I should have labeled both ends of the tube with X and Y, not just one end, sorry for the confusion.  Z would be the probe positioning along the bore of the tube that is mechanically tied to both XY tables.
I need support for the Z axis on both ends given the length of the tube.

I'll try once more - a STANDARD XYZ gantry machine supports AND drives the gantry at BOTH ends. Try googling "gantry router pictures".

OK - I think I see where the confusion started here.

In your original post you started off saying:

I need someone to point me in the right direction for controlling two stepper motors on one axis and keeping them in sync.

So far so good - this is the way you need to go (as I've been saying) - you've been given the answer already - slaving.

But then for some reason which I don't understand - you said:

I am building 2 XY tables that will be separated and I need them to work in sync.

I think I can see the target here - you want to build a pipe bore scanner that has a travelling head on a support that runs up and down the centre of the pipe?

You want to control the vertical and horizontal position of the scanner within the bore?

If so then its an interesting project

In my mind, X axis is the scanner head, Y axis would be towards/away from centre of pipe, Z axis is up/down from centre of pipe. This would be with my view having the pipe running left to right.

I would have my X on a removable support track, probably belt driven or nylon rack & pinion for weight saving, this would simply sit in two supports, one at each end and have both ends running slaved Y & Z motors so they track each other and keep the X axis / scanner support true to the bore of the pipe.

Am I following?

How big is the pipe?

It just sounds like two vertical X/Y tables facing each other and running slaved motors on both axes, apart from the mechanics, probably quite easy to do?

Obviously all we need is a travelling linear device - could be a trapezoidal screw in the vertical plane running on a linear rail, doesn't sound like there is a need for any serious rigidity or speed here. No idea how fast the scanner runs though??

Just thinking out loud

Quote from: thedude on February 28, 2016, 04:09:45 PM

Picture a 12 in DIA tube, 6 ft. long with an X-Y table at each end that will position a bar in the tube.  A probe runs along the bar (Z axis)
to scan the inside of the tube, thus mapping the magnetic field.  Positioning on X, Y, and Z.

Why do you need TWO XY tables for this?

An XY table cannot support a 6' long bar and hold much accuracy given the sag of the bar.....

Your labeling is probably guided by your familiarity with lathes. But if you swap the labeling for X and Z you have a standard XYZ gantry layout. Two slaved motors for Y and single X and Z. Sorry - I don't see a problem here. All pretty bog standard stuff. What am I missing?

Nope,, my labeling comes from the physicists that calculate the effect on the beam line from the magnetic fields.  They want the thousands of data points to be X and Y perpendicular to the field, (Along the radius) and for Z (along the axial bore) to be the field axially along the bore tube.
Oh I'm sure this is standard stuff to most folks on here.  Which is why I posted my questions on here.  I have always received great answers and alternative options to my projects from all the helpful folks on this forum. 

So Glad to hear that you already have the knowledge to build a project like this, but since I have questions to learn and gain the same knowledge, I appreciate everyone's help thus far.

I could ask you,,,  Why would you not label the bore of a magnet "Z"?  But I won't ask you that.

I'll try once more - a STANDARD XYZ gantry machine supports AND drives the gantry at BOTH ends. Try googling "gantry router pictures".

I'm not building a simple gantry whereas the Z...  "Head (spindle, plasma, router, laser) has a travel of a few inches....  read previous posts.
Sorry that you keep trying, but so far, everyone else gets it as I've got some great advice so far from them.

OK - I think I see where the confusion started here.

In your original post you started off saying:

Quote from: thedude on February 18, 2016, 06:16:21 PM

I need someone to point me in the right direction for controlling two stepper motors on one axis and keeping them in sync.

So far so good - this is the way you need to go (as I've been saying) - you've been given the answer already - slaving.

But then for some reason which I don't understand - you said:

Quote from: thedude on February 18, 2016, 06:16:21 PM

I am building 2 XY tables that will be separated and I need them to work in sync.

Whew.... ok.. again,,  In order to carry a 6' long bar inside a 6' long tube,,  I'm pretty sure I would need to support it on both ends, and that would mean I would need two XY tables working in sink as slaves to carry this bar as ostie answered for me in reply #3 and I thanked him in reply #5.  (thanks again ostie)......  then other posters offered alternative suggestions which I've given some thought,,, replied questions, got some feedback,   ya know like how forums do, overall, great dialog.  So far I have been helped greatly and I'm moving forward with my project because of it!!!  I love this forum!
So if your only going to offer options in the form of mild insults with no substance sorry, I'll focus on the others mentioned before.

Whew,, that was a chore.... Ok,, now back to the learning and productivity...

Thanks again,, and again all, (most),,  And I'm moving forward learning the way to expand beyond 4 axis.  I'm going to build a general schematic from what I've learned so far from you guys to look at and welcome any comments,, like to get your thoughts on IF I'm on the right track so far.  

Thanks again all.

TheDude.

I think I can see the target here - you want to build a pipe bore scanner that has a travelling head on a support that runs up and down the centre of the pipe?

You want to control the vertical and horizontal position of the scanner within the bore?

If so then its an interesting project

In my mind, X axis is the scanner head, Y axis would be towards/away from centre of pipe, Z axis is up/down from centre of pipe. This would be with my view having the pipe running left to right.

I would have my X on a removable support track, probably belt driven or nylon rack & pinion for weight saving, this would simply sit in two supports, one at each end and have both ends running slaved Y & Z motors so they track each other and keep the X axis / scanner support true to the bore of the pipe.

Am I following?

How big is the pipe?

It just sounds like two vertical X/Y tables facing each other and running slaved motors on both axes, apart from the mechanics, probably quite easy to do?

Obviously all we need is a travelling linear device - could be a trapezoidal screw in the vertical plane running on a linear rail, doesn't sound like there is a need for any serious rigidity or speed here. No idea how fast the scanner runs though??

Just thinking out loud

Absolutely accurate!!  Yes!  Other than the axis labeling, which is not standard I know,, but doesn't matter in my mind since I made my own control screen with MachScreen....  Due to the physicists requirement for X, Y and Z,,

The "Pipe",, or "Bore" of the magnet(s) is DIA 12-16 inches, (Designing to map different magnets).  Designing the XY tables to accommodate the variance in travel with a replaceable Z bar that carries the probe that will measure the field strength at each location along the length of the bore tube....  Thousands of them throughout the entire bore.