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

[Rambozo]

I'm curious if anyone has suggestions on maximum speed and acceleration rate...........

That all depends on the strength of your motors and the mass and friction of your machine. Ideally you want to be able to go as fast as possible without losing any steps. There are some motor tuning programs that will help you get in the ballpark. Also a lot depends on your step kernel rate in Mach. Run the drivertest to see what your system can support. Be aware that you can also have resonance problem at some speeds, there are tricks to fix that, if needed. One thing about steppers is that they have a wicked torque curve vs speed. So you need to test and tune from zero through your max feedrate, then at your rapidrate. If you have a resonance between max feed and rapid, you can live with that, but not if it happens below max feedrate. And of course you must never lose a step, no matter what. A general rule of thumb is to adjust velocity up until the motor stalls, then back down about 10%-20%. Then adjust acceleration as high as possible where they can still start from stationary. This will give the best position tracking. If you plan on using constant velocity, everything will have to be tuned really close, for exact stop you don't need to be as precise.

[acourtjester]

HI Empty
you may have the same problem I have with the "Z" axis, it look like your "Z" motor is a direct connect to rack via the motor gear.
What happens when you drop power to the motor the weight of the z axis will cause the motor to free wheel and the z drops to the limit.
Slam dunk kind-of-a-thing. I need to remember to prop it up before dropping power.

[SeanMurphy265]

This is an easy way to calibrate your steps per inch. I did mine with a tape measure because I do not have a dial caliper, but I'm ordering one soon. I'm not good at math, but this is an easy way to get it accurate.

[sportbike]

That thing looks pretty darned nice. I am looking forward to seeing how it works out. I have still been toying with the idea of building a small one for myself.

[EmptyNester]

I thought about a couple different ways to support the wire shelf for the energy cable. I ended up getting a U shaped wall bracket for holding shelf supports.



I didn't install the engery chain because I don't think the torch is long enough to make it. Hopefully, I'll have a longer torch in a couple weeks.



All I have left to do is:

• put in the X limit switches
• complete the wiring on the limit switches
• use silicone caulking in the problem area that may still have a leak
• finish leveling the slats

Before I try a test cut, I need to finish wiring my THC/interface. I don't plan on trying to get the THC working just yet, but it handles the relay for the "torch on".

[EmptyNester]

Rambozo - thanks. I ran that and it went as expected.

I took one of the odd ones I've generated and stepped through them to identify the commands. I deleted the circles. It seemed to work okay.

I'll spare the details, but I tried lots of different things and was always getting the conincentric circles in the Mach driver. I run Mach on a PC in the garage and have my drawing program and SheetCam upstairs. To try to save time debugging, I installed mach on the upstairs PC. Everything looks fine. The same file loaded on the table's Mach driver is messed up.

At this point, I think I have a very hosed installation/configuration on the table's Mach driver.

[Rambozo]

There are some options in the configuration for arcs. Every control is different, and Mach can be configured to behave in a few different ways. For instance I use an Anilam control that uses absolute coordinates for the centerpoint if the endpoint is absolute, while the standard for Mach and some other controls is that center points are incremental offsets, even when you are in absolute mode. In fact I had to switch my backplot program to get a proper display for your code. Just like some controls can't do a full circle with one arc command, some are limited to 90° and some to 180° so you have to break the circle into multiple arcs.

Here is a sample with an incremental centerpoint arc.
N100 G20
N110 G53 G90 G40
N120 M06 T1 F20
N130 G00 Z2.500
N140 X1. Y1.
N150 Z0.500
N160 M03
N170 G04 P.5
N180 G01 Z0.100
N190 Y3.
N200 G2 X3.Y1.I0.J-2.
N210 G1 X1.
N220 M05
N230 G04 P1.
N240 G00 Z2.500
N250 X0.000 Y0.000
N260 M30

And here is one with absolute.
N100 G20
N110 G53 G90 G40
N120 M06 T1 F20
N130 G00 Z2.500
N140 X1. Y1.
N150 Z0.500
N160 M03
N170 G04 P.5
N180 G01 Z0.100
N190 Y3.
N200 G2 X3.Y1.I1.J1.
N210 G1 X1.
N220 M05
N230 G04 P1.
N240 G00 Z2.500
N250 X0.000 Y0.000
N260 M30

And finally here is an example where all the X Y moves are in incremental by switching the mode with a G91.

N100 G20
N110 G53 G90 G40
N120 M06 T1 F20
N130 G00 Z2.500
N140 X1. Y1.
N150 Z0.500
N160 M03
N170 G04 P.5
N180 G01 Z0.100
N190 G91
N200 Y2.
N210 G2 X2.Y-2.I0.J-2.
N220 G1 X-2.
N230 M05
N240 G90
N250 G04 P1.
N260 G00 Z2.500
N270 X0.000 Y0.000
N280 M30