Well I got a case of the "wonder about that" and went up to our engineering Library and looked up Polycarbonate and found out the following, hope it helps. Called our Plastics supplier and he added some of the following. Polycarbonate is a thermoplastic manufactured under the following tradenames, LEXAN, HYZOD and TUFFAK to name a few. LEXAN is the G.E. tradename for Polycarbonate. It indicates the only difference is the name. The eyeglasses that I wear were coined "TUFFAK no scratch polycarbonate" when I bought them. The Machinery handbook recommends a drilling speed of 500-1500 rpm with a medium feed rate using a 60 degree drill point and polished flukes on the bit. I found 60 degree bits in the McMaster Carr catalog but unless you are a buisness you can't buy from them. Standard drill bits are ground to 118 degrees. Some woodworking bit are ground to 82 degrees. I have had decent luck using a standard drill bit with a slow feed rate and frequent draw outs of the bit to clear it of debris and a spray bottle of water to cool the bit while in the hole. I went over to the non-metalic shop (plastic shop) and we drilled about thirty holes in a scrap of 1/8" lexan with the above procedure and every one was perfect., no cracks. Again the experts in the shop recommended radiusing the edges of the holes to prevent stress cracks irradiating from the sharp edges. They further recommended sandwiching thin plastic between thicker material while drilling. Another consideration is expansion of the plastic. It does have a different rate of thermal expansion than aluminum so be sure to duplicate the hole diameter found in the existing(as provided by the factory)plastic, for if the holes are too small they could stress against the rivet body when heated and create a stress riser and cracks. Polycarbonate is easily bent using heat (hair dryer and a form) thus allowing you to duplicate the curve found in factory windows if you wanted to go that far. Question on a different subject; does anyone have a copy of the Continental memo that describes the process to upgrade a C75 to a C85? My logbooks indicate that N99997's engine was converted to a C85 but not what was done. Someone mentioned that the change involved the engine baffles and I do need new ones. Richard [EMAIL PROTECTED]
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