GB2472002A

GB2472002A - Heating device for evaporating volatile compounds

Info

Publication number: GB2472002A
Application number: GB0912535A
Authority: GB
Inventors: Matthew Adam Shoul; Matt Shoul
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-07-20
Filing date: 2009-07-20
Publication date: 2011-01-26
Anticipated expiration: 2029-07-20
Also published as: GB2472002B; GB0912535D0

Abstract

A heating device for evaporating volatile compounds into the air comprises a top surface 11, at least one support member 12, and a base 13. The top surface has a bowl 2 for receiving a quantity of a volatile compound, such as an essential oil, with at least one support member connected to and supporting the top surface, and a base connected to each support member to stabilise the heating device. The base has a heat source retainer 5 located beneath the bowl for retaining a naked flame heat source such as a candle 10, so that in use, a heat source is located beneath the bowl in order to heat a volatile compound placed in the bowl. The top surface and each support member are provided with heat dissipating elements which are capable of dissipating heat from the bowl during use. Preferably, the heat dissipating elements include round holes 3 in the top surface, which are arranged in an isometric array. The support members may include `S' shaped slots 4 to restrict the flow of heat from the top surface to the support members. Preferably, the heating device is made out of a metal, such as aluminium.

Description

Volatile Substance Heater

BACKGROUND

Technical Field of the Invention

Essential oils are used by people to fragrance their environment for a variety of reasons, some may involve alternative medicine, being used as a mood enhancer or to ease congestion or alleviate other symptoms. Others may use essential oils simply for the aesthetic pleasure of their scent or to mask unwanted smells.

Essential oil burners are predominantly used by women and those of a New Age disposition, in terms of their lifestyle choices, belief systems, fashion and other consumer tastes.

Description of Related Art

There are an increasing number of devices for evaporating essential oils, which work in differing ways, the more recent of which use electricity to either warm the oils directly or atomise water which contains the oils. The more traditional method involves floating a few drops of oil on water, which is heated using a tea light candle, of which WO 97/1 7996 (Davey) is an example. There are various problems with using any device which relies on electricity, in the current carbon footprint conscious era in which we live and there is certainly a major Green Issue encouraging a move away from the proliferation of consumer electrical devices and an over dependance on them. The two primary types of electrical essential oil heaters currently available include those which are ceramic blocks, housing a simple thermostatically controlled heating element, while the other type atomises water into fine air borne droplets, using an electric motor to vibrate an oil bearing water source. Both kinds of electric device run the risk of being left switched on indefinitely, due partly to their safety feature of not using a naked flame. This poses similar environmental criticisms about their use, as to those raised about recharging mobile phones overnight and the consequential wasteful use of electricity. People often use their essential oil devices as part of their bedtime routine and fall asleep with their heaters still switched on -as there is no perceived fire risk -or simply forget that they've left them switched on altogether, only realising the fact when they next come to use the electric essential oil device, days or possibly weeks later.

Aside from the general environmental issue.s against using electrical essential oil diffusing devices, in the event of wishing to enjoy essential oils in situations where electricity is not available, for whatever reason, a candle based device will function, whereas an electrical one will not.

A standard tea light cup, measuring 15mm high and 37mm in diameter, has a volume of 16.125cm3 containing 14.5g of paraffin wax, at O.9g/cm3, which is now being increasingly replaced with soy wax, sourced from soy beans, as a sustainable and ecologically sound alternative, with a lower hydrocarbon weight wax molecule. The ratio of Carbon to Hydrogen in paraffin wax is 1:2, whether the lightest or heaviest grade of paraffin wax is considered [C20H42 being the lightest & C40H82 being the heaviest]. If all the Carbon from a C40H82 paraffin tea light were converted into C02, on combustion, it would release 17.71g of C02 into the environment -although some wax is often left unburned and some is converted onto CO. The C02 produced in generating the electricity from a carbon fuel source, to power a 4W electrical heating element typical for an electrical essential oil heating device, over the same four hour period as a typical tea light burns for, exceeds this 17.71g of C02 carbon footprint figure, by 6%, if gas is the fossil fuel. Although the emissions are fairly similar, once the candle has finished burning, it's emissions cease, whilst the electric heater can be left switched on, unintentionally, indefinitely.

Current candle based devices will always present a significant element of risk, as the oil-on-water versions risk boiling dry, leaving the oils in direct contact with an overheating glass, ceramic or metal surface,, posing an ignition hazard, particularly with many oils having low flash-points, such as Cypress oil 39CC, Juniper Berry 41°C & Pine oil 42°C, being examples of the lowest three. Although the water initially helps to control the maximum temperature of the oil, if left' unattended, the standard 4 hour burn time of a tea light can completely boil away the water, leaving the burner without any cooling mechanism, which increases the likelihood of posing a burning or scalding risk, if the burner is carried after being alight for some time. The wax of tea light candles also tends to completely liquify, after being alight for a while, which can pose an ignition risk, of the pool of molten wax, depending on the level of ventilation of the enclosure housing the candle. Another failing in the oil-on-water style burners, is that cold tap water can take quite some time to heat up adequately for the oils to begin to impart their scent to a room, which encourages the use of hot water, to temper the burner, but this further increases the risk of the water boiling dry.

SUMMARY OF THE INVENTION

The present invention is set out in the claims.. The volatile substance heater overcomes a number of the failings described in conventional burners. The heater does not use water, so is therefore simpler to use and there is no boil dry risk. The heater employs a number of holes and slots which collectively manage the transfer of heat through the constituent elements of the burner: each of which need to be maintained within differing temperature ranges. Being candle operated, the heater does not add to the demands made on the national grid and has no electrical components which will fail in time and stop working as they were designed to. The heater has no moving parts and very few components, all of which are permanently fixed in place, adding to it's rugged reliability and longevity. The burner is almost entirely made from a single box section extrusion of aluminium alloy, rendering it shatter proof, highly corrosion resistant and very robust.

The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the present invention with reference to the drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an isometric view of the heater, from above.

Figure 2 is an isometric view of the heater from below.

Figure 3 is a side elevation.

Figure 4 is a perspective view of the disc, which may be nylon, acetal, PTFE-CF or PTFE-CGF, a ceramic material or absent altogether.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT'

A preferred embodiment of the heater is one in which the aluminium alloy box section extrusion, 1, is 4" x 4" square, has a wall thickness of 1/4" and it's overall form is that of a cube. This adds significantly to the stability and therefor the safety of the heater, affording it a low centre of gravity, so it is difficult to topple and will stay upright even if placed on an uneven or unlevel surface: up to almost 45 inclined.

The heater is comprised of a single aluminium box section extrusion, 1, in which there is an oil well, 2, a number of holes, 3, slots, 4, a candle mounting comprising a hole,. 5, a base disc, 6, with three tapped holes, 7, three socket head bolts, 8, fitting in 3 holes, 9. The candle mounting holds a tea light candle, 10. The box section has atop, 11, two sides, 12, and a base, 13.

i) The oil well, 2, is a partial spherical void, which is too shallow to contain a large volume of oil, this small capacity serves as a safety feature: a small amount of oil is sufficient for aromatic purposes and provides less fuel to feed a fire. In the highly unlikely event of the oil igniting, it would rapidly burn off, creating less heat than if a * larger oil well were present, capable of containing a larger amount of oil. The holes, 3, which surround the oil well, 2, are 12mm in diameter and pass through the top surface of the box section, 1, and are arranged in an isometric array. The isometric array of holes, 3, is such that there is a minimum amount of aluminium between each hole, to maximise the surface area of aluminium exposed to the air, and yet retain sufficient strength to maintain a robust panel structure. The hole spacing in the preferred embodiment is 16mm, centre to centre, with the hole diameters being 12mm, leaving a minimum hole to hole spacing of 2mm of aluminium. Other embodiments may alter this current preferred embodiment, to further increase the surface area of aluminium exposed to the air, to make the top surface of the box section, 1, lose heat gained from a burning candle, 10, even more efficiently. There are two slots, 4, in each side, which partially separate the top surface, 11, from the two sides, 12. The base, 13, has a hole through it, 5, which contains a thermally insulating disc, 6, made of acetal, a similar material, or a ceramic material, held in place by three socket head bolts, 8, which pass through holes, 9, in the base, 13, into three tapped holes, 7, in the disc, 6.

This candle mounting, comprised of elements 5, 6, 7, 8 & 9, locates a tea light candle, 10, centrally within the box section, 1, directly below the oil well, 2.

ii)The isometric array of holes, 3, help prevent the top, 11, from becoming too hot, by losing heat to the air within the holes, 3. The slots, 4, in this embodiment are such that an S shaped rod of aluminium is defined between them, which serves to thermally isolate the hot top, 11, from the sides, 12, maintaining a significant temperature gradient between the top, 11, and the sides, 12. This makes it possible to hold the box section sides, 12, in comfort, even after the tea light candle has been continuously lit for it's maximum burn time of four hours or more.

The candle mounting, 5, 6, 7, 8 & 9, holds a tea light candle, 10, in such a way that it is not in contact with the base disc or the sides of the candle mounting hole, 5.

This serves to thermally isolate the tea light candle from the box section, 1, and so prevent unwanted heat from entering the base, 13, from the tea light candle, when in it's liquified state, and migrating through the base, 13, to the sides, 12, which need to be cool enough to hold in comfort. The socket head bolts, 8, are held in place by the holes, 7 & 9, in a specific triangular configuration and spacing, so that when a standard tea light candle, with an approximate diameter of 37mm is pushed inbetween the heads of these socket head bolts, 8, the candle, 10, is slightly deformed and is firmly gripped by the bolt's heads. The surface area of contact between the base of the aluminium cup of the tea light candle, 10, and the socket cap bolt heads is small, reducing the efficiency of heat transfer between the candle, when in a liquified state, and the bolt heads. The blots, 8, may be made out of stainless steel or a thermally insulating material such as a ceramic. The thermal behaviour of the holes, 3, in conjunction with the thermal behaviour of the slots, 4, and the thermal behaviour of the candle mounting, 5, 6, 7, 8 & 9, help create and maintain distinct temperature zones, which are specifically suited to the function and purpose of those zones, within the box section, 1. The sides, 12, of this heater, which one could reasonably assume a person would hold onto, if they chose to pick it up while in use, will maintain a temperature significantly bellow 55°C, which is the maximum permitted by EU safety regulations, pertaining to the hand holding portion of metal cookware and metal devices such as this. The thermal behaviour of the parts described, collectively contribute to maintaining the thermodynamic behaviour of the device as a whole. The holes, 3, radiate heat to the environment surrounding the heater, with an efficiency which prevents the top, 11, from becoming so hot that the oil in the oil well, 2, burns or ignites. Cypress, Juniper Berry & Pine Needle oils have the lowest flash points of all the essential oils, at 39°C, 41 °C, 42°C respectively. In tests in which the Top, 11, was allowed to pie-heat for 3 hours plus, using a standard tea light in a draft free room with an ambient air temperature of 21°C, it has not been possible to create a high enough volume of air borne vapour, from 3 to 4 drops of these most volatile essential oils, to achieve any combustion, or a sustained ignition in excess of 5 seconds. In use, the tip of the candle flame does not touch the bottom surface of the top, 11, the flame being usually a distance of 50mm below the bowl, throughout the candle's burn time.

iii) The heater is manufactured from a 4" length of a 4" x 4" aluminium alloy box section extrusion, type 6082 T6, using a four axis CNC milling machine. 6082 T6 aluminium alloy is used in this preferred embodiment as it is particularly well suited to both the hard and soft anodising processes, which will be used to colour and protect the surface of the heater. The CNC four axis machine is highly efficient at machining the holes, slots and partial spherical void of which this device is comprised. The heater was designed to suit the CNC manufacturing process. The threaded holes in the acetol, ceramic or similar material, base disc, 6, are also machined using the CNC process. The box section, 1, once having all the holes, slots & a partial void CNC machined, is then given one of three surface finishes, to remove any unwanted machining marks: glass bead blasting, Vibro' finished [vibrated within a particulate media] or hand brush fihished. The box section is then hard or soft anodised in any of 80+ dye colours before the various components which make up the complete heater as previously described, are hand assembled.

iv) The heater has numerous advantages over the prior art. The heater does not use electricity so, even if the heaviest hydrocarbon grade of paraffin wax is used in a tea light candle, C40H82, it is still lower [6%] in C02 emissions, than an electrical essential oil heating device would effectively produce, through it's use of fossil fuel electricity generation. A tea light candle containing 14.5g of C40H82 paraffin wax produces 4.42g of C02 per hour: 17.71g14 hours. An electric heater with a heating element typically drawing 4W of electricity, would produce 4.68g of C02, from gas powered electricity generation -calculated from US Environmental Agency data, from Swedish utilities company Vallenfall figures, stating 1170g/KWh C02 from gas generated electricity. This comparison matches the highest C02 emitting candle with the highest C02 emitting fossil fuel, i.e. a like for like comparison. If a lighter or non-paraffin based wax is used, such as soy wax, which has a significantly lighter hydrocarbon make up than paraffin wax, the candle would create less grams of C02 per hour of burn time. The heater has no electronic components, so it will function as intended indefinitely, with no need for servicing. The heater has no moving parts and very few components, all of which are assembled into a permanent, configuration: increasing the maintenance free longevity of the design.

The heater is not disposable, being ruggedly made to withstand many years of repeated use, so it doesn't contribute to depleting limited landfill resources. The heater is made almost exclusively from one aluminium component, which may have recycled aluminium content and is itself able to be recycled, so it contributes to an increasingly valued recycling ethos. The heater is realised in the form of a cube, which has a low centre of gravity, making it highly stable and difficult to topple, an' important safety feature for a device which contains a lit candle when in use. The heater is made from materials which cannot combust and which will maintain their form and function in the event of unlikely accidents such as candle flame flaring, essential oil ignition or liquified tea light candle wax vaporisation & subsequent ignition, although it's open sided design is intended to make these sorts of occurrences highly unlikely. The heater can be held in comfort, without risk of burning to the user, even after the tea light candle has been lit for the full four hour duration of it's burn time. The heater does not use the oil-on-water method for controlling the oil temperature, so there is no boil dry risk. The risk of essential oils burning or igniting is unlikely, due to the heat loss from the top, 11, due to the cooling thermal effect of the isometric array of holes, 3, surrounding the oil well, 2.

The oil well is intentionally small, so it cannot be filled with a large volume of essential oil, reducing the size of the fuel source, so that in the unlikely event of the oil igniting, the volume of vaporised oil would be too small for sustained ignition and combustion. Other safety features of the heater include the size of the holes, 3, which are too large, at 12mm in diameter, for finger entrapment of children aged 0-6.5/7.5 and the slots, 4, are too small for finger entrapment of children aged 0-6.5/7.5, according to EU safety regulations on finger entrapment in toys for children aged 0-6.5/7.5. The part of the heater which contains the oil is an integral part of the one-piece aluminium box section design, so it cannot be dislodged, displaced or be incorrectly aligned with the candle heat source below it, unlike complex devices which have numerous fragile components. If the oil well is over filled, cleaning up any excess or spilt oil, from the simple box section form, is a quick & easy job, requiring no disassembly of numerous components. Having the oil well, 2, located centrally above the candle, 10, and well in from the outer edges of the device, is a safety feature, as it reduces the possibility of accidents involving touching the oil well, which would be more likely if the oil well was located around the perimeter of the device, or overhung the base, 3. The open nature of the square box section extrusion, 1, offers a large cooling volume of air to pass through the part of the device in which the tea light candle is housed, significantly reducing the risks associated with essential oil burners with an enclosed space which houses the tea light candle, such as vaporisation & ignition of liquified candle wax due to a build up of heat within the burner. The heater is designed to minimise heat transfer from the candle to the base, 13, so that surfaces which the heater may be placed upon are unlikely to be damaged by heat.

v) The current preferred embodiment of the heater may be amended with alternative arrangements of holes, 3, slots, 4, & the oil well, 2. There could be variants on the present design which enhance the performance of these elements, in their thermal regulation of heat transfer through the different parts of the device, such as having more numerous holes of a size bellow 5mm diameter, which would be too small for finger entrapment of children aged 0-6.5/7.5, or making the slots, thinner or wider, to improve on the thermal isolation of the sides, 12, from the top, 11. At present the slots are 2mm wide. It may be desirable to have openings in the top, 11, which are not round holes, but another shaped opening, and likewise, it may be desirable to alter the configuration of the slots, so that they no longer define an S' shaped piece of aluminium between them, to enhance the functioning of the device as a whole. Likewise the design of the candle mounting may differ, in the size and arrangement of the holes & openings within the base, 13, and the materials used for the bolts, 8, the disc, 6, and any additional elements or structures used to mount the tea light candle in a secure & thermally isolating manner. The holes, 3, in an alternative embodiment, could be upward projecting protrusions, instead of holes. These protrusions could be hollow tubes. The Top, 11, could have a combination of holes & protrusions in various arrangements. It is to be understood that various modifications to the preferred embodiment and the generic principles and features described herein will be readily apparent to those skilled in the art.

Thus, the present invention is not intended to be limited to the embodiment shown and such modifications and variations also fall within the spirit and scope of the appended claims.

Claims

-10 -CLAIMS1. A heating device for evaporating volatile compounds into the air comprising; a top surface having a bowl for receiving a quantity of a volatile compound, and at least one support member connected to and supporting the upper surface, and a base connected to each support member to stabilise the heating device, wherein the base has a heat source retainer located beneath the bowl, wherein the heat source retainer is capable of retaining a naked flame heat source, such that in use, a heat source may be located beneath the bowl in order to heat a volatile compound placed in the bowl, and wherein the upper and side surfaces are provided with heat dissipating elements which are capable of dissipating heat from the bowl during use.
2. A heating device in accordance with claim 1, wherein the heat dissipating elements are apertures in the top surface, which are round holes.
3. A heating device in accordance with claim 1, wherein the heat dissipating elements are apertures in the top surface, which are round holes arranged in an isometric array.
4. A heating device in accordance with claim 1, wherein the heat dissipating elements are apertures in the top surface,, which are round holes arranged in an isometric array, which number 38.
5. A heating device in accordance with any previous claim, wherein the matérial which the device is made out of is metal.
6. A heating device in accordance with claim 5, wherein the material'which the device is made out of is aluminium.
7. A heating device in accordance with claim 1, wherein the heat dissipating elements are protrusions, emanating from the top surface, which are round.
8. A heating device in accordance with claim 1, wherein the heat dissipating elements are an arrangement of solid protrusions and holes which are round.
9. A heating device in accordance with claim 1, wherein the heat dissipating elements are an arrangement of hollow protrusions and holes which are round.
10. A heating device in accordance with any previous claim, wherein slots are present in one or more of the sides of the device, which are arranged in such a way as to produce an S' shaped piece of material between their voids.
11. A heating device in accordance with any previous claim, wherein the heat source is a candle.

-11 -
12. A heating device in accordance with claim 1, wherein the structure of the device is comprised from a square box section extrusion.
13. A heating device in accordance with any previous claim, wherein the structure of the device is a square boxsection extrusion, having four sides.
14. A heating device in accordance with any previous claim, wherein the structure of the device is a square box section extrusion1 having four sides where the first side is the top surface of the heating device.
15. A heating device in accordance with claim 1, wherein the structure of the device is a square box section extrusion, having four sides where the second & third sides are the support members of the heating device.
16. A heating device in accordance with any previous claim; wherein the structure of the device is a square box section extrusion, having four sides where the forth side is the base of the heating device, 17. A heating device in accordance with claim 12 to 16, wherein slots present in the second and third sides restrict the flow of heat from the top surface to the support members.18. A heating device in accordance with any previous claim, wherein the structure of the device is derived from a billet of square box section extrusion, whose form is a cube.19. A heating device in accordance with any previous claim, wherein the side support members are also grips to hold the device by.20. A heating device in accordance with any previous claim, wherein the heat source retainer provides thermal insulation of the heat source from the base.21. A heating device in accordance with any previous claim, wherein the heat source retainer provides thermal insulation of the heat source from the base & sides.22. A heating device in accordance with any previous claim, wherein the heat source retainer incorporates a triangular arrangement of bolts, or similar fixings, which function to grip the heat source firmly and hold it above the base of the heating device, to thermally isolate it from the heating device.23. A heating device in accordance with any previous claim, wherein the heat source retainer is a thermally insulating material.24. A heating device in accordance with any previous claim, wherein the heat source retainer is a disc made from nylon, acetol, PTFE.-CF, PTFE-CGF or a ceramic material.25. A heating device in accordance with claim 1, wherein the method of manufacture is by four axis CNC [Computer Numeric Control] milling.26. A method of making a heating device of the type claimed in the preceding claims comprising the steps of: starting with a tube section, milling holes, milling a bowl, milling slots which terminate in radii to produce an S' shaped element or other forms.27. A heating device in accordance with any previous claim, which has the visual appearance that the top most surface has been formed by being folded into it's final, horizontal, position, although this is not the actual method of production.AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWSLAIMSI1. A heating device for evaporating volatile compounds into the air comprising; a top surface having a centrally located partial spherical bowl, who's deepest point is located directly above a centrally located heat source, for receiving a quantity of a volatile compound, and at least one support member connected to and supporting the top surface, and a base connected to each support member to stabilise the heating device, wherein the base has a heat source retainer located centrally beneath the bowl, wherein the heat source retainer is capable of retaining a naked flame heat source, such that in use, a heat source can directly heat a volatile compound placed in the bowl, and wherein the top surface and each support member are provided with heat dissipating elements which dissipate heat from the bowl during use.2. A heating device in accordance with claim 1, wherein the heat dissipating elements are apertures in the top surface, which are round holes.3. A heating device in accordance with claim 1, wherein the heat dissipating elements are apertures in the top surface, which are round holes arranged in an isometric array.*. 4. A heating device in accordance with claim 1, wherein the heat dissipating elements are apertures in the top surface, which are round holes arranged in SS** * an isometric array, which number 38.*.., 5. A heating device in accordance with any previous claim, wherein the material which the device is made out of is metal.:. 6. A heating device in accordance with claim 5, wherein the material which the device is made out of is aluminium. ** ** *: A heating device in accordance with claim 1, wherein the heat dissipating elements are protrusions, emanating from the top surface, which are round.8. A heating device in accordance with claim 1, wherein the heat dissipating elements are an arrangement of solid protrusions and holes which are round, 9. A heating device in accordance with claim 1, wherein the heat dissipating elements are an arrangement of hollow protrusions and holes which are round.10. A heating device in accordance with any previous claim, wherein slots are present in one or more of the support members, which are arranged in such a way as to produce an S' shaped piece of material between their voids.11. A heating device in accordance with any previous claim, wherein the heat source is a candle.12. A heating device in accordance with claim 1, wherein the structure of the device is comprised from a square box section extrusion.13. A heating device in accordance with any previous claim, wherein the structure of the device is a square box section extrusion, having four sides.14. A heating device in accordance with any previous claim, wherein the structure of the device is a square box section extrusion, having four sides where the first side is the top surface of the heating device.15. A heating device in accordance with claim 1, wherein the structure of the device is a square box section extrusion, having four sides where the second & third sides are the support members of the heating device.16. A heating device in accordance with any previous claim, wherein the structure of the device is a square box section extrusion, having four sides where the fourth side is the base of the heating device.
17. A heating device in accordance with claim 15, wherein slots present in the second and third sides restrict the flow of heat from the top surface to the support members..
18. A heating device in accordance with any previous claim, wherein the structure of the device is derived from a billet of square box section extrusion, whose * S. S S * form is a cube.*,.
19. A heating device in accordance with any previous claim, wherein the side support members are also grips to hold the device by.
20. A heating device in accordance with any previous claim, wherein the heat :::: source retainer provides thermal insulation of the heat source from the base.*
21. A heating device in accordance with any previous claim, wherein the heat source retainer provides thermal insulation of the heat source from the base & sides.
22. A heating device in accordance with any previous claim, wherein the heat source retainer incorporates a triangular arrangement of bolts, or similar fixings, which function to grip the heat source firmly and hold it above the base of the heating device, to thermally isolate it from the heating device.
23. A heating device in accordance with any previous claim, wherein the heat source retainer is a thermally insulating material.
24. A heating device in accordance with any previous claim, wherein the heat source retainer is a disc made from nylon, acetal, PTFE-CF, PTFE-CGF or a ceramic material.2. A heating device in accordance with claim 1, wherein the method of manufacture is by four axis CNC [Computer Numeric Control] milling.26. A method of making a heating device of the type claimed in the preceding claims comprising the steps of: starting with a tube section, milling holes, milling a bowl, milling slots which terminate in radii to produce an S' shaped element. * * ****I*.*.*I * * S. I. I.. I..S I.. * . * _* . S. *I -S