9x20 Collet & Jawed Spindle Chucks
Last updated on Wednesday, April 03, 2019 11:40:13 AM Mountain US Time Zone


5C Collet Chuck, Keys & Bars, Chucks with 5C Mounts, ER-40 Collets & MT3 Chuck, MT3 Collets,
4-Jaw Chucks, 3-Jaw Chucks, Total Indicated Readout, MT3 End Mill Holders,
MT3 to Taig Adapter

5C Collet Chuck

Tramming (centering) a 5C collet chuck that has 4-way built-in set screw adjustability in its adapter plate.
This is an important feature as this lathe has a threaded spindle nose which introduces setup variability.
A Swiss-made, jeweled, Brown & Sharpe dial test indicator (0.0005" resolution) is being used to tram.
Each position is stamped with a number. Use the 4-jaw alignment method to tram the 5C chuck.
See instructions on how to set tip geometry & illustration. Introduction to lathe chucks.

One of four adjustment set screws for tramming the 5C chuck.

A 5C collet set has a larger range of sizes when compared to ER-40 or MT3 collet sets but seventy 5C collets are
needed to make up a complete set of 3/64" through 1-1/8" sizes by 1/64". A 5C collet has a relatively small range
 for gripping a part. Best accuracy is +0 to -0.002". For a part above +0.005" you may damage the work, a part
 below 0.010" you may damage the collet. 1/32" (0.03125") increments are too large of steps & you will not get
 continuous coverage. Most 5C collets are open all the way through & thus allow holding long stock up to the
maximum of the lathe spindle hole, e.g.,
25/32" (0.78125")
for the 9x20. By comparison, an ER-40 chuck limits
the depth at which a part can be seated into its collet to a few inches. Collets, in general, do not mark the metal
 stock like jawed chucks & the total indicated runout (TIR) is low if it is a quality tool.

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See Collets Section for more information

Keys & Bars

Every chuck comes with a key.

Fabricated steel Tommy bars to tighten & loosen spindle chucks. Bottom two are supplied with the Jet lathe.

To tighten or loosen a 5C collet requires about 40 turns of the T-wrench. Mounted a hex to 3/8" (hardened)
adapter bit into the 5C square fixture & diamond ground the sides/corners down a little until it fit.
Using the cordless screwdriver now allows much faster operation. Start by installing the collet by
 hand to avoid cross-threading. Final tightening & initial loosening should be done with the T-wrench.

Chucks with 5C Mounts

4-inch, 3-jaw 5C chuck supplied with both inside & outside hardened jaw sets & a T-wrench.
The one-piece, integral 5C back plate is strong & accurate.

3-inch, 4-jaw, 5C mount lathe chuck & key. 4-jaw 5C specifications.

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MT3 Spindle Collets & Adapters
A collet is safer to use than a chuck & typically has a lower total indicated readout (TIR). The ER-40 double-angle
collet is an industry standard affording high precision & ready availability. An MT3 collet holder is available.
Each ER-40 collet has a wide (0.04") clamping range so a 23 collet set provides continuous size coverage from
 0.12" (nominal 1/8") through 1.02" (nominal 1") or 3.05mm ~ 25.9mm. The 15 sizes that come in the set (fitted
case included) are shown in the table in bold numbers; the other eight collets (all n/32nds sizes) were purchased
separately. Specifications: wide holding range, accuracy 0.0001", self-releasing design, high precision collet
chuck with different shanks available (MT3, MT-4, MT-5, R-8) & a spanner wrench. The MT3 collet chuck I
received had a 1/2-12 TPI tapped hole for the drawbar (not a common thread). I made a drawbar from rod threaded
 1/2-12 TPI on one end & 1/2-13 TPI on the other end. There are milled flats for a wrench.
Snap the collet into
 the nut's eccentric ring before screwing it onto the spindle. This ring is the collet extraction mechanism.
Do not tighten the nut onto an empty collet as damage could easily result.

ER-40 Collets & MT3 Chuck

ER-40 collet set (above). Collet chuck shown with a MT3 shank.
The plugs are used to fill the collet when
holding very short parts; allows good clamping without distorting/damaging the collet or part. Each plug is
stamped with the collet's nominal size. There are other types of ER-40 collet chucks, e.g., R-8 shank.

Threaded aluminum drawbar. Steel end plug machined to fit the spindle hole & a flare nut with a washer.

Collet table (below) showing continuous size coverage.
White sizes were the original set & green sizes were added.



1/8" 0.12500 0.12 ~ 0.16"
3/16" 0.18750 0.16 ~ 0.20"
7/32" 0.21875 0.200 ~ 0.236"
1/4" 0.25000 0.236 ~ 0.275"
5/16" 0.31250 0.275 ~ 0.316"
11/32" 0.34375 0.316 ~ 0.354"
3/8" 0.37500 0.354 ~ 0.393"
13/32" 0.40625 0.393 ~ 0.433"
7/16" 0.43750 0.433 ~ 0.472"
1/2" 0.50000 0.472 ~ 0.511"
17/32" 0.53125 0.511 ~ 0.551"
9/16" 0.56250 0.551 ~ 0.590"
5/8" 0.62500 0.590 ~ 0.629"
21/32" 0.65625 0.629 ~ 0.669"
11/16" 0.68750 0.669 ~ 0.708"
3/4" 0.75000 0.708 ~ 0.748"
25/32" 0.78125 0.748 ~ 0.787"
13/16" 0.81250 0.787 ~ 0.826"
27/32" 0.84375 0.826 ~ 0.866"
7/8" 0.87500 0.866 ~ 0.905"
15/16" 0.93750 0.905 ~ 0.944"
31/32" 0.96875 0.944 ~ 0.984"
1" 1.00000 0.984 ~ 1.020"

MT3 Collets

MT3 collet set & a
3/8-16 drawbar made from threaded steel rod.

MT3 collet set from Phase2+. Drawbar made from 3/8-16 threaded stock.
Collet sizes range from
1/8" to 3/4" by 1/16ths (no continuous size coverage).
To remove a part, make the nut flush to the end, hold the part & collet while 
gently knocking out the bar using a hard plastic-faced mallet or brass hammer.

3/4" MT3 collet mounted into the Jet's spindle.
A collet in a lathe spindle is much safer & accurate than a spinning chuck with protrusions.

4-Jaw Chucks

4" (above) manual & 6" (below), 4-jaw chucks on a standard 1-1/2-8 Jet threaded mount.

6-inch, 4-jaw instruction manual. Massive for this sized machine, it weighs over 26-lbs.

Tramming (center) the part using a digital indicator gage.

Use steel letter stamps to mark each jaw position on all chucks. I also indexed the adapter plate to the body.

How to center a round work piece in a 4-jaw lathe chuck

  1 - After rough alignment using the chuck rings, put a dial indicator on the work piece.
       Then, rotate the spindle through one complete revolution noting the highest & lowest indicator readings.
  2 - Continue rotating the spindle & stop exactly midway between the high & low readings, then zero the indicator.
  3 - Rotate the spindle to bring jaw #1 on plunger & iteratively adjust jaws #1 & #3 to re-zero the indicator.
  4 - Finally, rotate the spindle 90 deg & adjust jaws #2 & #4 to re-zero the indicator once, again.

Making a new compound pivot.

A six-inch, 4-jaw chuck from with a 1-1/2-8 threaded adapter plate. Screws right onto spindle of the Jet BD-920N.
Weighs about 26.4-lbs. (12-kg. Clamps part more tightly than a 3-jaw & allows perfect centering. It can easily
hold a 4" x 4" (square) part. A far more accurate & easier to use modern design when compared to the Jet-
supplied 7-inch, 4-jaw chuck. Note, even the empty chuck is quite heavy. Its momentum makes for extra nice
 cuts. This chuck is at the upper limit of the machine in terms of both weight & size. Verify everything clears
(e.g., the carriage)
before starting. Make sure to slip the belt idler, especially when starting fast &/or heavy
loads, otherwise you can break the V-belt. Reduce belt idler tension by installing an S-link. This large chuck
can also be mounted onto a 6" rotary table.

3-Jaw Chucks

The Bison 5", 3-jaw chuck (Poland) is smooth & accurate. The jaws are reversible. The counter
bore of the threaded back plate was undersized & had to be bored to fit the spindle shoulder.
The chuck weighs about 10-lbs. Faced the adapter plate to achieve best total indicated runout (TIR).
Verify your lathe is in alignment before facing a chuck adapter plate or a faceplate.





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Specialized rule that can be used on lathes & mills. Stop-Loc instructions.

Total Indicated Readout

To measure total indicated readout where TIR = (Maximum reading - Minimum reading), clamp a dowel pin in
the chuck (or collet) & put a dial gage on it. Slowly rotate the spindle & note max & min values. Dividing the
TIR in half yields the +/-tolerance. For example, a part having a 0.004" TIR has +/-0.002" tolerance. The
base shown (Noga) is very easy & quick to use. Loosening a large knob makes all the joints movable.
Just position indicator & tighten; the whole arm's position is then fixed. It can hold instruments with either a
" stem or a dovetail. It has a fine adjustment feature, too.






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The large Jet OEM independent 4-jaw chuck is 7-3/8" in diameter.

Adjustments of the jaws' rear attachment bolts are troublesome. Note the spindle safety set screw (right).

This chuck is more suited for wood applications as its accuracy is unacceptable for metal work.
There are no relief cuts in the jaw corners. One could use a surface grinder to clean it up, if needed.

MT3 End Mill Holders

These MT3 end mill holders from Phase2+ each have a set screw that engage the end mill flat.
These holders are for both
3/8" & 1/2" shank end mills. For use with the Jet BD-920N lathe spindle.

MT3 to MT2 taper adapter sleeve.

MT3 to Taig Adapter

MT3 to 3/4-16 TPI taper, allows using Taig or Sherline chucks & other accessories on the Jet BD-920N or
other MT3 machines. Allows accurate fabrication of large-shank end mill holders for use on the Taig mill &
lathe. I've made end mill holders by both reaming & boring. Boring is very accurate (0.0005" TIR) but a
slower process. It is better to mount the arbor by its threads before boring than to grip it on the outside.

Taig collet on the Jet 9x20. Taig collets are size limited & made of soft steel but can be easily customized
e.g., threaded for 10-32 to turn down screws. The 5C collet chuck, ER-16, or ER-40 are superior alternatives.


A Sherline 3.1-inch, 3-jaw chuck & a Taig 3-1/4-inch, 4-jaw chuck using a MT3 to 3/4-16 adapter.

A finished end mill holder for the original-design Taig lathe/mill. Blank arbors (steel) #1132, from Taig. 3/8"
shank end mill shown. Milled flats for a 7/8" wrench & uses a
1/4-20 set screw. This type of arbor is not needed
(nor mountable) if you use the (superior) upgraded Taig mill ER-16 spindle but is still usable for the lathe.

CAUTION: Large end mills easily exceed a Taig mill's capacity thus requiring small cuts.

For extra small parts, combine the MT3 & stubby holder to allow use of the ER-16 collet set on the Jet lathe.
There is a left-hand set screw in the shank that controls an end mill's depth in the collet.

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5C Collet Chuck, Keys & Bars, Chucks with 5C Mounts, ER-40 Collets & MT3 Chuck, MT3 Collets,
4-Jaw Chucks, 3-Jaw Chucks, Total Indicated Readout, MT3 End Mill Holders,
MT3 to Taig Adapter