I have just built a new CNC machine and am using a Chinese BOB 5 axis. windows 7, 32 bit with the LPT port and MACH 3

X, Z, Y(SLAVE A) so two motors on Y axis

All the axis work when tuned, however I find when jogging the Y axis slave axis will stall and in a very strange way.

if I have jogged the x axis, in one direction, the slave side of the Y axis will not jog (or is in step mode) until I have pressed jog in the opposite direction on the X axis.

I'm am not a total newbie to this as I've built CNC a machine before but not one with a slaved axis.

*ANY* ideas welcome as I am having trouble searching the forum to find anything

Regards

Les

pins(s/d)    axis
2-3           X
4-5           Y
6-7           Z
8-9           A (not angular)

this is so weird I have video but cant upload, if I move X++ then Y/A -- it wont work
if I move X++ then X-- then Y/A-- its fine, also does this from the jog screen

I'd try a reinstall, with the latest version of Mach3.

I'm on my third pc 

Hi,
if its not a software or PC issue, and it sounds like you have taken steps to prove that then I would suspect that its a fault of the BoB or
stepper drivers.

When working correctly  do the Y and slave A axis motors have to rotate in opposite directions?

The reason I ask is because most  simple BoB's have open collector outputs. Thus one direction will be signaled by the pull-up (or alternately the pull-down)
resistor, which may be of such a high resistance that the input opto-coupler of the stepper drive misses it. Thus  your steppers may rotate with authority
it one direction but with very much less authority in the other.

What model BoB are you using? Can you post a representative circuit diagram of the BoB outputs?
What model stepper drivers are you using? Can you post a representative circuit diagram of its input circuits?

If it sounds confusing I could probably come up with some simple circuit diagrams which would illustrate the problem. Let me know.

Craig

Thanks Craig,

I'm using this type of BOB, I do have another (always buy spares), I will try that next

https://warp9td.com/images/BOB_Vendors/StepperOnline/ST-V2.pdf

Hi,
unfortunately the manual does not discuss the output circuits at all. There is no way of telling
whether they are open collector or totem pole types. If you can read the buffer ICs part number
that would tell you.

It may or may not interest you given that you have bought spares (are they that rubbishy that you need spares?) to have
a look at the Homann Designs MB02 that I use. If you download the manual you'll find Peter Homan has detailed how the outputs are
driven and you are not left to guess.

https://www.homanndesigns.com/index.php?main_page=product_info&cPath=54_22&products_id=59&zenid=11oq21v419cogk8bc3fiaoren1

I have attached two pics using typical values that you might find in an open collector output BoB. The first shows sinking current. When the output transistor is
ON or conducting it sinks current from the stepper drive via the opto LED and the curent limit resistor. With 5V supplies the opto LED current is about
5 / 470 =10mA, easily enough to signal across the opto barrier. The second pic show the same BoB but sourcing current to the stepper driver.
When the output tranistor is OFF then the current flow from the 5V supply through the pullup resistor, thought the current limit resistor , through the opto LED
to 0V. The opto current is only  5 /(10000 +470) =0.5mA which is not really enough. Cheap stepper drive optos require 5-10mA to signal reliably.

I have probably, and deliberately, portrayed a worst case scenario to illustrate a potential problem. In absence of suitable documentation about
your BoBs outputs and your stepper driver inputs you can only guess. Unfortunately while these subtle details are often missed by documentation
what with the wide variance of design/manufacturing standards throughout the CNC world clashes of this type are common.

Unless you have some decent test gear and the knowledge to use it all you can do is guess.

Craig

Well well well, I think it may have been down to two possibilities

1, the board as soon as it was changed I never saw the same issue but at this stage I also did not have the limits switches connected
2, there was a very dodgy connection on the x axis motor, which might explain why I only saw this when moving the x axis?

I will let you know

thanks for the help

ALL good here, I think is was dodgy connection on the X