How much force can an acme lead screw handle?

I have a stepper motor that claims 425 oz*inches torque. I want the lead screw to span 2' supported on both sides. I'm trying to decide what diameter lead screw is strong enough to not be damaged by the motor, in other words I'd rather the motor started skipping steps before it caused damage to the lead screw. Equations and handy calculators for what force I could apply with a given lead screw are readily available. I suspect my motor would skip steps before it damaged any t8 lead screw if it were pushing against an unstoppable barrier.

However all the lead screws I've been browsing don't have a listed metric that says how much force it can handl.

From what I've read, the longer the unsupported stretch of lead screw, the less force it can push before it bends instead of moving. I also gather that a longer stretch of contact between the nut and lead screw increases the amount of force that can be withstood before the threads break.

Is there some way of estimating what the maximum force a lead screw can safely push at a given length, lead length, diameter, etc?

• If you found those formulae, then the others won't be far behind. Feb 14 at 22:21
• Roy Mech is one online reference I have used when I was doing this kind of thing, that I found had a good level of detail. Here is their page on lead screws Feb 15 at 0:41
• could you share the datasheet for your motor? Are you using a NEMA 23 or a NEMA 34? I am asking because torque is measured in $oz\cdot in$ not $oz/ in$ and I want to make sure that I've got the right values before starting to carry out calculations. Additionally, is the lead screw subjected to compression load (i.e. does it push up/down a load)? Feb 15 at 8:37
• lintechmotion.com/sizing/Thrust-Force/thrust-inputs.php basic thrust calculator for Acme threads. The size of your screw is also going to depend on what material it is.
– jko
Feb 15 at 12:48
• @NMech You're right, my mistake, it's supposed to be oz⋅in. I'll edit it. I found a datasheet for t8 lead screws, and while it might not reflect the lead screw I was looking at it made a good way to estimate and got the ballpark values I was looking for. Feb 15 at 16:48