Project 1 from EmptyNester. Category: Custom Shop Tools - CNC Table

[Rambozo]

Looks good. The acceleration vs velocity seems strange, but maybe that's just a limitation of running at 25kHz.

[EmptyNester]

The acceleration vs velocity seems strange

Strange how?

[Rambozo]

Your velocity actually seems pretty good for only 25kHz pulse rate, but is seems really lazy on acceleration and braking. That may be a function of how the jogging is handled. It's hard to see what is happening when actual gcode is running because the part is rather small, and I can't tell when it's rapid vs feed. I'm sure once everything is tuned it will be fine. The real test is constant velocity. I would think a plasma would benefit a lot from being able to run in CV mode. The parts should be a lot more accurate and with a better surface finish.
Congrats on getting it all going.

BTW if your router causes the Z to fall without power, you could counterbalance it with a small gas cylinder or even a weight. Another option is to hang an electric brake on the shaft of the stepper, since I see you have dual shaft models.

[sportbike]

Any chancec the gear or something is slipping on the shaft? A buddy of mine has a mill that does that on occasion and loses its position.

[EmptyNester]

Any chancec the gear or something is slipping on the shaft? A buddy of mine has a mill that does that on occasion and loses its position.

I hadn't thought of that. It would probably explain the noise a little better.

I'll have to take the gear off and check for scoring from the set screw.

[sportbike]

To make things easier to debug, maybe you would be better suited to just cut a simple square with no change in the corners at all. Or maybe a circle.

You could just manually program a square without any offset or any fancy stuff at all, just make the torch pierce then move in a square then stop.

[Rambozo]

To make things easier to debug, maybe you would be better suited to just cut a simple square with no change in the corners at all. Or maybe a circle.

You could just manually program a square without any offset or any fancy stuff at all, just make the torch pierce then move in a square then stop.

Personally I would make it real simple and program a straight line with a an increasing feedrate to learn what speed makes the best cut for my combination of torch, amps, and material.

Something simple like starting from X0 Y0:

G1 X1.0 F20
G1 X2.0 F30
G1 X3.0 F40
G1 X4.0 F50
G1 X6.0 F60

Run that across a 6" piece of your sample material and see what it looks like. If it completes the cut, crank up the speeds and run it again. Then you will see what speed you need to make the cleanest cut and where it breaks down both above and below. That will give you your speed envelope. You can do finer increments if you need to break it down further, once you have the ballpark numbers. The correct feedrate will allow your cam package to do the correct compensations for curves and such. You can also program a series of pierce delays to figure out how long to make that, just a series of holes spaced apart. Make each one shorter until it fails to pierce. I'm sure you want a little buffer there, but again it would give you some ballpark figures for your combination.

[sportbike]

Personally I would make it real simple and program a straight line with a an increasing feedrate to learn what speed makes the best cut for my combination of torch, amps, and material.

Something simple like starting from X0 Y0:

G1 X1.0 F20
G1 X2.0 F30
G1 X3.0 F40
G1 X4.0 F50
G1 X6.0 F60

Run that across a 6" piece of your sample material and see what it looks like. If it completes the cut, crank up the speeds and run it again. Then you will see what speed you need to make the cleanest cut and where it breaks down both above and below. That will give you your speed envelope. You can do finer increments if you need to break it down further, once you have the ballpark numbers. The correct feedrate will allow your cam package to do the correct compensations for curves and such. You can also program a series of pierce delays to figure out how long to make that, just a series of holes spaced apart. Make each one shorter until it fails to pierce. I'm sure you want a little buffer there, but again it would give you some ballpark figures for your combination.

That's a damn good idea Ram. Once a rough idea of speed is figured out, straight lines with variable THC voltage settings could be done to dial height in as well.

Probably could get a pretty good idea on speeds and feeds from using two or three material thicknesses and spending about to minutes on each one, then interpolating the results for other thicknesses.

[EmptyNester]

Sportbike - thanks for the offer, but I wouldn't be able to deal with the guilt of sticking you with a defective product

I can push the granty the entire lenght and the only time it hangs up is if I don't keep it square.

I spent last night working on the limit swiches and then this morning working on the grinding. I had thought that racking might be part of the problem. So, I have the limits and homing working, so I could rule that out.


Aaxiss - I thought that might be an issue with sag or bowing, but it seems to be based on the speed.

I did more testing. After everything was squared and homed, I could make it happen at high speed. At high speeds it seems to sound like the motor is running away but it's stuck in place. Then, if I'd rehome again, the X-axis was off inches (8" on one of the runs).

At this point, I'm wondering if I've driving my steppers too fast. On thinking about it, when I sit at the end of the table and move it toward myself "that's scary-fast" probably isn't the right speed.

I had read to set the motors as fast as you could and just slow them down until they work well. Mine work fine unless I use half the table to accelerate.

So, I started looking at my speed. I had it at 3800 in/min. From doing a quick search, it looks like I won't need to go over 100 in/min at the most. (I would assume even slower if I mounted a router.)

I haven't continued playing to determine max speed. I'd like to figure out how to use the touch and go so I can try a test cut.

[EmptyNester]

I am really confused.

I can't seem to figure out how to configure Mach to use the Arc Okay signal. The signal is working, but I can't find anything in the doc or online about how you actually configure Mach to use Arc Okay.

Anybody have any ideas?

I'm still trying to figure out why the torch cuts out while cutting. I don't hear the relay click off, or see the Arduino say the torch was turned off. It could be so fast that I don't see and hear it. I'll have to watch voltages. But, I really think its a configuration issue.

I feel like Mach and Sheetcam are each a "universal mounting bracket" from different companies that need to work together. But, you just can't figure out how.

Thanks.

[Rambozo]

I would think that ARC GOOD would have to be configured in that custom G28.1 routine for THC.

Since your corners end up a basically a big hole, maybe because you are going too slow the arc just cuts out from the gap, and not from any signal. I would think you would be able to tell from the relay and status indicators that the plasma has been stopped by a signal. Maybe that was part of the reason for the high speed in the corners? Now that you have your arcs fixed, you can go back to corner loops and maybe make them a little larger so there is some metal under the plasma jet and not a hole from the other part of the loop. All of these are more SheetCAM issues. I think you have Mach doing just what it is told to do.

[Rambozo]

Is Mach honoring your pierce delays?
This post seems to indicate that with the THC set, the arc ok signal is being used and the delay might be expected from the THC which is probably not the best system. You can modify a macro to fix this, but i believe it has been reported as a Mach bug.

http://www.machsupport.com/forum/ind...?topic=17435.0

I believe the proper path should be:

Move to pierce height
Start arc
Test for Arc ok and wait for it, with a timeout after a long time and end program with an error.
Start pierce delay
End pierce delay
Move to cut height
Start X-Y motion

It looks like you have to make some adjustments to get this to work.
It might be to be compatible with THC's that do their own pierce delay internally. Maybe research this a little to see if it's something you want to add. I think I would rather have that added by the CAM program. There are pros and cons to each method.

[sportbike]

Looks good. Congrats on your first "Real" part.

Best part of the whole thing is that your wife likes it. Time to call Alro and have them drop off a truckload of sheet materials...