Wednesday, April 20, 2016

Back In the Shop

My recovery from my nasty week has progressed enough that I can walk or stand around without pain, so I spent most of the day trying to figure out just how to hold the stock and make a small part.  It's not done yet. 
For scale, that's a half inch thick piece of aluminum that's 1 3/8" long by a half inch tall.  The raw stock I'm cutting it is taller than that; around 0.9 inches (toward the top in this view).  The part that's slowing me is cutting out that sector of a circle.  I have two small clamps holding this piece down to the table, pretty much at each of those holes.  The circle diameter is 1.11" which puts the center of the circular cutout just barely still on the metal. 

I started out thinking the way to do this is the way I cut the circular cutouts in my previous pieces, but the exact lines of code I used that time would be inefficient here.  That time, I cut circular holes in the solid metal.  This time, I only have a part of a circle to cut. If I used the previous routines, I'd spend about half the time with the cutter in mid-air.  It's true that there are worse ways to spend my time, but I also think it's worthwhile to figure out how to do it the most efficient way possible. 

The next part is going to be a bit harder, too, but in a different way. Pictured here, it's a replacement for an existing end cap on the long (X) axis of the G0704's table. 
This part is roughly 7.1 x 2.2", and most of it is thinned down from a 1" thick piece of plate to 1/2" thick.  I ran this through my CAM program, and it tells me I'm looking at roughly 18 hours of machining time.  I'm not comfortable with thinking that everything can run that long without issues.  The only alternative I can see is to use the big mill, since it's all still fully usable.  It just has to be done manually.  The G0704 can take take off much more per cut than the Sherline/A2ZCNC mill can - which is why I bought it in the first place!


  1. First the lower piece. Do you have to reduce the thickness from 1/2"? I went down and looked at my small mill, and other than needing longer allen headed bolts the thickness of the handwheel plate has no effect on function.

    Now the upper piece. While downstairs I also got out the boring head. I think it would dial down to bore the circle, but it would be an interrupted cut. If possible starting with a piece of raw material large enough to make the large hole easier, as well as providing a larger area for hold down. And yes, I think you could attach the upper part to a larger piece of scrap and thus be able to bore it in the lathe using the four jaw.

    I then decided to consult the hive mind of the internet, because the upper piece does not look very different from the lower half of steam engine bearings.

    My search of "small scale machining split bearings" yielded a number of forums and suggestions as well as some video. A quick skim showed that some could be applicable and some would not be applicable.

    What are the tolerances?

    1. The piece is mounted to a metric ballscrew/ballnut combination, and mounts that into the base of the mill. Tolerances for that cutout are fairly loose - the two screw holes have to match the ballnut. I'm pretty sure there's nothing in that circular cutout that's actually circular. It's just for clearance around the body of the ballnut; the ballnut doesn't rest in it. Well, pretty sure about that.

      I had thought of making the piece from a larger chunk of aluminum and cutting off the bottom half inch. I also thought of cutting off the 1/2x1/2 piece and working on just that. In fact, I started that way. Once I cut it off, I kinda held it in my hand and said, "nah... too small".

      I can see a few ways to do it, ranging from outrageous setup and fast cuts to fast setup and outrageous work time. I was trying for a compromise that looked fairly easy all the way around. I think I could drill out some holes in it and clean out the remaining aluminum with a Dremel or other grinder. Dress it clean and shiny with a half round file.

      As for the other piece, I've thought that I don't really need to thin it out, it just needs to be the right thickness where the mounting screws are. That's probably what I'll do. A possible approach would be to make two pieces and hold them together with screws, then machine the two pieces as one. I'll look at his videos again, but I think it's just for appearances. If it's just for appearances, I'll leave it at 1" thick. His Grizzly was already fully CNC'ed and working good when he used it to make up the pieces for the "Phase 3" version, and I think it's about an hour to cut them down on that machine. Maybe less.

  2. Well, I am no machinist, but-
    If your purpose is to gain CNC experience,go for it. If you need the parts made soon, use the manual mill and lathe, IMO. 18 hours? Seriously? That sounds like hacksaw and file time allowance..

    The tolerance question is all...

    The top part could be easily made by squaring up the stock, marking and drilling the holes, bolting it to a aluminum plate and either grabbing it with the four jaw or bolting it to a face plate and turning the semicircular cut. Or leave it on the mill and use a boring head. Or put it on a rotary table.

    Johns comment about simplifying the lower part seems spot on- is the thickness reduction necessary? Are the angles necessary?

  3. On the lower piece, why not rough-cut two pieces of 1/2", weld together with a perimeter weld around the smaller part with the large+tri-hole, and then machine / drill to shape...since the outer perimeter isn't critical, only the relative hole positions and sizes?

    1. The biggest reason is that I don't have a welder. I was thinking of just adding socket head cap screws, counterbored so they sit under the surface. Another piece mounts on top of that triangle-thingy.

    2. Ah. Guess it was kind of an ironic comment then...I have a TIG, but not a have mill, but not TIG.

      Which reminds me, I need to get a mill.

    3. ...and I need to get a TIG welder.

  4. The 18 hour machine time still has me puzzled- did the right parameters get fed in? It is too far out of whack to make sense.

    1. Remember this is a light duty Sherline "micro milling" machine (it's not exactly a Sherline, but it's more Sherline than not). It's taking light cuts at 2 IPM. I could conceivably speed that up, but I don't know how much flex to expect in the system.

      BTW, I figured out how to do a 180 arc in GCode, and the first light cut (.005") is fine. Time to go cut it out.