Today I started turning a pedestal disc for another large globe stand. These discs might qualify as fairly extreme turning, being over a metre in diameter and 50 mm thick, made of hard and dense timber. I glue up the blanks with biscuit joints. The cracks in the wood mean that on a piece this size I have to take safety precautions.
To make sure there is adequate support, I use an extra large, specially made steel faceplate, which carries a 30 mm thick mdf disc, one metre in diameter. I screw the blank to this disc, making sure that each component plank has fixing screws. Just getting the blank on the lathe is difficult. The whole assembly takes two people to lift, and getting it on the lathe is a three person job. I use the outboard side of the Graduate lathe, together with a free-standing tool rest.
To make the job easier, I have recently changed the method of loading. I now start by putting just the faceplate with the mdf extender on the lathe. This is just possible working alone, but still much easier with help. The mdf and the blank both have a central hole. I put a steel pin in the blank and offer it up to the faceplate. The pin centres it and supports the weight while I add a temporary G clamp then put in the screws. Then I remove the pin and the turning begins.
I am using second hand timber, with many grit-filled cracks. It is extremely hard on the cutting tools. It strikes sparks from ordinary scrapers, and makes really hard work of the project. But the customer supplies the timber and it is what he wants to use. I hate the stuff! I am doing a lot of the work with the Hunter Hercules tool. The wood quickly blunts even the Hunter carbide tip. When blunt, the tool starts to bounce and become hard to control. It was physically demanding to keep the blunted tool cutting. To replace the tip as necessary would be expensive, they blunt so fast.
Homemade pin tool rest
The answer was my homemade pin tool rest. This is a toolrest with a row of holes, into which I place a steel pin where required. The Hunter tool can then be stabilized by contact with the pin. It can still slide forward and swivel against the pin to make the cut.
I rarely use this toolrest, but it is invaluable for jobs of this kind. I made it years ago before I started turning these discs, I wish I had remembered it earlier instead of struggling with the tools held freehand.
A pin tool rest is easy to make. You need an ordinary tool rest with a bar that is stout enough to let you drill vertical holes at intervals without weakening it too much. Size and spacing are not critical, but about 8 mm diameter and 15 mm apart is OK. I drilled holes along the full length, but find that I only need three or four, all near the right hand end. Drill the holes using a drill press. The holes must go right through the rest so that chips can fall through.
Making the pin
The pin must be strong, say 10 mm diameter and 25 mm long, with an 8 mm lower section to fit the holes. You want it an easy but not wobbly fit. I turned the reduced diameter section of the pin in the lathe, but it would also be possible to use two bits of rod, one thick and one thin. Drill a hole in the end of the thicker bit and press or perhaps glue the thinner bit into the hole.
You can still use the rest as normal with the pin removed, as long as the hole positions don’t interfere with sliding the tool. Rests like this work for metal spinning too.