Nebula Controller Failure :(

One thing this episode reminds me is that over the years I've been using the Nebula it has always suffered from limit switch errors/warnings when we've tried aggressive cuts in dense hardwoods with it. Vibration bounces open the switches. Probotix has come up with a "soft limits" option in their configurator that should stop the switches from stopping a cut. That doesn't eliminate the vibration, but they are also working on that problem. They have recently been showing (on facebook) photos of a new 60mm x 60mm gantry beam that is thicker walled and considerable stiffer than the current 30mm x 60mm beam they use. I don't know if/when this will become the standard beam on all new Nebulas or Asteroids (or all their CNCs) but they imply you can get the taller beam by request on any new CNC you order from them.

4D

The spring/flex in the switch parts seems to fatigue over time, meaning they become easier and easier to "bounce" open the older they are. I can't see any way more voltage would change the metal to stiffen it/slow down this fatigue. Of course more heat and some solder could close them permanently, but that would defeat their purpose. I suppose some increased voltage might arc over a small gap though.

There are other types of proximity switches, but I'll guess they would be too expensive in the numbers needed for each CNC axis.
Their soft limits option uses the switches only to find "home" where it looks up the axis extents to keep the head contained from there on. The axis extents can be found and edited in the nebula.ini file (or whatever name is used for your configuration). I change mine to reflect the actual distances my head can move in X and Y directions. It is slightly more than the default setup permits.

4D

Each axis limit switch has a debounce variable in the HAL file. This is mainly used, I think, for signal interference. Could possibly increase the setting a little and see if it helps issues caused from vibration.

# debounce the y-axis switches and connect them to signals
net switches-y1-raw <= parport.0.pin-11-in
net switches-y1-raw => debounce.0.0.in
net switches-y1 <= debounce.0.0.out
net switches-y2-raw <= parport.0.pin-12-in
net switches-y2-raw => debounce.0.1.in
net switches-y2 <= debounce.0.1.out
setp debounce.0.delay 10

Another option possibly would be to remount one limit switch on each end of the bed and put the switch target on the bottom of the gantry (where switches are now). This would require some additional wiring, though.

Without much current running through those switches, it doesn't take much to open the contacts.

Just some thoughts...

Dave

So far the I've never seen any of the 3 Probotix CNCs (one my own) I oversee loose steps. When limit switches are active hitting one stops the machine (without losing track of where it is) before more damage can be done. The CNC Sharks (one mine and one in the same room as the 2 probotix CNCs) don't have limit switches and losing steps (by bumping into a hard limit during a cut) is a danger we've encountered more than once.

Yes, a coupler could come loose. That hasn't happened yet. The steppers probotix uses are very reliable and positioning is very accurate and repeatable. I suspect I'll be buying another one for the college before I retire. One with taller gantry sides and the new 60x60 gantry beam. We'll retire the old Shark then as we only keep it to do taller 3D projects that won't fit under the meteor/nebula gantry.

4D

I simply wouldn't have room for a 4' x 4' CNC in my personal shop, and where I work they now have a 5 x 12 multicam than handles all the large sheet work. Our small CNCs seem perfect for all the quick and dirty furniture parts we encounter. The 4' length of both is rarely used but gives us useful sections when I've split the area into 2 or three different work areas (flat, vertical/angled, and rotary on our Nebula). My personal meteor is on taller legs than I've got the college CNcs on. Came in handy yesterday when I could cut some end-grain joinery on parts that were too long to fit under the school's CNCs.

I have figured out a way to cut on the ends of even longer parts, but that takes re-mounting the router to a horizontal position. Not worth doing until someone wants to make a tiny house using all CNC-cut joinery on the 2x framing.

That will be a whole new adventure.

4D

Dovetail joints are one of the most challenging I encounter as even Aspire can't render what a dovetail bit cuts.

There are half blind and through dovetails, as well as french dovetail slots and tapered french dovetail slots. I occasionally do half blind mitered dovetails too. I've made a few samples of ramping dovetail joints between boards meeting at a sharp angle. I always start with a vertical section view of the bit I'll be using to show me how wide it cuts both at the bottom and at the top when it passes through wood at the depth I've set it to. What I do next depends on the type of joint I'm making.

One half of a through dovetail joint can be cut with a straight end mill. Both halves are cut with the boards clamped vertically.
Both halves of half blind dovetails are done with the same dovetail bit. One half is cut with the board clamped vertically and the other half with the board laying flat.
The french dovetail slot or tapered slot is cut on boards laying flat, while the male part is cut one the end/edge of a board clamped vertically.
Doing half blind mitered dovetails both halves are clamped at 45 degrees and are done with the same dovetail bit.
For ramping dovetails one half is clamped at the angle between the 2 boards. The other half is clamped at half (or is it double?) that angle.

Generally I'm keeping track of both the bottom width and at-depth width when laying out a vector path for the bit to follow centered ON the line. I often realize I've made a mistake and how to fix it before saving the toolpaths to cut the joint out with. When my sample cut doesn't fit tight it usually means my dovetail bit wasn't exactly the width or angle it claimed to be.

4D