[mental4astro (Alexander)]

Hooray! Some more logic in the conversation! One key here is the Obsession design. It is a very heavy, 30 year old but brilliant design. But that is not the only point. It is important to understand why the combination of PTFE (Teflon) and textured laminates work, and why a less textured laminate WILL work just as well. This is something that the Good Book does not explain well. What Matt is coming up with is wonderful, and my comments should not be taken out of context.

With 4552-50, the surface is highly textured and in practical terms only has a small surfahttp://www.iceinspace.com.au/forum/showthread.php?p=1196879#post119687 9ce contact with the PTFE at any one time. Critical to this is the flow point of the PTFE which coincides with the Golden Rule of 15lb/sq inch.

Now, use a less textured surface, and the effective surface area that is in immediate contact with the PTFE is significantly higher per square inch compared to the 4552-50. So to achieve the same flow characteristics with a less textured surface, the Golden Rule ratio needs to change to greater than 15lb. Closer to and even higher than 20lb/sq inch. In other words, the PTFE pads get smaller.

A glossy laminate will actually work too! But the PTFE needs to be a sharp point, which when put under load will deform until the flow point is achieved, and a dob will actually move just as well as with 4552-50. The problem here is that the PTFE will abrade quickly, increasing its surface area and so the quality of the action goes down hill quickly. This is not the problem when using textured laminate until the laminate itself eventually wears away.

4552-90 is as effective as 4552-50. The Golden Rule needs to be altered to suit.

4552-90 is still in production. I ordered more of it last week from the Australian importer.