Wednesday, June 15, 2016

CNC Project Update

Work continues on my G0704 CNC conversion project.  I finished the triangular stepper mounts (well, irregular pentagonal), boring the main hole to proper diameter (which probably isn't critical) and tapped the holes that are supposed to be 8-32.  Then I assembled the stepper mount and the angle piece, which is a standoff for the NEMA 23 stepper motors I'll be using (yes, the motors mount with three screws instead of four).  When assembled, the angle section is positioned as a shield to keep debris from above from hitting the motors. 
Those all lined up and went together easily.  Next, I watched one of the videos from the Hoss DVD showing how to assemble the spacers and bearings for the Y axis, then built that. 
The big block on the left is the Y axis spacer that I talked about finishing last week.  It's hard to see in this picture, but there's a thin metal washer (shim) across the right most ball bearing.  Between the leftmost nut on the shaft and the ball bearing housing.  The motor mount is sized to press onto that shim and the bearing, causing some compression of the bearing races and reducing backlash.  That shim is why I think the exact size of the bore on the motor mount isn't critical. 

Finally, I assembled the complete stack up.  
And that's where I ran into a small holdup.  See the pan head screw with the slotted drive?  That's supposed to be a socket head cap screw, only I don't have any of those in 8-32.  Whut?  Why not?  Went through all the files of what I needed to buy from the DVD and don't seem to see 8-32 x 3/4" SHCS screws anywhere.  After a bit of a search, I ordered a box of 100 from Bolt Depot (FTC - I have no affiliation except for having spent money there for various pieces of hardware - they're a good outfit).  It kinda annoys me to spend more for shipping than the screws I need, but the three local stores I checked were more expensive, even including the shipping, and didn't have any in stock! I'll have my order from Bolt Depot faster. 

So now I have only one piece left to cut: the big one.  This part is just under 7.1" long and 2.1" tall.  The thick section is 1" thick and the thinner section is 1/2" thick.  That's a pretty large amount of aluminum to remove, probably the largest amount I've ever done in my time with machine tools. 
This will take several hours of machine time to do, since I don't have cooling fluid.  That means I can't cut as fast as the system could because I need to keep the cutting edges cool.  For the unfamiliar, aluminum has a nasty habit of welding itself to your cutting tools so that they suddenly don't work very well.  For the hole drilling and light machining I've been doing, a smear or single drop of cutting fluid works fine.  For something this big, I think I'll need to rig up some sort of mist cooler, or something.

Wish me luck! 


  1. WD40 works OK on aluminum.

  2. Tap Magic also works well, but probably costs a LOT more than good old WD40!

  3. Does the smaller raised portion have to be an irregular pentagon shape?

    If you left the entire piece at one inch thick would it still mount up, or does the irregular pentagon have to fit into a recess?

    Or, a two piece part. The irregular pentagon made from half inch aluminum, and then the two pieces bolted together with a your left over 8-32 socket headed cap screws.

    I have been reading Live Steam and Outdoor Railroading magazine for a number of years, and they have made a lot of complex shapes by building them up instead of machining them down.

    I thought about the cooling issue. I did not consider a home built coolant system for the small mill. (I think it might be an option for the big mill for later)
    I thought about using compressed air and a bracket to provide a degree of spot cooling and chip removal. I thought of the effects of spraying aluminum swarf across a huge area and drew back from that idea.
    Maybe a shop vac suction hose, necked down to a smaller diameter and placed near the end mill. Chip removal, and some degree of cooling.

    One of my earliest memories of working with metal was helping my machinist father drill some holes in a piece of bar stock. (a splint for a bent axle on a child's wagon) My job was to use the oil can as directed. Even today, that perfume of hot metal and oil means good times.

    Everything is looking great. Well done.

    1. Was that 3-in-1 oil by any chance? I had that experience.

      Probably the best way of answering the big question is that I think I could do that. I need to double check the drawings, modify this one, and make a new drawing for the small piece. The irregular pentagon matches the ones I cut out already - and one of the two mounts on top of this. Conceptually, this piece is like the Y axis spacer, only thinner.

      The counterbore on the cap is 0.638 deep, so it would split with the bottom piece making it .138 deep and the (new) top piece would just be the counterbore diameter. That just makes the top one bore diameter and moves the dual diameter bore to the bottom piece.

      The bore in the thick part of the end cap matches the Y-spacer except the Y spacer is longer, but the bearing stack up is the same. Where the Y axis has a 3/4" spacer, the X gets 3/8". Basically, the design on X matches the compression applied to the ball bearings on Y - it's the same parts stack up on both axes except for that spacer.

      On the Shop Vac or compressed air coolant, I've used the shop vac on the Sherline. It doesn't seem to make things cooler, but that system runs under such low chip loads that I don't think it matters.