www.modelboats.co.uk Model Boats September 2013

steam basics

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Boiler Room Part Thirty Three: Basic Lathe Work - Making a Part

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RICHARD SIMPSONs series on model steam plants

Having now looked at the basic aspects of the lathe, how they work and then thought through the planning of how we are going to make a part, I thought it might be time to put it all together and actually cut some metal. So this month, I am going to go through the process that we planned in the last issue and actually see what the stages look like in real life on the lathe. Just to give you an idea of what is achievable, the part I made for this article took about 20 minutes to make, which just goes to show that this is not a lengthy and dif ficult thing to do, but is something that is well within the reach of any modeller with a small hobby lathe.

The particular bush I made was not to a specific drawing as I simply wanted to show the process and it is slightly larger than the normal boiler bush that you may want to make, which was for no other reason than to make photography a bit easier.

of the bush as shown in Photo 1. Notice what a good surface finish can be achieved with good tool shape and condition, even when the cut is made by hand. The trick is a nice steady slow movement from the free end of the piece to the end of the cut, not taking too much off and turning the chuck at the right speed.

Next we are going to run the tool across the face to true the face up as in Photo 2. If you have the tool set at the correct height, you should be left with a very fine pin of metal protruding from the face in the centre, which should be easily removed by your finger. If your tool is too high, then you may have experienced chattering or noise from the tool and scuffing of the surface. If it is too low, you will end up with a larger diameter pin that is dif ficult to remove. When this cut was completed, the pin broke away by hand.

The next process simply combines the first two operations into a single process. We are going to turn the diameter down to the smaller diameter and then face the inside of the boss flange, Photo 3. If the tool is well designed, it should also cut on the back face as you extract the tool from the finished diameter, but if not, you might need to run across the face from the outside in. Here you need to take care of not just the diameter, but also the facing operation, so you have two measurements to consider. Lubrication of the cutting tool for these small parts is not always essential, but equally can do no harm.

Having done the turning for now, we are going to move on to using the tail stock. A chuck has been fitted to the tapered socket and a suitably sized tapping drill for the thread to be cut has been put into it. The speed for the drilling operation will almost certainly need to be increased to ensure a clean cut. The tailstock is released from the bed and slid along until the drill bit is close to the job. Then the tailstock is locked to the bed and the drill slowly fed into the work by turning the handle on the tailstock. If you are cutting a deep hole, the drill may need removing once or twice to

The first stage of the process is to get yourself set up and bearing in mind the plan we discussed last month; just what size material you will need; whether it can be supported at one end only, or whether it needs supporting from the tailstock as well; and finally what tool type and shape you are going to need. For this job I ground a blank piece of high carbon tool steel and mounted it in the tool post at a slight angle which would enable me to cut across the diameter as well as across the end face without having to move the tool. The tool must be set at the correct height as was discussed a couple of months ago and the job set up in the chuck. Ensure all the safety precautions are in place such as wearing goggles, removing loose items of clothing, having the lighting set up and of course, turn on the lathe!

The first cut then is simply to turn down the outside diameter to the large diameter

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Photo 1. The simplest of all lathe procedures is turning externally down to a given size. With the right tool shape and sharpness and correct turning speed, even when hand turning very good surface finishes can be achieved.

Photo 2. Probably the second most straightforward operation will be the facing cut. Here the tool height is critical to a successful cut and again the finish with a manual operation can still be very good.

Photo 3. Combining the two operations gives you the opportunity to check two dimensions at the same time. Here we need to pay attention to the size of the smaller diameter as well as the position of the finished face.

Model Boats September 2013 www.modelboats.co.uk 57

clear the swarf, taking great care not to wind the chuck back so far as to release it from the taper again Photo 4! In this case we need to ensure that we drill deep enough to allow the tap itself to cut deep enough to ensure a full thread has been cut right through the job. If you dont drill deep enough and the tap bottoms before the full diameter thread is cut right the way through, anything you will try to screw into the thread

in the future may be too tight and dont forget that lubrication of the drill bit will keep it cooler and make the cutting and swarf exit from the drill hole easier.

The next part of the process is one of those little procedures that you pick up over the years that make life so much easier and are as a result of the thinking and planning that you put into a job. You may think that the easiest way to tap a hole is to put the job into a bench

vice and turn the tap down it with a tap wrench. If you think of the set-up you have though, then you already have a means of holding the tap as well as a means of rotating the piece. In this case, the tap is going to be held in the tailstock chuck and we are going to rotate the chuck by hand as in Photo 5.

The first task is to switch off the lathe AND turn off the mains power and just in case you missed that, switch off the lathe AND isolate the mains power. This is a hand operation and so it would be extremely dangerous if the lathe was to turn under power suddenly. With the lathe isolated, bring the tailstock up to the job until the tap is located in the hole and slowly rotate the chuck by hand. As you rotate the chuck the tap will be drawn into the hole and cut the thread while remaining perfectly concentric with the hole. Dont forget to ensure that the tailstock lock isnt on!

Finally we are back to a turning operation and we are going to finish off with a parting cut, Photo 6. The parting tool can either be used to part at a set point to give you a finished size, or more frequently, we part slightly oversize then rotate the finished part and re-chuck it to finish off the face to size. This has the downside of possibly marking the diameter with the chuck, so if the surface finish is important to the part you might want to consider parting the piece off to the finished size.

So, finally we have our own home made boiler mounting boss, Photo 7. Basic lathe skills can help you achieve this and many other simple to make parts which can be a huge source of satisfaction to a modeller. It also enables you to make those one-off parts that you would never be able to purchase, but that can make your model that bit more individual to you. l

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steam basics

Photo 6. The final turning operation is parting the piece of the bar stock. The parting tool needs to be correctly ground to ensure a good clean cut and again the speed of rotation is important.

Photo 4. The key to a successful drilling operation is always the condition of the drill tip. Worn or badly ground tips will run off-centre, overheat, clog with swarf and ultimately quite possibly break. Always use a good quality HSS drill bit and if in doubt, use a brand new one.

Photo 5. Do not do this unless the lathe is completely secured and unable to turn under power. Preferably remove the plug from the socket if it is fitted. Then make the most use of the set-up you have created and ensure yourself a clean, neat and concentric tapped hole.

Photo 7. Something to be proud off, a finished homemade item ready to be fitted to your plant somewhere. You cant beat the feeling of being able to say, I made that, from scratch.