Chain gauge

Apparatus is disclosed for measuring characteristics of chains, preferably of the type utilized on chain saws, having a semicircular holder affixed at the end of an elongated scale and a semicircular shoe slidable along the scale, the scale having graduations indicative of the number of chain links and the apparatus having sight holes for measuring chain link pitch and gauge.

BACKGROUND OF THE INVENTION 
This invention relates to an apparatus for measuring certain 
characteristics of chains, and more particularly to an apparatus for 
measuring such characteristics of chains commonly used in chain saws. 
A particular problem in the maintenance, repair and replacement of chains, 
particularly of the type utilized in chain saws, is making a proper 
determination of the physical characteristics of the chain in order that 
maintenance, repair and replacement may be accomplished. For example, when 
replacing a particular chain from a chain saw it is necessary to know 
exactly the number of links which the chain to be replaced has in order 
that a proper fit of the chain on the chain saw may be accomplished. 
Heretofore it has been customary to count the number of links by a manual 
count, usually by marking a starting link and manually counting each link 
around the chain loop. This method lends itself to inaccuracies, as it is 
easy to miss a link count or count a link twice. If such an error is made, 
and a replacement chain is constructed with one or more missing links or 
additional links, the replacement chain is useless for the purpose 
intended. Another technique which has been used in attempting to measure 
the overall length of a chain loop is to lay it on a flat surface and 
extend it into an elongated form and measure the length from end to end. 
This technique also leads to inaccuracies, as it is dependent upon the 
degree of loop elongation while making the measurement, and requires that 
the loop shape be identical both in the chain to be replaced and in the 
new chain to be constructed. 
Chains are frequently replaced by a dealer who purchases chain in bulk 
lengths wound around spools. This replacement chain may be withdrawn from 
the spool to any selected length, and then assembled into a new chain look 
for replacement purposes. For the reasons described above, it is important 
that a replacement chain have precisely the same number of links as the 
chain to be replaced. 
In the case of chains in general, and particularly in the case of chains 
utilized on chain saws, repair, maintenance and replacement is made more 
difficult by the fact that such chains are available in a number of 
different link sizes. The size of a chain link is typically referred to as 
the chain pitch, and chain pitch is commercially available in up to six 
different link dimensions. The foremost common chain pitches are 0.250 
inches, 0.325 inches, 0.375 inches, and 0.404 inches. Since these chain 
pitch sizes are relatively similar in size dimensions, it is difficult to 
ascertain with the naked eye precisely which of the several chain pitches 
one is observing in a particular case. Measurement with a ruler or other 
linear scale is possible, but even this measurement must be done precisely 
in order to ascertain the relatively close dimensional tolerances which 
exist between the various chain pitches. 
SUMMARY OF THE INVENTION 
The present invention comprises a chain gauge having a holder for accepting 
a chain loop, one end of the holder being slidable over a linear scale so 
that the chain loop may be distended to its maximum length. The slidable 
holder portion comprises a slidable shoe having a cursor thereon, which 
enables the operator to read a graduation on the linear scale to determine 
the number of links on the chain. Further, the holder has a plurality of 
pairs of sight holes aligned so as to view the chain links, and by 
alignment with the sight holes the pitch of the chain links may be 
determined. 
Accordingly it is an object of the present invention to provide a chain 
gauge for measuring certain physical characterstics of chains. 
It is another object of the invention to provide a chain gauge having a 
fixed and movable holder section, operable in conjunction with a scale, to 
enable a measurement of the number of links on a chain. 
It is yet another object of the invention to provide a chain gauge having 
means for measuring the chain link pitch. 
It is a further object of the invention to provide a chain gauge having 
additional calibrated apertures for measuring various chain 
characteristics.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring first to FIG. 4, the pertinent elments of a typical saw chain 
will be described. A saw chain is comprised of a plurality of links of 
several different nomenclatures. For example, saw chain 10 has a right 
hand cutter link 12 and a left hand cutter link 14. The cutter links are 
respectively connected to drive links 15, and coupler links 16 are used 
for the remaining link interconnections. All of the links are held 
together by rivets 18. 
The "chain pitch" is determined by measuring the distance P between 
adjacent drive links 15. The "gauge" of the chain is determined by 
measuring the thickness of a drive link 15. Typically, chain gauges may be 
found in dimensions of 0.050, 0.58, and 0.063 inches. 
If chain 10 is subjected to severe usage wear occurs between the respective 
moving parts. Typically, the rivets 18 and/or the holes through which the 
rivets pass are subjected to wear, and the overall effect of this 
cumulative wear is a slight expansion in the overall length of the chain. 
For severely worn chains, the cumulative wear may extend the overall chain 
length by the equivalent one extra link. Thus, when measuring the length 
of a chain consideration must be given to the degree of wear of the chain 
in order that the precise number of links may be ascertained. The length 
of a chain is typically measured in terms of the number of drive links 15 
which the chain has, and a severely worn chain may be elongated to nearly 
the extent of an additional drive link. 
Referring next to FIG. 1, the invention is shown in front elevation view. A 
scale 20 having one or more parallel lines of graduations thereon is 
affixed into a holder 22. Holder 22 has a semicircular face plate 24 
covering a curved surface 26, face plate 24 being sized so as to construct 
a protruding lip beyond the edge of surface 26. A hanger bracket and gauge 
30 is affixed to surface 26 and projects vertically therefrom. 
Hanger bracket and gauge 30 may have additional calibrated apertures 
therethrough, as for example holes 32, 33, 34 of different predetermined 
diameters for serving as a file gauge. Hanger bracket 30 may also have 
apertures such as apertures 36, 37, 38, which may be made of predetermined 
size to serve as gauges for measuring the thickness of drive link 15. 
Faceplate 24 has a plurality of pairs of sight holes, as for example sight 
holes 42a, 42b, which are elongated holes arranged in a predetermined and 
precise spacing relationship. For example, sight holes, 43a, 43b may be 
spaced at a 0.250 inch spacing, sight holes 42a, 42b may be spaced at a 
0.325 inch spacing, sight holes 44a, 44b may be spaced at a 0.404 inch 
spacing; sight holes 45a, 45b may be spaced at a 0.375 inch spacing. The 
respective pairs of sight holes are spaced to coincide with the chain 
pitches of commercially available chains, and one or more pairs of such 
holes may be positioned along faceplate 24. Alternatively, these holes may 
be positioned along upper lip 52 of slidable shoe 50. 
A slidable shoe 50 is fitted around scale 20 to permit sliding motion of 
shoe 50 along scale 20. Shoe 50 has an upper lip 52 formed around a curved 
radius and a lower lip 54 similarly formed around a curved radius. Lips 52 
and 54 project from a curved surface 53 to form a channel therebetween 
along surface 53. Shoe 50 has an opening 58 therethrough to expose a 
portion of scale 20, and a cursor line 60 may be utilized to read scale 20 
as will be hereinafter described. 
FIG. 1 shows a chain 10 mounted in position for use of the invention. Chain 
10 is looped around curved surface 26 at its upper end, and is distended 
at its lower end while being held along curved surface 53 by means of 
upper lip 52 and lower lip 54 of shoe 50. 
FIG. 2 shows a side elevational view of the invention, eliminating chain 10 
for clarify. The spacing of hanger bracket 30 relative to faceplace 24 
provides a channel over curved surface 26 for containing chain 10. 
Similarly, the spacing of upper lip 52 relative to lower lip 54 on shoe 50 
provides a channel over curved surface 53 for containing chain 10. Shoe 50 
has a guide member 48 which extends around scale 20 in a relatively loose 
fit, to permit shoe 50 to be slidable along scale 20. A stop 49 is 
attached at the end of scale 20 to prevent shoe 50 from sliding off the 
end of scale 20. 
FIG. 3 shows the invention in rear elevation view. The rear side of scale 
20 may also contain graduations along the length of the scale to permit 
additional calibrations of the parameters to be measured on a typical 
chain. Guide 48 has an opening 59 bridging scale 20, and a cursor line 62 
may be utilized to obtain an accurate reading along the graduations on the 
reverse side of scale 20. 
The respective elements of the invention may be constructed from molded 
plastic to thereby provide a gauge at a relatively inexpensive cost. As is 
apparent from the drawings, scale 20 may be made of any convenient length 
to accommodate chains of varying sizes. In the preferred embodiment scale 
20 is in excess of 36 inches long to measure chains having over 80 links. 
Further, the front and reverse sides of scale 20 may be segmented into 
parallel series of graduations, each series of graduations corresponding 
to different chain pitches. In this manner, the device may be useful for a 
wide range of different types of chains. Further, the reverse side of 
scale 20 may be calibrated with one or more lines of graduations 
corresponding to the chain pitch graduations on the front side of scale 
20, but offset by a predetermined amount to compensate for the measurement 
of severely worn chains. For example, the graduations along the reverse 
side of scale 20 may be offset by one chain link increment from the 
graduations on the front side of scale 20. In this manner, if it is 
apparent that one is measuring an extremely worn chain, the number of 
links may be more accurately determined from a reading taken on the 
reverse side of scale 20. 
In operation, a chain is looped over the curved surface in holder 22 and is 
distended downwardly. Shoe 50 is slidable along scale 20 until it accepts 
the lower loop of the chain, and is further distended until the chain is 
tightly contained between shoe 50 and holder 22. Next, the chain is 
longitudinally moved while viewing the chain through the sight holes 42a, 
b through 45a,b until adjacent drive links are observed through a pair of 
the sight holes. These drive links are shifted until an ajdacent pair of 
drive links appears in a particular pair of sight holes, and the pitch P 
is derived from the spacing of the particular sight holes wherein adjacent 
drive links are seen. For convenience, the respective pairs of sight holes 
may be labeled with the respective chain pitches they represent. Once the 
pitch of the chain is known, the number of links in that chain may be 
determined by observing the cursor line 60 and reading scale 20 along the 
particular line of graduations corresponding to the chain pitch P observed 
in the sight holes. Having thus determined the chain pitch and the number 
of links in the chain, it is a relatively simple matter to select the 
proper replacement chain as well as the proper length of that chain for 
replacement purposes. 
The present invention may be embodied in other specific forms without 
departing from the spirit or essential attributes thereof, and it is 
therefore desired that the present embodiment be considered in all 
respects as illustrative and not restrictive, reference being made to the 
appended claims rather than to the foregoing description to indicate the 
scope of the invention.