Wt4603 unit4 week5

WT4603Wood Processing Safety & PracticeLecture Unit 4 (Week 5) ,[object Object]

Notes prepared by: Mr. Donal Canty, Mr. Des Kelly and Mr. Joseph Lyster

Notes available on www.slideshare.net/WT4603,[object Object]

Surface Planer WT4603 Planers can have 2,3,4,6……. Cutter knives. Most smaller machines such as those found in schools will have 2,3 or 4 knives. Department of Manufacturing & Operations Engineering

Surface Planer WT4603 Knives can be made from Chrome Vanadium steel alloy. This is suitable for machining softwoods and non abrasive hardwoods. However with advances in machining technology better materials have been developed to machine wood and wood composites. Chrome Vanadium knives dull quickly on harder more dense material. This requires more sharpening, setting up and leads to a lot of time wastage. Department of Manufacturing & Operations Engineering

Surface Planer WT4603 High Speed Steel (HSS) is a cobalt steel alloy with a small percentage of Tungsten added. It is more suitable for machining all types of wood than the chrome steel compounds. Department of Manufacturing & Operations Engineering

Surface Planer WT4603 Abrasive stock should be machined using solid or tipped cutters. Tungsten Carbide (TC) is the best tool compound for machining manufactured boards. For general work HSS cutters are preferred to TC Cutters can be re-sharpened easily. A keener edge can be achieved on HSS giving a better finish Department of Manufacturing & Operations Engineering

Surface Planer WT4603 The reason for this is that steel compounds are smelted and shaped by rolling and forging while the metal is close to melting point. The molecules of the compound flow and align themselves in response to this pressure giving the material maximum strength and edge holding capabilities Department of Manufacturing & Operations Engineering

WT4603 Surface Planer Tungsten carbide is a sintered compound. The fine grain powder from which the cutter will eventually will be made is compressed into a mould ( the ‘blank’ un-edged cutter required) under extremely high temperature (1500C) and pressure to form a solid block. Tungsten does not flow – it retains a granular structure and will chip rather than deform if abused. Department of Manufacturing & Operations Engineering

Surface Planer WT4603 Because if its brittle nature TC cutters require a more obtuse sharpness angle than the HSS cutters (more support for the cutting edge). This makes it less satisfactory for cutting softwoods than HSS knives which can be ground to a more acute cutting angle. Department of Manufacturing & Operations Engineering

WT4603 Surface Planer Department of Manufacturing & Operations Engineering

WT4603 Knife Cutter geometry Rake or Cutting angle Angle created between the face of the cutting knife and the centre of the cutter block Can have a wide range Softwoods 27° to 35 ° Hardwoods 15° to 25 ° Department of Manufacturing & Operations Engineering

WT4603 Knife Cutter Geometry Bevel or Lip Angle Angle formed to give the cutting edge Minimum of usually 35° Greater for tipped cutters Department of Manufacturing & Operations Engineering

WT4603 Knife Cutter Geometry Clearance Angle Angle formed between a line tangential to cutting circle and the bevel angle of the knife Must be present Has a bearing on the life of the cutting edge Usually 10° to 15° Department of Manufacturing & Operations Engineering

WT4603 Knife Cutter Geometry Peripheral Cutting Speed A constant speed in the range of 35-45 m/s will give best results Increase in speed may cause loss of dynamic balance due to vibrations Poor finish Increased noise levels Department of Manufacturing & Operations Engineering

WT4603 Pitch distance Combination of a rotary cut and a linear feed will leave the surface of the material with a series of arcs on it called Curtate Trochoids The pitch and depth of these arcs will determine how smooth the surface finish will be Department of Manufacturing & Operations Engineering

Department of Materials Science & Technology University of Limerick WT4603 Pitch Distance 2mm to 3mm for non obvious joinery and painted external work. 1mm to 1.5 mm for internal painted work. 0.5mm to 1mm for hardwood joinery and furniture. Department of Manufacturing & Operations Engineering

WT4603 Pitch Distance The SI unit of time is the second , but the minute is acceptable. Feed rate on wood working machines is expressed in metres per minute. (m/min) The formula for the pitch of the cutter marks is given by: f p = ------- nR where p = pitch of cutter mark f = feed rate n = number of effective cutters R = revolutions per minute of block Department of Manufacturing & Operations Engineering

Pitch Distance WT4603 The unit for “p” will be metres (m) f m/min m min p = ---- = --------- = ----- x ------ = m nR 1/min min 1 Department of Manufacturing & Operations Engineering

WT4603 Pitch Distance Problem 1 Calculate the cutter pitch of a 4 cutter block revolving at 4200 rev/min with a feed speed of 24m/min. F 24 24 p = ------- = ------------ = --------- = 0.0014m = 1.4mm nR 4 x 4200 16800 (Internal painted work) Department of Manufacturing & Operations Engineering

Pitch Distance WT4603 If a graded surface is specified and the machine has a multi-speed feed gearbox, the same formula is used but “f” is expressed in terms of n ,p, and R. f p = -------  f = nRp nR Department of Manufacturing & Operations Engineering

Pitch Distance Problem 2 From a cutter block which rotates at 4200 rev/min and has two cutting knives, a surface finish of a 4mm pitch is required. At what speed should the feed gearbox be set. f = nRp = 2 x 0.004 x 4200 = 33.6 m/min WT4603 Department of Manufacturing & Operations Engineering

WT4603 Chip formation Department of Manufacturing & Operations Engineering

WT4603 Riving Department of Manufacturing & Operations Engineering

Riving WT4603 Cracking occurs below the cut depth Department of Manufacturing & Operations Engineering

WT4603 A On the surface planer the in-feed table (A) acts as chip breaker and the downward pressure exerted by the operator also makes it act as the pressure bar. Department of Manufacturing & Operations Engineering

WT4603 Chip formation Chip breaking aid and pressure bar prevent riving and splintering Department of Manufacturing & Operations Engineering

WT4603 Square cutter blocks Department of Manufacturing & Operations Engineering

WT4603 Square cutter blocks ,[object Object]

Tension force increases with rotational speed

Will be ejected at failureDepartment of Manufacturing & Operations Engineering

WT4603 Square cutter blocks Clamping bolts are in tension Department of Manufacturing & Operations Engineering

WT4603 Circular cutter block Clamping bolts are in tension Department of Manufacturing & Operations Engineering

WT4603 Circular cutter block ,[object Object]

Can run head at higher speeds (RPM)

Easier and quicker maintenanceDepartment of Manufacturing & Operations Engineering

WT4603 Knife clamping mechanism Department of Manufacturing & Operations Engineering

Cutter projection WT4603 Round form tool with limited cutter projection Department of Manufacturing & Operations Engineering

Cutter projection WT4603 Use of a limiter to achieve limited cutter projection Department of Manufacturing & Operations Engineering

Cutter design WT4603 Cutters should preferably be designed to be used in dimensionally similar pairs, formed to the same profile. Pairs should be mounted directly opposite one another. The manufacturer should ensure that instructions on balancing the pairs of cutters after grinding are given to the user. Department of Manufacturing & Operations Engineering

Cutter projection WT4603 The design of cutter blocks should, as far as is practicable, be such as to prevent excessive cutter projection. Where the mounting arrangement permits projection which could subject the cutter to unsafe stresses, the maximum permissible projection for given cutter types should be specified in the user’s instructions. Department of Manufacturing & Operations Engineering

Hand-fed machines WT4603 For machines designed for hand-fed operations, where cutters are necessarily exposed, the use of chip limiting cutters should be recommended For other hand and semi-mechanical feed operations, cutter blocks should have as little cutter projection as is practicable. Department of Manufacturing & Operations Engineering

WT4603 Surface Planer Cutter and Machine Maintenance Involves: Grinding and setting of knives Roller and pressure bar setting Prevention of resin build up on table and rollers. Attention to: bearing wear feed complex adjustments rise and fall table Department of Manufacturing & Operations Engineering

Surface Planer WT4603 The grinding angle of a cutter can vary between 30 to 35 This is increased to 40 for hardwoods (cutting edge lasts longer) Department of Manufacturing & Operations Engineering

WT4603 Surface Planer Overheating May produce micro cracks in the cutting edge which can run into gaps when the cutter is used. May cause the cutter to bow due to expansion. Department of Manufacturing & Operations Engineering

WT4603 Surface Planer Overheating can be avoided By taking light cuts. By ensuring that the grind wheel is ‘dressed’ when required to ensure that the face is open and not glazed when grinding the knives. By using a ‘soft’ grinding wheel on HSS cutters – the soft structure of the wheel allows its grains to break away as soon as they are blunt revealing sharper ones. By wet grinding – this is the grinding of cutters while partially submerged in a mixture of water and soluble oil. The water is a coolant to prevent frictional heat developing and to disperse it should it occur. The oil prevents rust in the cutters and it provides a degree of cutting lubrication. Department of Manufacturing & Operations Engineering

WT4603 Surface Planer Setting Cutters in Block Before setting the following points should be checked. The out feed table and cutter block must be clean and free from dust resin. Method of adjusting cutters. Area where setting device is used from should be free from resin and damage. Straightness of cutters. Cutters correctly balanced both in weight and end for end. Department of Manufacturing & Operations Engineering

WT4603 Surface Planer Setting devices There are a number of cutter setting devices. This device and procedure will often be supplied with the machine. They can be loosely placed into the following four categories: Bridge device Precision cutter setter device Pin locater device Wooden straight edge device Cutters require accurate setting in the block because if the knives are not revolving in the same cutting circle a poor finish will be produced. Department of Manufacturing & Operations Engineering

WT4603 Surface Planing Department of Manufacturing & Operations Engineering

WT4603 Setting Planer Knives When planing wooden material a number of factors combine to generate the flat surface. Number of cutting knives in the block Speed of the revolving block Feed speed of the material Knife cutter design Chip breaking aids Nature and species of the material Department of Manufacturing & Operations Engineering

Knife cutter design & Chip breaking aids These factors combine to produce an acceptable surface finish Tip of the cutter splits away the chip The chip is forced away from the stock and up along the face of the cutter which is exerting a tearing effect on the grain fibre As the knife exits the stock the chip is either cut or will “rive” or tear deeply along the grain line and lift as a long heavy splinter WT4603 Department of Manufacturing & Operations Engineering

Knife cutter design & Chip breaking aids The cutter projection and the shape of the block face cause the severed chip to bend back causing a crack across its width This makes long grain riving less likely (Chip breaker not shown) WT4603 Department of Manufacturing & Operations Engineering

WT4603 Knife cutter design & Chip breaking aids Sharp tooling (a) will aid in the chip bending back and cracking across its width Blunt tooling (b) will aid riving Department of Manufacturing & Operations Engineering

WT4603 Chip Formation Before knife makes its cut Department of Manufacturing & Operations Engineering

WT4603 Chip Formation Chip to be formed Department of Manufacturing & Operations Engineering

Wt4603 unit4 week5

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