Patent Application
20170355103
The present application claims priority under 35 U.S.C. §119 of Great Britain Patent Application Nos. 1610155.2, filed Jun. 10, 2016, and 1613753.1, filed Aug. 10, 2016, the disclosures of which are hereby incorporated herein by reference in their entireties.
The present invention relates to drill bits, and in particular to drill bits having an annular cutting portion.
With drill bits used for cutting holes from tiles and the like, an annular cutting surface is provided which on rotation of the drill bit removes a circular disc from the tile or other object being drilled. Such drill bits are often known as hole saws and to prevent excessive heating of the abrasive cutting surface, a wax plug can be incorporated within the hollow annular body of the hole saw, the wax melting to provide a fluid that can cool the cutting surface by evaporation. Unfortunately, as drilling takes place, loose waste material is generated which combines with the melted wax, eventually forming a slug located within the drill bit which blocks the flow of wax to the cutting surface. This prevents cooling taking place and heat damage occurs, shortening the useable lifetime of the drill bit.
In accordance with the present invention, there is provided a drill bit for cutting tiles comprising a hollow body portion, typically cylindrical and so tubular, bearing an abrasive annular cutting surface at one end and a wax plug located within the hollow body portion, wherein an internal wall of the hollow body portion has at least one region of reduced wall thickness, thereby to provide a channel within the wall along which liquid wax can flow. This ensures that the wax can reach the region where cutting is taking place faster, which reduces heating occurring at the cutting surface, so improving the lifetime of the drill bit.
The region of reduced wall thickness preferably extends along the body portion at least as far as the wax plug.
The hollow body portion may be formed by a passage offset from the cross-sectional centre of the hollow body portion. As the drill bit is rotated by a drill or angle grinder, the rotation of the body portion with its region of reduced thickness provides a channel extending along the body portion and along which melted wax can flow to reach the cutting surface.
The passage is preferably offset from the cross-sectional centre of the hollow body portion by 50% or less of the width of the hollow body portion. Thus, the passage may be offset from the cross-sectional centre of the hollow body portion so that the region of reduced wall thickness has a minimum wall thickness of 0.5 mm.
The region of reduced wall thickness may be provided by at least one channel formed within the internal wall of the hollow body portion.
The hollow body preferably has an external diameter of between 3 to 16 mm, and more preferably between 3 to 7 mm with the wax cooling particularly effective for an external diameter of 7 mm or less.
If desired, a plurality of channels may be provided, preferably as circumferentially equispaced grooves around the internal wall of the hollow body portion.
The at least one channel may be a helical groove, and may be a reverse spiral thread such that the handedness of the helical groove is opposite to the sense of rotation of the drill bit during use. One or more helical grooves may be provided, for example as two, three or four threads.
The drill bit as aforesaid is particularly advantageous when used with a drilling tool, operating between 500 to 30,000 rpm such as corded and cordless drills, angle grinders and high speed rotary tools and of particular advantage for angle grinders operating between 8000 to 14000 rpm.
The invention will now be described by way of example with reference to the accompanying drawings in which:
Internal passage 20 through tube 14 is circular in cross-section and is offset by at most 50% from a centre axis 22 about which drill bit 10 rotates. Passage 20 is thus typically displaced between 0.1 to 1 mm from centre axis 22 so that the wall thickness of tube 14 varies, with a minimum wall thickness of around 0.5 mm at the narrowest region 24. Wax plug 26 is located within passage 20 close to cutting surface 16. Wax plug 26 gradually melts from heat generated by friction as cutting takes place, with liquid wax acting as a coolant on cutting surface 16 and passing between the granular cutting material to achieve cooling.
Rotation of drill bit 10 results in an elliptical rotation path 28 of offset passage 20 as shown in
The creation of a channel that cannot be blocked by slug formation maintains wax cooling at abrasive cutting surface 16, ensuring cutting material 18 is not damaged through excess heat. This increases the working lifetime of drill bit 10 as can be seen in Table 1 below where the number of holes drilled through 8 mm thick porcelain tiles at 1100 rpm was compared for prior art hole saws with wax plugs and hole saws according to the invention with an offset internal passage and wax plug. Drill bits of external diameters 5 mm and 6.5 mm were compared, with the offset passage or offset hole version increasing the number of holes drilled by over 130%. This is a significant improvement on existing hole saws.
A second embodiment shown in
In a third embodiment shown in
Increasing the number of helical threads or helical channels provides increased flow of coolant/lubricant, delivering more cooling.
While the present invention has been illustrated by description of various embodiments and while those embodiments have been described in considerable detail, it is not the intention of Applicants to restrict or in any way limit the scope of the appended claims to such details. Additional advantages and modifications will readily appear to those skilled in the art. The present invention in its broader aspects is therefore not limited to the specific details and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of Applicants' invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1610155.2 | Jun 2016 | GB | national |
| 1613753.1 | Aug 2016 | GB | national |
