Is This a Fanuc Soft Limit Parameters Issue or Something Else?

[AmericanMaker]

My VMC is a Sharp SV-2412. It has 24” of travel in X, 12” of travel in Y, and 18” of travel in Z. When I jog to the positive and negative X/Y/Z limits with my jog wheel (set at x1 to travel in tenths), I’m expecting to see these relative/absolute position values when I hit the limits (or at least when the machine is homed):

X: +12 / -12
Y: +6 / -6
Z: +18 / 0.

Instead I am seeing the numbers written below on the blue tape. And when added together:

X: 12.5786 + 11.5944 = 24.173 (0.173" over expected travel)
Y: 6.5487 + 5.4197 = 11.9684 (-0.0316" under expected travel)
Z: 16.6826 + 1.5848 = 18.2674 (0.2674" over expected travel)

And when I home the machine the relative/absolute position values seem wrong (see the first Fanuc screenshot) and I can jog beyond those relative/absolute position numbers when my jog wheel is set at x1 to travel in tenths (see the second Fanuc screenshot).

Am I misunderstanding how this works? Is this a soft limit parameters issue? Or is it another issue?

Thanks!

 

[13engines]

Incremental or Absolute machine?

 

[Garwood]

Incremental or Absolute machine?

OP may not know the difference. Abs machines have powered encoders so they never lose position. Abs machines do not need to be homed when you turn them on. Incremental machines set each axis' base position off an encoder strobe after a home switch is tripped.

 

[Vancbiker]

In a previous thread we determined via parameter settings that the OP’s machine has incremental encoders. The zero return point is not the same as the overtravel position.

 

[AmericanMaker]

OP may not know the difference. Abs machines have powered encoders so they never lose position. Abs machines do not need to be homed when you turn them on. Incremental machines set each axis' base position off an encoder strobe after a home switch is tripped.

OP did not know the difference, but based on the comments by @Garwood and @Vancbiker, and the fact that I have to ZRTN the machine before I can use it, I now believe it is an incremental machine.

 

[13engines]

To the best of my knowledge... On an Incremental machine, centering your travels equally from center travel would take a combination of perfectly set Grid Shifts, and the physical location settings/adjustments of your Hard Overtravel Trip Dogs. If ever a Servo or it's potential Timing Belt has been removed and the Servo or ballscrew rotated, you would loose the factory settings. And of course, if ever the Parameters were lost.

One would also expect a small amount of travel beyond the Book Spec amount given by the Manufacture. That amount of overtravel would be slightly larger when reached at a Rapid rate as opposed to sneaking up on it a tenth at a time.

BTW - whenever you're dealing with Grid Shift and Default Machine Settings, keep your eyes glued mainly on the Machine Coordinate Display. That is your Master. All things like Absolute & Relative, Tool Offsets, you name it, are derived from that unflinching set of numbers.

I'm not sure if Soft Overtravel settings exist on Incremental machines. They may be set or referred to as Stored Stroke Check which are set by Parameter. I think this function is also sold as an option, so you might not have it. (I might have that wrong.)

 

[AmericanMaker]

Out of curiosity, tonight I scrolled through the parameters on my control. To my surprise I found this ...


Those are the same coordinates I see when I zero the machine ...


Apparently one can use parameters 1221-1226 to set default work zero offsets (G54-G59) and then rapid traverse to them with XYZ set to zero like so ... G00 G90 G54 X0 Y0 Z0. The previous owner of the machine set all seven of the work zero offset parameters with different values. I guess this is how they handled setups of repeat jobs for the same part(s).

 

[dandrummerman21]

Those work zero parameters are the same values that are in the work offsets page. That's where they are stored.


Your machine will have soft overtravel limits in the parameters. Parameters 1320 and 1321 are your positive and negative limits. You may be able to adjust them to be slightly higher to squeeze out more travel. But be careful to avoid crushing way covers or hitting hard overtravel switches.


Those values in 1320/1321 are likely metric, you might have to convert them to inches by dividing by 25400 or 254000 or similar


I would bet that service, such as thrust bearing replacement or home switch replacement has happened, and the "home" is a tad off when it comes to your expected travel in each direction. As long as you can home it repeatably, it makes no difference.

 

[dandrummerman21]

I also didn't mention, since this is what seems to be the confusion you had; As 13engines explained above, keep a look at the "machine coordinates" on your position page. Not the absolute or relative.

Generally speaking, the absolute will default to where G54 is set to when you turn the machine on. When you have a different coordinate set in your program, like G55, it will show your absolute position compared to where G55 is. Depending on your parameter settings, hitting reset will default "absolute" back to G54, although you can change a parameter to make it display your position relative to the last coordinate that the machine had active.

But if you want to know where you are compared to home such as when you are setting work coordinates with an edgefinder or indicator, always look at the machine coordinate display.

 

[AmericanMaker]

Those work zero parameters are the same values that are in the work offsets page. That's where they are stored.

Ahhh ... that makes sense.

Your machine will have soft overtravel limits in the parameters. Parameters 1320 and 1321 are your positive and negative limits. You may be able to adjust them to be slightly higher to squeeze out more travel. But be careful to avoid crushing way covers or hitting hard overtravel switches.

I did some reading on stroke limits last night so I theoretically understand the purpose behind the numbers. After, I looked up those parameters on my machine. Now I'm trying to visualize how these values are affecting the current travel before I edit them.


Or maybe I'll just stop nerding out and leave them as is. But I am really enjoying learning as much as I can about the VMC.

 

[AmericanMaker]

I also didn't mention, since this is what seems to be the confusion you had; As 13engines explained above, keep a look at the "machine coordinates" on your position page. Not the absolute or relative.

But if you want to know where you are compared to home such as when you are setting work coordinates with an edge finder or indicator, always look at the machine coordinate display.

That is helpful, will do.

 

[dandrummerman21]

Ahhh ... that makes sense.

I did some reading on stroke limits last night so I theoretically understand the purpose behind the numbers. After, I looked up those parameters on my machine. Now I'm trying to visualize how these values are affecting the current travel before I edit them.
View attachment 386119View attachment 386120

Or maybe I'll just stop nerding out and leave them as is. But I am really enjoying learning as much as I can about the VMC.

Those values are metric. So your machine can go 2mm (.0781") in the positive direction for all 3 axis, and can go 612,302, and 462mm in the negative direction. Those distances are measured from home. If you try to exceed those distances, the machine gives you a soft overtravel alarm.

if you change those numbers to larger numbers, you may be able to move further, but you're limited to however far you can go before hitting something. Whether that's the end of the ballscrew, some solid stops, or switches that basically put the machine into an e-stop condition until you get off of them, is up to the machine builder.

I wouldn't edit them unless you need to squeeze out another .100" of travel for whatever part you're machining.

The machine behind my desk is a "1300 mm machine" which means it should only go about 1300mm or 51.18" or so in the X direction. But we have extended the travels by moving the hard overtravel switches, and editing the soft limit parameters, so we now have 55.8" of travel in X.

 

[AmericanMaker]

I wouldn't edit them unless you need to squeeze out another .100" of travel for whatever part you're machining.

Agreed! I'm just getting started and have lots to learn. I don't think another .100" of travel is my biggest concern right now.

But this was very helpful in better understanding my machine and the Fanuc control. When I was first got the machine I was really intimidated by the Fanuc control. I guess I spent too much time watching Haas videos. But I am becoming more and more comfortable with it. This forum has been a huge help to me. Thanks for all your replies.

 

[Garwood]

Something worth mentioning is that there are lots of Fanuc manuals that cover your machine. If you like learning about it you might grab a few. The parameter and connection manual for your control is very useful. The drive manuals for spindles and servos.

You won't ever need 90% of what is in them, but they have some treasures inside if you skim through them. And they are often on Ebay for $20-$40 each or free pdfs are out there too.

 

[13engines]

The OP reminds me of when I got my first VMC. An OM. It had all these numbers still present in the Work and Tool Offset pages. I spent a few months rebuilding the machine and never touched them, as I wasn't sure what they were or how important. It wasn't until I was ready to do something that I had decide what to do about all these numbers.

So happens that my long time buddy from grade school had a next door neighbor who ran an OM Supermax. He came over for about an hour and gave me what is the totality of my CNC training that I didn't teach myself. Anyway...the first thing he did was start deleting all the offsets I'd been blindly saving. (As my jaw was dropping)

So my point to the OP is... Clear all your Work and Tool offsets. They are meaningless to anything you've got going on. And again I want to stress the importance of the Machine Coordinates Display. Any number you will type in or perhaps set using Z EOB INPUT (Tool offset setting on OM) will be directly and correctly illustrated by the numbers in the Machine Coordinate Display. No other Position Display can promise that. I can honestly say that in all my years of CNC work, I have never even touched or purposely looked at the Relative Display, and only watch the Absolute Display when I'm bored and want something to watch as the machine runs. Distance To Go and the Machine Coordinate Display are the only gods I bow too. Your CNC life may differ, but just sayin.

Garwood is also right about the books. You'd be surprise at all you can learn and all the tid bits and tricks you'll run across that you never knew your machine could do. I bring piles of Fanuc manuals on vacation to fill some of the down time. A sickness for sure but...

 

[AmericanMaker]

So my point to the OP is... Clear all your Work and Tool offsets

That's exactly what I did once I realized what I was looking at.

I want to stress the importance of the Machine Coordinates Display.

The Machine Coordinates Display and Distance To Go will get all my attention.

Garwood is also right about the books.

I spent days looking for every PDF I could find on my Sharp VMC and the Fanuc 0i-MD control. I may have gone a little overboard. Eventually I will sort out what I don't need. The ones I starred are what I pay attention to most. The Sharp SV-2412 is actually a First MVC-300 VMC so I found those manuals too.

 

[13engines]

That's some list. And I thought I had a folder full. :-)

Unless you like insanely deep rabbit holes, I'd stay away from most of them until you get your feet good and wet.

Reiteration and expansion of what Garwood said.

If the machine is working fine. Start here.
Any and all Machine Tool Builders Manuals. Programing/Maintenance/ Parts/Etc.

Then when you have time:

Fanuc: (Only those specific to your exact control/servo model(s))

Operations and Maintenance Handbook (Super Handy. Smaller physical size)
Operators Manual
Maintenance Manual
Parameters Manual
Connection Manual (Function)
Connection Manual (Hardware)
Control Motor Maintenance Manual (Get the one that matches your Servo Type)
Control Motor Parameter Manual (Same as above)
AC Spindle Motor (Params and Maint.) Not too important as you likely won't ever touch these settings.

Have fun...