Am I doing this right? Motor Tuning..

[racedirector]

While I wait for parts for my machine I have been playing with the demo version of Mach 3. I have read the docs and calculated the Steps Per based on what I am using but the process of executing the gcode seems awfully slow.

Heres what I worked out based on my parts, can someone tell me if I am doing this right?

First up, being in Australia, I want to use MM as the native units. My leadscrews are Acme 1/2" 6 tpi. What I worked out after converting that to metric ( x 25.4) was .2362158mm per revolution. I did that by taking 1, dividing it by 6 giving me 0.1666666 * 25.4 = the above.

I will be using SLAMStepper boards and will, as an example, use 16 microsteps per giving me 3200 steps per revolution.

So, the Mach manual tells me to multiply 3200 by .2362158 giving me 755.89056 steps per revolution of the leadscrew. I also set the velocity to 1200 and the acceleration to 500, not really knowing what these values should or will be.

Have I got all this right? Any help would be appreciated.

Cheers
Bruce

[ger21]

.166*25.4 = 4.233, not .236??
You want steps/mm not steps/revolution
(3200 * 6) / 25.4 = 755.9055 steps/mm

The actual velocity and acceleration will need to be determined after the machine is finished.
1200mm/min is rather slow, I'd guess you should be able to get 3000-4000mm/min, so, for testing, set the velocity to that, and don't worry about the accel.

The actual cutting speed is controlled by F words in your g-code. You'll want to have something like F2000 or F3000 in there.

[racedirector]

Awww crap, I blame the conversion error on going to my wifes Christmas party Friday night!

Thanks for the rest of it, still trying to get my head around everything CNC. I hate waiting for parts.

I will be using a post processor of some kind until I learn a bit more about gcode programming. Now I'll know to set the speed in whatever I end up using.

Thanks again

Cheers
Bruce

[racedirector]

OK, I have been playing some more with dxf/gcode files and have this weird thing in Mach3. As suggested by Gerry I "should" be able to get a reasonably high rapid rate out of my leadscrew so I set the velocity in Motor Tuning to 3000mm/min to see what would happen. Well it wasn't good. The display was indicating that sharp 90 degree corners were being rounded off something terrible so I reduced the velocity to 500 and that worked. However, 500mm/min is only about 19"/min which is abysmal.

Out of interest I repartitioned my hard drive and installed EMC2. Excatly the same configuration was put into EMC2, that is 3000mm/min and when the gcode was run EMC squared off the corners perfectly, slowing down at each corner to do so.

So my question is why would Mach3 be steamrolling its way around corners making square corners look like an oval bike track whereas EMC with the same config does what its meant to? Have I not set something correctly in the 5 zillion config screens? I do like Mach3's display and the information it provides but if it is going to be soooooo different from EMC.....

Again, any help would be appreciated.

Cheers
Bruce

[ger21]

It's Constant Velocity mode that is causing rounded corners. In CV mode, Mach3 attemts to maintain a constant velocity at all times. the laws of physics won't allow you to go around a corner without slowing down, so Mach3 has to round off the corner to maintain the constant velocity. Acceleration plays a large role in the amount of corner rounding. As you raise the acceleration, the rounding will decrease.
One alternative is to run in Exact Stop mode, but it's really not an option in most cases, as it can result in jerky movement, and longer run times.
I think what most people do is turn on the CV angle setting in General Config. Check the box and set it at 89°, and you should get much better corners.

[racedirector]

Once again Gerry to the rescue, thank you Sir! that adjustment works just fine on the display. I had read in another thread above CV's etc and went looking for a CV editing screen and couldn't find one. You see I am a model railroader and the DCC decoders I use have CV settings so I thought that Mach used something similar, what a fool I feel now

I was hoping someone would have an answer to this question as I wasn't really enjoying the EMC experience with some gcode it didn't want to run.

I am really busting to get my machine done so I can play for real. I ordered the acme rod today, my bearings are on their way and I am off to buy the rest of what is needed to at least get it to the point of needing electronics tomorrow so hopefully by Friday this week I can get on with that side of it. Then it is only the painful wait for the electronic bits to arrive from overseas.....

Anyhoo, thanks again Gerry, much appreciated.

Cheers
Bruce