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Tag: CAM

Universal Bulkhead Ring Part 2

I’ve been bounding around design and work on some different parts of the AUV but had been meaning to get back to working on the bulkhead ring prototypes. I’ve made some tweaks to the design, mostly so that I can mount internal components directly to the inside of the ring, necessitating the creation of some flat spots on the inner surface, where I can drill and tap mounting holes. These should be fairly easy to cut out on the mill when doing the finishing drill steps.

Universal Bulkhead Ring

I had some time today to sit down and make some progress on the machining and managed to get most of the lathe work done, minus the external grooves which will seal up against the body tube. For the most part, things went well, although I made a fairly stupid mistake and zeroed off the wrong side of the grooving bit when cutting the face grooves — Luckily, not all the rings will need seals and o-rings, so I can put this one into a “wet” compartment where that mistake won’t matter.

Inside Turning large parts on the Sherline

One frustrating battle I did have to fight, however, was with chatter. I had significant chatter on the external turning operation. I think I’ve tracked that down (a little too late) to one of the gibs in the slide, so will need to tweak that before spinning anything more.

One tricky part about the setup is that the part needs to be flipped part way through. To make sure that everything is lined up, I had to place a dial indicator behind the part and very carefully adjust it in the chuck to make sure that I had very little runout. In the end, I got about 2-3 thou peak-to-peak deviation at 2.7″ radius. Not too shabby, and good enough for my purposes.

Aligning the part after flipping, using a dial test indicator on the back face

All in all, however, the g-code works well, and future rings should be much faster/smoother to machine. I ended up settling on a feed speed of 145mm/min and 0.1mm depth of cut with the mill’s motor geared down (~1400rpm with carbide tooling, so a very fast surface speed). I wouldn’t push the machine any harder than this at these large diameters (~5″), especially since the chucking method isn’t super secure, and subject to going out of alignment relatively easily. I suspect I’m feeding too fast with too light of a cut, so on the next ring I’ll experiment with deeper cuts and slower feeds to see if I can improve the chatter/finish/headaches. — Disclaimer: Do not take any of this as good advice. I’m not an expert machinist! This a very non-ideal method for clamping large parts on a small lathe, and can be dangerous if not secured properly. 

Next steps will be to finish this part, and work on the next batch. I’ll need about 8 with my current design, so it may take a bit of time to get them all done…

Universal Ring Progress! Most of the cutting is done at this point.
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Setting up a CNC Mill and Lathe Part 2

I didn’t write a post for it, but I did the CNC conversion on the Mill and Lathe about a month back, and for the most part, it went well. This weekend, I finally had enough spare time to get back to working on getting it actually up and running. I’ve somewhat trammed the machine and gotten rid of most of the backlash, but will need to do a bit more work on that before working on real parts — The big “fun” thing I did was get some g-code running on the mill, and do some practice engravings with a sharpie and some paper. Things are working pretty well, and there’s definitely something cathartic about the sound of the steppers working through circular profiles. (Even if the knobs on the handwheels are rattling somewhat. I’ll need to tape those down)

eCam Engraving Test
eCam Engraving Test

For a CAM program, I’ve been looking for something that can handle non-trivial profiles on the lathe, so that I can use it to machine the profiles of the AUV’s Kort nozzle and nose-cone. Affordable lathe CAM programs are hard to find, but one that has piqued my curiosity is eCam — I’m playing around with the trial version right now, and it seems to be working well for my uses so I think I’ll shell out and purchase a copy once I’ve confirmed it can output effectively to LinuxCNC for some specific uses cases I have. It’s definitely in the lower price range for CAM software, at least for hobby usage.

Some minor modifications to eCam’s post-processor were needed for the basic engraving routine:

  • Update the “Head New Program” section by removing the line “O{PRG_NUM}({PRG_NAME})” and splitting the line “G0G28G91Z0” into three unique lines, one for each G code command. (LinuxCNC doesn’t support multiple G-code commands with a coordinate in a single line. Multiple G-code commands without coordinates appear to be fine)
  • Disable incremental moves.
CNC Testing, "Engraving" With a Sharpie.
CNC Testing, “Engraving” With a Sharpie.

Loading up the code was pretty painless, and the milling machine is working well so far! The lathe tests are showing I need to do a bit more work on the postprocessor to get it to play nicely with LinuxCNC, but it doesn’t look like it will be too onerous.

I’ll try to get some materials soon, after which if all goes well I can start working on some of the AUV’s structural components.

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