Messages

1301

General Mach Discussion / Re: Homing position is not absolute

« on: May 05, 2011, 04:18:38 AM »

Ray - Neither Burkhard nor I have ever questioned accuracy - but then I think you know that...

Terry was just having the good grace and balls to admit he was wrong. Give you any ideas Ray?

Burkhard - don't forget Gerry's macro and my comment after it. As long as the second homing speed is below that which requires an accel ramp then it will be independant of your max vel and accel settings and will stop as soon as it's off the switch regardless.

Ian

1302

General Mach Discussion / Re: Torch volts control

« on: May 04, 2011, 09:20:28 AM »

It's for setting plasma torch volts using the spindle PWM.

Ian

1303

General Mach Discussion / Re: Recovering from hard drive crash THC300 settings

« on: May 04, 2011, 07:39:21 AM »

Ian, I did not have the spindle relay function enabled but I enabled it and set it to output#1. I still have to response from the THC.  I reloaded my 2nd port driver last night and it says its working. Anything else to look for?

OK but leave this enabled and set to output1 - because even when you find the problem the torch won't fire either from the button or from an M3 if you don't. It might say "Torch On" on the THC300 screen button but it's still a regular spindle start CW function (OEM 110) to Mach.

Switch to the diagnostics screen. What do you see happening to the output1 LED when you toggle the "spindle toggle" button?

Ian

1304

General Mach Discussion / Re: Homing position is not absolute

« on: May 04, 2011, 07:15:06 AM »

Burkhard - just a post script. I set up a temporary home switch on my system (turned the accel waaaaay down so I could measure things - I'm normally at 2500mm/s/s) and found one slight twist. I homed from a distance and noted where it stopped (I'll call this the ORIGINAL home point) and then moved closer to the switch (about half way) and then re-homed. Because of the switch hysteresis it actually travelled slightly FURTHER off the switch than I started from. I then just kept re-homing from wherever it finished, and this effect builds until eventually it gets back to the ORIGINAL home point. Of course once there it "settles" and returns there no matter how many times you re-home as we'd expect. I think the biggy though is (as you've said) - if you change your homing %speed then your home position WILL change.

Cheers

Ian

1305

General Mach Discussion / Re: Recovering from hard drive crash THC300 settings

« on: May 04, 2011, 05:06:33 AM »

you do have your spindle relay enabled and set to output1 in spindle setup right?

Ian

1306

General Mach Discussion / Re: Homing position is not absolute

« on: May 03, 2011, 10:08:30 AM »

Hi Burkhard

I'm darn sure your English is waaaaaaay better than my Deutsch 

CV - is so called "Constant Velocity" contouring. See 10.1.16 Path Control Modes in http://www.machsupport.com/docs/Mach3Mill_1.84.pdf

Cheers

Ian

1307

General Mach Discussion / Re: Homing position is not absolute

« on: May 03, 2011, 05:30:40 AM »

Hi Burkhard

I think we're agreed that this issue is amplified the lower the accel capabilities of the machine. Putting my practical hat on, I think the accel issue alone is probably going to prove your real problem. I don't know how far down the road you are with your build, but CV for example must be (or will be) a PITA. Although I put home and limits on machines I build for others, I don't have either on my own wood router and to be honest I've never missed them, but I'd be lost without CV and to get that to perform you need hot acceleration.

Just an (alternative) thought.

Ian

1308

General Mach Discussion / Re: Homing position is not absolute

« on: May 02, 2011, 01:02:18 PM »

Hiya Terry - Before I start we have to promise not to fall out on this one OK?  

I tried to argue the same point with ART. BUT after he explained how it actually worked and I spend days testing it, the results were that mach homing is NOT speed dependant, other than the time span of one step cycle(very very fast).

Shoulda argued harder. Do the SCOPE thing. Mach comes off the switch, slows down, stops and sets THAT position as home. It's not just a case of speed, it's more acceleration but obviously the two are linked.

Yes the final stopping point will change BUT not the actual trip point of the home switch. The trip point is where the home position is recorded not where the motion stops.

But what do you mean, IF Mach records the actual trip point somewhere, it would only be any use if it then moved BACK to that point before setting that as home - but it doesn't do that.

This is subtly different from G31 which does indeed store the trip point.

FWIW I've come up with these observations...

For a given acceleration and homing speed:

Let's call "D" the distance it takes to accelerate from rest to the homing speed.

If we commence homing at a distance from the switch greater than D then the homing position will be set at D from the switch.

If we commence homing at a distance from the switch LESS than D then the homing position will be set at that same position we started from.

If we reduce the homing speed but keep our accel the same then D will get smaller but the above will still hold.

However, once we reduce the homing speed to a level that requires NO acceleration curve, home will be set at the very step that deactivates the switch REGARDLESS of whether we start at, greater or less than D.

Increasing or decreasing acceleration just makes the above less and more obvious respectively.

Cheers

Ian

1309

General Mach Discussion / Re: Homing position is not absolute

« on: May 02, 2011, 03:56:32 AM »

Hi Burkhard

FWIW I think you've made a good catch and a quick scope of Mach's step stream and dir pin would tend to confirm you're correct.

I'd just make a couple of observations re: Gerry's method if he doesn't mind. The crux is that the second homing speed can be anything up to the maximum reliable speed that your axis can move without an acceleration curve. (a bit like the Z axis under THC control).

Also, I think there may be another issue. Whilst this method will allow the axis to stop on a dime the instant the switch deactivates on the backoff phase, depending on the type and quality of your switches this could mean you're setting home at the switch jitter zone. This could be an issue particularly if home and limit share a switch. Maybe at the end of the script, you could move some predefined constant distance further off the switch to counter this.

Ian

1310

General Mach Discussion / Re: Limit switch question

« on: April 30, 2011, 01:38:09 PM »

Hi - tick auto limitoverride on the settings screen.