United States Patent 3673689

This specification discloses an instrument intended for field use in marking pipe insulation for the cutting of miters so that the insulation may be applied to a pipe elbow. The instrument comprises an elongate strip having a working face and flanges at one edge normal to the strip and extending in opposite directions from the strip. A straight edge is pivoted adjacent to one end to the strip and over the working face. The latter displays two sets of indicia. One of these is an angular index which indicates the angle which the straight edge is to assume with respect to an edge of the strip for a particular range of pipe sizes and the other is a lineal index which indicates where a second cut is to be made in relation to a first cut as determined by pipe size.

Application Number:
Publication Date:
Filing Date:
Primary Class:
International Classes:
B25H7/00; (IPC1-7): B43L7/06
Field of Search:
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US Patent References:
2327058Instrument for establishing points for drawings1943-08-17O'Keefe

Primary Examiner:
Haroian, Harry N.
What is claimed is

1. For use in marking a semicylindrical piece of pipe insulation having a semicylindrical inner surface and flat edge faces for the purpose of cutting miters therein, an instrument comprising:

2. The instrument of claim 1 together with a handle on one end of said strip.

3. The instrument of claim 2 in which the handle is formed with a slot which receives an end portion of the straight edge when the instrument is collapsed into a condition of nonuse.

4. The instrument of claim 1 in which the pivot means comprises a sleeve having a threaded bore and a head and a screw received in said threaded bore.

The present invention relates to scribing instruments of the type commonly known as bevels and is concerned primarily with an instrument which, due to its structural characteristics, is particularly adapted for use by a mechanic in the field for the marking of pipe insulation to facilitate the cutting of miters thereon.


At the present time the covering of pipe with insulation is widespread. In many instances pipe elbows must be covered. Pipe insulation as provided by the manufacturer comes in semicylindrical lengths for pipes of different sizes. If the 90° curve of an ell is to be covered it means that miters must be cut therein. The number of such miters varies with pipes of different sizes and the angle of a miter cut is related to the number of miters for any particular elbow and hence to the pipe size.

When insulation is prepared in a shop there is no problem attending the cutting of miters because miter boxes are ordinarily available and may be conveniently used. However, the occasion often arises when the miters must be cut in the field without shop conveniences. Present day field practices are at best awkward and carried out with difficulty.

For a good understanding of the problems attending the field cutting of pipe insulation it is necessary to set forth the conditions which must be accommodated. Thus welded ells are of two types. One is of short radius and the other of long radius. Then as mentioned above the number of miters in the insulation for an ell varies with the sizes of pipes.

Pipe ordinarily is classified in three size ranges. Thus one range embraces pipe having a diameter of from 1 to 4 inches. For pipes within this range four miters are formed in the insulation. This means that each miter has edges at an angle of 22 1/2°. Thus each cut which determines a side of the miter is at an angle of 11 1/4° with respect to a longitudinal dimension of the insulation.

The second range embraces pipes 5 and 6 inches in diameter. For such pipe six miters are formed at each ell. This means that the sides of each such miter are at an angle of 15° each side of one of these miters at an angle of 7 1/2° to the longitudinal dimension of the insulation.

The third range are pipes of 8 and 10 inch diameter. Eight miters are required for this range which means that the angle of each miter is 11 1/4° with each side of the miter being at an angle of 5 5/8° to the longitudinal dimension.

It is now common practice for a mechanic to make a mark on the insulation where the wide end of the first miter cut is to be made. It is now necessary to inscribe lines on the two flat edge faces of the insulation at the proper angle, determine where the second cut is to be marked, and inscribe lines on the edge faces for the second cut. It is these operations subsequent to making the first mark which have presented difficulties to the mechanic.


With the foregoing conditions in mind the present invention has in view the following objectives:

1. To provide a simple instrument which may be used by a mechanic in the field to mark a semicylindrical piece of pipe insulation where a miter is to be cut therein.

2. To provide an instrument of the character noted which will accommodate the two types of welded ells now commonly used and the three ranges of pipe sizes.

3. To provide an instrument of the type noted which includes an elongate strip having flanges normal to an edge thereof and extending in opposite directions therefrom and a working face, together with a straight edge pivoted adjacent one end to said strip over the working face.

4. To provide an instrument of the kind described in which the working face displays two sets of indicia. One of these is an angular index for determining the angle of the straight edge with respect to an edge of the working face for pipe of a particular size. The other is a lineal index which indicates where the second mark is to be made on the insulation as a base for inscribing the lines on the insulation faces for the second cut of that miter.

5. To provide, in an instrument of the character noted, a pivot which includes means for clamping the straight edge to the strip with sufficient pressure to generate friction which will maintain the straight edge and strip in an adjusted position whereby the instrument may be inverted after the lines for the first miter cut are inscribed on the insulation and the adjusted relation maintained for inscribing the lines for the second cut.

Various other more detailed objects and advantages of the invention such as arise in connection with carrying out the above noted ideas in a practical embodiment will in part become apparent and in part be hereinafter stated as the description of the invention proceeds.


The foregoing objects are achieved by providing an instrument comprising an elongate strip having a working face terminating in parallel side edges. A pair of flanges normal to the strip extend in opposite directions from this edge. A straight edge is pivoted at a point spaced from one end to this strip over the working face with the pivot being of the type which will generate a desired degree of friction between the strip and straight edge. The working face displays two sets of indicia. One is an angular index which indicates the angle at which the straight edge is to be position for pipe of a particular size range and the other is a lineal index for indicating where a second mark is to be made on the insulation for determining where the lines on the insulation face are to be inscribed for the second cut of the miter.

For a full and more complete understanding of the invention, reference may be had to the following description and accompanying drawings wherein:

FIG. 1 is a perspective illustrating a piece of insulation and the instrument of this invention positioned thereon at the first mark where the lines for one side of a miter are to be inscribed.

FIG. 2 is a top plan depicting the straight edge as adjusted to the angle required for a particular range of pipe sizes.

FIG. 3 is another top plan showing the instrument inverted and positioned for inscribing the lines for the second cut of a miter.

FIG. 4 is a transverse section through the insulation and a portion of the instrument, being taken on the plane of the line 4--4 of FIG. 3.

FIG. 5 is a detail, taken on an enlarged scale, of a portion of the working face of the strip and illustrating the angular index.

FIG. 6 is an elevation of a pipe ell covered by insulation and depicting the miters therein.

Referring now to the drawings, and first to FIG. 6, a pipe ell is therein illustrated as including two pipe elements 10 and 11 in right angular relation. Purely for exemplary purposes this pipe is of a diameter ranging from 1 to 4 inches. The ell is covered by insulation 12 which means that four miters 13 are formed therein to accommodate the 90° bend in the ell.

Referring now to FIGS. 1 to 4 inclusive a piece of semicylindrical insulation is shown at 14. The latter has a semicylindrical inner surface 15 and flat edge faces 16 which meet surface 15 at corners 17. Faces 16 must have lines inscribed thereon where cuts are to be made to remove material resulting in miters 13.

The instrument of this invention comprises a strip 18 of any material having the required properties of strength and rigidity such as metal or plastic. Strip 18 has a working face 19 terminating in parallel edges 20 and 21 (FIG. 5) which function as indicating edges. Extending from edge 20 of strip 18 are two flanges 22 and 23 which are normal to strip 18. At one end strip 10 is provided with a handle 24 formed with a slot 25 for a purpose to be later described.

A straight edge 26 which is preferably of the same material as strip 18 is of a length sufficient to span the faces 16 of any piece of pipe insulation for all sizes of pipe. It has a scribing or guide edge 27. Straight edge 26 is pivotally mounted on strip 18 at pivot point 28 which is offset from the center of straight edge 26.

Referring now more particularly to FIG. 4 this pivot is provided by a well known screw and sleeve device. The latter comprises a sleeve 29 having a head 30 and a threaded bore. A screw 31 is received in this threaded bore and may be tightened to a degree providing the pressure for generating a desired friction between engaging surfaces of strip 18 and straight edge 26.

The shorter portion of straight edge 26 may be received in slot 25 of handle 24 when it is desired to collapse the instrument for storage purposes.

Referring again to FIG. 5 working face 19 displays an angular index 32 at edge 21. This index comprises a line 33 for the angle of 11 1/4°, a line 34 for the angle of 7 1/2° and a line 35 for the angle of 5 5/8°. These are the angles formed between scribing edge 27 and edge 21.

Working face 19 also displays a lineal index made up of two scales. One is for long radius ells and is marked LR on FIGS. 2 and 5. The other is for short radius ells and is designated SR. Each scale includes numerals designating different pipe sizes of the ranges above noted and a line extending from each such numeral to edge 20 in a direction perpendicular thereto and terminating at the inner face of flange 23.


While the mode of operation and manner of using the instrument are believed to be obvious from the illustrations of the drawing and description of parts set forth above they are outlined as follows:

Screw 31 is first just threaded into sleeve 29 to the extent to create that degree of friction between straight edge 26 and strip 18 which may be overcome to adjust the relative position of these members yet hold them in adjusted relation during subsequent manipulation of the instrument.

Ordinarily a mark is made on the insulation where the wider end of a miter cut is to be marked. The instrument is now located at this mark. As an alternative this mark may be made after the instrument is positioned. The mark is indicated in FIG. 1 at 36. In this position flange 22 engages surface 15 just below corner 17 and by urging flange 22 against the insulation the position is fixed.

Straight edge 26 is now swung on its pivot to bring scribing edge 27 into coincidence with one of the lines 33, 34 or 35 of the angular index. As shown in FIG. 2 edge 27 is at line 33 and thus at the angle for pipes ranging in size from 1 to 4 inches in diameter. A scribing implement such as indicated in phanton in FIG. 1 is now used to inscribe lines 37 and 38 on faces 16 of the insulation.

With the instrument still in this position a second mark such as shown at 39 (FIGS. 2 and 3) is now made on the insulation 16. The location of this second mark is determined by the type of ell and size of pipe as indicated on one of the scales of the lineal index.

The instrument is now inverted with strip 18 and straight edge 26 maintaining the adjusted angular relation. It is positioned with scribing edge 27 at second mark 39. Scribing edge 27 is now used as a guide in inscribing a second set of lines corresponding to lines 37 and 38 on insulation faces 16. The instrument is now removed and the two miter cuts made in a well known manner.

While a preferred specific embodiment of the invention is hereinbefore set forth, it is to be clearly understood that the invention is not to be limited to the exact construction, mechanism and device illustrated and described because various modifications of these details may be provided in putting the invention into practice.