This document describes the design and fabrication of a mobile wood chipper. Key components include an electric motor, infeed chute, chipper disc assembly with three knives, discharge chute, and frame. Wood waste is fed into the infeed chute and engages with the rotating chipper disc equipped with three knives. The chips are ejected through the discharge chute. The machine is mounted on a framed platform equipped with wheels for mobility. Fabrication details are provided for each machine component. The chipper is designed to process wood waste up to 3 inches in diameter.

1. BUILDING A MOBILE WOOD CHIPPER
Engr. Segun R. Bello
Department of Agricultural Engineering Technology
Federal College of Agriculture, Ishiagu
E-mail: segemi2002@yahoo.com
Prof. Onilude M.A
Department of Agricultural and Environmental Engineering
University of Ibadan, Nigeria
E-mail: ma.onilude@mail.ui.edu.ng

2. Introduction
Wood chips have various uses such as being spread as a ground cover, being pressed into
particleboard or fiberboards, or being fed into a digester during papermaking. The use of
wood waste in animal bedding is known to be widespread (CALU, 2005). Dry woodchip has
been used as an alternative to straw under sheep and cattle housed in sheds (Frost et al,
2005). Initially woodchips are spread across the shed floor to a depth of 10cm (CALU, 2005).
The farmers using the system have been pleased with the results compared with straw. The
woodchip utilization in animal bedding is less labour intensive and stock remains clean with
low incidences of foot problems and reduced need to belly clip lambs before dispatch to the
slaughterhouse. Chip compost has been re-used as bedding and as a growing medium for
tree seedlings. There have also been research interests on the suitability of composted
woodchip bedding as a substrate for growing exotic mushrooms (CALU, 2005).
Wood waste converted to mulch covers the soil and absorbs the erosive impact of rainfall
and reduces the flow velocity of runoff, significantly reducing soil loss from a site. Wood
chip mulch may be applied after the site has been rough graded to control erosion. It
provides a temporary cover that reduces soil loss and allows vehicular and foot traffic over
the area. Mulch also provides benefits to the site beyond erosion control. The wood chips
form a blanket over the soil, and moderate its temperature, conserving moisture and
providing an environment conducive to seed germination. Wood chip mulching is a
versatile practice that is applicable on sites where sheet flow is maintained and slopes do
not exceed 3:1(DNR Publication, 2004).
The local herb producers equally improves the market value of their products by locally
chipping roots and herbs to increase the surface area for increased water absorption
consequent release of the chemical constituents required for curative uses.
Chipping is a fast, simple and environmentally friendly way of disposing agricultural wastes
to high quality fiber value which has various uses such as being spread as a ground cover,
being pressed into particleboard or fiberboards, or being fed into a digester during
papermaking as well as bottom cover and covering for paths with a low traffic pressure. The
use of wood waste in animal bedding is known to be widespread (CALU, 2005).
Due to the economic value of wood waste, a significant portion of them does not
adequately meet the needs of the consumer industries. The complexity of different
attributes of wood waste and other considerations provides criteria for the selection of
materials and the design of suitable size reduction technology and equipment. The
equipments vary with respect to the forms of wood wastes that can be effectively handled,
and the quality of the product produced.
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3. General Machine Description
The chipper consists of a chipper disc assembly, frame, a disc housing, an infeed chute and
an exhaust or discharge chute. The disc chipper employs a rotary cutting steel disc secured
to a shaft and simply supported on friction bearings to cut wood into chips. The cutting disc
is formed from mild steel 25.4mm (1’) thick. There are 3 cutting knives; 200mm in length
fixed to the cutting sides of the disc bolted directly to the rotating disc.
In operation, the disc is spin by a suitable electric motor to drive the shaft and the disc. The
wood to be chipped enters the machine through the infeed chute, and resting on the anvil
attached to the chute bracket. The wood is drawn against the anvil as the knife cut a chip
which is ejected through the aperture and out of the chipper through the discharge spout.
Machine Fabrication Procedure
The design of my chipper revolves around the rotary action of the chipper disc and three
knives enveloped in a round housing and two side plates made from the same material. The
entire system was powered by a 15hp electric motor to drive the disc.
Other components and shapes are produced from secondary machining operations
including cutting, grinding, and trimming, drilling, sawing, and turning. The conditions of
tools used for machining has greater influence on component performance, hence adequate
care was taken to establish and maintain the optimum tool conditions. Detailed description
and fabrication process is discussed as follows:
The Infeed Chute: The components of the infeed chute were designed to give protection
against both upper and lower limbs of operator from being pulled into the machine. 1/8"
thick steel metal plate was used for the construction of the chute sides. The angle of
o
inclination of the chute to the side plate is 35 . Outer edge opening of the infeed chute is a
minimum of 41” wide x 39” high. Opening at feed spout is designed to be a minimum of 14”
wide x 12” high. It was constructed from 14 gauge steel on top, sides, and bottom up to the
chute bracket. The external length from feed spout to ground level is 800mm. The chute
edges have a ¾ square pipe welded right round to prevent the sharp edges from causing
accident.
Side Plate and Chute Bracket: The anvil and the chute bracket were constructed and
o
set at 35 angles and welded to the chute opening on the side plate. Other sides of the
chute were also welded to the anvil support and in place.
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4. Plate 1: Infeed chute side plate
Anvil and the Infeed Roller: The anvil and the infeed roller were constructed and
installed to control the knife clearance and the material feed into the knife respectively.
Plate 2: Anvil and Infeed roler
The vertical height of the roller is limited to the maximum feed capacity of the machine
(76.0mm). The roller also prevents log lifting when it comes in contact with the knife
especially when the length is small.
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5. Plate 3: Anvil and infeed roller (close up view)
Chipper Side Plates: The side plates were cut from a flat metal plate, marked and cut
into sides as shown and the housing was cut from and rolled into desired size on a hydraulic
sheet metal rolling machine. The housing was then welded to the discharge housing
permanently.
Plate 4: Chipper housing welded to the discharge side plate
Chipper Disc Assembly: This is concealed within the chipper housing and comprises of
the disc, knife, and chip thrower. The function of the disc assembly is to develop enough
inertia to chip wood fed into it and to eject the chips through the chip discharge chute.
The Chipper Disc: Blank material sourced from the Agodi Gate steel market was smooth
and appeared to have been cut with an automated torch to 24” diameter. The roundness
actually saved a lot of work in squaring and cutting. Because of the initial cutting forces
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6. required by the machine to chip wood, the disc must be dynamically balanced and heavy to
carry the cutting inertia.
Plate 5: Marked piece of steel recovered from local metal market
The disc was laid out according to design specifications, marked and after a lot of cutting,
trimming and grinding to required size and shape, the slots were grinded using a hand
grinder.
Knives: There are three knives and chip throwers arranged radially at an angle of 120o to
each other on a massive steel disc which develop a lot of kinetic energy and inertia to slice
through wood fed into it. Each knife has a dimension of 190 x 76 x10mm and was fastened
to the disc by three 14mm countersunk bolts and nuts. The knives material was recovered
from an out of service swipe blade, cut into sizes and sharpened into double sided 9.0mm
thick, 190.0mm (7”) long and 76.0mm (3”) wide. Once the knives get dull you can turn them
around.
Plate 6: Disc showing mounted blades (Front side)
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7. The Disc Assembly: The chipper disc was balanced on a balancer built prior to welding
the shaft to the disc. The balancer comprises of two bearings on each side of the stand with
a V- grooved metal plate welded to each stand. The disc is fully assembled with knives and
the chip thrower is a piece of 50 x 50x 5mm angle iron 190mm in length and was attached
to the disc with three grade 8 1/2" bolts and LocTite nuts to prevent them from vibrating
out. The shaft and disc assembly is positioned on the bearings for balancing.
Plate 7: Disc showing mounted chip throwers (Back side)
The Drive Shaft: The shaft was turned from a solid piece of 76.0mm (3") stock on a 9” x
20” metal lathe. The 21" disc has a 2 1/2" center hole and fits over the widest portion of the
shaft.
Plate 8: The drive Shaft
Before welding the shaft to the disc it was ensured that all the knives and chip thrower
holes were correct and also ensures that the shaft fits all the bearings properly. The disc was
then centered and welded to the shaft by a 200 amp AC welder (ESAB) and 6011 electrodes
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8. for the first two welding passes then used 6013 electrodes for two more passes. A total of
four beads each were made.
The Discharge Chute: The chip delivery channel was made of gauge 14 mild steel plate
formed into an s-shaped chute ending in a rectangular flat plate bracket for fasteners to the
main housing.
Plate 9: Discharge chute
Chip discharge from the chute is accomplished by a combination of centrifugal force and air
created by a separate impeller/thrower mounted on the discharge end of the disc. The
discharge chute is equally equipped with a hand adjustable deflector at the end of
discharge. This is attached to chute with one hinge and can be folded back for easy access to
rear of chipper.
Plate 10: Chipper outlet
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9. The Frame: The frame is built from two 2" x 2” angle irons faced together and welded to
form square tubing. Angle iron forms the platforms on which the chipper and the electric
motor were mounted. The frame was equipped with two wheels at the rear to ensure
transportability and optimal weight distribution.
Plate 11: The chipper frame mounted on two wheels
The Chipper: The outcome of machine design and fabrication is as shown in Plate 12. The
overall dimensions of the machine are; Length: 1676.4mm, Width: 609.6mm and Height:
800.0mm. The height is adequate for ergonomic reasons considering the bending and
feeding of the machine.
Plate 12: The wood chipper
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10. The machine consists of five functional component parts; infeed chute and bracket, chipper
disc assembly, an exhaust or discharge chute, frame and power drive.
Machine Specifications
The machine specifications are as shown in the table below.
Table 3: Machine components and specification
COMPONENTS SPECIFICATIONS
Engine: Atlas 3-phase double winding 15hp synchronous electric motor
Speed: 1440rpm, voltage 1.2v, frequency; 50Hz
Chute opening at chipper disc; w180mm x h150mm /w450mm x
Infeed Chute:
h360mm at feed point
Discharge chute: provided with directional flip cover. 900mm
Discharge Chute
from wheel
Disc Size: 1100mm x 60mm, Disc Weight: 86kg, Disc Speed: 540
Chipper Disc:
rpm
Three knives made of hardened spring steel. 190mm x 76mm x
Knives:
10mm double edged, reversible and re-sharpen able.
Drive Belts: Industrial "V" B51/5L540 (two)
Anvil: Made from hard wearing metal with easy external adjustment
38.2mm diameter steel roller, in-between the anvil and the
Infeed Roller:
knives
Chipper Housing 12mm plate front and back, 6mm plate disc cover.
Chip thrower Minimum feed rate approximately 80 feet per minute.
The frame is a network of angle iron and squared pipes welded
Frame Support:
together.
Land wheels: Wheels 15 x 6.00
Machine Capacity 76mm (3 inch) – rated to 3 inches whole log
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11. PARTS LISTING
DIMENSION
COMPONENT MATERIAL QTY
(L X B) MM
3mm (1/8”) 540 x 800 2
Infeed chute
thick ms plate 600 x 800 2
3mm(1/8”)
Discharge chute 1200x1200 1
thick ms plate
12.7mm (1/2”) 170 x 250 2
Infeed bracket
thick ms plate 208 x 250 2
12.7mm (1/2”)
Anvil 1
thick ms plate 170 x 250
12.7mm (1/2”)
Side plates 2
thick ms plate 609.6 x 609.6
3mm (1/8”) Diameter =549.4
Disc housing 1
thick ms plate Width = 93
25.4mm (1”)
Chipper disc Diameter = 533.4 2
thick ms plate
Frame 2” x 2” square tube 50x50x1200 2
10mm (3/8”) 190 x 76 x 9
Knife 3
thick spring
60mm (3”) dia. ms steel
Drive shaft 50 x 228.3 1
rod
Motor seating 2” x 2” Ms angle iron 2
Side plate M19x1.5x50 6
Bearing seating M14x1.5x50 4
Knife (c/sunk) M14x1.5x50 9
Thrower M13x1.5x25 8
Bolt and nuts Anvil M17x1.5x25.4 3
Discharge M13x1.5x25 6
Motor seat M19x1.5x25 4
Infeed chute M19x1.5x50 2
seating M19x1.5x25 8
Side plate bracket 2”x2” Ms angle iron 80 x50 x 50 4
Bearing seat 2”x2” Ms angle iron 24PMF.02.017 2
Washer Split washer GB93-87 14
Bearing KG Bearing 38UCP208 2
15HP motor 3-phase low speed 1
Drive Wheel 3.5kg weight 1 pair
Wheel shaft Ms Rod 1” diameter 1
Wheel bearing KG Pillow Bearing 25UCP206 2
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12. Small pulley 125mm dia
24PMF.02.104 1
Double grooves
192mm dia Double
Big pulley 24PMF.02.103 1
grooves
Fiber reinforced rubber V-
Belt B-62 17 x 1625 2
belt
Bibliography
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document. Modified on 3 August 2008
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Unpublished Doctoral thesis, Swedish University of Agricultural Sciences, Uppsala
2006
BS EN 294:1992. Safety of machinery – Safety distances to prevent danger zones being
reached by upper limbs British Standards Institution 1992
CWC, 1997. Wood Waste Size Reduction Technology Study NIST MEP Environmental
program (# CDL-97-3) www.cwc.org.
Frost D., McLean B. and Wildig J., 2005. The Multi-Use of Woodchip - From Animal Bedding
to Mushroom Production. Farm Woodland Forum Meeting, 29 June – 1 July 2005.
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