Also refer to the Hand-tapping Section.
3-Wire Method
3-wire set (chart) & plastic color-code wire (micrometer anvil ) holders used to measure thread size.
3-Wire Method, 60° Center Gage, Thread Cutting Reference, Lathe Gears, Gear Ratios, Thread Indicator, Thread Micrometer, Thread Gages
Threads:
parts & basic thread shapes, reading thread designations, 3-wire method of measuring pitch diameters.
Also refer to the Hand-tapping Section.
3-Wire Method
3-wire set (chart) & plastic color-code wire (micrometer anvil ) holders used to measure
thread size.
This Starrett attachment is useful for holding the center gage firmly against
the lathe arbor or
faceplate when setting either internal and external screw cutting tools. A slot
containing a flat spring
holds the gage. The V-groove in the other side permits locating the attachment
against the lathe arbor.
Using the
center
gage to setup the 60° tool bit cutting angle.
When cutting U.S. Standard Threads, set the
compound at exactly 29º,
adjust the chasing tool
on center and to conform to position
with the
60º center gage. Move the tool in to just touch
the work. Re-check setup. Feed
the tool in by moving only the compound.
By using the compound,
there is less stress on
the tool bit and the cut is cleaner.
| THREAD CUTTING REFERENCE | |||
| THREADS/INCH | DEPTH @ 29º |
THREADS/INCH | DEPTH @ 29º |
| 2 | .3713 | 18 | .0412 |
| 4 | .1856 | 20 | .0371 |
| 5 | .1485 | 24 | .0310 |
| 6 | .1237 | 27 | .0275 |
| 7 | .1060 | 28 | .0265 |
| 8 | .0928 | 30 | .0247 |
| 9 | .0825 | 32 | .0232 |
| 10 | .0742 | 36 | .0206 |
| 11 | .0675 | 40 | .0186 |
| 12 | .0620 | 48 | .0155 |
| 13 | .0570 | 50 | .0148 |
| 14 | .0530 | 64 | .0116 |
| 16 | .0464 | 72 | .0103 |
Gear Ratios
Gear ratios for feed rates. See
Jet feed gears.
Other 9x20 lathes have additional gear
sizes that are interchangeable with the Jet
BD-920N.
Gear ratios differ among the machines (e.g.,
Jet vs. Enco).
I bought additional gear sizes (e.g., 120t), 127t) to have more ratios.
Thread Indicator
A manual lathe has a thread indicator that shows the operator when to close the
half-nut. For CNC threading,
Mach3 makes use of the pulse from the spindle index sensor to know when to start
cutting. By timing
the index pulses, Mach3 calculates the feed per revolution that corresponds
to the pitch of the thread.
As an example, for one revolution of the lathe spindle, a ¼-20 bolt has a
thread every 0.050" (1/20).
Screw
thread micrometer with five different anvil pairs to measure both
unified &
metric external pitch diameter.
0" to 1" measurement range with a 0.0001" scale.
A much easier pitch measurement method than the 3-wire method.
SCREW THREAD MICROMETER ANVILS ANVIL #
1
2
3
4
5
TPI RANGE
64 - 48
44 - 28
24 - 14
13 - 9
8 - 5
METRIC RANGE
0.4 - 0.5
0.6 - 0.9
1 - 1.75
2 - 3
3.5 - 5
Anvil pairs are clearly marked for pitch range.
Example measurement of a ¼-20 screw. The micrometer reading is 0.2160". Table pitch value is 0.2175".
A fast & accurate thread measurement tool. The bolt can freely rotate around the micrometer's anvil axis.Thread Gages
Standard Unified & metric thread gages.
3-Wire Method, 60° Center Gage, Thread Cutting Reference, Lathe Gears, Gear Ratios, Thread Indicator, Thread Micrometer, Thread Gages
