Backlash , Any suggestions ?

[philgiggins]

Tool geometry was incorrect on that toolpath, quite a mistake on my part. I had issues earlier that with steps as i have said before and that evening i thought ill try some circles it should be a good test and when they didnt join i just assumed .... and then posted it ... thats what i get for rushing it!
Thanks Philip

To me it just looks like the tool geometry is wrong, as Komatias said are you using a ballnose ?. If so and the software thinks it is an end mill, then you will be left with material like you have in the pictures on the end points of the circles. You can change to an endmill or you can simply tell the machine to overrun the toolpath by a few mm.

If those steps were caused by backlash you would see signs of it on the top and bottom of the circles on the direction change, but they look fine, so it looks to me like you just have the wrong settings in.

The reason the steps arent in a straight line is becasue i assume each vector is starting in opposite directions and that is just the bow wave effect pushing material infront of the bit, so you get that alternating step effect, if you ran the same program with all the startpoints and directions the same on the vectors you would still have the steps but they would all be in a straight line, either overrun the bit or use an endmill, and even then i would overrun a few mm.[/QUOTE]

[JAZZCNC]

Nothing to do with Mach3 so forget that.!! . . . . They are correct thou that those motors are more than good enough when run at that voltage and with those drives.
It's a common mistake to blame motors and go for larger motors only to find out they weren't the problem and now your performance is less.!!

If really is loosing steps(I don't think it is.!!) This will be down to setup with motors being over tuned or mechanical issue causing binding.
My own feeling is that some coupler or pulley is slipping.? Missed steps tend to be one of two states.? Incremental showing slowly over the course of job in tiny amounts. Or Random with no ryhm or reason.?
Incremental often comes from wrongly setup motors/drives. Random from Electrical noise or poor wiring.

Give us some info on the tuning for each axis. Also Info on the Pitch of pinions or screws etc.

[JAZZCNC]

There is one thing you can try that does happen and will cause a missed step on each directional change.
This happens when the Step Pulse is sent out on the wrong pulse edge to what the drive is set to expect. Resulting in the drive sees the Step pulse at the wrong time and one step or micro step is dropped on every direction change due to the fact step pulse comes before the direction pulse so it gets dropped.

This is easy tested by knocking some G-code to move each axis back n forth 1000's times then returning back to start. Make a mark before running and see if it returns to same mark after run the test.

If it doesn't then you have the Pulse edge set wrong. Easy fixed by changing the Active Lo setting in Motor tuning. ( Or some drives have a setting for this) This will then make your motors turn the wrong way so you'll have to go into Homing and limits and use the Reverse axis option.
People Often make the mistake of thinking swapping the Dir active low is for changing axis direction when it's not. It does but it's not correct way.

[philgiggins]

Hi Jazz,
The first thing i did was go around and check every relevant nut bolt and coupler ! They all seemed to be fine. But no harm to have another look.
Rack and Pinion are 20' pitch, pinion moves 94.2mm per revolution. Geared down by 5:1. Ball screw on Y is a 2010 its ran from a belt 1:1 (2 no 34-5M-15mm (TL) Timing Pulley) and on Z its a direct drive 2505,

I was having some resonance issues at slow speeds when i first started cutting so i upped the microstep setting on the driver and it helped a lot. I upped it to 4000. When i talked to company they suggested putting it back down to 800. I will try this on Monday.

Im pretty sure its not a binding issue. I can jog around no hassle as 10/12 m/min. Although maybe that could change under load. I need to eliminate it 1 thing at a time.

Acceleration is set to 100 ( this is low i think ) Max speed is set to 5m/min.
If i cut below 2.5m/min i have no issue its when i go above this the problem starts....

Thanks Philip

[paulus.v]

The easiest way to measure the backlash is with a dial indicator and manual jogging. There are a lot of vids on youtube about it.

To find out if you had lost steps, just program and run in the air a straight line for each axes and the same speed you did the circles (with a higher Z) and try to stop the movement by grabbing the Z axis with your hands and determine how much force is needed for the motors to start skipping. You can even measure it with a hook scale.