Re: [ATM] Shaping a focuser board to match tube

["Don Clement" <clement.focuser@verizon.net>]

I should have mentioned that the 1/2" end mill was a ball end type.

-Don


I use a method of making the focuser base  (rectangular cross-section  solid
6061-T6 aluminum block) curve to match a given tube diameter using a
vertical mill and ½" solid carbide end mill running at 6.3K rpm. The method
takes a series of cuts with a piece-wise incremental approximation of a
circle using the formula: depth of cut = sqrt(R^2-d^2) + s -R where R=1/2
tube diameter, s=saggitta of base curve, d= distance from centerline of base
curve to base edge. This method could be adapted for use  with wood on a
table saw or router table if the depth of the saw blade or cutter could be
adjusted and using an adjustable fence. The depth of cut and distance from
the center could be laid out using an Excel spreadsheet. A cut could be
made,
then the part reversed with the opposite side against the fence and repeat
the cut. Increment the depth of cut and fence distance for the next two
cuts. This method approximates a circle very well and accuracy is limited
only in how small and increment one uses. Any piece-wise deviation from a
circle could be finished with sandpaper around the tube and some matching
handwork.



Don Clement

Running Springs, California

www.ClementFocuser.com

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