Saturday, September 30, 2017

Always Have At Least Two Of Every Drill Bit Size

I finished making the base plate on which the mirror sits: 3" diameter 1/2" thick.  I really only needed a hole slightly larger than 1/2" in the center to hold it on the outside of the jaws for turning the exterior.  I center drilled on the lathe, then used a 1/4" twist drill in the tailstock, then a 1/2" end mill.  Next step was trying to use a 19/32" twist drill bit in the tailstock.  This was not as successful as I had hoped, so I used the 1/2" hole to center the 19/32" drill bit in the drill press.  Then I bored the interior on the lathe to get an even centered hole.

Now comes the next step.  Getting holes 120o apart on the face using the rotating table is easy; getting them on the edges, not so easy.  For some reason when I bought this rotating table, I was under the impression it would mount on Sherline's tilting table, to allow a right angle use.  No, it won't.  They do sell an adapter for using the rotating table at a right angle to the bed, but both price and apparent complexity of using it scared me off.

There is a lip on the rotating table that is .385" high.  There are two .188" diameter through holes on that lip.  I bought some .390" thick hot roll which I will fit on that lip giving me a flat surface to go on the bed, with some T-fasteners to lock the assembly in position.  The threaded holes in that piece of hot rolled steel require drilling two .144" holes, then tapping to 8-32.  Unfortunately, my drill bit was an older not very sharp one, and it melted in use.  I changed sides, but the closest size that might still tap okay is not very sharp (likely the problem that melted the other bit).  A much finer drill bit, with the titanium coating sliced right in.  I need to buy some titanium tipped .144" drill bits tomorrow.

1 comment:

  1. Good point about having at least a couple bits of each size, I have 4 or 5 full indexes, at least of the 1/16 -> 1/2 by 64ths. But, I also have a Drill Doctor that does a good job of sharpening, up to 3/4". But, every machinist should know how to sharpen drills on a bench grinder. There should be some youtube videos.....