I don't know whether this has been mentioned previously but a good source of tufnol (and other plastics) sheets and rod of many sizes is
www.directplasticsonline.co.uk. I think that their p&p charge is a bit high (£5.95) so it pays to order several items at one time. I have just ordered some tufnol sheet to make extended servo arms and found their service very quick and reliable and can recommend them.
Derek B.
