Summing Z axis on bridgeport

Hi all,
I have a interact1 with the quill under linuxcnc control, but more often of late, I'm hitting travel issues because the workpiece is larger than my travel with different tool lengths. So I'm considering putting the knee crank itself under linux cnc control for more travel rather than cranking it about manually and trying to fiddle everything in between touchoff's.
I'd like to if possible specify somehow that the quill is to be used in preference if the Z move is inside the limits, but move the knee for the extra component of the travel when the quill travel limits are to be exceeded. My quill has a ballscrew feed on it already and the knee is still the original handcrank one so wont be a ballscrew like the quill though it has gravity to reduce backlash... I have a spare axis driver hardware already in my cabinet (I was building a trunnion table but I've just bought a fixer upper full size vmc so it'll be going in that instead) and enough psu to run a extra 1700oz/inch stepper so I hope that's sufficient overhead with appropriate (to be worked out) gearing.

Can anyone point me at further reading on this subject? I've searched around but my google fu has failed me it seems.

Thanks
Phil

hi welcome
are you sure the connection of the motor wirer are Right
your description let me think you messed up on A+A- B+ B-
and ofcause did you use a low Microstepping
1/2 is best(400) 1/4 is good(800) and then it starts to loose Torque on speed

I think it is common when you have automation of both the knee and quill to control one as the Z axis and the other as the W. If you set the knee as the W, then you can adjust and control them separately as you wish. If you try to do it fully automatically with kinematics or something else, you risk it potentially doing something you might not want it to at some point in time.

Thanks for your response Todd, actually getting my cam toolchain and post to understand that Z is split into Z and W fills me with more dread than tinkering round with linuxcnc...
I may just keep the machine as is and just use it and focus my attention on the vmc as it will have a single means to move the head.

Depending on what you are doing the cam may not even need to know about it. If your cutting depth is typically within the range of the quill's stroke. You should only need to make up the difference between tools and cutting area with machine work coordinates and tool offsets with W on the knee.

Todd, that's similar to the current situation. In the cam software all the tools are set to the same length, then when loading the tool, gmoccapy auto touches them off to a toolsetter and this sets the true tool length for that instance, so linuxcnc manages the tool offsets automatically and the cam just provides controlled point the same for every tool.
But If the manual knee is moved by a stepper or cranked up and down, the z height config of the toolsetter & difference to z height of workpiece have to be reconfigured manually for the toolsetter automation to work correctly. if these values can be altered automatically on the fly from the result of a offset calculated from a knee position value that would make life a lot easier. Probably the manual crank/encoder will be quicker to do and actually get done in a reasonable time frame.

I'll read up more, thanks.

So I've been thinking more about this, and playing with my autoprobing setup and got it all working smooth and... I feel dumb. I already have a encoder that measures the height differences between movements and plumbs it into the offset calculation. The toolsetter.

Now I properly understand how gmoccapy touch off works, i.e, I have the height above the bed as a parameter, and the height above the bed of the toolsetter touch off mechanism. Nowhere is the bed height itself defined, and it measures this every tool change as part of the automation.
So I can call a tool change for a long tool, drop the knee down a few cranks without being precise about how far, as long as its enough to fit it in the travel, and when it touches off the tool, it does all the calculation to heights and offsets automatically.
Its really simple for this use case, and I've been testing it the past few days.

I only need to do more once I add a stepper to move the knee, and even then the toolsetter touch off will deal with precise positioning and I could do something like tell the knee to move and how far for a tool change if its over x length and let the toolsetter deal with it in travel.

No R8 Its on QC30, so swap R8 issues for having cheap tool holders come loose because the flange thickness doesn't conform to the QC specs. Or pay for genuine BE or German QC30 holders that don't have this issue.

The toolsetter is one of those generic ebay four wire ones and sits with its top 80mm above the bed on a mount and I could always mount it on a taller block to raise it up further if the occasion ever demands it.