The third post in my trivet series. There is a video at the end of this post. Having marked out the centres and marked them with a scratch awl the next thing is to get turning. The two piece jam chuck allows the blank to be moved. The backing plate is attached to the lathes by a face plate in this instance. It is possible to glue a piece of wood to the backing plate or if thick enough turn a Tenon. The choice is really yours. I thought that a $12 face plate was cheap enough. I can always reuse it for another project.
The chuck that takes the turning plank has recess 6 mm recess that is 150 mm in diameter. The idea is that the blank will be a push fit. I had to use hold hot melt glue to hold a couple of my blanks. I also discovered that the first side the one with the concentric circles must be flat. I couldn’t understand why the blank was not running true. I realised that the face was raised in the middle. I resolved this by flattening the blank with sandpaper on my bandsaw table.
The piece of the chuck that holds the turning blank can be repositioned by means of the 2 screws that hold it to the backing plate. Using the tail stock with alive centre installed position the blank around one of the previously marked centres on the 70mm circle.
Once in position secure the jam chuck to its backing plate with the screws. The whole assembly will now rotate on the new centre. It pays to mark a circle that just touches the 140mm circle. Using a ¼ parting tool I turned two circles at each position. I tried three on a test piece and had terrible tear out, but that why it did a test. It is important that the circle are deep enough to touch the underside of the concentric circles from the other side.
Some clean-up will be required with either a scalpel or other sharp thin bladed knife. The closer the circles are to the other side the less clean-up will be required. After turning all three circles I repositioned the jam chuck on centre and used a sanding pad to clean up and remove all pencil marks.
The next post will feature the feet and finishing.