* Bottom line for me is that teflon at about the 15 lbs/sq in loading on Ebony Star laminate worked best for this weight range of dob (maybe about 50 to 70 pounds total).
* Teflon seems to have an interesting property that the coeff of friction goes down with increased loading. Thus the many random points on the Ebony star laminate produce high point loading and relatively low friction.
* Teflon seems to have low stiction i.e. the dynamic coeff. of friction is close to the static coeff. of friction. For non-motor driven scopes you don't want zero friction, you want a small amount to keep the scope from wandering and low stiction to minimize stick-slip and overshoot.
* Teflon is reported to be better than other materials for this load range better than ultra high density polyeythelene and nylon/delrin materials.
* I tried experiments with telfon on glass (very smooth) and on very matte finish laminate. Both had higher apparent friction than on Ebony star though on glass the "feel" was different it that it seems that there was a different stick-slip reaction. Why I don't know. Also, with a material like glass it may be possible to get wringing of the surfaces whereby the air is removed from the interface and you get the added loading of atmospheric pressure.
* Another thing to keep in mind are the geometries involved. Rotating the azimuth requires adding torque to overcome the resistive torque from the bearing. Torque is the product of the friction force and the radius from the center. Thus the farther out the pads, the greater the torque needed to rotate.
* Epoxy bondable teflon is available but I had only seen it in 0.060 thickness. The back surface is somehow etched to provide good grip.
* Of course the basic pad design calls for three pads at 120 degrees separation at some distance from the center, maybe about 8 inches radius for a ten inch dob. Another degree of freedom in the design in terms of loading can be obtained by spring loading the center pivot point to off load some of the weight. Since the center bearing surface is at very small radius relative to the main pads, the bearing surface is not as critical. So instead of having, say 30 pounds on each of the three pads, you could off load, say 50 pounds on the center and substantially reduce the torque required.
* The geometry of the dob inherently means that the torque applied as you cruise the sky changes as a function of elevation (for the bottom bearing but not for the trunions). Thus the "feel" is a function of what you are looking at(!). So it seems impractical that you can get a constant "feel" for the dob nudge.
* One of the more interesting thoughts I encountered in talking with people is to provide the required "friction" using specialty greases which are available or were developed for use in things like camera lenses. You know that beautiful feel when you focus a fine 35 mm camera lense. Apparently the grease is "sticky" but smooth. In that kind of design you would separate bearing from control. Use quality roller bearings for the support and tune in the friction/stickyness with plates coated with grease.
* I ran into one guy who claimed that liquid water very much aggrevated stiction of teflon on things like stainless steel. Any experience out there with dew and changes in the feel of a dob steering?
* Last but not least someone wisely cautioned me not to leave a dob resting with all its weight on the teflon pads since teflon is very prone to cold flow resulting in impressions in the pads and a pronounced bump in the feel when you rotate past the resting position.
I think I feel better now that I have shared this with all of you,
Steve