Tormach limit switch question **FIXED**

GunsOfNavarone

GunsOfNavarone

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So you fellow Tormachers are very aware...I bought a used 440. Been very happy but one thing that I have noticed. If you jog an axis too fast, you can pass the soft limit and hit the hard stop. This is a huge problem on the X as I have a fixture plate which makes it a PIA to get the limit switch cover off. Anyway, today I thought I'd remove the fixture plate and remove about a pound of metal shavings out of T-slots and fixture plates holes. I stoned the table and cleaned it up. I thought I'd try and figure out the X axis issue. That is, if you jog the table all the way right (not screaming fast) the limit switch will soft stop. If you jog table all the way left, even creeping speed, the limit switch will hard stop. I prepared and had a new switch (though the left/right uses the same switch...uh-oh) I replaced it, no difference. I swapped the 2 wires on it...no difference.
Why would one direction on the SAME SWITCH/SAME AXIS soft stop and back off a tiny bit automatically, but the other direction stops and locks up (have to remove sensor block to get a reset)
I put a call into Tormach, guessing it will be awhile. In the mean time I thought I trace the wire back to the driver and make sure the wire has continuity. Other than that....I'm stumped.
 
OK, if this ever happens to anyone else, here's the fix;
The X must have 10" of travel. If you have the limits switch stops (dogs) too close in and the travel is under 10", its gonna freak when it hits the right side dog (as that is the 10" mark, the left side is 0) I moved the right side out as far as I can, now I was hitting end of travel, but still not 10". There was caked shavings under table packed and working as a hard stop. Cleaned that out and I got and extra .200. I moved the left side out until I just hit 10 inches.
Now when the table hits the right side stop, it stops, backs off and no hard reset just as the left side does!
The Tormach folks actually called me back in less than 24 hours and were super helpful. It's just reinforcing my feelings on the purchase. A used machine is going to need parts and support.
 
The soft limits in PathPilot are one of the neat things about the system. The controller recognizes the set limit and you can approach the limit at G0 speed and it will stop at the limit. Back off and resume operations. This occurs where running manually or a program.

The x and y far end limits are user configurable. On the MDI line type ADMIN SET_X_LIMIT or ADMIN SET_Y_LIMIT and then a value for the limit. Properly set, the only time you will hit the limit switches is with the initial referencing of the machine and you should never hit a hard stop. This is a good feature if you plan on setting a custom fixture plate or other fixture that might hard crash before the factory set soft limits are hit.

I have optical homing installed on my 770 because it is an order of magnitude more repeatable than the OEM microswitches. However, I left the OEM switches in the system as a fail safe. I have the microswitches set to trip about .030" before the hard stop and my optical system to trigger about .020" before the microswitches. My x soft limit is 14.350" and my y limit is -7.500" The x soft limit is actually .350" more than the specified travel.
 
So what you're saying RJ is....you had you the answer all along.... that's ok, I learned a bit more about the machine.
Clarify what you're saying about soft limits. My physical/mechanical X travel limit is 10". The dogs are also set to that limit. If I go into the MDI and set it for 8" instead, the machine will limit the machine within the steppers? I do have a fixture plate, that is what started this whole ordeal. I need as much as space as possible so setting the limit within the MDI line isn't necessary, but O would like the machine to soft limit me before the limit switches hit the dogs.
 
The hard stop is when the travel can go no further and the motor stalls. The limit switch mechanism is intended to err out the machine before you hit the hard stop. They also serve double duty as a means of referencing the machine, necessary for establishing the machine coordinates. In addition, once the machine is referenced. the PP software knows it cannot go past 0 on each axis and the set_x_limits or set_y limits determines the point that the machine cannot travel past. To that end, as it is approaching those points, it automatically starts a deceleration routine so the machine will not overshoot the points. Since the microswitches aren't activated, the machine hasn't erred out.

When you reference your machine, set your DRO to 0,0,0. Now move the respective axes until the limit switches are activated at the far end of travel. Note the DRO reading. Set your soft axis limits at slightly less than that position via the MDI This would be the maximum safe travel.

If is possible that you could extend the limits slightly beyond the factory settings.. This gets a little more complicated. It involves resetting the limit ramps on either end and measuring the travel, limit to limit and setting the software limits to slightly less.
 
There is a setting in PP in the "SETTINGS" tab that lets you turn off the limit switches. I don't know why you'd do that, but I would imagine someone on the CNCZONE Tormach forum has a good explanation. You can also go into the ADMIN settings and change your travel limits. I don't know the complete command off the top of my head, but it's been documented at CNCZONE.

As RJ mentioned, you might be able to get a little more travel by moving the limit switch stop. But then you have to change the total travel as PP "knows" how far it can go in each axis. That's something like 17" on my 1100. Guys will move the hard stop and gain 1/4", but the machine will still only move 17" unless you tell PP it can go a touch farther.

Bruce
 
So the limit switch bypass I found is handy when you have the situation I did. Because I was only moving 9.5" AND hitting my limit switch, my machine freaked out and locked up. The only way I could figure to unlock it was, to remove the dog and reset. That worked. Also, if you don't reference your machine and hit a limit switch, same thing, it locks up. I have learned the value of the limit switch on/off option, but a bit too late.
I'm not trying to get more travel, this was all because I needed to remove my fixture plate and clean the table and tram the head. Many issues happened after that.
All is good in the world, tram is great, vice is indicated in and ready to do some more cuttin'!
 
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