BUILDING YOUR OWN LATHE

Building a lathe from scratch is a complex and sometimes frustrating task. In hindsight, I believe that a good second hand propriety built machine can prove more satisfactory. However, I can give the sum of my experiences in producing a unit which is versatile and capable of producing high quality work.
Firstly you must determine the usage and scope of the proposed machine. Is it to be used as a hobby lathe, perhaps once a week? Do you propose to produce very small items, large items or a whole range? The cost and complexity of the machine depends on these and other factors.
Secondly, what metal working expertise do you have? Obviously you must be able to handle quite a range of machinery or have a friendly "tame" engineer. What access do you have to a well equipped metal working workshop?
Unless you can satisfy your self on all these points, I would suggest a shop bought unit would be more satisfactory.
My lathe was one of five built as a small "production" run by five people. Not having ready assess to a metal shop, we persuaded the local Technical College to run a course - "Wood Lathe Production". The instructor had previously produced several small lathes, which to my way of thinking, were too small and fragile to be any use to me. I produced a set of specifications, some of which were not fulfilled, mainly because the instructor, being a metal worker, did not understand what really was required. So the result was a compromise. Since then I have made a number of modifications which have resulted in a very versatile and usable machine - more of this later.
All lathes are similar in basic design - they require a bed, a headstock, tailstock and a tool post holder. Let's deal with them one at a time.

The Bed

Ideally this should be constructed of very heavy cast iron. In a less than ideal situation there are two viable alternatives.
1 A pair of solid steel bars, either round or square.
2 A pair of heavy gauge square or oblong (preferably) steel tubes.
As Ernie Conover would tell you, timber is another alternative, but for really accurate work I don't think this is realistic. While speaking of accuracy, I don't accept a commonly held belief that a wood lathe doesn't need to be as accurate as a metal lathe. Particularly with small work, accuracy is paramount.
I would suggest that a pair of 3" x 2" heavy gauge steel tubes would be a good starting point. These can be cut to length, drilled and fitted with spacers at the head and tail to leave a 1" space between them. Check that your tubes are perfectly straight and when bolted up, are perfectly parallel. Two short pieces of tube can be welded across the bed tubes at each end to provide feet.

The Headstock

Again, ideally, this should be constructed of heavy cast iron and have a 1" shaft and large diameter sealed bearings. You may be able to pick up a headstock from an old metal lathe . In my case the head was fabricated from steel plate and tube. The base and vertical section were cut from ½" steel plate with a slot being milled in the base plate into which the vertical plate fitted. This was jigged up clamped and welded. The heavy steel tube which was to carry the shaft and bearings was turned at each end to allow the bearings to be inserted. A slot was milled out on the bottom of the tube and this was fitted to the vertical section, clamped up and welded. The shaft was turned to the bearing size and a 1" B.S.F. thread turned on one end. The other end was turned down to ½" to allow the 3-ring pulley to be fitted. Because of the shaft construction/design it was not possible to include a No.2 Morse taper. This is a serious fault and can be very limiting. It does mean that every accessory has to be specially made. Apart from the external thread previously mentioned, a hole was drilled and tapped into the business end of the shaft to take the spur drive. The lack of a Morse taper in the headstock shaft means that every accessory must be threaded to fit the external or internal thread.

The Tailstock

The bottom of the body which rested on the bed was relieved on the milling machine to leave a 1" section which fitted between the bed tubes with another milled steel plate to clamp onto the bottom of the bed tubes. When the clamp was loosened, the tailstock could be slid along the bed and then clamped in any working position. I thought at the time that the threaded shaft should be drilled so that an auger could be passed through to allow long hole boring- in fact I spent several hours boring the five spindles. I found that, in practice, the tailstock design did not allow this to be accomplished easily. Again, the lack of a Morse taper seriously restricts the possibility of accurate drilling from the tailstock end. It is virtually impossible to fit a drill chuck without a major modification.

Tool post and holder (Banjo)

Accessories

Essentials (for the novice)

1 A spur drive for the headstock. If your lathe has a Morse taper, most tool dealers can supply a propriety unit. You will find that a large and a small spur will cover most work.
2 A tailstock centre is essential for spindle turning. There are a number of types available, (you can make your own), all of which carry a Morse taper. I would recommend a "ring" centre - these are very safe, don't split small section timber and if using a removable centre point, can help with long hole boring.
3 Several sizes of faceplate for bowl turning.

Nice to have

1 A drill chuck which fits to the headstock and tailstock.
2 A four jaw scroll chuck which operates in both expansion and contraction mode. Once you have used one of these it will become essential.
3 A well made screw chuck with a replaceable screw.

Since first making my lathe I have made a series of modifications which have made it a more useable machine and a pleasure to work.
When I first used my lathe, I found that the bed tubes were curved so that the gap between them was around .080" wider in the middle of the bed. This meant that accurate work was not possible. To overcome this I lifted off the head and tailstocks and fitted steel "bed bars" to the tubes. The bars were 2" x ½" and had a similar bar fitted inside the tube. They were drilled and tapped in pairs and fitted to the tubes. They were set up to give an exact 1"gap between them.
Apart from giving an accurate bed, the bars also added to the general rigidity.

This was mounted onto a fabricated heavy steel box incorporating a quick release camlock. This has worked extremely well.
Originally I fitted up the motor and drive with a three ring pulley. Because of the mounting system, speed changing was slow and clumsy. I obtained a simple mechanical variable speed drive from an old gluing machine and this gives me a stepless speed range of around 350 - 1800 RPM The only drawbacks with this system are noise and belt wear. Once you have used a V.S.D. you wouldn't want anything else.

It's been a lot of work, but the result has been worthwhile.
I would suggest again that you investigate the possibility of buying a good secondhand machine.