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Патент USA US2114448

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April 19, 1938.
Q. E. KOEHLER ET‘ AL~
2,114,448
TAP
Filed Nov. 10,1956
_
Patented Apr. 19, 1938
2,114,443
UNITED fsrAres PATENT.
rice _,
2,114,448
TAP
"(Oscar E. Koehler and Earl R. Koonz, Green?eld,
'
Mass., assignors to Green?eld‘ Tap and Die
Corporation, Green?eld, Mass, a corporation
ofMassachusetts .
Application November 10, 1936, Serial No. 110,063
1 Claims. - (01. 10-441)
This invention relates to taps and more espe
cially to taps having relatively wide lands.
When holes to be threaded have key-ways or
slots, the lands of the tap used obviously must be
5 wide enough to span the key-way or slot, and
when the tap is of large diameter, wide lands are
necessary to hold it in‘ position and prevent chat
tering while the thread is being cut.v It has been
found, however, that excessive friction is devel
10 oped in using such taps ‘and various expedients
have been proposed for reducing it.
'
'
A conventional solution of this problem is to
“relieve” the thread by progressively deepening
and widening the grooves between'the threads
1 GI from or near the cutting edge to the heel of each
tween the cutting edges l8 and the heels l9 and
converting the arc of the root of the thread into
substantially a chord 20, as shown more clearly
inFig;4'.
5‘
1'
"
'
.
’
_
, Inv most cases, su?icient “relief” is obtained by
merely reducing the width of flat portions 2| of‘
the threads without cutting them away entirely,
so that thecrestx 22 of the threads remains ‘con
centric and there is no substantial reduction of
thread diameter even at the centerpofvthe land re
where the_“relief” is‘a maximum. At both the
cutting edge and the heel the cross section of
thread is unchanged, as' shown in Fig. 5, but at
the centerv of the relieved'portion the ?anks of
the threads will assume the’ shape indicated by "
land. While this procedure is effective in reduc
ing the friction, it is found'when'the' rotation of
the tap is reversed to remove it from the hole,
the dotted line 23.
Alternately, the relieved area may be of the
that chips often lodge in the “relieved” or re
at the root of thejthread is converted into a
20 cessed portions of the lands and are dragged into
the threads which have just been cut, thereby
impairing or completely destroying the ?nished
work.
The object of this invention is a tap of simple
and inexpensive construction which is capable of
cutting a clean thread without excessive friction,
and which may be readily removed without in
jury to the work.
We have found that the friction is minimized
30 by a special reduction of the central portion of
the lands, leaving both the heel and the cutting
edge at full pitch diameter. This gives the de
sired relief and at the same time avoids objec
tionable wedging on reversal because chips can
' not enter the “relieved” portion during the re
verse motion of the tap.
In the drawing,
Fig. 1 is a perspective view of a tap according
to this invention.
40
Fig. 2 is an enlarged cross-sectional view of the
tap showing the “relieved” portion of the lands.
Fig. 3 is a plan view of a portion of one of the
“relieved” lands.
Fig. 4 is a sectional view of the land along the
' root of the threads shown in Fig. 3.
Fig. 5 is an end view of the portion of the land
shown in Fig. 3, and
Figs. 6 and '7 show a “relieved” land of an al
ternate construction.
50
The tap of Fig. 1 comprises a shank II with a
plurality of threaded lands l2 separated by ?utes
l3 and tapered at the end [4 in the usual man
ner. The section in Fig. 2 taken at the root i5
of the thread shows the “relieved” portions l6 ex
55 tending over the central parts of the lands be
shape shown inll‘ig. '7, in which the convex'arc
slightlyconcavev are 24', but asin the previous
case‘the'?ats 2| of the thread are preferably not
reduced beyond the point where the crests come
to a sharp edge 25 of full pitch diameter.
In making the tap of this invention, the grind
ing wheel is set to grind the lands on the cor
rect pitch diameter and is then given a prede
25
termined inward shift cutting into the root cir
cle as the wheel approaches and recedes from the
center of each successive land so as to relatively
reduce the ?anks over the central part of the 30
lands and convert the are at the root of the
thread to a chord or to a concave are as the case
may be. Or the threads may be ground in usual
manner and the grinding wheel passed through
the thread in separate operation, giving the de
sired cutting action at the centers of the lands.
The type of relief shown in Figs. 6 and 7 may
be obtained by rotating the tap intermittently
and moving the grinding wheel 26 radially of the
tap into the groove between the threads to the 40
position shown in Fig. 7 while the tap is at rest.
The wheel is then retracted beyond the root cir
c-le 21 and the tap is rotated to bring the next
land into grinding position. This procedure is
repeated until the tap is relieved throughout the
full length (or any desired portion) of the thread,
it being understood that the wheel is being con
tinuously advanced under the control of the lead
screw, as in the ordinary grinding operation.
Other methods of grinding this chordal type
of relief will be obvious and will vary in the shapes
of the parts ground away and in the conforma
tion of the bottom surface of the groove, the lat
ter being either concave as shown in Figs. 4 and 55
2
2,1 14,448
7 or substantially ?at or convex, depending upon
the particular method used.
The tap of this invention lends itself readily to
accurate formation during the grinding of the
tap threads, the grinding tool simply being moved
both the cutting edge and the heel toward the
center of the land.
3. A tap having threaded lands separated by
flutes de?ning cutting edges and heels on the
lands, and with threads on each land having in
termediate portions diminishing in width from
both the cutting edge and the heel toward the
center of the land while maintaining the apexes
of said threads undiminished in height.
4. A tap having threaded lands separated by 10
with relation to the threads to give the desired
relief. The resulting construction preserves the
full thread formation at each end of the land and
at the same time obviates the objectionable fric
10 tional drag and substitutes for this a helpful ?utes de?ning cutting edges and heels on the
distribution of the lubricating oil. The central
portions of the lands cut away in accordance with lands and with threads on each land diminished
this invention provide extended shallow pockets in width at intermediate portions between the
cutting edge andthe heel, the grooves between
on each side of each thread catching the lubri
the threads being deepened adjacent the inter 15
15 cating oil and carrying it and spreading it over mediate thinner portions of the threads.
the freshly-cut surfaces of the threads as they
5. A tap having threaded lands separated by
are formed by the tap. This relieving of the cen
flutes de?ning cutting edges and heels on the
tral portions also maintains the strength and ri
gidity of the threads and preserves an accurately lands, and with threads on each land having in
> termediate portions ground to diminished width 20
20 centered continuous connection between the cut
ting and trailing portions so that the full strength from both the cutting edge and the heel toward
of the entire thread is available in support of the the center of the land while maintaining the
apexes of said threads undiminished in height.
cutting edge in each direction.‘
While this invention has been described in con
25 nection with speci?c embodiments, it is not lim
ited thereto. Other methods of providing the
relief may be used and cam control of the grind
ing wheel may be employed to give any desired
form to the out including, for instance, a precise
30 ly straight lined chord 20 at the root of the relief.
We claim:
'
1. A tap having threaded lands separated by
?utes de?ning cutting edges and heels on the
lands, the threads on a portion of each land hav
35 ing crests diminishing in width from both the
cutting edge and the heel toward the center of
the land.
2. A tap having threaded lands separated by
?utes de?ning cutting edges and heels on the
40 lands, and with threads on each land having in
termediate portions diminishing in width from
6. A tap having’threaded lands separated by
?utes de?ning cutting edges and heels on the 25
lands, and with threads on each land ground to
diminished width at intermediate portions be
tween the cutting' edge and the heel, the grooves
between the threads being deepened adjacent the
intermediate thinner portions of the threads.
30
7. A tap having threaded lands separated by
?utes de?ning cutting edges and heels on the
lands, and with threads on each land ground to
diminished width at intermediate portions be
tween the cutting edge and the heel, the grooves 35
between the threads being deepened on lines of
concave curvature adjacent the intermediate
thinner portions of the threads.
‘OSCAR E. KOEHLER.
EARL R. KOONZ.
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