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Mach Discussion => General Mach Discussion => Topic started by: stirling on June 07, 2010, 06:30:21 AM

Title: Plasma Initial Height sensing - perceived wisdom?
Post by: stirling on June 07, 2010, 06:30:21 AM
Floating head.
G28.1 method OR G31 method?
Pro's vs Con's
Reason for asking is that G28.1 effectively prohibits using Ref All Axis to drive Z UP for homing so would seem a "strange" choice. My POST uses G28.1 and I'm thinking of changing it to G31. Or am I missing something?

Cheers

Ian
Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: manmeran on June 07, 2010, 07:42:52 AM
i use G31 and "probe" pin
if you want use G28.1 ,then you must configure Z home.

Amir
Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: BR549 on June 07, 2010, 08:42:05 PM
THe G31 seems to be the best bet.

The plasma will also NOT run G68 with the G28.1 style. G68 can be darn handy sometimes.
Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: stirling on June 08, 2010, 03:52:54 AM
Thanks Terry I'll give it a whirl. Must admit I've never really got why you would use G28.1 when G31 seems taylor made for the job. The only reason I was using it was because the "default" thc300 post is that way. Another look at the posts available and I found thc300-g31. Job done as long as G31 doesn't play up :-)

Cheers

Ian
Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: BR549 on June 08, 2010, 07:38:47 PM
HI Ian, I think they picked the G28.1 for its ease of use. Its motion is perfect it goes down till it hits the switch then back up to untrip the switch.

AND it works every time(;-) . Most Jet cutting is very basic 2d work with the z  just to get the head to the proper height. so really the homing is not missed.

BUT it looses some of the functions that I think are handy, such as z homing UP(;-) G68, softlimits for z ,etc


Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: stirling on June 09, 2010, 05:01:30 AM
Hi Terry, yes after thinking a bit more I can see the advantages of G28.1 over G31 and visa virsa. However neither actually do a complete job. G28.1 has the particular advantage that the switch can be both home and limit, wheras if you use G31 the switch can't afterwards take over as a limit (well AFAIK anyway). Then as you say G28.1 screws homing north, wheras G31 doesn't. Seems to me we could do with a bespoke floating head command that allows everything to work - i.e. IHS, *normal* homing and limits. Don't suppose there's a way to toggle homing direction at run time is there?
Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: poppabear on June 09, 2010, 09:11:44 AM
stirling,

   Look under VB Parameters and see if you can swap directions that way, I am not at the work comp, so can t look it up for you,
another option may be, Made 2 (or more), custom macros one that does the G 28 or 30 thing, a second one that flips the dirctions, or sends a VarifySingleAxis(2) command....

scott
Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: BR549 on June 09, 2010, 09:16:32 AM
well limits are not a problem as the floating head does not contain the limit switches just the home switch for the TOM routine.

HUM let me think on this one for a while.

IT really would be nice to have a specific TOM gcode for JET cutting.

BUT the G31 seems to be the best OVERALL solution. and it allows the G28.1 to function normally, that way you can still have softlimits in z,the g68 works. G30 home is where it is suppose to be for safety reasons,etc,etc

both work and both have their quirks(;-)
Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: BR549 on June 09, 2010, 09:43:18 AM
HIYA Scott, The general Idea is to stay inside of Gcode. That way the CAM does what it needs to do directly AND it works for everyone.

IF we run a macro THEN everyone must be supplied the  macro.

Must operators do NOT want to fiddle with macro code they just want to cut metal as simply as possible.

(;-)
Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: stirling on June 09, 2010, 01:20:25 PM
Thanks both - I'll take a look asap - I'm a bit otherwise involved for the next couple of days.

Cheers

Ian
Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: stirling on June 13, 2010, 04:21:03 AM
Hi Scott - tried your suggestions and a few ideas of my own but haven't been able to get anything that works. I can home down with G28.1 and up with RefAllHome but can't set the position right. i.e. home pos is home pos so it's zero (or whatever) at the bottom and the same at the top - so no real use. I'm stumped I think. Looks like if you want a "proper" homing action then G31 is the only way to go for IHS.

Ian
Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: poppabear on June 14, 2010, 07:31:39 AM
I suspect I dont understand what you want it to do then? If you can would you mind posting exactly what you want it to do, and the order of it? Mabey, (or mabey not), I can try and lend a better or more useful hand to your prob.

I know you guys dont like, or want macros, but Let me ask you this. Would you want a "Custom Plugin" solution? OR mabey add some VB code to an already existing OEM M Code....  I just dont think you can get around without doing some custom stuff........  IF I understand correctly what your wanted, which mabey I dont.

scott
Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: stirling on June 15, 2010, 07:39:48 AM
Hi Scott - personally I'm not against any method of doing this at the moment. I just want to see if it can be done. Actually I have a couple more ideas that I will try but any help is much appreciated. Without going into all the ins and outs of using either G31 or G28.1 for inital height sensing here's a short version of your mission should you decide to accept it. Imagine an axis with a home switch at each end. Now if you command a G28.1, it homes to one switch and sets that position to be 0. If on the other hand you press the RefAllHome button, it homes to the other switch and sets that position to (say) 100. i.e. you have two homes, one at each end of the axis.

Cheers

Ian
Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: poppabear on June 15, 2010, 08:21:04 AM
ahhh, well if that is the case and the VB params wont allow you to switch homing axis directions, then I would do it in a plugin and use a custom macro that sends a "Notifyplugins(#####)" to key the plugin to switch the homing direction of that axis............

at least that would seem to be an "Easier" answer, since standard methods (i.e. Mach Specific VB appear to fail? in this area).

scott
Title: Re: Plasma Initial Height sensing - perceived wisdom?
Post by: stirling on June 23, 2010, 06:02:05 AM
Hi Scott - sorry it's taken a while to get back. I now have a macro that I THINK does what's needed - we'll see. I've posted it over in the VB forum. http://www.machsupport.com/forum/index.php/topic,15182.0.html (http://www.machsupport.com/forum/index.php/topic,15182.0.html)

Cheers

Ian