gantry weight

[Boyan Silyavski]

The steppers that could change the servos on that weight will not be that cheaper than servos, drives must be AC high voltage, etc. I have not used, but the cheap servos from BST will do the job fine .

If you gear them like me on 2510 screw / 2020 or 2010 is too small for that job and price wise is same from china/ at 20t puley and inside rotating nut 30t puley, speed and resolution will be more than enough.


2510 screw makes 10mm per rev, so 3000x10x1.5=20 000mm/min max speed , so at 2500ppr / the KRS servo motors from BST/ will give you 2500ppr/10mm=250x1.5=375ppr resolution which is 1mm/375=0.0026666666666667 resolution on the axis and bigger on Z as there screw would be 1605.

So not so bad after all, 99% of people working on cnc will envy you to have such a machine at home


PS thats exactly the resolution of my motors
ps2/ 2048, not 2500 , only my z is 2500 ppr, so thats why at my video you see other number than 375 steps per rev/

[Robin Hewitt]

Just to make sure my poor old brain is still working...
If you put a 1m radius pulley on a 3Nm motor
One rev gives you 3N over a distance of 2 meters
One rev on a 10mm screw only moves you 0.01m
so the force increases in proportion (3 x 2 ) / 0.01 = 1885N force
1N will accelerate a 1kg mass at 1 m/s/s
So 1885N will accelerate a 132kg mass at 1885/132 = 14.2m/s/s
Sounds okay, 1G is 9.8m/s/s and 1G with a safety margin is good acceleration.
Also we know that 132kgf will accelerate a 132kg mass at 1G because that is what happens when you drop it.
So you get about 132kgf to drive the tool dead slow with the same margin.

[JAZZCNC]

What you smoking Robin.? . . . 1m radius pulley.

Also mach3 works in mm/s/s and nobody runs machine any where near 1G (9800mm/s/s).

[Robin Hewitt]

What you smoking Robin.? . . . 1m radius pulley.

I gave up smoking 7/3/13
It's a 3Nm motor, the motor is specified in meters.
However, I am confusing my table types. Large accelerations are only necessary for plasma tables and even then 1G would be excessive

[Jonathan]

The mass of the gantry alone is of little concern. As has been highlighted, the mechanical advantage you get from ballscrew is significant, so the motor doesn't directly 'see' the mass of the gantry. You have to consider the equivalent inertia of the gantry, i.e. the mass the motor 'sees'. This combines the gantry mass with the inertia of any pulleys you use and the motor itself. Choosing large pulleys can have the same effect as adding 10's of kg to the gantry mass.

Ideally, you pick the motors to match the gantry. If the motors required aren't affordable, I'd sooner use undersize motors and have the machine acceleration be a bit less, than have the gantry less strong.

Just to make sure my poor old brain is still working...

Better than most ;)