relative to the longitudinal axis of the duct. The remaining two faces of the duct must be cut along lines that are perpendicular to the longitudinal axis of the duct; however, the cuts through the ductboard wall thickness must be angled to match the acute angle used for the first angled cuts.

The user first determines the orientation of the desired bend in relation to the duct dimensions to identify a starting point110. Staring point110is located on a first longitudinal corner112of workpiece50. If the duct cross-section is square, the location of starting point110is immaterial. For rectangular cross-sections, the user's determination is based on whether the miter bend occurs on the major side or on the minor side of the duct. For major-side miters, the user makes cuts displaced by an angle from a line perpendicular to the longitudinal duct axis on the major sides of the duct to form the miter. Cuts on the minor sides are made perpendicular to the longitudinal duct axis. For minor-side miters, the user makes the angled cuts on the minor sides and perpendicular cuts on the major sides.

Next, the user determines the miter angle necessary for the desired fitting. Layout tool10is useful for making 22.5-degree and 45-degree miter bends in rectangular cross-section ducts. A 45-degree miter bend is used in this description. Forming a 22.5-degree miter bend from this description requires only substitution of 22.5-degree straight edge16with 11.25-degree straight edge18in the following description.

Once starting point110is determined, the user positions layout tool10on workpiece50so that the intersection of base flange22and main body structure12rests along first longitudinal corner112, main body structure12rests on first face114, and 22.5-degree straight edge16is aligned with starting point110oriented in the desired direction of the miter cut as shown inFIG. 5. First planar surface24faces away from workpiece50, but if the desired miter is in the opposite direction, layout tool50could be turned over so that first planar surface24is adjacent to workpiece50. With layout tool10positioned, the user makes first layout line116on first face114along 22.5-degree straight edge, extending from first longitudinal corner112to second longitudinal corner122. Second point120is located at the intersection of first layout line116and second longitudinal corner122. The user cuts the ductboard material along first layout line116with the cutting blade oriented perpendicular to the plane of first face114.

InFIG. 6, the user positions layout tool10on workpiece50so that the intersection of base flange22and main body structure12rests along second longitudinal corner122, main body structure12rests on second face124, and 90-degree straight edge20is aligned with second point120. Second face124is adjacent to first face114. With layout tool10positioned, the user makes second layout line126on second face124along 90-degree straight edge20, extending from second longitudinal corner122to third longitudinal corner132. Second point120is located at the intersection of first layout line116and second longitudinal corner122. The user cuts the ductboard material along second layout line126with the cutting blade oriented parallel to first layout line116.

The method of making a layout line and cutting third face134is shown inFIG. 7. Third face134is adjacent to second face124and opposite of first face114. The user positions layout tool10on workpiece50so that the intersection of base flange22and main body structure12rests along third longitudinal corner132, main body structure12rests on third face134, and 22.5-degree straight edge16is aligned with third point130and oriented such that it is parallel with first layout line116. Aligning 22.5-degree straight edge so that it is parallel with first layout line116generally requires the user to turn layout tool10over so that the planar face that was adjacent to workpiece50to make the first and second layout lines now faces away from workpiece50. As shown, second planar surface26faces away from workpiece50. With layout tool10positioned, the user makes third layout line136on third face134along 22.5-degree straight edge, extending from third longitudinal corner132to fourth longitudinal corner142and parallel to first layout line116. Fourth point140is located at the intersection of third layout line136and fourth longitudinal corner142. The user cuts the ductboard material along third layout line136with the cutting blade oriented perpendicular to the plane of third face134.

As shown inFIG. 8, the user positions layout tool10on workpiece50so that the intersection of base flange22and main body structure12rests along fourth longitudinal corner142, main body structure12rests on fourth face144, and 90-degree straight edge20is aligned with fourth point140. In this position, straight edge20also aligns with starting point110on first longitudinal corner112. Fourth face144is adjacent to first face114and opposite of second face124. With layout tool10positioned, the user makes fourth layout line146on fourth face144along 90-degree straight edge20, extending from fourth longitudinal corner142to first longitudinal corner112. The line should intersect first layout line116at starting point110. The user cuts ductboard material along fourth layout line146with the cutting blade oriented parallel to first layout line116.

InFIG. 9, cutting plane150is defined by first layout line116, second layout line126, third layout line136, and fourth layout line146. Cutting plane150is oriented at miter-cut angle152which is measured from a plane perpendicular to the longitudinal axis of the duct, 22.5 degrees in the described example. Cutting workpiece50along cutting plane150results in a first segment160and a second segment170.

FIG. 10shows mitered fitting180. Mitered fitting180is formed by joining first segment160and second segment170at cutting plane150after rotating either first segment160or second segment170by 180 degrees about its longitudinal axis. The two segments are joined at cutting plane150using conventional adhesives and tape. Miter angle154is the angular displacement of the longitudinal axis of mitered fitting180. The value of miter angle154is twice the value of miter-cut angle152.

Users can form a variety of duct fittings by making additional cuts specifically oriented relative to first cutting plane150and selecting an appropriate miter angle for the cutting plane using layout tool10and the method described. Referring toFIG. 11, a three-segment, 90-degree elbow can be formed by marking a second cutting plane250on workpiece50using layout tool10such that the angle between first cutting plane150and second cutting plane250is bisected by a plane perpendicular to the longitudinal axis of the duct. First cutting plane150and second cutting plane250are separated by inside measure164. The user determines inside measure164by selecting the desired throat166to suit construction needs. Throat166may also be referenced as an inside radius of the elbow fitting. The user locates the desired throat on first data table30and selects the corresponding inside measure164. When the user cuts workpiece50along the first and second cutting planes, three segments result, shown inFIG. 11as first segment160, second segment170, and third segment162. Third segment162is in the shape of an isosceles trapezoid when a face on which miter cuts are made is viewed perpendicularly. By rotating third segment162by 180 degrees about its longitudinal axis and joining the three segments at the cuttings planes, the user can form a 90-degree, three-segment elbow280having two 45-degree miter joints and a desired throat166as shown inFIG. 12.

FIGS. 13 and 14show a five-segment, 90-degree elbow fitting that can be formed by selecting a miter cut angle152of 11.25 degrees which may be accomplished by using 11.25-degree straight edge of layout tool10to lay out and cut the angled faces of workpiece50. Five-segment, 90-degree elbows are desirable since their use results in less resistance to air flow in a completed duct. A five-segment, 90-degree elbow380can be formed by marking a second cutting plane250, a third cutting plane152, and a fourth cutting plane252on workpiece50using layout tool10. The angle between first cutting plane150and second cutting plane250is bisected by a plane perpendicular to the longitudinal axis of the duct. Third cutting plane152is oriented parallel to first cutting plane150. Fourth cutting plane252is oriented parallel to second cutting plane250. Each cutting plane is separated from the adjacent cutting plane by inside measure164. Inside measure164is determined by selecting the desired throat166to suit construction needs. Throat166may also be referenced as an inside radius of the elbow fitting. The user determines inside measurement164by locating the desired throat on first data table30and selecting the corresponding inside measurement164. When the user cuts workpiece50along the cutting planes, five segments result, shown inFIG. 13as first segment160, second segment170, third segment162, fourth segment262, and fifth segment352. Third segment162, fourth segment262, and fifth segment362have the same geometric shape and dimensions. The segments have the shape of an isosceles trapezoid when a face on which miter cuts are made is viewed perpendicularly. By rotating third segment162and fifth segment362by 180 degrees about their longitudinal axis and joining the five segments at the cuttings planes, the user forms a 90-degree, five-segment elbow380having four 22.5-degree miter joints and a desired throat166as shown inFIG. 14.

FIGS. 15 and 16show an offset transition fitting fabricated using layout tool10and the described method for making a cutting plane. Offset transition fitting480may be fabricated by making a second cutting plane250on workpiece50such that second cutting plane250is oriented parallel to first cutting plane150. First cutting plane150and second cutting plane250are separated by offset measure264. The user determines offset measure264by selecting the desired offset266and miter angle152to suit construction needs. A miter angle of 22.5 degrees results in 45-degree miter joints and is referred to as a sharp offset. A miter angle of 11.25 degrees results in 22.5-degree miter joints and is referred to as a gradual offset. The user locates the desired offset dimension on second data table32, selects either sharp offset or gradual offset, and selects the corresponding offset measure264. When the user cuts workpiece50along the first and second cutting planes, three segments result, shown inFIG. 15as first segment160, second segment170, and third segment168. Third segment168is in the shape of a parallelogram when a face on which miter cuts are made is viewed perpendicularly. By rotating third segment168by 180 degrees about its longitudinal axis and joining the three segments at the cuttings planes, the user forms a three-segment offset480having a desired offset266as shown inFIG. 15.

It is to be understood that the form of this invention as shown is merely a preferred embodiment and the methods described are ones most commonly used. This invention may be embodied in several forms without departing from its function. Various changes may be made in the function and arrangement of parts; equivalent means may be substituted for those illustrated and described; and certain features may be used independently from others without departing from the spirit and scope of the invention as defined in the following claims.