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

[SeanMurphy265]

I was looking at your carriages and they are almost exactly like the ones I purchased from No Sleep Studio. I think the guy from PP called out the guy at No Sleep Studio on CNC Zone for making his kit very similar to PP. Is this kit the same as their Iplasma? Have you kept up with how much you have spent?

[EmptyNester]

I was looking at your carriages and they are almost exactly like the ones I purchased from No Sleep Studio. I think the guy from PP called out the guy at No Sleep Studio on CNC Zone for making his kit very similar to PP. Is this kit the same as their Iplasma? Have you kept up with how much you have spent?

It's funny for calling someone out on a simple carriage design like that. I would bet that's a pretty common design approach. Sadly, they are different enough that my NoSleep Z-axis mounting holes don't match those on the PP carriage.

The guy at PP said they don't make any tables with that carriage any more because it is the least precise and the rails need to be kept clean. I did think the price was a little high ($325), but the hovercraft project taught me that its worth paying more for a kit so you have somebody you can call if you need to. (But in hindsight, I might have gone with the NoSleep gantry had I known about it at the time.)

I have kept track of the spend. I haven't totalled it lately but will post a total cost and parts list. It was a mixed bag of spending more or less than expected, but I think I'm still coming out significantly less expensive than buying. The biggest costs were $325 for the gantry, about $450 for steel (including water table) and $400 for motors/drivers/power supplies (I don't recall the cost of the cabling and gear and racks).

[EmptyNester]

I did a quick video of the test.

[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.

[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...