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Model Engineering Glossary: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Turning

The process of turning in a wood or metal lathe.

The Basics of Turning in the Metal Lathe for the First Time

So you have bought a lathe, installed it and now ready to turn for the first time. It is best to start with cylindrical stock and for the first time some mild steel is a good choice.

  • overhang - it is best if the metal is held in the full depth of the chuck and that the workpiece does not overhang the chuck more than needed. If the workpiece overhangs too far then it will not be as stiff and may result in vibration or movement of the part away from the cutting tool. The result may be just a bad finish, wrong size or damage to a part.
  • donít over tighten the chuck
  • tool height - a set of feeler gauges are great for adjusting the tool height
  • cutting speed
  • turn face
  • turn OD true
  • centre drill before drilling - a centre drill is short, stiff and ideal as it produces an angled cone that the next drill can align with.
    • drill in stages if you want to get an accurate final hole size
  • Cutting fluid - if you are machining lots of steel then it is worth investing in a pump and fluid delivery system, however, this can be over the top in the case of the weekend model maker. A good alternative is a jar of cutting fluid and a paint brush. This way you can apply an amount of fluid with each cut. The other thing with cutting fluid is that it can mean a lot of cleaning up afterwards and if you only machine a few parts it can add a lot of time. The oil based cutting fluids are easy to use and you do not need to clean up as thoroughly as with water based or diluted fluids that can cause rust to develop on slides.

If you plan on using a file to finish an edge in the lathe then use extreme caution. Protect the lathe bed with a cloth or wooden sheet.


We thought it would be good to build a page with some hints, tips and useful information around using a lathe. The basic description of the different parts is available in the lathe page

We have a page with lathe reviews and links through to manufacturers and further resources Lathe reviews.

Aligning Parts

There are a number of times when you will want to align a part so that it is running true.

With thin cylindrical parts they are not wide enough to naturally get gripped and aligned perpendicular to the axis of rotation.

For large discs the best way is to use a dial gauge which is magnetically fixed to the cross-slide.

The part is then rotated in the lathe by turning the chuck by hand until the needle on the dial gauge nolonger moves - this can take some time so be patient.


Cutting Fluid

If you are machining steel or aluminium you may want to use a cutting fluid. This will improve the cut and improve the surface finish.

Lots of cutting fluid can make a mess and mean that you need to clean the lathe down and oil the slides after use. I like using a neatcut oil that does not contain water.

Also, I use a brush to apply the oil as this allows me to apply the cutting fluid to the part and reduce the amount used.


The cutting fluid tends to smoke quite a lot and so best to keep some airflow through the workshop.


Cutting Tools

The tool that is held in a toolpost on the lathe cross-slide and which is feed into the rotating workpiece to machine it to size.

Lathe tools are made from high speed steel (HSS), Tungsten Carbide or other very hard materials such as diamond. more...


Drilling

When drilling in the lathe it is standard practice to first use a centre drill. Centre drills are short and so do not bend when used and accurately locate the centre of the rotating part. The cone created by the centre drill is also great for locating the next drill.

This shows the part having been centre drilled and now a normal twist drill being used


For large holes it is best to drill the hole to size in increasing steps. This will result in a much more accurate final size and in an easier series of cuts for the lathe.

When making deep holes it is best to remove the drill from the workpiece and brush out the swarf - I have a 1" brush to hand that I use on the machines to brush away swarf.

Facing

This is the process of turning perpendicular to the axis of rotation. It is important that the saddle does not drift whilst traversing the cross-slide and so best to lock the cross-slide to lathe bed.

It is very important that the cutting tool is exactly aligned with the lathe centre or the result will be a "pip" - a piece of uncut metal, a bump. This pip can cause a centre drill to run off and break.

Set up the lathe tool so that the very top edge of the tool is at centre height, you can do this by aligning the tool with a centre in the tailstock and then packing under the tool with shim.

If the tool is too low then you will leave a "pip" in the centre of the bar when you face it.

A set of feeler gauges makes a good starting set of shims.


This shows the result when the tool is at the correct height.

I use a mixture of brass, steel and aluminium shims. Thin brass shims are great to get the height exactly correct.

With a larger lathe and so larger tool sections it is still useful now and again to use small tools. The Warco WM240B takes 12mm tool steel and this only needs a slight height increase to reach centre. Now and again I still want to use 6mm tools and for these occasions I have a piece of 6mm thick mild steel shim to bulk up the tool height.


Filing

If you are going to file or use any abrasives then first cover the bed, I use a piece of board, as this will stop most of the abrasive going into the slides where it will cause wear.

Also, be very care of lose clothing as this can catch in the chuck and I doubt you will stop it rotating!


See also: Lathes.

Model Engineering Glossary: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z