Wednesday, March 17, 2021

Focuser Knobs

They slip on the rod that controls focus just perfectly; not a press fit, but almost tight enough to skip the setscrew. I also decided that there was no need for milling cuts into the edge.   There is no shortage of traction.   

My attempts to reduce weight with lightening holes was disappointing.   From the back they look pretty good. 
from the front,  not so good:

Even worse,  I only saved 11 grams per hole, to do all six holes would have been a lot of work for 66 grams per knob.  Also, those saucers are melted Delrin on the end mill.  You cannot really sand it off without damaging the sharpness of the mill, so I used what worked last time: a 5.5" convex lens.  It burns the Delrin away without enough heat to damage the hardness of the steel.  (It took about fifteen minutes, and where the bright spot was, is temporarily blank.  It will come back.)

The setscrews that are original with the focuser are m1.5 x ?.  Since I am not changing the original knobs, I do not need to use the same,  with all the struggle of finding a metric tap.   Somewhere,  I had some nylon tipped setscrews.  After an exhausting search,  I found them on the bench where the mill sits.  They are 8-32x3/16 so I drilled and tapped a hole in the stem on the really ugly knob.  Somehow I managed to get that hole enough to one side that the setscrew was not exactly square.  

I put it on the focuser so that one side is 1.25" diameter and one is 2.5" diameter.   The difference in how finely it can now focus is immediately obvious.  

I will now cut another piece of Delrin and not put it lightening holes this time. 


1 comment:

  1. If the concept of lightening holes is sound, then maybe drilling them with a Forstner bit from the hidden side without breaking through would work.
    Or drilling all the way through with the disk clamped to a sacrificial backing board.