I was advised by a guy that makes boat windshields that if you drill any holes to relieve the outer edge of where you drill to help prevent cracking.
Madmike, for those of us who have never worked with Lucite could you explain how to "relieve" the outer edge?
Thanks
From experience I have learnt that there are different grades of acrylic "glass" available, some are more scratch resistant and durable than others. If you are contemplating making some wind wings up you will want to discuss what you are planning with the supplier in order to get something that will satisfy your needs. In Canada I have always been able to get small quantities (1/4 sheet) of Plexiglass or Lexan from any glass shop.
After you have drilled the holes take a larger bit and just start into the hole - but only take the edge off of the corner so that there is no longer a 90° corner there. This should help prevent the stress from concentrating at the sharp corner and lessen chances of it cracking there - this is a common practice in design and metal fabrication/machining (radiused corners on a crankshaft is a good example).
When you are working on the plastic you have to be careful that the bits don't grab and self feed on the soft material. You may want to play with a scrap piece and get the feel for what you want to do before you learn on a project. A drill press is nice if you have one as you can hold back on the bit. You may be able to relieve the holes by hand with a good bit and a tap wrench.
Another thing that you may want to consider is make up some spacers that are marginally longer than the plastic is thick (i.e. - 5/16" long spacers used with 1/4" thick lexan) so that the fasteners don't actually clamp the plastic but clamp on the spacers instead. This allows the plastic to flex on the fasteners yet the fasteners will stay tight. Stainless tubing is excellent for making the spacers from, the 1/4" ID is adequate for most common screw sizes, you can cut it with a tubing cutter and it doesn't corrode or discolour like steel tubing will. It is used extensively for industrial controls and actuators. Any Instrumentation shop that handles "Swagelok" fittings will have it - they may even have some "used" or scrap pieces that they will give you if you ask and tell them what you are doing with it. When I did the windshield on my Boston Whaler I did it this way and have had good success with it.
