We planned on taking all of last week for a family vacation, but we didn’t end up leaving town until Wednesday night.  Since work has been particularly draining lately, I decided to take this week off and spend some time in the Secret Laboratory (TM).  There are a number of projects that I want to work on, but the first one is getting my new mill converted to CNC.

The kit that I purchased (from CNC Fusion) comes with ball screws as well as the applicable motor mounts.  The kit does not come with instructions.  Since I can only work on the mill at odd intervals, I found it in this state this morning.  The X and Y ball screws are attached, and I needed to add the X axis motor mount.  No biggie, right?  Yeah.  I sighted in the motor mount plate and put the screws in.  One of them was sticking a bit, but it didn’t feel too bad until it, erm, snapped off.

Fortunately, a friend of mine picked up a really cool stocking stuffer for me last Christmas.  It’s called Grabit.

For some silly reason, I don’t have a center punch.  It makes no sense to speak of, and it also made getting the drill started a bit difficult.  Finally, I got the hole properly centered on the broken screw and drilled to a proper depth.  Nearly quivering with excitement, I put in the Grabit bit and pulled the trigger on my drill.  This happened:

CRAP!

The people at Grabit understood and appreciated the tremendous loads that must be endured by a screw extractor, so they made their extractor out of hardened, forged kryptonite.  Yeah, I didn’t believe it either until I completely destroyed four drill bits trying to drill through the Grabit and re-tap the hole.  Fine, I thought to myself, I’ll go get a better bit.  And I did.  The bit was one of the Cobalt silver bits.  It didn’t seem to make any progress at first, but it didn’t dull instantly either.  After 10 minutes of trying to drill into the screw extractor (seriously!) I got impatient and kicked up the speed.  A funny thing happened…chips started coming out of the hole.  So, I carried on like this until the hole was a reasonable depth. 

Can you predict what happened?  Take a moment to formulate a hypothesis.  Are you ready?  The Kryponite forged screw extractor was so freakishly hard that it deflected the drill bit into the steel adjacent to the original screw.  The very best part?  I couldn’t even tap the hole because the Grabit was still next to the hole and my taps have a warranty exclusion forbidding their purchaser from trying to thread Kryptonite.  Naturally I tried anyway, and succeeded only in tearing the threads off the tap.  Seriously.  Finally, I drilled out the alignment hole you can see in the picture and I tapped that.  Very fortunately for me, this was not the end of the table where the thrust bearings mount, so I don’t need to worry about torsion on the aluminum plate.

Oh, yeah, the punch line?  I broke the original screw because it was too long…as in, I tried using the wrong screw in the hole.

Act II: Absolution

X Axis stepper is finally mounted.

Y Axis stepper is mounted.

  
These two pictures show the thrust bearings installed on the ball screws.  These bearings are not included with the kit…you must remove them from the lead screws which come with the mill.  This step can be really confusing, particularly because there aren’t any instructions with the kit.

At this point, things were going along just ducky.  In fact, I was beginning to feel pretty darned self-satisfied!  In case you’ve never noticed, cockiness often seems to precede disaster.  While awaiting my next disaster, I began getting ready to install the Z axis ball screw.  It was, in fact, while poking around the back of the mill that I noticed something amiss with the table.  If I had been missing that hard lump in my throat, it might have been a relief to have it back.  Since I wasn’t missing it, the return of the lump was no relief.

Act III: Humility

Ball screws use a special nut called (unceremoniously) a ball nut.  Inside the ball nut, we get to the heart of ball screws.  I am referring to balls.  Lots of little balls.  These little balls should have been locked up inside the aforementioned ball nut, however they were not.  They were congregating under the saddle of the mill as depicted in the following, rather depressing, picture.

My guess is that while I was taking pictures of the Y axis, I managed to get the ball nut too close to the end of the screw and let a bunch of the balls fall out.  If anybody can point me in the direction of information on how to get the balls back into the nut, I’d be grateful.  In the meantime, CNC week will continue because, well, I’ve got one more machine.  In all seriousness, there is also a lot of work to be done on the new mill before it can be used anyway.  Look for some of those details tomorrow!

G