Home

Collets & Jawed Chucks

A 5C collet chuck (5 inch) with 4-set screw adjustability for minimizing the run out with a dial indicator.
The 4-screw adjustability is a must for lathes that have threaded spindles.
The 5C collet has a larger range of sizes when compared to ER-40 or MT-3 collets 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; run out is low.

To tighten & loosen a 5C collet requires about 40 turns of the T-wrench.
I mounted a hex to ⅜" (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.

MT-3 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 MT-3 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 (MT-3, MT-4, MT-5, R-8) & a spanner wrench. The MT-3 collet chuck I received had a ½-12 TPI tapped hole for the drawbar (not a common thread). I made a drawbar from rod threaded ½-12 TPI on one end & ½-13 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 result.

ER-40 collet set (above). Collet chuck shown with a MT-3 shank. The plugs are used to fill the collet when holding very short parts;
allows good clamping without distorting/damaging the collet. Each plug is stamped with the collet's nominal size.
There are other types of ER-40 collet chucks, e.g., R-8 shank. Also see chucks for 5C collets & ER-16 collets.

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

MT-3 collet set from Phase2+. Drawbar made from ⅜-16 threaded stock. Steel end plug machined to fit the spindle hole. Flare nut with a washer used. Collet sizes range from ⅛" to ¾" 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 large, hard plastic-faced mallet or brass hammer.

MT-3 collet set from Phase2+ & a ⅜"-16 drawbar made from threaded rod.

¾" MT-3 collet mounted into the Jet's spindle.

4" (above) & 6" (below), 4-jaw chucks on a standard 1½-8 Jet mount.




Center the work piece using a dial indicator gage.

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

1. After rough aligning to 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° & adjust jaws #2 & #4 to re-zero the indicator once, again.

Drilling 1" hole in cast iron before boring to size for a Hit-Miss Engine cylinder.

Making a new compound pivot.

A six inch, 4-jaw chuck from Enco with a 1½-8 threaded adapter plate. Screws right onto spindle of the Jet BD-920N. Weighs about 26.4 lbs. (12 kgs). 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.

A Bison 5", 3-jaw chuck from Poland; smooth & accurate (Enco). 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 run out (TIR). Verify your lathe is in alignment before facing a chuck adapter plate or a faceplate.

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 magnetic base shown (Noga from Enco) is very easy & quick to use. Loosening a large knob makes all the joints movable. Just position indicator & tighten; the whole arm's position then is fixed. It can hold instruments with either a ⅜" stem or a dovetail. It has a fine adjustment feature, too.

A Sherline 3.1 inch, 3-jaw chuck (above) &
a Taig 3¼ inch, 4-jaw chuck (below)
using an MT3 to ¾-16 TPI adapter from LMS.

These MT-3 end mill holders from Phase2+ each have a set screw that engage the end mill flat.
These holders are for both ⅜" & ½" shank end mills. For use with the Jet BD-920N lathe spindle.

MT-3 to ¾-16 TPI taper (from LMS), allows using Taig or Sherline chucks & other accessories on the Jet BD-920N or other MT-3 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 indicate (mount) the blank arbor by its threads before boring than to grip it on the outside surface.

A finished end mill holder for the original-design Taig lathe/mill. Blank arbors (steel) #1132, from Taig.
⅜" shank end mill shown (Enco). Milled flats for a ⅞" wrench & uses a ¼-20 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's capacity thus requiring small cuts.

Taig collet on the Jet 9x20.  Also see small chucks mounted on the Jet using the MT-3 to ¾-16 TPI taper.
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 better work-holding alternatives.