[artman60]

Knowing how it is supposed to look is what let me spot the problem.... once I bothered to kneel down and peek under the side rails for the Y switches. In the history of the 2 Probotix CNCs in our shop those Y limit switches had never been a problem before. I had no reason to imagine that one might have been re-wired wrongly. Yet that is exactly what had happened... over a weekend when no one should have been using the CNCs.

I'll know better next time, but hopefully all new-building work is done now and there won't be a next time. I suspect no other Probotix CNC has suffered the odd problems mine have. Mine live in a college where for the last 2 years they've been moved 4 times. They've gone from a classroom shop under my oversight to a larger all-college shop where potentially any student/faculty might use them without going through me.

4D

That is the reason I’ve come to pick Probotix as my future cnc. They stand up to all the different students, learning how to use a cnc machine. I’l probably make my share of mistakes, but i’ll be the only student making them on my machine. Now I gotta just find a way to come up with the funds for one.

 

[beltramidave]

Interesting. Glad you finally got it figured out. I had been following your journey, but didn't have any suggestions for you (that you hadn't already tried). I agree that the Y limit switches are very prone for accidental issues. I just had issues last week with those on one of the machines I oversee...

Dave

 

[4DThinker]

Figured out, lubed up, and back to use today. Very nice to have both of our Probotix CNCs working as today both were being used to cut parts for student projects. Between now and the end of the semester the dedicated room they are in will be very busy/dusty/noisy/productive.

4D

 

[4DThinker]

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

 

[honesttjohn]

4D

Will that also give a little more Z axis height??

 

[4DThinker]

4D

Will that also give a little more Z axis height??

The new beam alone doesn't add more Z height, but they also have taller side brackets that DO lift the gantry up for more Z height.

4D

 

[SteveMI]

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.

I have read about increasing the voltage levels for limit switches to eliminate false openings.

Steve.

 

[4DThinker]

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

 

[beltramidave]

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

 

[4DThinker]

Your idea is appreciated, Dave. At the moment the "soft limits" option in their configurator has solved the switch problem for now. We had devolved to using a jumper to bypass the X switches after homing the machine at one time in its history. Soft limits does essentially the same thing.

The Z switch is the one I've had to replace the most often though. My students tended to bring the router up until smashing it before jogging the head around. I'd find the switch's internal bar/lever bent after a while.

4D

 

[beltramidave]

The Z limit is a tough one to access too..

The soft limit is a nice idea, but if you were to lose steps because something bound up or whatever, the PC is going to keep counting and eventually you will crash because your limits will not be there to protect you from a hard stop. Hopefully though, someone will figure it out and stop it before that happens...

 

[4DThinker]

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

 

[beltramidave]

Yep, well aware of the capabilities of the Probotix machines as I oversee 1- Comet, 2- Meteors and 3- Asteroids as well as using their controllers, PC and motors to build a couple of XY positioners and my first DIY machine. Great product with awesome service!! Haven't seen the 60x60 gantry yet, (I don't do FB).

Was real close to buying an Asteroid for myself, until I saw the 4x4 FLA Saturn. Got that instead...

Dave

 

[4DThinker]

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

 

[beltramidave]

I envy you and your joinery talents. I have been trying to master dovetail joints (cut vertically) the last few days, without much success. Think I have watched every video ever made, but can't seem to get it right. Have tried Vectric's Dovetail gadget, but just don't like the overcut corners.

Any advice or files that you care to share would be appreciated. I mainly use VCarve Pro V9, but have AutoCad as well. Want to make some drawers for a dresser. Coming from working in a cabinet shop (elect. maint.) and seeing how easy it is for them with all their specialized machinery makes it even more frustrating that I can't accomplish it on my own.

Dave

 

[4DThinker]

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

 

[beltramidave]

Thanks 4D for the info. I am mainly interested in the thru and blind dovetails. Some of my issues are that I am using a bit that I had laying around and am unsure of the angle, think it is either 14 or 15 degree, 1/2" dia. I was also experimenting using some 1/2" plywood which seemed to tear out badly. My last test was in some poplar, which did cut much better.

GWizard told me I should be running my spindle at 8k or less with a feedrate of 129ipm. Does this seem right? I tried it that way and also up to 12k @ 60ipm. What are your recommended feeds and speeds.

I think I am on the same track of toolpathing as you described, so I will keep plugging away. Thanks for your help.
Sorry for hijacking your thread!

 

[4DThinker]

Unless I remove the center of the dovetail cuts with a straight end mill I keep my feed speed under 60ipm. Larger dovetail bits I may slow down my router spin rate to 12k or so. We just use routers with a variable speed dial 1-5 or 1-6 so I'll set them on 3 or 4 for larger diameter bits.

I will only use plywood for the flat cut of half blind dovetails. I never use plywood for any vertically clamped finger or dovetail cuts as (you've discovered) it will tear out too easily.

4D

 

[4DThinker]

BTW, you don't have to be a facebook member to see the photos Probotix has posted.

https://www.facebook.com/probotix/p...971063415323/1540079426037806/?type=3&theater

Just click on "not now" when asked to sign up or log in.

 

[4DThinker]

Speaking of joinery, I came up with a sample I'm calling a tapered tenon array. The goal was to make a joint with considerable holding friction when it was together, but was also easy to tap apart. Thus the tapered tenons. I may regret showing it to the students as it is time consuming to cut, and takes careful vector layout to end up with a good fitting joint.

Our 4th year students have to design and make small furniture projects that can come apart to fit into a UPS suitcase box. The tapered tenons are an experiment. Wood may compress and shrink/swell to make a good fit seasonal. The students can glue the joint together once they've proven it doesn't need to be glued. Many are foreign exchange students who will keep the project in that UPS box to ship it home.

4D