When you want to do turning, boring, or other operations on a lathe you need tool holders and tool posts. In this article I am going to explain the different types of tool holders used on lathe machine, their uses, which one should you use and which one you should avoid.
But let’s get familiar with the terminology.
Let me begin by explaining, what is a lathe tool holder, a tool post, and the difference between the two.
- Tool Holder vs Tool Post
- Types of Lathe Tool Holders
- Types of Lathe Tool Posts
Tool Holder vs Tool Post
- Tool Holder: A tool holder is a generic term used for the adapters that hold a cutting tool and if the adopter holds a lathe tool, it is called a lathe tool holder. The term may be used to refer the small cutting insert retainers, or a device that holds the solid cutting tool. More on this in the next section.
- Tool Posts: A tool-post is a device firmly fixed on the cross slide (on the compound rest) of a lathe and has the provision for mounting one or more tool holders on it. The tool post may also have the facility to index/swivel by 90° or any angle and lock in that position.
Conventional tool posts can directly accommodate one or more lathe tools.
We shall discuss the tool holders and tool posts in detail in the following paragraphs.
Types of Lathe Tool Holders
Basically, the lathe tool holders can be of two types.
1. Insert Tool Holder
The first type of tool holder is used for holding and clamping index-able carbide inserts. These tool holders are made from toughened steel and have an arrangement for holding and clamping the index-able carbide inserts.
The advantage of this type of tool holder is, you can use the same tool holder and replace the worn-out inserts with new ones. These tool holders are designed to hold turning, facing, parting off, threading, boring, and other types of inserts and each holder can hold one type of insert.
These inset tool holders are often designated as turning tool holders, threading tool holders, and other tool holders, and each tool holder is given an alphanumeric code. These tool holders can be directly held and clamped in conventional tool posts.
2. Quick Change Tool Holder
The second type of tool holder is the tool holder designed work with quick change tool posts. Such tool holders are designed to hold the insert tool holders (discussed above), carbide cutting bars, boring tools etc. These tool holders can be designed to hold any tool viz. turning, facing, boring, threading, knurling, or they can be designed to hold a drill, a drill chuck, etc.
Depending on the type of tool clamped in the tool holder, these tool holders are designated as (i) turning, facing, and boring tool holder (ii) turning and facing tool holder (iii) knurling tool holder (iv) collet holder (this has the arrangement to open/close the collet) (v) Morse taper holder (can hold drills and reamers of the matching Morse taper) (vi) threading (ID or OD) tool holder, etc.
Tailstock as Tool Holder
Since the lathe tailstock spindle can be used for holding drill chucks, taper shank drills and reamers, and similar tools, you can consider the tailstock as a tool holder. A tailstock turret is a versatile and useful tool holder that can be held in the tailstock.
The tailstock turret has a tapered shank at one end and a turret at the other end that has provision for mounting 6 tailstock tools. The taper shank of the tailstock turret fits into the tailstock spindle and you can mount 6 tailstock tools on the turret (center drill and different sizes of drills or taps mounted in drill chucks).
The tailstock turret allows you to index the required tool to face the workpiece, lock it with the lever, and do the center drilling, drilling, tapping, reaming, and other operations. A tailstock turret saves your time spent on repeated mounting and removing the tailstock tools.
Types of Lathe Tool Posts
A lathe tool-post is a device for rigidly holding and clamping lathe tools or lathe tool holders (mounted with a lathe tool). A lathe tool post is firmly clamped to the T-nut of the lathes’ compound rest. There are various types of lathe tool posts and they may have the capability to hold 1 to 4 lathe tools or lathe tool holders.
The tool post can be of the conventional type or quick change type. A conventional tool-post is normally used with integral high-speed steel tools with low cutting forces since the position of the tool/tool-post may get disturbed with heavy cuts. Also, the operator needs to set the height of each tool using packing.
A quick-change tool post has better rigidity, ease of setting the center height, and faster tool change.
Different types of tool posts are:
- Single-way tool-post (also called pillar-type tool-post or American-type tool-post)
- British type tool-post
- Four-way tool-post (also called square tool post)
- Quick change tool post
1. Single-way Tool Post (also called Pillar-Type or American Tool Post)
A single-way tool post has a cylindrical base that sits on the lathe compound rest and is clamped to it. It has a cylindrical body (pillar) with a slot through its cross-section to accommodate the tool. It has a rocker for adjusting the tool height, and a clamping bolt running from the top to clamp the tool.
Insert the lathe tool into the slot, push the boat-shaped rocker forward and backward to adjust the tool height as required, and clamp the tool with the bolt. You are ready to go. Some designs of the single tool-post do not have a rocker and you have to use aluminum or brass packing for adjusting the tool height.
The single-way tool post is very old and unproductive and not of much use now. Occasionally, this is used for holding special and unconventional tools.
2. British Type Tool Post
This is a simple type of tool-post used on old British lathes. This has a flat plate mounted on the lathe compound rest and a clamp that can be bolted to the flat plate to clamp the lathe tool placed on it.
This is an obsolete tool post and is not used on modern lathe machines.
3. Four-way Tool Post (also called Square Tool-Post)
This is a conventional tool post found on most lathe machines and it is made from toughened alloy steel. This consists of a square-shaped milled piece with slots milled on all four sides and has 8 clamping bolts running from the top (two numbers on each side).
This tool post is centrally mounted on a stud screwed into the T-nut on the lathe compound rest (the other end of the stud protrudes at the top). A hand lever at the top of the tool post is used to clamp or de-clamp the square head (the hand lever has female threads matching the stud).
You can mount 4 tools at a time, adjust the tool heights with metal packing, clamp the tool with the bolts, and you are ready to go. The lathe operator has the flexibility of choosing four tools. You can loosen the hand lever, swivel the tool post to the required angle to bring the next tool to the operating position, and lock the tool post with the hand lever. The indexing is completely manual. You can lock the tool post at any angle.
Based on the general design of the four-way tool post, many machinists make their own tool posts with 1 to 4 slots for clamping tools and suiting their specific requirements. Such tool posts may be available in the market.
4. Quick-Change Tool Post
A quick-change tool post (multi-tool holder) is a versatile productive device and saves your tool changing time.
You are familiar with conventional four-way tool posts and you know how much time is spent adjusting the tool height with metal packing. A quick-change tool-post saves you from this trouble. The turning of a workpiece can involve multiple operations and setting so many tools on a conventional four-way tool-post affects productivity. A quick change tool-post uses a tool holder pre-mounted with the required tools and the operator can go on using the required tools holder one by one with minimum energy. Quick change tool posts allow easy adjustment of tool height.
The quick change tool-post and the tool holders are made from a good quality toughened/hardened alloy steel and machined to high accuracy and repeatability.
The shape of a quick change tool post may differ from manufacturer to manufacturer, but they all function in the same way.
How Does a Quick Change Tool Post Work?
This tool-post comes in two parts, a quick change tool-post (clamping block) and a set of matching tool holders. It has a male dovetail on one of its sides and the tool holder has a matching female dovetail on its side. The tool holders supplied with the quick change tool post are designed to hold different tools like turning, facing, parting off, grooving, threading, boring, etc.
The quick change tool post can be easily mounted on any lathe by removing the four-way tool post. You can mount the clamp block of the quick change tool post on the lathe compound rest and clamp it using its T-nut.
After clamping the quick change tool post on the lathe compound rest, select the required tool holder and slide it down on the male dovetail of the tool post. You can slide the tool holder up or down to adjust the center height and then clamp it by using the hand lever. You can do the finer adjustments of tool height by using the screw adjuster on the tool holder (which can be operated by your thumb and index finger).
After you are done with one tool holder, loosen the tool holder with the hand lever, take the tool holder out, select the next tool holder, clamp it on the tool post, and resume your work.
Different designs of quick change tool posts are available in the market for holding up to 4 tools and with an indexing facility.
You can mount the quick change tool post on a hydraulic copying attachment also.
The quick change tool posts come in different sizes to suit the center height of different lathes and tool shank sizes. The repeatability of the quick change tool post can be up to ± 0.01 mm. Some designs have a square shape with the top half milled to a triangular shape for better visibility. The shank size of the general lathe tools are 1/4ʺ and 3/8ʺ and the tool holders of the quick change tool post should be able to accommodate the tool size used by you.
You have to specify the center height of the lathe and tool shank size for purchasing a quick change tool post.