Splitting an axis signal/Controlling more than 6 axis?

[Mtntop]

Here is the scenario.  A standard 3 axis router table with a 4th slaved to the X axis.  The gantry will have 3 routers mounted so that I can make 3 identical cuts at the same time.  This requires a Y and Z control for each of the three which brings the total control up to 8.
 Now the first two routers will take up the last 4 axis (Y,Z) that Mach can control.  But what about the last router?  Is there a way to split the signal of the last 2 channels as they leave the computer and run them into a seperate 2 axis system (power source, driver etc) to run these last router's Y&Z axis?  Remember the Ys and Z movements will all be identical.
  If this is possible what hardware do I need?  Just a way to split the wires to run to the seperate driver, power?
  
  Thanks in advance. Mtntop

I know how to do this mechanically, I'm looking to do it electronically.

[giannis121]

I have worked with 2 identical Z drives, as following:
From the parallel port a buffer state with 74HC244 (and 5V regulated power supply).
The output of the buffer directly to the pulse and direction inputs of the drives in parallel.
Enable switches (on the drives) will select the drive needed (or both).
Seperate home switches (and make 2 times Z homing), so the router heads will be at the same position.
Hope that helps...
Giannis

[rrc1962]

I tried that a while back with three small routers.  It worked but wasn't reliable enough.  I forget what I used for electronics, but it was a similar setup to what Giannis mentioned.  Missed steps now and then on one or more routers made it hard to keep them in sync.  I ended up using a belt to drive all three Z lead screws.   The mechanical route ended up being the most reliable and least expensive to implement.

[Mtntop]

Thanks for the info.  What was causing the missed steps?  Did you ever figure out what was causing the missed steps?  Electrical interference between the two routers maybe?
At least this gives me a place to start.

[rrc1962]

I never perused the issue.  The fact that (1) The motors could get out of sync and (2) The mechanical solution was far less expensive to implement was enough for me.  Since the machine never missed a beat other than this, my guess is that the step and direction signals were not coming out of my amplifier circuit accurately.  It may have been an easy fix, but I know that once I went to a single motor and drive driving all three routers, I never had another issue.  I always tend to over-engineer.  I think that was one of those times.  It was so much simpler, cheaper and more reliable to drive all three with one motor.

[giannis121]

Well, at the beginning i experienced loosing steps, but it was matter of bad grounding of the machine.

After connecting the common ground everywhere (computer, printed board, drives, bridge of machine),
the machine does not lose any step.

If the pusles are not strong enough, you can use common input to the buffer state and seperate outputs.
(See figure).

In my opinion the motors will never get out of sync, unless:
they dont have the same parameters in the drive units,
or if one drive unit fails to become enabled (or there is a damage).

To solve this matter, you can have an output from the drive (most of them have programmable outputs),
informing the computer to stop, whether there is a fault.

Good luck...

Giannis

[Mtntop]

Thanks Gianis121.
  The mechanical solution won't work in my case and it would be much harder to switch back to a single router when needed.  My table design has 2 steppers each for the X, Y and z so that takes care of 6 axis.  But if I can run each axis off of one signal split then I'm left with 3 free.  The plan in the future is to add 2 more axis to each router so that I would have 2 mirrored 5 axis machining heads.