[D_Turner]

I am completely new to Sinumerik controls. We are working on a Sinumerik 840D/MMC - 103 control from around 2002.
**edit - Just an FYI, this is on a 3-axis vertical mill**

I have successfully wrote a working program and understand most everything, but I am missing something when it comes to the Tool Offsets and how they work with setting your work offsets. Here is an explanation of what I have done(kinda long but wanted to provide enough details to understand what I HAVE tried):

I went into Parameters->Tool Offsets and on T1 I jogged the tip of the tool down to the table of the machine and used a 3" height gauge to position against table. I hit the Determine Offset(think this was the wording of it....not currently in front of machine) softkey. Here I hit Calculate softkey and it gave me a Tool Offset of -14.1(rounded decimal points off for simplicity). I changed the Reference value to 3(to adjust for the 3" height gauge under the tool tip) and did calculate again and it gave me a -17.1 in the tool offset. Okay, so far things were making sense. The tip of the T1 tool touching the top of the machine table is "-17.1" in MCS. I checked another drill in T2 and a shell mill in T3 in the same fashion and got similar values(something like -17.15 and -17.3) so everything still makes sense.

I wanted to be able to just use T1 to be able to determine my G54 Z offset in the offset screen. So I jog down to the top of my part that is clamped in a vice. I touch off on the top of the part just using a piece of paper as the feeler gauge. This is all under the jog screen under the 'Scratch' softkey function. I have the offset set to G54 and T1 shows to be active. I go to the Z offset location and press the yellow 'enter' key and it writes the MCS value of Z which is something like -12.1 to the Z offset table for G54. Just imagine a part in a vise 5" above the table hence the 5" difference in tool tip to table and tool tip to top of part in MCS values.

When I try to run my program using G54(-12.1) I get a Z soft limit areas which indicates to me something is wrong with the offset. So I decided to try entering the value of (-17.1,tool length value) - (-12.1,MCS value the control showed for the work offset) = -5.0 into the G54 Z offset and this -5.0 is to low. I then put in a +5.0 and now things are exactly where they should be in Z. This places the work coordinate system exactly where it is supposed to be and the program runs properly using this (tool length value - Top of part MCS value) in a + form for G54 Z offset.

So I am missing something with these Sinumerik controls and I am sure it is something simple. I tried putting a -17.1 in the Base Z0 softkey screen under Tool Offsets screen which represents the T1 offset. This actually makes the work offset value come out to a +5.0 when checking Z workset with T1 in scratch mode but this appears to me to not be the intended purpose of this because if T1 ever changes this number needs changing....and I also want to be able to check Z work offsets regardless of which tool # is in the spindle. This could create some unforseen headaches and potential mistakes.

So, my conclusion so far is I need to leave Base Z0 alone(set at 0) and figure out why when I am on the scratch screen and try to let the machine calculate the Z work offset it doesn't properly use Tool Length offset of the active tool.


My goal is to be able to set my tools off the machine table. Then be able to go into Jog->Scratch and then go to Z offset and hit the yellow enter key and the proper Z value load to the offset no matter the tool I am checking with as long as the correct tool # is "active" and not having to do math by hand. I know this has to be possible as every Fanuc/Haas/Heidenhain I have ever used properly calculates all this and saves the hassle and possible mistakes.

So now the million dollar question, what simple step am I missing on this Sinumerik 840D to get the PROPER Z Offset value to load to the table without pulling out the calculator and doing it by hand? Know of any step by step tutorials of the procedure anywhere for this old of a version of 840D?

Thanks for any advice!!

[pearrx123]

Hi, Is the tool length offset active? This is done by calling D1 for the tool in the spindle.

[D_Turner]

Inside a toolpath program I am calling a D1 to activate the tool length offset for the tool that I am currently machining with and that works properly.

Does the tool length offset not get activated automatically on the "Scratch" screen when setting the work offsets? There is a place in the top right of the Scratch screen that shows an active tool(tool in spindle). But I can't see where it actually uses this tool length offset in figuring out the Z work offset.
Should I try going to "MDA" and entering a D1 there and then coming back to "Scratch" and see if the numbers are different?

I am just having to do an extra manual calculation which seems unnecessary from previous experience with other controls.