CA2140327A1 - Hole cutting tool for soft materials - Google Patents

Abstract

A tool for cutting round holes in thin, soft or friable materials. In this invention, a tube with an open wall section and with a sharpened end such that the outer diameter is the cutting edge, is held against the material surface and rotated to cut circumferentially into the subject material to produce a round hole. The tool may be operated by manual rotation or by powered means. The cutting action of this tool does not cause surface splintering, tearing or splitting in soft or friable materials. The tool may include an additional internal cutter to provide the desired base surface in blind holes.

Description

SPECIFICATION

This invention relates to a m~nll~lly operated or power driven tool for cutting round holes in soft, thin or friable materials.

Conventional twist drills or Forstnertype bits do not perform s~ti~f~ctorily in soft or thin materials ~ eg. Ieather, card, rubber or thin section woods) due to the surface tearing action of the cutting edge which pulls the m~teri~l into the drill spiral and due to damage from the radial and tangential splitting forces ge~ ed by the drill tip and cutting edge. These drills normally require a centering location for initial entry. Also, a lack of positive centre as the twist drill tip penetrates the exit surface of thin or soft materials can produce a 'lobed' hole effect when using h~nllh~.ld manual or power operated tools.
Tubular cutters that are totally enclosed can only be used s~ti~f~ctorily in a fixed drive system (eg. a drill press) and may require signifir~nt pressure in operation to force the cut-offcore material through the bore of the cutter. This pressure can distort or crush the surrounding material. Such con~ll ained operation is also neces~ry to provide a fixed axial location for operation of this type of cutter to prevent unpredictable lateral motion on initial contact with the m~teri~l surface.
Hole pllnrhing methods normally require a matched punch and die set which must be accurately aligned to operate. The application of the plmr,hing method is restricted by material thickness and can crush or distort softer materials during the pllnr,hing process. Punches which cut through the material using a ~hal~ened edge only with no m~tçhing tool, are subject to the same limitations. Holes punched near the edges of m~teri~l can distort or split the material.

I have found that the disadvantages exhibited by rXi~ting cutters, drills and punches for cutting holes in soft, thin or friable materials may be o~elconR by using a tubular cutting tool having an externally sharpened end with a small rake angle and incoll,olaling an open section of the tube wall at the cutting end. The sharpened end of this open sided tool is pressed against the surface of the material to be cut and the tool rotated to produce a round hole without splintering or tearing the material (anti-clockwise as shown in Figure 2).

~ 1 4 0 3 2 7 , The cutting operation may be pelrol,lled by manual rotation of the tool (with an attached handle), using a hand held manual or power drive or by fixed drive means (e.g. a powered drill press or lathe). The maximum depth of hole cutting possible, beyond any collsll ~ s of the drive method, is restricted only by the overall length of the cutting tool.
Depending on its characteristics, the material removed by the cutting action of this tool usually remains in discrete pieces whose size depends on the plopel lies and thickness of the material, rather than small cllippil~gs or particles produced by some other drilling methods. During the cutting operation, the core material is pushed towards the open section of the tool by the wall of the tool. As it rotates, the cutter wall produces a lot~ling lateral force on the core material which tends to shear-offdiscrete pieces. This cut-offmaterial is free to be move in and subsequently be expelled from the bore ofthe tool via the slotted section without j~.,.""~ in the bore, due to the clearance provided by the slotted tube. This action prevents crushing of sensitive materials which would otherwise occur due to compression of the core material in the bore of the cutter. During the cutting operation, the tool may be periodically withdrawn to remove the core material as necess~ry. The bores of the holes cut with this tool are of smooth finish in most materials.

In dl~wh~gs which illustrate embodiments of the invention, Figure 1 is a side elevation of the embodiment. Figure 2 is an end view and Pigure 3 is a top view of this embodiment. The tool illustrated comprises a tube (3), partially slotted (4) and sharpened at the open end (2) such that the outer diameter forms the cutting edge and provides a small rake angle with the high side being the leading cutting edge in the direction of rotation. A rake angle of approx. 2 is suitable for cutting soft woods, wood veneer, leather and similar materials. The leading part ofthe cutting edge has a small radius (1) with a sharpened edge to provide a smooth entry into the material being cut. The open section of the tool is a slot in the tool wall which is the same width as the tube internal ~ met~r. The length of the slot is the miniml~m neces~ry to provide clearance for removal of the core material during the cutting operation. The tool outer circulllrelel-ce provides the m~ximllm bearing surface area so as to ",~i"~ , its concentric location in soft materials during rl~el~ld operation, while allowing lateral clearance for cut-offpieces of material to be removed without j~.",~ in the bore ofthe tool.

~1~0327 The cutting tool may be rotated m~nu~lly or by powered means. For manual rotation the tool should have a suitable handle attached. In freehand operation (manual or power rotation), the tool is rotated initially with its axis normal to the surface ofthe material being cut, while ~"~ ;ng sufficient pressure to pe~ the material. Once the tool has cut into the material surface, the tool axis may be changed while Ill~il~l~ining rotation and axial pressure to cut a hole at an angle to the surface. Manual operation could be used for delicate, soft or thin m~t~o.ri~l~, or where poweled means are not available.
~xim~m lolalional speed is limited by the heat generated from the friction between the tool and the m~teri~l being cut and thus varies with the rnaterial frictional characteristics.
As this tool does not require a centering location for its operation, holes which are eccentric to existing smaller holes can be cut without any tendency to track any previously cut hole. Where a centering location is required, an additional centre point may be located in the bore of the tool such that the tip protrudes slightly beyond the tool cutting edge.
This tool can also be used to cut slots in some materials such as soft woods, by making repeated overlapping cuts, provided that the tool is laterally con~ ined in a m~rhine such as a drill press.
This tool can be used to cut holes in thin sheet material of soft metals such as ~ l;n.~ln and brass, provided that the tool is operated in a fixed drive system such as a drill press.
Freehand operation of the tool in very flexible materials (e.g. soft rubber) requires that additional bearing support be provided to Ill~ Iateral location ofthe tool during cutting. This support may be provided by an additional layer of more rigid material such as thin plywood or card attached to the top surface of the material.
Holes may be cut in multiple layers of thin materials provided that the layers are coll,pressed sufficiently such that the cut-offpieces do not become lodged between the layers.
The tool is primarily intentled for cutting completely through the material thickness, however blind holes can also produced. To ensure that all core material is removed from the bottom of a blind hole drilled with this tool, an internal cutter can be inserted in the tool bore and attached to rotate with it. This internal cutter may be of any type such as a conventional twist drill positioned such that it does not protrude beyond the tool cutting edge.

~lgO327 Using this tool to cut from the reverse side of sheet material can produce a circular core piece which exactly fits the hole from which it was cut. This effect may be utilised to produce plugs or covers for holes cut in various types of materials.
Holes may be cut close to the edges of material without splitting or breakout using a fixed axis drive such as a drill press.

Claims (6)

1. A tool operated either manually or by powered means to cut round holes in suitable materials. This tool consists of a tubular cutter having an open section and externally sharpened end with a small rake angle. The tool is operated by rotation under axial load to cut through the material.

2. A tool as defined in claim 1, in which an internal cutter or centering device is used.

3. A tool as defined in claim 1 in which the open section width is reduced to contain or partially contain the cut-off material.

4. A tool as defined in claim 1 in which the bore contour or surface is adapted to produce high friction effects on the core material to aid breaking-off of the core material near the cutting edge.

5. A tool as defined in claim 1 in which the rake angle of the cutting edge is altered to provide improved cutting performance in specific materials.

6. A tool as defined in claim 1 in which the cutting edge is made from a different material from the tube structure eg. tungsten carbide.