G'day
Here is a new design I have developed combining wood and resin . Bangles are usually made from end grain timber . If made from crossgrain they would have two very weak points and may break .
Blanks are usually rough cut when they are green and left to dry on the shelf .The blanks need to have one face fairly flat . Sometimes I will flatten the face on a belt sander .
I mount the blank between the face of a chuck and the live centre and turn it down so's it will just fit neatly in my mould .I have three different size molds which are plastic screw top containers .
The walls of the mold are slightly tappered but the blank should should be turned with straight sides .In this case the mold has a slight bump in the centre so I held the blank in a large chuck and bored a shallow hole so's the blank would fit neatly in the mold without rocking .I then turned the blank over in the chuck and , using the hole saw that I will latter use to bore out the bangle ,I bored a shallow groove .
I then mounted the blank between a steb centre and the live centre .
I then set up my router jig on the banjo , checked that the tail stock was tight and cut eight grooves to the depth of the hole saw groove using the indexing facility . I needed to do two passes with the router for the silky oak blanks and three for the camelia blanks .I then did a little bit of sanding to clean up the grooves .
I give the mold a wipe with car polish which I think helps the casting to release .
The blank was then put in the mold and epoxy resin poured in to just overfill the slots . A large nut wrapped in glad wrap stops the blank from floating, then into the pressure pot overnight .
Next day I had to top up the resin then back in the pot overnight .
Next day I remove the mold from the pot and leave it stand for at least another day to cure.
I remove the casting by giving the top of the mold a hard bang on a solid surface .
I screw a wooden chuck on the lathe and run a thin bead of hotmelt glue round the outer edge of the lower face of the casting and mount it on the chuck using the live centre to align it .
After about 10 minutes, I bore out the centre with a hole saw .
I then radius the edge and true up and sand as much of the outer rim as I can get to .
Next I remove the bangle from the mounting by heating in a microwave oven .I find that heating will soften the resin so don't over do it . I find about one minute and 15 seconds is all it takes in my oven .
I now mount the bangle in expansion mode in a chuck, using a strip of leather to protect the surface ,while I finish off the other edge . Sometimes it will not run dead true, but it is close enough that a bit of sanding will blend it all in . Because of the mounting method I use to turn the second side , a 20mm thick bangle is about the minimum thickness I can make .I usually make them 25-30mm.
I hope this is of interest and it all makes sense .Some of these pictures got a bit out of order ,but I think you'll work it out .
Comments welcome .
Ted
