U.S. patent application number 11/309509 was filed with the patent office on 2008-08-14 for three ply bolted temporary road mats and apparatus for manufacturing same.
Invention is credited to Ronald Harrison.
Application Number | 20080193213 11/309509 |
Document ID | / |
Family ID | 32965356 |
Filed Date | 2008-08-14 |
United States Patent
Application |
20080193213 |
Kind Code |
A1 |
Harrison; Ronald |
August 14, 2008 |
THREE PLY BOLTED TEMPORARY ROAD MATS AND APPARATUS FOR
MANUFACTURING SAME
Abstract
An apparatus for making temporary road mats characterized by
multiple layers of mutually perpendicular elongated timbers having
an array of vertical intersections aligned in lateral rows. The
apparatus includes a gang drill that moves relative to a roughly
assembled mat for sequentially drilling the lateral rows of
intersections.
Inventors: |
Harrison; Ronald; (Plymouth,
NC) |
Correspondence
Address: |
KENNEDY COVINGTON LOBDELL & HICKMAN, LLP
214 N. TRYON STREET, HEARST TOWER, 47TH FLOOR
CHARLOTTE
NC
28202
US
|
Family ID: |
32965356 |
Appl. No.: |
11/309509 |
Filed: |
August 15, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10750272 |
Jan 2, 2004 |
7210211 |
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11309509 |
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10407992 |
Apr 7, 2003 |
6745452 |
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10750272 |
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Current U.S.
Class: |
404/35 |
Current CPC
Class: |
Y10T 408/385 20150115;
Y10T 29/5124 20150115; B27B 5/04 20130101; B27C 3/00 20130101; Y10T
408/3811 20150115; Y10T 29/5136 20150115; Y10T 29/49948 20150115;
Y10T 408/3828 20150115; E01C 9/086 20130101; Y10T 29/5107 20150115;
Y10T 29/49947 20150115; Y10T 29/53978 20150115; B27M 3/0046
20130101; Y10T 408/35 20150115; B23B 39/161 20130101 |
Class at
Publication: |
404/35 |
International
Class: |
E01C 9/08 20060101
E01C009/08 |
Claims
1. A bolted three ply temporary road mat comprising; a bottom layer
of elongated timbers aligned in parallel rows in a first direction;
a middle layer of elongated timbers aligned in parallel rows on
said bottom layer extending to a second direction transverse to
said first direction; a top layer of elongated timbers aligned in
parallel rows on said middle layer and vertically aligned with said
timbers of said bottom layer whereby said timbers of said layer
overlie at an array of vertically aligned intersecting surfaces;
through hole formed through said timbers at said intersecting
surfaces; and bolts having threaded shanks extending through said
through holes with heads engaging the upper surface of said timbers
of said top layer; and nuts threaded on said shanks and
compressively engaging the lower surface of said timbers of said
bottom layer thereby forming a bolted composite assembly of
timbers.
Description
RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. Ser.
No. 10/750,272, filed on Jan. 2, 2004, which is a
continuation-in-part application of U.S. Ser. No. 10/407,992 filed
on Apr. 4, 2003, now U.S. Pat. No. 6,745,452, issued Jun. 8, 2004,
in the name of Ronald Harrison.
FIELD OF THE INVENTION
[0002] The present invention relates to temporary road surfaces
and, in particular, to apparatus for manufacturing and assembling
three ply temporary road mats.
BACKGROUND OF THE INVENTION
[0003] Temporary road mats are used extensively to allow vehicles
and equipment to reach locations not serviced by permanent roads,
particularly under conditions where ground surface would not
support the traffic or where the temporary nature of use does not
warrant the time and expense of a permanent road. The mats are
generally constructed in multiple layers of heavy wood timbers in
crisscrossing layers. The mats may also be provided with
interlocking joints for connecting with adjacent mats as disclosed
in U.S. Pat. Nos. 4,462,712 to Penland; 5,032,037 to Phillips et
al.; and 4,889,444 to Pouyer. Commonly, each layer is nailed to the
underlying layer. The final layer is fastened with an extended
length nail having a protruding tip that crimped over to secure the
assembly as disclosed in U.S. Pat. No. 5,234,204 to Hunt. The
manual assembly, even with air powered nailing guns in time
consuming and tiring and prone to misalignments. For heavy duty
applications, three ply mats are employed. Initially, two layers
are nailed as a subunit, with the third layer nailed thereto in a
separate assembly sequence. This type of nailed construction
provides limited torsional and bending strength, resulting
loosening of the nailed joints and timber breakage. Replacing a
damage timber requires time consuming removal of all overlying
timbers. The entire length of timber must be replaced inasmuch as
limited compression and shear strength precludes splicing with
shorter lengths. Where the nail loosening occurs at the
intermediate layer, supplemental nailing from both the top and
bottom surfaces may be required to regain suitable strength at the
joint. Such supplemental nailing can also splinter the timber
resulting in a complete loss of nail holding strength.
[0004] Various assembly devices have been proposed for more
accurately aligning the timber layers prior to nailing. U.S. Pat.
No. 4,922,598 to Pouyer discloses an assembly table having an array
of alignment stops for assisting positioning the timbers prior to
nailing. U.S. Pat. No. 5,234,204 to Hunt, referenced above,
discloses a dual stage assembly table facilitating nailing on
opposite sides of the mat. Crimped extended length nails are used
on the final layer to resist a lifting of the nail heads that can
damage vehicle tires.
[0005] The nailing of the timbers also precludes convenient repair
and replacement of damaged timbers. Typically, the mat must be
substantially disassembled to access and replace damaged members.
Bolted constructions have been suggested in the art, however, such
mats are not known to be commercially available. Therein, holes are
drilled at the intersections of the crossed timbers for receiving
threaded fasteners. The resulting construction provides a smooth
upper surface free of protruding nail heads. When replacement of a
member is required, only the fasteners in the affected area need to
be removed to allow substitution. Notwithstanding the advantages of
the bolted construction, production rates, even with fixtures and
assembly tables, have been limited by the cycle times of the
serially required operations.
[0006] Moreover, three ply mats have not been successfully
produced. The cumulative tolerances in the hole arrays for the
three layers present's extreme alignment problems for assembly.
Approaches increasing the clearances between the holes and bolt
shanks result in a loss of lateral structural stability. Leveraging
the boards to align the holes for assembly results in a stressed
assembly condition that can result in timber fracture and surface
warping.
[0007] Accordingly, a need continues to exist for three ply bolted
temporary road mats that may be assembled accurately under low
stress conditions.
BRIEF SUMMARY OF THE INVENTION
[0008] The present invention provides an improved method for making
bolted three ply temporary road mats wherein fastener holes are
drilled concurrently by a gang drill apparatus into the freely
assembled mat, the apparatus and mat indexed to successive
positions for drilling while the preceding rows are fastened by
carriage bolts, continuing until the mat is fully assembled.
Resultantly, the completed mats can use fastener holes having close
sliding fits with the bolts providing increased bilateral
stability. Moreover, the fasteners are connected with only
compressive forces substantially reducing assembly stresses on the
timbers.
[0009] In one aspect of the invention, a mat assembly line includes
a pair of in-line, phase opposed multilevel assembly tables
supplied with precut timbers from conveyor systems including a
trimming station. The precut timbers are oriented into multiple
layers of mutually perpendicular timbers atop the table. A mobile
gang drill carrying a plurality of drill heads travels along rails
at the sides the assembly tables and sequentially drills through
holes at each lateral row of timber intersections. Carriage bolts
are inserted downwardly through the drilled holes as completed. At
lower bays beneath the assembly tables, nuts are assembled on the
bolts to provide a unitized assembly. During the drilling at the
first table, another mat is assembled at the other table. Following
completion at the first table the gang drill indexes to the second
table and performs the drilling sequence thereat, while the bolts
are fastened at the first table. The gang drill alternates between
the tables, with upper and lower crews transferring between tables
for continuity and efficiency.
[0010] In another aspect of the invention, there is provided a mat
assembly line wherein an indexing conveyor is supplied with precut
timbers from conveyor systems including trimming stations. The
precut timbers are oriented into multiple layers of mutually
perpendicular timbers atop the table. The indexing conveyor shifts
the timber stack to a stationary gang drill whereat a plurality of
drill heads drills counterbored holes for a single row. After
drilling, the indexing conveyor shifts the timber stack to drill
the next row of holes. Concurrently, the bolts are inserted and
fastened at prior set. The sequences are repeated until the mat is
fully drilled and assembled.
[0011] In one aspect of the invention there is provided an improved
apparatus for making temporary road mats of bolted construction
characterized by multiple layers of mutually perpendicular
elongated timbers having an array of vertical intersections
comprised of longitudinally spaced lateral rows, wherein said
apparatus comprises: a pair of assembly tables spaced along an
assembly line of a work floor, each of the tables having an upper
layout surface spaced vertically above the work floor and providing
a work bay therebelow, said layout surface having indicia for
orienting the discrete timbers in each layer whereby said timber
may be roughly assembled thereon into said layers with said
intersections; a gang drill assembly supported for controlled
movement in a longitudinal path along said assembly line with
respect to said pair of assembly tables, said gang drill assembly
carrying a plurality of drill units above said layout surface
aligned for drilling the lateral rows of intersection; means for
aligning said drill units at said lateral rows and for downwardly
for moving said drill units to form through holes through said
timbers at said intersections subsequent to which bolts are
inserted in into said through holes from above said layout surface
and fasteners are connected with said bolts in said work bay, the
movement of said gang drill assembly and the sequence of said
drilling being alternated between said assembly tables.
[0012] Accordingly, it is an object to provide an improved
temporary road mat having threaded fasteners releasably
interconnecting the various components.
[0013] Another object of the invention is to provide a three ply
temporary road mat fastened by carriage bolts.
[0014] A further object is to provide an improved apparatus for
assembling temporary road mats wherein rough timbers are feed on a
conveyor system through a trimming station to provide precut
timbers to a pair of spaced assembly tables for positioning into
multiple crossed layer orientation and a longitudinally
positionable multiple drill assembly alternately drills fastener
holes in the timbers at each table.
[0015] Another object is to provide an apparatus for assembling
bolted temporary road mats wherein a gang drill assembly is used to
simultaneously drill lateral rows of through holes for receiving
fasteners for interconnecting the mat components.
BRIEF DESCRIPTION OF DRAWINGS
[0016] The above and other features and advantages of the invention
will become apparent upon reading the following written description
taken in conjunction with the accompanying drawings in which:
[0017] FIG. 1 is a side elevational view of an apparatus for the
manufacture of temporary road mats in accordance with a preferred
embodiment of the invention;
[0018] FIG. 2 is a top view of the conveyor and trimming station
for the apparatus showing the trimming of rough timbers to
length;
[0019] FIG. 3 is a top view of an assembly table and surrounding
walkway for the apparatus;
[0020] FIG. 4 is a front elevational view of the assembly table and
mobile gang drill;
[0021] FIG. 5 is a cross sectional view illustrating the drilling
of the timbers;
[0022] FIG. 6 is a cross sectional view of the timbers and carriage
bolt fasteners;
[0023] FIG. 7 is a perspective view of the temporary road mat in
accordance with one embodiment of manufacture;
[0024] FIG. 8 is a side elevational view of the temporary road mat
as shown in FIG. 7;
[0025] FIG. 9 is a top view of the temporary road mat as shown in
FIG. 7;
[0026] FIG. 10 is a front view of the temporary road mat as shown
in FIG. 7;
[0027] FIG. 11 is a front view of an apparatus for the manufacture
of temporary road mats in accordance with another embodiment of the
invention;
[0028] FIG. 12 is a side elevational view of the apparatus
illustrated in FIG. 11 taken along line 12-12 in FIG. 11;
[0029] FIG. 13 is a fragmentary cross sectional view of the
countersunk holes of the temporary road mat in the apparatus of
FIG. 11;
[0030] FIG. 14 is a fragmentary cross sectional view of the
assembled carriage bolt maintained in the countersunk holes by the
pressure plate prior to assembly; and
[0031] FIG. 15 is a top view of an embodiment of the temporary road
mat illustrating the splicing of the timbers.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0032] Referring to the drawings for the purpose of illustrating a
preferred embodiment of the invention and not for limiting same,
FIG. 1 shows an assembly apparatus 10 for the manufacture of
temporary road mats. The apparatus 10 comprises a pair of in-line
multilevel assembly lines 11. At the outer end of each line 11
rough wooden timbers 14 are delivered to a loading area 16,
transferred by conveyor 18 through trimming station 20 to produce
finished timbers 22 and unloaded at transfer area 24. The finished
timbers 22 are assembled on assembly tables 26, drilled at vertical
locations by a mobile gang drill 28, and fastened at underlying
fastener bays 29. Fully assembled mats are removed from the
assembly tables 26 by suitable material equipment such as overhead
cranes or mobile fork lifts.
[0033] Referring to FIGS. 7 through 10, a completed temporary road
mat 30, according to one embodiment, comprises three mutually
perpendicular layers of spaced finished timbers. The width and
length of the mat are generally in two foot increments and the mat
is rectangular in shape, for instance 8 feet by 12 or 16 feet.
Depending on load requirements, two layers may be sufficient and in
severe environments, greater than three layers may be preferable.
Moreover, the ends and sides may have staggered ends adapted for
interlocking assembly. Further, the top lay may be configured for
distinct vehicle tracks. For each of the above and the like, the
layers must be securely interlocked to maintain structural
integrity during use.
[0034] The mat 30 comprises a first or base layer 32 having
longitudinally extending, laterally spaced members, a second or
middle layer 34 having laterally extending, longitudinally spaced
members, and a third or top layer 36 having longitudinally
extending, uniformly laterally spaced members vertically overlying
the first layer. The assembly thus forms distinct, mutually
perpendicular layers of intersecting rows and columns in grid array
of mutually overlying intersections. Through holes, as hereinafter
described, are drilled through the overlapping members at such
intersections. Suitable fastener systems 37, as described below,
extend through the holes and bolted for mutually clamping the
layers together. In the present invention a carriage bolt is
inserted downwardly through each hole and a nut threaded thereto at
the lower surface.
[0035] As shown in FIGS. 1 and 2, timbers roughly to length are
delivered to a loading area in front of the conveyor 16. The
conveyor 16 includes a support assembly 40 having a pair of
laterally spaced guide rails 42. The guide rails 42 include
upwardly curved, arcuate entry legs 44 merging with horizontal top
legs 46. A drive chain 48 is guided on sprockets for guided
movement adjacent the guide rails. A control motor 50 is
operatively connected to the drive chain 48 for operating the chain
under manual or automatic control. Each drive chain 48 carries a
plurality of spaced transfer dogs 52 that project outwardly of the
guide rails 42. The rough timbers 14 are sequentially loaded on the
dogs 52 and transferred forwardly by the drive chain upwardly along
the entry legs 44 and inwardly along the top legs 46.
[0036] The conveyor 16 extends through the trimming station 18 and
delivers the cut timbers to the transfer area 26. The trimming
station 18, as shown in FIG. 2 includes a laterally adjustable
circular saw unit 62, a fence 64 and a transfer roll 66. The
transfer roll 66 is operatively connected to a drive unit 67 for
rotation as shown by the arrows. The saw unit 62 is mounted for
adjustable transverse movement as indicated by the arrows. As the
rough timbers 14 are carried into the trimming station 18, the
transfer roll 66 laterally shifts the timbers outwardly against the
fence 64. The circular saw unit 62 is positioned downstream beyond
the transfer roll 66 and laterally positioned to make a cross cut
on the timbers representing a selected length between the saw blade
and the fence, corresponding to the lengths in the desired mat
layer. The range of adjustment between the saw unit and the fence
is sufficient to handle sizing of the various timbers for the
manufactured mat designs.
[0037] After trimming to length, the timbers for a layer are housed
at staging area 24 prior to layout on the assembly tables. The
assembly tables 26 are carried on support frames 70 elevated above
the work floor at a sufficient height to establish a work bay 29
therebelow to enable workers to bolt the mats together as described
below. The elevation of the tables 26 is slightly above the
transfer area for providing ease of manual alignment of the members
on the assembly tables. The tables 26 are surrounded and mutually
spaced by elevated walkways 71 for permitting movement of the
workers thereabout. Depending on production rates, a single crew on
the upper level may alternate between the tables, and bolting crews
alternate between the bays. Alternatively, a single crew may
sequentially handle upper and lower level operations.
[0038] Referring to FIG. 3, the assembly tables 26 are provided a
top frame including peripheral end supports 74 and side supports 76
interconnected with interior supporting members 78. A lateral fence
80 is aligned and attached at one side support 76, and a
longitudinal fence 82 is aligned and attached at the inner end
support 74 thereby providing an alignment surface for accurately
positioning the ends of the timbers of the respective layers.
Additional pivotal fences and clamps may be provided at opposed
ends of the respective fences to mechanically position the timbers
against the prime fences 80, 82. Additionally, the lateral and
longitudinal sides are provided with spaced indicia 84 and/or
affirmative locators for accurately referencing and establishing
respective timber placement. For assembling the bottom layer, the
timbers 22 are removed from the transfer area 24, positioned
against the end fence 82, and aligned with the indicia 84 to
provide a longitudinal array of laterally spaced timbers for the
bottom layer. Concurrently therewith, the trimming station 18 may
be adjusted to trim the next set of timbers traversing the conveyor
16 to the determined length and in the required number for the
middle layer. Alternatively, the middle layer timbers may be sized
at a separate location and transferred to the assembly table for
positioning atop the bottom layer.
[0039] After location of the bottom layer, the ends of the middle
layer timbers are positioned against the lateral fence 80 and
aligned with the indicia 84 to provide an aligned lateral array
perpendicular to the bottom layer. Thereafter the upper set of
timbers is trimmed and aligned mutually perpendicular to the middle
layer, as described above, ready for drilling with the mobile gang
drill 28.
[0040] The mobile gang drill 28 comprises a shuttle 90 having side
support legs 92 laterally on either side of the line 10 and
interconnected by a cross member 94. The legs include a horizontal
base 93 carrying rollers 96 that are supported on longitudinal
guide rails 98 spaced on the lateral sides of the assembly tables
11. A drive motor 100 is operatively connected with the rollers 96
is operable manually or automatically to move the gang drill 28 to
controlled positions along the guide rails. A tool bar 110 is
supported by a parallel linkage 112 at the cross member 94 and
moved vertically by actuating cylinder 114 between raised and
lowered positions. A plurality of drills 116 including drill bits
118 are carried on the tool bar 110 and adjustable laterally to
register with the overlapping intersections of mat timbers for the
design being manufactured. A press plate 120 is slidably supported
at the legs 92 for vertical movement under the manual or automatic
control of actuators 122. The press plate 120 is lowered to
compressively clamp the timber layers adjacent the drills to
prevent any misalignment of the timbers during the drilling. For
the drilling sequence, the gang drill is indexed, manually or
automatically, to position the drills over the outermost lateral
row of timber intersections. Thereafter as shown in FIG. 5, the
drills are energized and the actuator 122 extended to lower the
press plate 120 to clamp the timbers. The actuator cylinders 114
are extended to lower the tool bar 110 thereby simultaneously
drilling a lateral series of vertical holes completely through the
three layers timbers. The drills 116 are withdrawn by the actuator
cylinder 114, the press plate 120 raised by actuator 122, and the
gang drill 28 moved to the next lateral set of intersections for
repeating the foregoing drilling sequence. The drilling continues
until all holes have been drilled. Thereafter, the drill assembly
is parked intermediate the tables prior to undertaking the drilling
sequences at the other table.
[0041] Referring to FIG. 5, following the drilling on the first
row, the carriage bolts 140 are manually inserted into the drilled
holes as available and until completed. After insertion of all the
carriage bolts, a cover plate 130 is lowered onto the table over
the bolt heads 142 to maintain position thereof during fastening. A
work crew in the assembly bay 29 then fastens the nuts 144 and
washers 146 to the threaded shank 148 of the bolts 140 using
powered socket wrenches to unitize the assembly. Following
completion, the cover plate is removed and the finished mat
transferred from the table by suitable material handling equipment
such as a forklift or mobile crane.
[0042] The apparatus above described allows work crews to
continuously operate on both tables. During the drilling sequence
at one table, the mats are rough assembled on the other table.
During the fastening at the first table, drilling is done at the
other table. During assembly at the first table, the fastening is
performed at the other table. In this manner, both tables are
continuously used with the workload shifting between the levels.
Moreover, the work crews may alternate between the tables at both
levels or between levels at one table thereby efficiently utilizing
both labor and machine component. It will thus be appreciated that
the two bays working in tandem are able to balance machine and
manual time content to utilize the equipment and labor in a
productive efficient manner. Compared to serial drilling and
fastening wherein about 2 mats per hour could be produced, the
inline dual table of the present invention outputs completed mats
at the rate of about 10 per hour with comparable labor content per
mat.
[0043] It will be appreciated that the foregoing apparatus may be
employed for the manufacture of differing sizes, layout and number
of intersecting timber layers. Interlocking and/or staggered mat
designs may be accommodated by table and drill layout. Further,
dedicated wheel track patterns of current design may also be
produced.
[0044] Referring to FIGS. 11 and 12, there is shown another
embodiment of the invention wherein the assembly apparatus is
provided with stationary drilling assemblies and a mobile assembly
platform. More particularly, the assembly apparatus 200 comprises a
longitudinal assembly line 202 for routing timbers 2203 in layers
onto a mobile assembly platform 204 including an indexing conveyor
206, past upper and lower drill assemblies 208, 210 respectively,
for sequentially drilling a lateral series of holes in a roughly
assembled mat 212, followed by bolting of the layers of timbers
into compressive engagement to form a finished mat in upper
assembly area 214 and lower assembly area 216.
[0045] The timbers 203 are transferred to the assembly platform by
conveyor and trimming stations including end station 220, and side
stations 222, and 224. The stations 220, 222, and 224 may be the
same as the conveyor 18 and trimming station 20 described with
reference to the first embodiment. The timbers may be inventoried
at storage areas at the ends thereof or manually transferred as
available to the assembly table.
[0046] The apparatus 200 includes an elevated platform 230 mounted
on a base 231, such as a plant floor. The platform 230 extends
along the assembly line 202 and supports the indexing conveyor 206.
The drill assemblies 208, 210 are carried by a support frame 234 at
about the center of the platform 230. The support frame 234
includes a pair of laterally spaced legs 236 attached to the base
231 and interconnected by cross arm 238. The apparatus 200 provides
the capability of assembling extended length platforms and
accordingly the lateral timbers comprise the top and bottom layers
32, 36 and feed from the side stations 222, 224, with the
longitudinal timbers comprising the middle layer 34 and supplied
from the end station 220.
[0047] The indexing conveyor 206 includes a pair of laterally
spaced motor driven drive chains 240 driven by motor 241 and
extending longitudinally along the frame 234. The drive chains 240
include projecting lugs 242 engagable with the base layer timbers.
By appropriate automatic or manual control, the conveyor 206 is
intermittently operated to index successive lateral timbers at the
drilling assemblies whereat the vertical fastener profile is
formed.
[0048] The upper gang drill assembly 208 is supported on the frame
and is substantially the same as the drill assembly in the first
embodiment and reference may be made thereto for details thereof.
The lower gang drill assembly 210 comprises a laterally spaced
series of drills 244 supported on a cross bar 246 carried on the
legs 236 of the frame 234 for movement by a hydraulic actuator 248
between the illustrated normal lowered position to a raised
drilling position.
[0049] To provide for recessing on the fastener to avoid surface
projections on the top and bottom surfaces of the mat, as shown in
FIG. 14, the drilled fastener profile includes a through hole 250,
an upper counterbore 252 for the head of the bolt, and a lower
counterbore 254 for the nut of the fastener.
[0050] The profile is formed by a drill bit on the upper drills
comprising a main drill bit for forming the through hole 250 and a
counterbore bit for forming the upper counterbore 252, and a drill
bit on the lower drills 246 comprising a pilot drill and a
counterbore bit for forming the lower counterbore 252.
[0051] In operation, with a lateral row of timber intersections
indexed at the drill assemblies, the actuator 248 is extended to
raise the lower drill assembly 210 for drilling the lower
counterbores. Thereafter the upper drill assembly 206 is lowered
for drilling the through hole and upper counterbores. The sequence
is repeated for the remaining lateral rolls of the mat.
[0052] After the first row of profiles is formed and the mat
indexed, the carriage bolts are inserted. This provides for low
stress assembly inasmuch as the holes are coaxial at drilling and
the short transfer area presenting little opportunity for timber
shifting. After assembly of the first row, the alignment becomes
increasingly stable thereby allowing the close sliding fit between
the fastener and holes. To prevent the upward movement of the
carriage bolts during attachment of the nuts, a slightly downwardly
inclined plate 250 is supported above the table and timbers,
downstream of the bolt assembly area. In the lower bay 260 below
the table, the nuts are assembled on the bolts to create the
composite mat. Upon completion, the composite mat is transferred
from the line by appropriate material handling equipment. Depending
on the front length of the indexing conveyor, initial assembly may
commence on another mat while the preceding mat is finishing
drilling and assembly.
[0053] The three layer composite mats possess substantially
improved bending and torsional strength in comparison with
conventional nailed mat constructions. Such strength enables
assembly used sliced timbers. As shown in FIG. 15, the top layer
may comprise columns having spliced timbers 270, 271 thereby
permitted the use of easier to obtain and cost effective timber
lengths. The spliced construction may be used for all or a portion
thereof. In such a spliced construction, it is desirable to stagger
the spliced joints. Similar techniques may be used for the middle
row 34 using spliced timbers 272, 273, and bottom layer 32 using
spliced timbers 274.
[0054] Having thus described a presently preferred embodiment of
the present invention, it will now be appreciated that the objects
of the invention have been fully achieved, and it will be
understood by those skilled in the art that many changes in
construction and widely differing embodiments and applications of
the invention will suggest themselves without departing from the
spirit and scope of the present invention. The disclosures and
description herein are intended to be illustrative and are not in
any sense limiting of the invention, which is defined solely in
accordance with the following claims.
* * * * *