R-8 Spindle Accessories
Last updated on Tuesday, September 19, 2023 03:59:28 PM Mountain US Time Zone


R-8 Collets, ER-40 Collet Chuck, Arbor,
Boring Heads,
Fly Cutter, End Mill Holders, Drill Chucks

RF_R-8_accessories.jpg (54427 bytes)
R-8 tooling is readily available.
n extra 5C collet holder modified with
an oak insert
to hold R-8 sized shanks

R-8 Collets

Lyndex (Japan) R-8 collet set 1/8" x 7/8" x 1/16";
very accurate
& high gripping power.

A rotary collet holder is compact.

ER-40 Collet Chuck

An ultra-high precision (Maritool USA) ER-40 collet
chuck with R-8 shank for
RF-25 mill use. Best in class.
Made from alloy steel hardened to 54 - 56RC, balanced
to 15,000 RPM, its concentricity is less than 0.0001"

at the collet's face & the rear internal thread is 7/16-20.
This chuck type allows use of odd shank sizes of drills

& end mills with only one collet system. The ER-40
collets & clamping nut can be changed-out within a

smaller space than the longer R-8 collets. There are
other types of ER-40 collet chucks, e.g.,
MT3 shank.

ER-40 collet nut wrench.

Set of ER-40 collets (import) that provides
continuous sizes from 0.12" to 1.02"

Each size has a labeled filler plug that is used when
gripping short parts so as to not distort the collet.



1/8" 0.12500 0.120~0.160"
3/16" 0.18750 0.160~0.200"
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"

Cannot measure error using a 0.0005" resolution indicator.
The chuck body has flats for a 1-3/4" open-end wrench.

See Precision Mensuration Section

Super low runout. Measured +/-0.00015" or 0.0003"
total indicated readout (TIR); within dowel-pin error.


One-inch arbor with an R-8 shank
with various spacers & left-hand nut.

Slit-cutting soft steel.

Boring Heads 

Two-inch boring head with 7/8-20 threaded
arbors MT2, R-8, & 1/2" straight type shanks.
Uses 1/2" boring bars. Steel boring-bar adapter
1/2" to 3/8". Use
d a reamer for the 3/8" hole.

Also, see how to use a boring head in a lathe tailstock for turning tapers.

The ID is measured using a self-centering
telescopic gauge with a caliper or a micrometer.

Two-inch boring head animation.

This boring head type's dial reads radius so the
diameter of the hole increases by twice the adjusted size.

A 2-1/2" boring head that uses 1/2" boring bars.
The head has
a rigid, integral R-8 shank &
a direct
-read dial
so the diameter of the hole
increases exactly by the adjusted size (USA).

Multiple hole positions, with set
screws, for a 1/2" boring-bar shank.

Again, this scale reads out the diameter changes;
some are the radius. Note the adjustable gib dovetail.

A 3-inch boring head with 1-1/2-18
threaded interchangeable 3/4" & R-8 shanks.

The 3-inch boring head uses
boring bars with 3/4" shanks.

Mounted in the Rong-Fu mill using the R-8 shank.

A comparison of 2, 2-1/2, & 3-inch boring heads.

Fly Cutter

2-1/2" carbide fly cutter (supplied).

End Mill Holders

R-8 to MT2 adapter. R-8 end mill holders.
Sizes: 3/16", 3/8", 1/2", 5/8" & 3/4".
Indexed end mills will not slip.

Drill Chucks

Jacobs ball bearing Super Chuck, 1/8" ~ 5/8" (3mm ~ 16mm)
capacity with R-8 to JT3 ETM Precision arbor
Large size shown relative to a US quarter (0.955" or 24.26mm).

Jacobs Super Chuck mounted
on the
RF-25 Mill & turning.

Keyless 1/2" capacity drill chuck on R-8 shank.

Use low-cost chucks for light duty work, only.

R-8 Collets, ER-40 Collet Chuck, Arbor,
Boring Heads,
Fly Cutter, End Mill Holders, Drill Chucks