CNC – Head crash!

There are some days when things just don’t turn out right.

I needed to solve the motor startup problem, so I sanded off the white paint (I’d used some really old WiteOut — yuck) and re-painted the shaft, this time with fabric paint (can’t find the fancy white-ink pen grr). I decided to paint the other half of the shaft black, as well, although it was already pretty dark; I had it open, and I didn’t want to have to deal with it again, so why not?

I created a little test pattern; some straight lines, 1/4″ deep, at various feedrates and spindle speeds, surrounding my calculated feedrate (6000rpm at 100ipm, which sounds awful slow for wood to me, but … *shrug*).

Got everything put back together, ran an aircut, and ran the real cut… The lines were Not Straight. The brand new endmill was not ripping out wood like a hot knife through butter, the machine was really struggling for some reason.

I spent some time fiddling with the Y axis bearings (all the tests were in Y), but I decided to take a little break, and see if I could get a board etched (but that’s another post).

I came back, twiddled the feeds and speeds a little, and decided to do a 2-pass (1/8″ per) cut this time. Same guts. Awful, totally not straight lines, and to top it all off, the machine freaked out on the last plunge, plunged the bit all the way into the surface of the table, and then tried to cut sideways, causing sparks, and yanking the endmill out of the collet and leaving it embedded a full inch into the table!

Yikes.

I admit that I considered taking an axe to the gantry at this point. The plan was to have another woodworking tool; some work is best done on the table saw, some on the drill press, some on the chop saw, and some on the CNC. You just push your work to whatever tool is necessary to get the job done.

The CNC has been a boondoggle. I’ve been fighting the thing for 15 months now, and having a non-working “project” around the shop is irritating, but I can live with it. This unfinished project comes with a 5’x10′ work table, after all.

But I looked at that endmill sitting in the table, and thought about what would have happened if it had been kind of halfway yanked out of the router, but came *out* of the table (think 15,000rpm carbon steel missile with wood-cutting blades at the end), and frankly, I’m done for now. If I can’t make this thing cut right, at least I need to be able to make it safe. And if I can’t make it safe, it’s not going to be in the shop.

I have no idea how the Z-axis decided to make that move in the first place (I checked the G-code, and it definitely does not have a “G0 Z-6” or whatever in it), so it’s probably some kind of electrical interference — the new cable I put in might not be shielded? I can start troubleshooting that, but it’s a scary thought that the machine is sitting there, waiting to throw an endmill across the room. And even when I figure that out, the cuts aren’t straight, and this is just in Y. One assumes that I’ll have to test X and will run into similar problems there, too.

The machine *was* cutting OK. And in principle, nothing has really changed except the router motor. But in practice, since the last time I did a cut, I ran several new cables, installed the Super-PID, home switches, and a new Z-axis… I can come up with a list of stuff to try (replace the Z-axis cable again, try an ACME screw in Z, which will have better mounting to the gantry, set better soft limits, try again with better feeds and speeds). But the question remains: what if I do all of that, and I still can’t get it to cut right? Would I be better off with a commercial machine? A Laser cutter? A 3D printer?

So I don’t know what to do at this point.

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One Response to CNC – Head crash!

  1. Pingback: CNC Build – Once more into the breach, … again. | The Circuit Farm

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