By Ron de Weyer

On club night 16 May 2017 Granville demoed methods of finishing off the bottoms of turned pieces.

Starting off with Cole jaws he showed his version which had MDF extensions added to the standard aluminium parts to increase the size significantly. Not having much confidence in the standard rubber block Granville has made his own dovetails shaped wooden blocks lined with some cork for protection. He is using it up to 750 revs (please note that the manufactory advice is not to exceed 600 revs). Granville also advised to not be too vicious when taking cuts.

Next were the vacuum chucks.
First samples he showed were flat MDF discs with a thick relative soft rubber layer glued to it. These were not in use anymore as the thicker rubber is not favourable for holding work pieces solidly. Granville advises to use a thin pieces rubber of about 2 mm thickness.

The vacuum chucks were deep bowl shaped forms made from several layers of MDF glued together. The outer ring was tapered outwards on the bigger chucks and tapered inwards on the smaller one.The bowl shaped chuck have as advantage that it acts as a “reservoir” for the vacuum.

Talking about the part that the vacuum cleaner hose connects to, Granville advised to use a grub screw to hold the bearing but not to have that screw to tight as the bearing easily can get damaged.

Shanes tip: Take the bag out of the vacuum cleaner to reduce the resistance.

When finishing a vacuum chucked work piece, Granville is using an old doorstop between the tailstock and work piece leaving the tailstock as long as possible for extra security. Plastic wine bottle stoppers will work too.

To prove that the vacuum chuck work well Granville tried to pull off a bowl that was hold on to the chuck by the vacuum cleaner. The vacuum cleaner won that round.

Granville’s tip: DON’T switch of the vacuum cleaner BEFORE switching off the lathe.

Granville went on to make some dust to demonstrate that sanding is not a problem on a vacuum chucked piece.
Sandpapers (Astro Dot) used were 120 – 150 – 180 – 240 – 320 and 400 grid.

For a finishing touch a texturing tool was used on the bottom of the bowl highlighted by some tram lines around the textured part.
The work pieces was signed and Kaureem was applied for a beautiful finish.

Granville continued with showing the holding power of different shaped work pieces on the different shaped chucks. The one piece that didn’t “stick” very well to the bowl shaped chuck stuck extremely well to the flat vacuum chuck.

Alison’s tip: Use a light coloured rubber so that you can draw lines on it to aid with lining up of the work piece.
As last advice, Granville mentioned the importance of having it balanced.
Centrifugal forces can be substantial.

Thanks Granville, it was very informative and very well demonstrated.