Wednesday, October 11, 2017

Machining Steel; Yuck

I mentioned, I think, that I needed some 1/2" thick, 1.5" ID donuts to hold the Crossbow equatorial platform to Big Bertha's wheeled conveyance.  What a task it turned out to be recessing the holes to make the Allen wrench heads flat to the surface.  (They did not really need to be completely flat, which is good; some heads are about 1/16" high.)

I tried milling the recesses with a 3/8" end mill without success.  The Sherline lacks the power to cut steel, even at .001 inches per minute.  So I tried to create them with a .390" drill in the drill press.  I had to work my way up from .25" and still I am sure ruined several drill bits.  The end of the bit glowing red is a giveaway

Eventually I put a 3/8" end mill in the drill press at 200 rpm.  This did the job, but not well.  An end mill is held by a set screw in a holder.  A drill press chuck just isn't that effective at holding it.  (Someone must make an end mill holder for use in a drill press chuck.  What is it called?)  In addition, my 3/8" square end mill is double ended and will not fit into the drill press's chuck, so I used a ball 3/8" end mill.  Not a flat bottom, but should work okay.

Next time, aluminum, even if I have to cut it down from a much larger diameter.

Fortunately, I have enough 1/4"-20 x 1" Allen head bolts that will mate to nuts on the underside of the conveyance..


  1. A squirt/spray bottle of coolant would help. Usually, if it turns red, you are spinning it too fast, and/or not feeding it fast enough. Lots of heat generated from dragging it around in shallow cuts.
    A hex drive end works best, otherwise, use the biggest round drive end for a drill or milling bit that your machine can grab. Trying to use a stepdown drive end is a study in frustration, unless it is a hex.

    Generally, attempts to run milling bits in drillpresses are problematic due to loose bearings in the head. Any play sets up a chatter, which tends to cause the bit to spin in the chuck, besides the very rough finish and lack of precision. Upgrading the bearings may be feasible.

  2. If I understand you correctly, what you need is a counterbore. It's like a countersink, but sized to bore the clearance for the head of a given sized allen bolt.

  3. Will: Used coolant, but speed was probably the issue. The end mill worked well at 200 rpm.