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.
9x20 Lathe Single-point Threading
Last updated on
Wednesday, November 21, 2012 07:01:21 PM
Eastern US Time Zone
3-Wire Method,
60°
Center
Gage,
Thread Cutting Reference,
Retractable Tool Bit Holder,
Lathe Gears, Gear Ratios,
Thread Indicator,
Thread Micrometer, Thread Gages,
CNC Threading
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.
60° Center
Gage
The 60°
satin chrome-plated tempered steel Starrett No. C391
center (or fishtail) gage.
The different scales measure threads/inch. The double depth of American National
threads are
shown for different screw sizes but threads are best cut using the compound at
left 29 degrees.
This Starrett attachment is useful for holding the center gage firmly against
the lathe arbor or
faceplate when setting either internal & 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 a round part.
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 & 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 & 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
Using an angle jig to set & then (four-bolt) lock the lathe compound at 30 degrees.Retractable Tool Bit Holder
Retractable tool bit holder.Gear Ratios
Gear ratios for various 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 0.2164".
A fast & accurate thread measurement tool. The bolt can freely rotate around the micrometer's anvil axis.Thread Gages
Standard Unified & metric thread gages.CNC Threading
Two movies showing a Taig CNC lathe threading a ⅜-16 aluminum bolts.
3-Wire Method, 60° Center Gage, Thread Cutting Reference, Retractable Tool Bit Holder,
Lathe Gears, Gear Ratios, Thread Indicator, Thread Micrometer, Thread Gages, CNC Threading
