Choosing a Cutting Tool

The figure above shows a typical cutting tool and the terminology used to describe it. The actual geometry varies with the type of work to be done. The standard cutting tool shapes are shown below.

• Facing tools are ground to provide clearance with a center.
• Roughing tools have a small side relief angle to leave more material to support the cutting edge during deep cuts.
• Finishing tools have a more rounded nose to provide a finer finish. Round nose tools are for lighter turning. They have no back or side rake to permit cutting in either didection.
• Left hand cutting tools are designed to cut best when traveling from left to right.
• Aluminum is cut best by specially shaped cutting tools (not shown) that are used with the cutting edge slightly above center to reduce chatter.

Standard Cutting Tools


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How to Choose a Lathe Machine

Lathe machines are machines built to serve a specific purpose and even though there's a lot of variety to choose from, you really must choose the one that suits your needs the best. The average hobbyist will likely be best off with a mini lathe, which has a limited scope of operations but can be very useful for small and personal projects. These are mainly used by beginners who are testing the waters for turning out shapes and designs.

Whilst these mini lathes are not at all suited for professional lathe projects, those who want to make a slower transition to bigger lathe machines do have options to upgrade their mini lathe machines. These upgrades add functionality like variable speeds, arms etc. This also makes sense for those who want more out of their machine without spending a lot of money for a new and bigger machine.

However, there is a limit to how much a basic lathe machine can be upgraded, so it is advisable that professionals who have discovered the power of a lathe machine upgrade to as big a lathe as they possibly can. This is meant for those craftsmen who can see a long future of them using the lathe machine. For those who are unsure of how long they will use one or those who are on a tight budget, there are mid segment lathe machines that usually have a size between 12x34 and 16x36. They cost in between $400-600 and offer enough features and sturdiness for the professional craftsman without burning a hole through his pocket.

There are a few things to consider before jumping in and buying the cheapest or the biggest machine out there for your budget. You need consider the spindle you are getting. The spindle is the core to the operations of lathe machines and they come in standard and non-standard sizes. The is usually a good idea to go for standard sizes like the 1"x8tpi spindles. The bed capacity is also important, as this will determine the size of material with which you can work. Variable speed is another aspect because most professionals prefer to work at different speeds while doing different things to the material. Like for sanding you would prefer a higher speed but for carving, you might want a medium to low speed depending on the detail you want to work in.

Be careful of cheap lathe machines because their parts are often non-standard and are hence very easy to replace. As with other power tools and hardware, buying from a reputed company is always advisable. If you are buying used machines, do not purchase without getting to check it out first. For used lathe machines, try to purchase locally from a shop you know. If you are buying over the Internet even, try to buy from somewhere nearby and pick it up yourself after checking it out properly. Again, keep in mind the purpose of your machine while making a purchase.

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Parts of the Lathe Machine

The lathe is a machine tool used in metal cutting operations called "turning." The work piece is rotated as tooling is applied to it to remove material. Lathes can be manually operated or operated by computer numerical control (CNC). In either case, the basic parts are similar.


The Bed

1. The lathe bed is a mounting and aligning surface for the other machine components. Viewed from the operating position in front of the machine, the headstock is mounted on the left end of the bed and the tailstock on the right. The bed must be bolted to a base to provide a rigid and stable platform. The bed ways are a precision surface (or surfaces) on which the carriage slides left and right during machining operations. The ways are machined straight and flat and are either bolted to the top of the bed or are an integrally machined part of the bed.

Headstock

2. The headstock holds the spindle and drive mechanism for turning the work piece. The spindle is a precision shaft and bearing arrangement rotated directly by a motor or through a motor-driven belt. Gears or sliding pulleys mounted at the rear of the headstock allow spindle speed adjustment.

A work piece is held in the spindle for turning or drilling by a jawed chuck or a spring collet system. Large, unusual shaped, or otherwise difficult to hold pieces, can be attached to the spindle with a face plate, drive dogs and special clamps.

Tailstock

3. The tailstock supports long work that would otherwise sag or flex too much to allow for accurate machining. Without a tailstock, long pieces cannot be turned straight and will invariably have a taper. Some tailstocks can be intentionally misaligned to accurately cut a taper if needed. The tailstock has a centering device pressed into a shallow, specially drilled hole in the end of the work piece. The center can be either "live" or "dead." Live centers have a bearing, allowing the center to rotate along with the work piece. Dead centers do not rotate and must be lubricated to prevent overheating due to friction with the work piece. Instead of a center, a drill chuck can be mounted in the tailstock.

Carriage

4. The carriage provides mounting and motion control components for tooling. The carriage moves left and right, either through manual operation of a hand wheel, or it can be driven by a lead screw. At the base of a carriage is a saddle that mates and aligns with the bed ways. The cross-slide, compound rest and tool holder are mounted to the top of the carriage. Some carriages are equipped with a rotating turret to allow a variety of tools to be used in succession for multi-step operations.

Cross Slide

5. The cross-slide is mounted to the top of the carriage to provide movement perpendicular to the length of the bed for facing cuts. An additional motion assembly, the compound rest, with an adjustable angle, is often added to the top of the cross slide for angular cuts. The cutting tools that do the actual metal removal during turning are mounted in an adjustable tool holder clamped to the compound rest.

Lead Screw

6. The lead screw provides automatic feed and makes thread cutting possible. It is a precision-threaded shaft, driven by gears as the headstock turns. It passes through the front of the carriage apron and is supported at the tailstock end by a bearing bracket. Controls in the apron engage a lead nut to drive the carriage as the lead screw turns.



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Different Types of Lathe Machines

Lathes literally keep the manufacturing world spinning. Almost all manufacturing companies have their own lathe machines. A lathe works by spinning a piece of material, such as wood or metal, at a high speed while a cutting tool is applied to the rotating material. The result is a symmetrical cylinder.


Below is a list of the different kinds of lathes being used today.



Wood Lathes

1. Popular with both hobbyist and professionals alike, the wood lathe makes everything from baseball bats to chair legs and bedposts. Most round wood pieces are spun on a wood lathe to achieve a smooth feel and look.


Metal Lathes

2. Found mostly on factory floors, and often hooked up to computers with robotic arms, metal lathes are used for precision operations like threading and boring.


Glass Lathes

3. Whether forming the next piece of high-end art or filling an order for a scientific lab, glass workers use a lathe to shape their medium. Glass lathes safely spin glass tubing over a flame until the material is pliable for shaping.


Pottery Wheel

4. The pottery wheel is the only lathe where the operator may safely use her hands to shape the material. Though most lathes are horizontal, the pottery wheel spins its material about a vertical axis.

Fun Fact

The pottery wheel has been around for thousands of years, dating back to ancient Egypt and Mesopotamia.



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