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  #1  
Old Thu 04 November 2010, 12:43
salewis
Just call me: Stan #67
 
Littleton, NC
United States of America
Z Home/Limit with ATO Plate....

Ok, I'm looking for some input/opinions on the following scenario....

Proximity switches on x/y used for home/ref (run softlimits in Mach3).
Pretty much use Auto-touch off (ato/atz) for the z.

My thoughts are that the proximity switch on the z is redundant (maybe even useless) for referencing the z axis as the reference z plane is set by the ato (top of stock, bottom of stock, top of table, etc).

Besides as has been noted/commented on before using a "bottom" limit on z gets complicated (bit length changes with tool change etc.)

Here's the scenario.... Hit ref. all. MM goes to the home positions on x/y, zeros the machine coordinates and all is well in the x/y planes, z is referenced "manually" by ato at tool change...

So why would I want/not want z limit? Invitation to think out loud with me!
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  #2  
Old Thu 04 November 2010, 15:44
Regnar
Just call me: Russell #69
 
Mobile, Alabama
United States of America
I think you would want the z axis limit to set your z axis soft limits. No soft limits on the Z would allow you to start a program that might be trying to route on the floor. Think deep plunge.

Most of the guys here home the z axis first so that when they home the x and y they dont have a tool crash with things on the table.

You never know what new invention might come out. If you take a look at Craftsman Quickrout they almost had it right. These would have allowed you to have a tool index that was repeatable. Hoss over on the cnczone was able to make them into a automatic tool change with some effort. With CNC machines making into more and more garages I would think that I would stick to the norm as much as possible.
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  #3  
Old Thu 04 November 2010, 16:11
salewis
Just call me: Stan #67
 
Littleton, NC
United States of America
sorry but I definitely would run soft limits.

Yep, reference the z or at least retract it out of the way....

If we were using a tool changer or at least something like cat/ntmb (?) tool holders, then I could see a bottom limit switch....that way the bottom of the bit would be the top of the table....

my thoughts are more about reference/home than limits but I don't want to get myself into a jam..

still thinking aloud....
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  #4  
Old Thu 04 November 2010, 18:37
Regnar
Just call me: Russell #69
 
Mobile, Alabama
United States of America
Z axis is referenced in positive direction (Up) and the ato touches off in the Negative (Down). This will give you the known axis travel length and allow for soft limits in the Z axis. Without it you would have to manually define the reference point by jogging the z axis up and hitting home on the machine coordinates. You would then switch to the program and do your ato reference to find that home (top of the surface).

Just doing the ATO after turning Mach3 on will not allow/ be active for soft limits in the Z axis.

To be truthful you dont need any of the proximity switches but if your going through all the trouble to wire 3 of them might as well do the 4th one as it will save you time every time you home your machine.
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  #5  
Old Thu 04 November 2010, 21:57
salewis
Just call me: Stan #67
 
Littleton, NC
United States of America
ah there it is... I knew I was overlooking something. I would have to manually reset the z, zero the z, then reset from the ato.

I was really only thinking of using 2 switches, since it seems that the z (top) kinda gets in the way of things (one side - gas cylinder, other side - motor bracket, back - dust collector.)

Not really sold on the "autosquare" function of Mach3 so 4 switches seems to not be needed.

This is why I'm thinking out loud as I have the provision (cables, switches, and relays) to accomplish 2 (x,y), 3 (x,y,z), or 4 (x, y, z, a) arrangements.
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  #6  
Old Thu 04 November 2010, 22:05
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
After ten years of operation and with five MM's currently in production, we still havn't felt inclined to fit any switches. Ten years ago there weren't any soft limits either, and they hadn't found their way onto our machines when I last looked.
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  #7  
Old Thu 04 November 2010, 22:15
salewis
Just call me: Stan #67
 
Littleton, NC
United States of America
Geez, even with softlimits I crash the bit....

Maybe I shouldn't rely so much on what I "think" I know

I'm trying to think through ways to restart a run. We've got some parts that could take 12-18 hours of running (3d molds, mind you that is start to finish with several bit changes).

I'd hate to ruin 10 hours of work because the power glitched. Yes, it is probably a longshot to restart the job and not ruin the work. But if I had a chance to not losing a piece of stock that is several hundred dollars, I need to take it.

Stan
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  #8  
Old Fri 05 November 2010, 00:24
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
If I had a power glitch, I don't think that I would trust the settings (proxy or soft limits) after that. But, we absolutely do trust the hard stops (or top surface) and can go back there if we want to.
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  #9  
Old Fri 05 November 2010, 07:01
salewis
Just call me: Stan #67
 
Littleton, NC
United States of America
After the power glitch, my restart process (what I am thinking through) would be the following:

1) manually move the z to top of travel (disengage the pininon and lift)
2) move the x/y to the hard stops (whatever is easiest - depends on distance)
3) power up machine
4) jog x/y off the hard stops a few inches (enough to close the proximity switches)
5) ref all, which would move y and then x to the proximity switch opening, clears the machine coords for x,y,z. Z does no moves.

at this point the x/y are at a "known" starting point very similar to starting at the hard stops... (hmmm, maybe I wasn't considering something here Gerald, more a bit later..)

6) reference the tool using the ATO.

Now at this point x/y and z are at a "known" starting point. Now deal with the Mach3/Gcode issues....

Now for the later..... restarting the machine on the stops (for x/y) and ato on the z will accomplish the same thing as far as a power glitch scenario is concerned..


This is why I like thinking aloud on the forum
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  #10  
Old Mon 08 November 2010, 17:53
KenC
Just call me: Ken
 
Klang
Malaysia
Thinking a loud too....
Mine started cutting since march & even though I've already purchased the proximity switches, I don't see the need to installl them in any time soon... I too don't trust the accuracy of proximity switches...
If I must reference my axis, I will definately install a physical position stopper & let the motor crash on it & loose a few steps. the I'll sleep well knowing it is physically accurate...
Its only my opinion, others may have their own...
I follow someone's track ( can't remember who or which thread there are just too many good advices everywhere in this forum ) by using a physical hole to reset tool position in case of power glitch or other mis-fortune, all I need to do is to push the tool bit into the hole with the power down & turn on the power when I'm happy that the tool bit is in as center as I could get them to be. then use ATO for the Z-axis & I'm back in business...
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