X and Y axis direction Problems

Probably posted this in the wrong section but I'm new. I have a new Sherline 5400 Mill running under Ubuntu 2.6.32 and Linuxcnc 2.5 on an HP with 16mb ram thru a Sherline 8760 controller.
Problem is that the system seems to loose track of what it's doing and seems to 'add' minus movements to plus movements.
In other words when it should be moving 1" in positive X and then 1" in minus X it moves 2" in positive X if that makes any sense. Same happens in the Y axis. I'm using gcode that runs okay on other machines and thru backplotters so I don't think it's the code. Replaced the cables. Retightened the couplers. checked the drive screws and everything looks great.
I did use the search function and found one thread describing a similar problem but there was no resolution. As it now stands the machine is non-functional for me. Hoping somebody can point me in the right direction.

It sounds like the direction pins are not connected correctly or are not working. That is where you should start looking, IMHO

That's the first thing I suspected so I bought new cables. When the machine is first booted I can jog in X and Y properly but after a program is terminated the X axis always jogs in positive direction even if told to go negative. The z axis always works correctly and the y-axis sometimes works and sometimes doesn't. I don't think it's an ini problem as the ini on our smithy machine looks similar to that for the Sherline. I guess I'll have to buy a different controller and try that out.

can you clarify what you mean by program terminated ! , if the jog works fine then it should always work correctly , i'll suspect a configuration problem , post your hal and ini files
alternatively you have a direction pin perhaps reversed , but this would not account for the axis moving correctly at first .

you say the Y axis sometime works and then does not .. this points to a bad connection on the direction pin , or if an enable pin is used check that too
what controller are you using ?

Further searches on the net seem to point to a parallel port signal problem with newer computers causing this problem which aparantly is fairly common. Found out that Sherline now has a signal booster to add to the lpt port as a fix so I'll try that route

if you can point to the information , perhaps we can confirm this is the problem your experiencing

I had a drive and motor behave like this once because of a bad connection between the motor and drive. (plug was not seated properly)

Please post your config files, so we can look at them and see if it is a setup problem...those files tells us an awful lot that we need to know to help you troubleshoot your problem my friend...


Regards,

Will

I didn't save any of the urls for the forum threads I read but I was surprised how common the problem is, more so for Mach3 users than EMC users. Anyway here's a product description of the device. Sherline doesn't have any pictures or specs for the unit they sell but I suppose they're all alike.
www.cnc4pc.com/Store/osc/product_info.php?products_id=203
I'll update my situation when the part comes in. I'm sure it's not a config problem since I've been using EMC2 for quite a while on other machines and am fairly familiar with the setups.