Weekend Projects - Polyester hollow form archive

Friday 13 November 2015

George Watkins shares his hints and techniques for creating a hollow form with a difference, using a custom made polyester resin blank

Gallery

I made my first acrylic resin pen back in January 2010, and I was so taken with the vibrant colours present in the finished pen, coupled with the fact it was so easy to turn, that I started to make resin boxes soon after. Ever since then I've been thinking about making a hollow form from resin, but would it be possible? How big could I make it? After a long chat with my friend Mervyn Cadman, I decided to give it a go and Mervyn agreed to cast a blank for me which would be large enough to accommodate a hollow form. In this article, I wanted to show some of the techniques for working with acrylics, but also show that many of the processes are the same as those for wood, and it's perhaps not as daunting as you may think. The finished piece measures 140mm wide x 95mm tall.

Tools used:

6mm parting tool

12mm shaft swan-neck hollowing tool

6mm homemade straight hollowing tool

6mm 45° homemade hollowing tool

16mm bowl gouge

20mm negative-rake scraper

STEP 1

Here you can see how the blank was delivered to me from Mervyn Cadman - it measured 145mm wide x 165mm tall, including the wooden block. The wooden block has a male dovetail tenon cut on the resin side and has holes drilled into it; this allows the resin to grip the wooden blank which in turn allows you to attach a faceplate or cut a chuck tenon

STEP 2

The first step is to attach the blank to the lathe via a 75mm faceplate and then it is ready for turning

STEP 3

Next, you need to true up the blank as, even though it was cast in a round mould, it isn't perfectly concentric. Here I am using a negative-rake scraper

STEP 4

True up the end with a negative-rake scraper; this isn't strictly necessary but I like to do it to be able to fully see the markings to help me decide what sort of form will look the best

STEP 5

Using a very gentle touch and a very sharp 16mm gouge, round over the corner of the blank and start to form the upper part of the form. I make this same cut on 99% of my hollow forms

STEP 6

The initial upper shaping of the hollow form is now complete

STEP 7

The next step, using a 16mm gouge, is to start to define the lower section of the form and eventually blend the upper curve into the lower. Just like on a wooden piece, remember to leave extra material to add strength whilst hollowing

STEP 8

Here you can see that extra material, and you can also see the finish left by the gouge. You may think that there's a lot of waste resin near the base; this is partly to allow access to the lower part of the form but also, you're not able to remove any of the width from the resin/wood block as it may compromise the strength of the join. So in effect, there are two waste blocks: the wooden one with the faceplate screws in it, and the resin one which forms the mating surface

STEP 9

Here I am using a 20mm negative-rake scraper to improve the finish and help blend in some of the curves

STEP 10

The polyester form is now ready for hollowing

STEP 11

Start with the 6mm homemade straight tool and perform cut number 1 on the diagram

STEP 12

Use the 45° homemade tool to undertake cuts 2, 3, 6 and 7. Use the swan-neck tool to complete cuts 6 and 9, and use the straight tool for the remaining cuts

STEP 13

Once the top two-thirds of the form is hollowed out to its final thickness, come back to the outside and use the 16mm gouge to remove some of the waste material and finalise the shape of the form. Once you are happy with the form you can go back to the inside and finish the last part of the hollowing

STEP 14

Here I am using an offcut of skirting board and a 12mm dowel to check that the depth of the hollowing is correct

STEP 15

Here is the final form, all hollowed out and ready to sand

STEP 16

Starting at 240 and working through to 800 grit, sand the piece being careful not to apply too much pressure. Also, ensure that the abrasive does not get too hot

STEP 17

With the lathe speed reduced and using a 6mm parting tool, reduce the size of the tenon which is holding the base of the piece to the scrap

STEP 18

Stop the lathe and use a fine-toothed hand saw to cut through the last piece. You can reverse the piece between centres if you wish, but here I removed the stub using a sanding arbor mounted in a Jacobs chuck in the headstock of the lathe. Holding onto the piece very firmly, work your way through a three-stage buffing process until you achieve a mirror perfect finish

STEP 19

The completed polyester hollow form should look something like this


Briony Darnley

Tagged In:

Weekend Projects , George Watkins


Diagrams Click an image to enlarge

Handy Hints

1. Negative-rake turning techniques will produce the best finish on your workpiece, but it is worth noting that most normal tools will work with a very sharp edge and light touch
2. Before moving on to the next polishing compounds you need to check the surface for imperfections using a very good light source
3. Still try to achieve an even wall thickness but don't attempt to get the walls thinner than 3mm as they may shatter. I try to achieve a thickness of around 10mm on my turnings
4. A matte finish can be achieved by cutting back the gloss surface using a 1,500 to 2,000 grit wet and dry abrasive, used wet with water as a lubricant
5. Make sure you have adequate ventilation and use eye and lung protection
6. Keep the lathe speed low during sanding, as excessive heat can cause problems, or in extreme circumstances, can melt the resin
7. Allow extra support material around the base of the form whilst hollowing is carried out; the resin is heavy and dense and without adequate support, will chatter/vibrate easier than most timbers would