Saturday, December 10, 2016

Cutting Metal Again

The continuing story of the problems with my small milling machine losing motion came to a happy conclusion this afternoon, and I was able to complete the cuts for oil grooves that I was setting up to make when I discovered the problem.
This is the last pass on the last oil groove.  Groovy, huh?

So what was the fix?  Did you think I'd let you get away without telling you?  First off, let me just show you the parts cross section again. 
As I said in the most recent piece, I just wanted to replace the coupler, pre-load nut and 5-40 screw.  That's basically everything except the leadscrew and the Sherline motor mount with its two sets of ball bearings.  I rebuilt this on Tuesday using blue LocTite on the taper of the leadscrew and set it aside for a few hours (which ended up being Wednesday morning).  On Wednesday, I started slowly moving the X-axis and all was fine.  I had written a simple G-code file to exercise the X-axis, moving it from -4.0 inches to +4.0 inches and back several times.  The table stopped moving in less than five minutes.  

I took it apart, of course, and found that the LocTite had sheared.  All I did was just reassemble it with LocTite on everything.  I put a light smear on the taper, a small drop on the 5-40 screw and another drop on the 1/4-20 threaded lead-in threads on the leadscrew.  Then I went to LocTite's website to look up just how long it should take to cure, and found a data sheet.  The answer was that it really takes 24 hours to get to full strength.  So I said I'll leave it until 24 hours is up, Thursday around noon.  Again, I started slowly and moved the X-axis back and forth for a while, then ran my short exercise file.  This time it worked.  Then I ran an extended version, which took about 45 minutes.  All in all, I ran it for over an hour with no issues.   After an hour of doing things it wasn't capable of doing at all a few days ago, how long does it take to get confidence it can keep moving?  Put it this way: if one of those parts had snapped in two, would this even be a question?  There would be a broken part and a new, unbroken part, and the only question would be whether it was put back together properly.  

Thursday night and Friday featured Christmas parties, so I didn't get back to it until today.  This time, instead of my X-axis torture test, I wrote a little exercise routine for the mill to run all three axes simultaneously for a half hour.  Everything held together just fine, so I moved the Grizzly's cross slide back onto the little mill's table, zeroed the coordinates to match the drawing, and then proceeded to cut the slide.   It did hiccup, the table started shaking too much.  It turned out that when I put the X-axis gib strip back in, I didn't seat it properly.  That didn't show up with the X-axis not carrying the 10 pounds of cast iron.  Once I shut everything down and reassembled that last detail properly, everything was fine. 

Now it's on to drilling the 1/8" diameter, 4" deep hole. 


  1. Dang. Is this a case of "red" (locktite) is your friend? Is that hole to connect oil supply to the grooves?

    You know, one thing about using a drill press instead of a mill to drill holes is better feel for load.

    1. For what I just did? I was a bit too chicken to use red, but if this pops loose again, you can bet I will. And, yes the long hole connects the oil supply to those grooves.

      On the second one - the G0704 is a mill/drill. When used as a drill press, the headstock has just over 2" of travel and a handle that's just like my drill press. OTOH, my drill press as too much TIR with a short drill bit. With that 6" bit it's going to have a foot of runout. OK, that's an exaggeration, but less than you'd think. Like most mill/drills, the G0704 is a very good drill press.

      I think I can do the hole in two two inch deep sections. At this point, it would be nice to have the motor on z-axis, because moving the headstock up is rough.


    I would have suggested red LocTite, too, but if the blue has sufficient holding power, well....what works, works!

  3. So here is a question- if that hole is just oil supply, why is the diameter limited to 1/8"? I would be tempted to drill it 1/4" -it won't flow any more oil as the limit is the oil groove. Or you could drill it 9/10 deep and finish with 1/8". Is it a space issue, where the hole could break through into another area? Probably won't be any real difference in drilling in the cast iron, , just wondering why the spec of 1/8".

    1. Good questions. Unfortunately, this aspect of Hoss' plans isn't really documented. It's just "here's what I did" on the public pages of his website.

      I think that making a 1/4" hole for the length of a jobber drill bit and finishing with 1/8" is a fine idea. There's nothing in the casting we're trying to avoid, and the whole thing is pretty much "stick it together and it'll work". When I question Hoss he kind of says, "you're over complicating this".

      Today, I have got to figure out what I need to get to hook everything up. For example, he talks about using an old fuel pump he had sitting around. I don't have one. If I look for a fuel pump, everything I can easily find uses 5/16" tubing, not the 1/4" he talks about. A quarter vs 5/16 isn't a big deal, except it changes the size of everything else.

      I have a bunch of the plastic barb fittings, but I'm missing a lot of miscellaneous stuff. If I get a pump that uses 5/16 tubing, do the things I have even work? He used quick disconnect fittings, which are nice, but they seem to be about $5 each, which seems pretty high.

      It would be much easier if I knew what I was doing.

    2. I would think that you could find a fuel pump here:
      with NPT inlet and outlet. Then dig up NPT-to-hose barb fittings in whatever size you want.

  4. Zee grooves look gud. (kinda hard to write a thick German accent!)

    Another milestone passed, well done.