Consider the gear boxes only have one flat spot not two.

I wasn't clear. While holding the pinion gear, I can rock the y-carriage back and forth exactly .015" - no more. The pinion gear rotates, but the motor shaft (my motors have dual shafts) does not. Further, my machine zeroes repeatably.

My steppers are not the OM steppers they are the less expensive fulling units with straight cut gears.

I said in an earlier thread the the fulling steppers have comparable backlash to the OM ones, but I no longer think that is the case.

If the motor shaft does not rotate and the pinion gear does then your set screws are not tight. The motor shaft should turn when the pinion gear turns. Maybe I am not understanding correctly.

Can you list your motors. I have not seen motors with two shafts but I am new to motors.

Thanks

Nils, many stepper motors are available with a option to have the shaft extend out of both ends of the motor - this is commonly used to add a sensor to provide feedback on the actual shaft motion / position and detect lost steps (*)

I think that Jeff is observing that at one end of his gearbox and motor combo, he can see the .015" motion occurring at the pinion connected to the gearbox, while at the other end, he's seeing no motion of the motor shaft. That is a good description of backlash in the gearbox.

(*) Whenever this comes up, there's a temptation to think "Cool, I should have that to detect missed steps." However, the reality is, if your machine is missing steps, the workpiece is already ruined. There's nothing useful to do with this information, other than rework your machine / software so that it never misses steps. So it's an expensive boondoggle, really, in our application.

Yes Brad, exactly.

The motors were an inexpensive eBay find, I wouldn't have ordinarily purchased dual shaft motors.

I hadn't really intended to put encoders on those shafts, but it is my understanding that Mach and EMC can use that feedback to stop the machine immediately when it detects mismatch before it becomes severe.

I know this is an older thread but I to have seen the backlash in the PK296A2A-SG7.2. All of mine have between 9.5 and 10.3 thousandths. They probably have less than 90 hours runtime on them with no crashes. I have not noticed any problems with circles or carvings but on complex carvings with 3d models inset in a dish you can tell there is backlash. I measured it, and used Mach's backlash comp to eliminate it. I think the PK296A2A-SG7.2 are a great motor for the x and y but not for the Z. Just my 2 cents.

What were the numbers you entered int he Mach3 backlash settings Pete?

That is best done with a dial indicator and use the jog with step only to find your true backlash. Mine was 0.009" (0.2286mm). I will say it does work but it is not the best solution to the problem. Remember all gearboxes have some backlash, they cannot be absolute. They are not a wave generator. So 9 thousands was my setting but I then converted to belt drive to truly minimize it.