Upgrade? Chinese CNC Machine

[Ricardoco]

Why not get Mach to do the work for you ? go into "Settings tab", just above the reset button "set steps per unit" start with X enter 100 measure how far it moved then tell it how far it moved and will set steps up for you.
Do the same for all axis do a test cut if not correct go though it again.

Phill

Yep that would be better, ide forgot about that.

Rick

[Jonathan]

I dislike just scaling the step/mm values to make it work as it can mask more fundamental issues, and generally isn't as accurate. You should be able to measure the ballscrew pitch and work it out. The comment earlier saying the 'the Y however seemed to jerk' implies it could be stalling as the motion should be very smooth. If that is the case you need to find what's causing that, else the distance readings for that axis are meaningless.

Instead of just measuring a small distance along the screw, measure say 20 turns and divide the result by 20. Assuming you can access the motors, you shouldn't have to dismantle anything. Just measure the distance between the axis and a convenient point, turn it 'n' times by hand and measure the distance again. Divide the difference between those distances by 'n' and you have the pitch. If you've got a digital caliper then measure it over about 150mm to get the most accurate reading.

Doing a test cut is not the best way either, since spindle runout and tool deflection can introduce small errors and it's not possible to measure in wood that accurately anyway. Instead measure how far the axis moves. Measuring the distance between two parallel lines would be easier, and a bit more accurate, than measuring the length of the line, since you're measuring between straight edges not arcs.

Assuming the '3 turns per cm', i.e. 3.3mm pitch is reasonably accurate, the step/mm values we've ended up with don't make much sense. The motors are run from TB6560 ICs, which only support microstepping settings which are powers of 2 up to 2^4 (16). Assuming (as there's a slight chance it may not be) the motors full step resolution is 200 step/rev, that means your motors can be set to 200*2^n where 0<n<4. We need to find steps per mm, so divide by the pitch-> 200*2^n/3.3 = 60.6*2^n, where 0<n<4. That means the correct step/mm value could be one of the following (rounded to 2DP); 60.61, 121.21, 242.42, 484.85, 969.70. None of those seem anywhere near the 408.1 and 512.8 you tried... so I reckon there's something else causing problems here.

You could measure the voltages at the M1 and M2 pins of the TB6560 ICs on your driver board to determine what the microstep setting actually is. The datasheet here shows which pins to probe.

[Ricardoco]

I dislike just scaling the step/mm values to make it work as it can mask more fundamental issues, and generally isn't as accurate. You should be able to measure the ballscrew pitch and work it out. The comment earlier saying the 'the Y however seemed to jerk' implies it could be stalling as the motion should be very smooth. If that is the case you need to find what's causing that, else the distance readings for that axis are meaningless.

Instead of just measuring a small distance along the screw, measure say 20 turns and divide the result by 20. Assuming you can access the motors, you shouldn't have to dismantle anything. Just measure the distance between the axis and a convenient point, turn it 'n' times by hand and measure the distance again. Divide the difference between those distances by 'n' and you have the pitch. If you've got a digital caliper then measure it over about 150mm to get the most accurate reading.

Doing a test cut is not the best way either, since spindle runout and tool deflection can introduce small errors and it's not possible to measure in wood that accurately anyway. Instead measure how far the axis moves. Measuring the distance between two parallel lines would be easier, and a bit more accurate, than measuring the length of the line, since you're measuring between straight edges not arcs.

Assuming the '3 turns per cm', i.e. 3.3mm pitch is reasonably accurate, the step/mm values we've ended up with don't make much sense. The motors are run from TB6560 ICs, which only support microstepping settings which are powers of 2 up to 2^4 (16). Assuming (as there's a slight chance it may not be) the motors full step resolution is 200 step/rev, that means your motors can be set to 200*2^n where 0<n<4. We need to find steps per mm, so divide by the pitch-> 200*2^n/3.3 = 60.6*2^n, where 0<n<4. That means the correct step/mm value could be one of the following (rounded to 2DP); 60.61, 121.21, 242.42, 484.85, 969.70. None of those seem anywhere near the 408.1 and 512.8 you tried... so I reckon there's something else causing problems here.

You could measure the voltages at the M1 and M2 pins of the TB6560 ICs on your driver board to determine what the microstep setting actually is. The datasheet here shows which pins to probe.

Hi Jonathan, this was initially to find out if it was an electrical or a mechanical problem, or indeed both, as i understand it there is no way to change the steps on the drivers that could be discovered. So Im glad you are here to cast your eye over it, we also dont know if the screws are metric or imperial although the chap has said they all measure the same..

Rick

[Shinobiwan]

This won't fix your axis scaling issues but in general config are you set to exact stop or constant velocity? I'd recommend constant velocity for smoother movement and less chance of lost steps.

[martin54]

dislike just scaling the step/mm values to make it work as it can mask more fundamental issues, and generally isn't as accurate. You should be able to measure the ballscrew pitch and work it out. The comment earlier saying the 'the Y however seemed to jerk' implies it could be stalling as the motion should be very smooth. If that is the case you need to find what's causing that, else the distance readings for that axis are meaningless.

This is pretty much what I was going to do with the gerber when the time came so how would I go about setting that up? It's belt driven via gearing rather than being a ballscrew.

[Carlb1058]

I dislike just scaling the step/mm values to make it work as it can mask more fundamental issues, and generally isn't as accurate. You should be able to measure the ballscrew pitch and work it out. The comment earlier saying the 'the Y however seemed to jerk' implies it could be stalling as the motion should be very smooth. If that is the case you need to find what's causing that, else the distance readings for that axis are meaningless.

Instead of just measuring a small distance along the screw, measure say 20 turns and divide the result by 20. Assuming you can access the motors, you shouldn't have to dismantle anything. Just measure the distance between the axis and a convenient point, turn it 'n' times by hand and measure the distance again. Divide the difference between those distances by 'n' and you have the pitch. If you've got a digital caliper then measure it over about 150mm to get the most accurate reading.

Doing a test cut is not the best way either, since spindle runout and tool deflection can introduce small errors and it's not possible to measure in wood that accurately anyway. Instead measure how far the axis moves. Measuring the distance between two parallel lines would be easier, and a bit more accurate, than measuring the length of the line, since you're measuring between straight edges not arcs.

Assuming the '3 turns per cm', i.e. 3.3mm pitch is reasonably accurate, the step/mm values we've ended up with don't make much sense. The motors are run from TB6560 ICs, which only support microstepping settings which are powers of 2 up to 2^4 (16). Assuming (as there's a slight chance it may not be) the motors full step resolution is 200 step/rev, that means your motors can be set to 200*2^n where 0<n<4. We need to find steps per mm, so divide by the pitch-> 200*2^n/3.3 = 60.6*2^n, where 0<n<4. That means the correct step/mm value could be one of the following (rounded to 2DP); 60.61, 121.21, 242.42, 484.85, 969.70. None of those seem anywhere near the 408.1 and 512.8 you tried... so I reckon there's something else causing problems here.

You could measure the voltages at the M1 and M2 pins of the TB6560 ICs on your driver board to determine what the microstep setting actually is. The datasheet here shows which pins to probe.

Hi Jonathan,

Clarification on the following please:
1) measure the distance between the axis and a convenient point
Tipping the machine over gives me clear access to the Y screw, both X & Z have a lot of body work around them which seriously limits any access - so with that said, please define axis and convenient point, don't forget you're talking to a total newbie here, the only machines we had in school were a bench drill and lathe - damn, calculators didn't even surface until years after I left!!
2) measure the voltages at the M1 and M2 pins
All I have in regards to voltage measurement gear is a simple multimeter that I use for checking the wiring on the Meriden and my FLH will this suffice?

[Jonathan]

1) measure the distance between the axis and a convenient point

Measure how far the axis moves. So for example on X move the gantry to one end, then turn 20 turns (or whatever) and measure how far it moved. You don't need access to the screw.

The meter you have will be fine. Just connect the negative probe to negative, (i.e. ground) and the other one to the correct pins. You may have to unscrew the board to access one of them.

[Carlb1058]

Measure how far the axis moves. So for example on X move the gantry to one end, then turn 20 turns (or whatever) and measure how far it moved. You don't need access to the screw.

The meter you have will be fine. Just connect the negative probe to negative, (i.e. ground) and the other one to the correct pins. You may have to unscrew the board to access one of them.

Access to the chips wasn't too bad - off all three I got a reading of between 2.2 and 2.3 and occassionally -2.2 & -2.3 but I'd say that's my multimeter playing silly buggers.

As for turns per 20 on the X gave me 80mm, 10 on the Z gave me 40mm (couldn't turn it 20) and 20 on the Y gave me 62mm

[John S]

Recheck Y in a couple of places and in both directions
Reason for this is 62 mm doesn't work out to a normal pitch and you did say y was jerky.

I'm wondering if you have a loose coupling or similar ?

[Ricardoco]

Recheck Y in a couple of places and in both directions
Reason for this is 62 mm doesn't work out to a normal pitch and you did say y was jerky.

I'm wondering if you have a loose coupling or similar ?

I concur

Rick