Friday, September 22, 2017

Next Step on the Mirror Cell

I needed three holes for 8-32 machine screws at 120 degree angle from each other.  So I secured the rotating table to the mill's table. and attached the 3-jaw 2.5" chuck.  (The table has a 3/4"-16 screw that holds it.)  Then I locked the base to the chuck using the internal jaw setting.  Here you can see that I have drilled six holes 60 degrees apart.
You can see the coarse degree markings on the round part.  This gets you close, but this handwheel:
Each division is 1/10th degree.  The coarse measure gets you close enough to find the right line.

Why six pilot holes?  Three are for the 8-32 bolts, three are where I will make lightening and airflow holes.  Probably overkill for this size, but why not?

Are these machining posts of interest?

UPDATE: One bad thing about centering the hole this way is that it is never perfectly centered, unlike centering in a lathe with a drill in the tailstock.  But since I am enlarging 1.25" to 1.5" by boring, the result is decent.   For the mirror cell base, yes.  The bottom of the mirror holder was far from centered.  The 6" chuck was big enough to hold the workpieces for center drilling.  This piece is functional but ugly, so I will get another chunk of 3" aluminum and try again.


  1. Thumbs up on these types of posts! (now if you would just upsize your mill and lathe...) :)

  2. If your mill doesn't have a digital readout, or sufficient x,y travel to find center, use a digital caliper. Measure diameter, adjust to half, and scribe across the center from three equidistant points around the outside. This should give you a center point to drill from.

    Got a Criterion Boring head? You may be able to use it on your lathe tail, and not have to bother manually finding center, just set the offset and cut out the center. Not sure if your lathe is stiff enough to do this.

  3. I also like reading about your milling adventures.