Lathe Toolholders for internal grooving – a review for the hobbyist or small workshop machinist
1. What is Internal Grooving?
Internal grooving (also known as ID grooving) is most commonly used to create a recessed groove inside a tube or bored cylinder for placement of an o-ring to seal in or out oils or gases. Less commonly it is used for to provide clearance for circlips or retaining rings to prevent axial movement of an armature. It can also be used to create baffles or channels to act as reservoirs for air, oil or other working fluids to facilitate movement through a closed system.
2. What toolholders are there for internal grooving on a lathe?
The following sections detail 3 of the most common and useful indexable toolholders for internal grooving.
2.1. MGIVR/L type holder
| PROS | CONS |
|
Largest shank diameters and lengths for work on larger lathes and large workpieces Good for deep internal grooving High rigidity and low deflection, especially on the thicker shanked models Good depth of cut. Good and diverse range of two sided inserts widely available at low prices (MGMN, MRMN, MGGN, etc) |
Large minimum bore diameter – not suitable for small projects Large minimum shank diameter – not suitable for small lathes or toolposts with less than 20mm shank capacity Blocky toolhead means limited clearance at minimum bore depth Limited to 1 cutting width per holder (MGIVR2016-2 limited to 2mm, MGIVR2016-3 limited to 3mm, etc) Limited range of cutting widths available |
MGIVR/L Series Toolholder Dimensions Table
| Toolholder Designation | Cutting Width | Shank Width | Shank Height | Overall Length | Socket Cap Screw |
| MGIVR/L 2016-1.5 | 1.5mm | 16mm | 15mm | 160mm | M4 x 12mm |
| MGIVR/L 2016-2 | 2mm | 16mm | 15mm | 160mm | M4 x 12mm |
| MGIVR/L 2016-3 | 3mm | 16mm | 15mm | 160mm | M4 x 12mm |
| MGIVR/L 2520-2 | 2mm | 20mm | 18mm | 180mm | M5 x 16mm |
| MGIVR/L 2520-3 | 3mm | 20mm | 18mm | 180mm | M5 x 16mm |
| MGIVR/L 2520-4 | 4mm | 20mm | 18mm | 180mm | M5 x 16mm |
| MGIVR/L 2925-2 | 2mm | 25mm | 23mm | 200mm | M5 x 16mm |
| MGIVR/L 3125-3 | 3mm | 25mm | 23mm | 200mm | M5 x 16mm |
| MGIVR/L 3125-4 | 4mm | 25mm | 23mm | 200mm | M5 x 16mm |
| MGIVR/L 3125-5 | 5mm | 25mm | 23mm | 200mm | M5 x 16mm |
| MGIVR/L 3125-6 | 6mm | 25mm | 23mm | 200mm | M5 x 16mm |
Best suited for : Hobbyists and workshops with larger lathes, working on larger bore grooving. Commercial runs, heavy duty work.
2.2. SNGR type holder
| PROS | CONS |
|
Small diameter straight shanks available – ideal for small lathes and deep narrow bores. One holder can support inserts of many different widths – cut many widths with only one holder Widest variety of grooving widths available (0.1mm increments from 0.5-3mm) Double ended inserts available on large shanked holders |
Limited depth of cut (typically limited to insert groove width) Smaller shanked holders fit only single sided insert type GR Inserts less common and more expensive than MGMN type holders |
Shank diameter range : 8mm to 20mm (whole length)
Shank length range : 100mm to 200mm
Best suited for :
-Small lathes and small projects. Hobbyists who don’t want a separate holder for each grooving width.
-One off projects, prototyping.
-Production runs on small parts.
2.3. Comma type holder
| PROS | CONS |
|
Thick shank to narrow head – low minimum bore diamter at shallow depths Variety of widths and depth available for each holder – cut many width and depth grooves using only one holder Versatile insert options available - threading inserts, crowning inserts. Narrow head allows for good chip clearance |
Limited bore depth before shank thickness affects minimum bore diameter. Not suitable for deep internal grooving. Expensive and uncommon, Single sided inserts only Limited support, unsuitable for hard or interrupted cutting |
Shank diameter range : 12mm – 20mm
Machinable depth range : 10mm - 30mm
Best suited for: small and medium sized lathes that only need to bore grooves at shallow bore depths