EMCO Compact 5 lathe with Mach3

[crystallattice]

Hi guys,

My friend has a EMCO Compact 5 lathe which I have equiped with Mach3 using some Gecko's and the original steppers. We can turn pars but the X demensions were not perfect. I did not know the "steps per mm" so we played around to get it to work. It turned out to about 392 or so. I've set the feed max to about 150 and only go up to about 100.

The problem we have been experiencing is that if you run the same code again and again the parts get smaller! I wrote some G code to turn two steps on a part and on every run of the code the steps are fairly accurate except that the part diameter gets smaller every time....

The DRO tells us that the machine is at x5,z5 as I have told it to do in the code. We set the 0,0 point on the tip of the part and made it use absolute values. When the code finished the DRO says it is at x5,z5 but in actual fact it is more like x-3,z0 although the Z does lose its accuracy over a few repeats of the code.

We first started with a fillet wizard and thought that the wizard was faulty but that was not the case. I think if the steppers were loosing steps then it would happen in both directions of X not just the X-???

Any help will be greatly appreciated!

Regards

[Hood]

Try increasing the pulse width and direction prechange on the motor tuning page to 5 and see if that helps
Hood

[RICH]

You can use Mach to assist you in finding the steps per unit. That feature is only available in the Mill screen. So open the mill screen, configure the motor same as in turn, click the Settings tab ( alt 6) and you will see just above the reset button Set steps per unit. Click on the button, in the fly out you will be asked to put a move in and again asked how far it moved, Mach then calculates the chnage in steps per unit, after the move,when the axis move is correct you will have the correct steps per unit. Make note of the steps per unit value and put that in Turn.
RICH

[crystallattice]

Thanks Guys,

These are some very useful replies. When I next go to my friend I'll try it and see what happens. Any explanation as to why it only happens in one "direction", if one may call it that? My theory is that if the stepper is losing steps it will do so in the X+ and the X- and thus almost cancel itself out?

Regards

[Hood]

It could be either the direction prechange or could even be you have the active state of the Dir set wrong for your drives. If you reverse the active state of the Dir pin in Ports and Pins, motor setup it may help. If you do that your motor will be running the wrong way so  you will need to go to Config menu then Homing and Limits and change the Reverse setting for that axis.
Hood

[crystallattice]

Thanks Hood,

Ok will check that, but bear in mind that the stepper is going in the right direction. It is just as if during a Gcode run it loses its position in the X axis and always in the same direction. Like I mentioned, if you make a part and run the code again it takes more material off, and again and again.... eventually you have no part left!

The reason we converted the EMCO was because we could not get the Gcode to repeat as it would not "remember" the code when you pressed rewind. I feel that we have not really made any improvements with the conversion yet.... It remembers the code but not the position....

Does the Mach manual explain the prechange and the effects of the active state and reverse settings? I would like to read up on it to check the logic behind it.

Regards

[Hood]

The Dir state will depend on your drives, some dont really care but some need it to be either Hi or Lo, not sure about the Geckos as its been a long time (7yrs) since I set them up in the Bridgeport.
 It going in the right direction at the moment has no bearing on whether you have it set right or not as there are other factors that can control which direction the motor moves, these are obviously the Dir state, the Reverse setting in Homing and Limits and lastly the motor wiring itself. The two that can be used for Dir change, if it is wrong, are the latter two and the former should be kept at the manufactures recommended setting. Obviously changing the wiring is not so easy as choosing the Reverse setting in the software so the reverse setting is the usual one that is used.

The Dir Prechange setting could also be your problem as if its not set high enough for your drives then it may be missed until the next step by the drive so again could lead to accuracy issues. I always had my Geckos set to zero for both pulse width and  dir but it all depends on the computer you have. Zero is obviously not zero and the actual time will depend on the latency of your computer, so setting zero on one computer may be the equivalent of setting 2 on another with less latency.


Hood