stepper and drive sizing

[Claude Boudreau]

Hi,
Being in the process of building my second home made router and trying to size my stepper and drive for a 150 lbs gantry using 5 tpi ballscrews and llinear rail thk25.
According to gecko formula a 150bls gantry and a wanted speed of 200 ipm /531=56 watts should keep me in stepper territory...so far so good
The next formula is ...desired IPM xRPI / 60= RPS (revolution per sec)
in my case 200 x 5 / 60 =16.67 RPS
The following formula is...RPS x 200(steps) = PPS
in my case 16.67 x 200 =3334 pps

the statement about determining how much oz-in is needed to move and accelerate the load is not explained and they state
that PPS x oz-in / 4506 =watt needed , yet on their examples at the very end, they arrived at a value in oz-in
could someone clarify this ?

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[ger21]

Why is your desired speed only 200ipm, and why are you using 5tpi ballscrews?
How big is this machine? What diameter and length are the screws?

200ipm is quite slow for a router.

5tpi ballscrews will require 1000rpm from your steppers to get to 200ipm. This may be difficult to achieve with larger size motors.

[Claude Boudreau]

How do you find out how much torque is required from your stepper for a 4 x 4 router using 1610 c7 ballscrew equiped with 2 hp rotor .at 100ipm
Its a bit late for me to change to rack and pinion since I ve already bought and installed my ballscrews
How much mechanical power do you add to do the actual wood cutting ? Is it the 40% added

Any suggestions welcome

[ger21]

You can use this calculator and work backwards to find how much torque you need to provide a given amount of force.
Linear Force Calculator

With a 2HP router at 100 ipm, your cutting forces will be very low, probably 10-15 lbs maximum.

The force required for acceleration will be the most important, and depend on how fast you want to be able to accelerate.

[Claude Boudreau]

My 1610 ballscrew is actually 10 mm lead so about 0.4 in lead. ( 2.5 TPI )
So at 200 ipm my stepper rpm would be around 500 rpm

As far as acceleration I need to check my setting on my first build but It was set as high
as possible without making the stepper loose steps...

I dont see no speed-torque curve in any of gecko documentation ...

How much Rpm would a gecko g-723-400-4 stepper driven with a g-540 attain ?

Thank for the link ger21,
linear force according to calculator 320 oz in .38 in lead .8 eff. =264 lbs
unfortunately their site is incompleted as far as motor and drive selection is concerned..

I realize you pretty well need an engineering degree to really figure it out, but for us hobbyist trial and error
is an expensive option. So we have to lower our expectation as far as speed is concerned with those
rules of thumbs and short cut formulas...

Any ideas on improving speed and choosing motor / driver would be greatly appreciated.

[Claude Boudreau]

I ve check my Mach 3 motor tunning setting today : step per 8128 , velocity 45 , acceleration 3
kernel speed 25000
200 steps per turn stepper motor x 8 microstep=1600 step per turn X 5.08 turn per inch(1605 screw)=8128 step per inch

my first build xylotex 425 in oz stepper had quite a high inductance ,over 8 mh if I remember well, my driver could only handle 24 volts
with a safety margin , so I was hoping the g540 at 48 volts and lower inductance motor with 1610 screw would improve performance...