Stepper strength

[pminmo]

125ozin stepper 10 tpi ACME thread. What king of strength can I plan for?

[motomitch1]

hi pminmo
That would work on a small machine I have a small mill with 200 ozin stepper motors and 16 TPI. I live in st.peters also if you want to stop by sometime and look at my set up.

[umrk]

Acording to This Info (see Pg25) a Acme 1/2" x 10tpi using a plastic nut requires .039 in/lb (.624 in/oz) to lift one pound, so a 125oz/in stepper Should be able to lift 80 lbs. Of course that is going to drop as speed increases.

mike

[balsaman]

I used that rod with 100 oz steppers. worked great.

Eric

[pminmo]

Motomitch1, small world, check you email, I'd like to see your machine.

[motomitch1]

Me check mail

[snokid]

along the same lines.

if 10 tpi yeilds about 80# of force wouldn't 20 tpi give more force?

if that is the case why not use the threaded rod instead of the lead screw arrangement?

the only things I can come up with is amce rod would last longer and travel faster, but with a reduction in torque.

Bob

[anoel]

Originally posted by snokid
along the same lines.

if 10 tpi yeilds about 80# of force wouldn't 20 tpi give more force?

Yes, 160# of force at half the speed. (in theory)

Originally posted by snokid

if that is the case why not use the threaded rod instead of the lead screw arrangement?

If you've got enough torque with the acme rod then you have a speed advantage.[/B][/QUOTE]

[umrk]

With 125oz/in steppers you should have plenty of power for 10tpi, unless you have a very heavy carrage to move.

Its my understanding that Acme rods were designed for linear motion applications, lathes, mills... do use them, rather than typical V threads. It seems to me that the angle and shape of the threads would be more suited for motion and its forces rather than just fixed holding strength and ease to cut like wth a V thread.

V threads do work on smaller machines but I suspect that they will wear faster. I've not seen V threads used on larger machines.

Yes, by going with 1/4 x 20 rod you should get close to 2X the power (depending on their efficency), at 1/2 the speed. Your resolution will also double. IOW with a 200 step motor and 10 tpi you need 2000 full steps to move one inch, or .0005" (half a thousandths) per step. 20tpi would give .00025" per step

This sounds great for accuracy but it is basically wasted resolution due to backlash and flex, unless your building a Very strong (heavy) machine with zero backlash nuts and making Very light cuts. Even big lathes, mills... the cutter and what your cutting, will flex to some degree. Also the stepper motor can rotate a bit under load without missing a step, and those 200 steps may not be dead on accurate anyway. Then factor in wear on every component as you use it. It all adds up and real life accuracy suffers.

As I understand it 160lbs of force will accellerate 160lbs at 1G, or 16lbs at 10G. Do you really need that kind of force, while limiting your top speed by 1/2?

Acme rods aren't expensive, Enco has them for $3.49 per 3' section.

mike

[ger21]

Here's a question for you guys. If you look at just about any chart showing torque curves for steppers (at ~ 24V anyway), you'll see that the torque drops off rapidly as rpm's increase. So if you spin the motor twice as fast with the 1/4-20 to get twice the torque, don't you lose a lot of that 2x torque because the stepper is spinning twice as fast? This would mean that the 1/2-10 would be the better choice in most situations, unless you've got pretty small motors and / or are not planning on cutting very fast.


Gerry

[fyffe555]

umrk

Re; '160lbs of force will accelerate 160lbs at 1G, or 16lbs at 10G'

I think you'll find that the reference you've given talks about the torque required to keep one lb in motion and not accelerate it at 1G which is a totally different order or magnitude.

As you suggest a 125oz/in stepper on 10tpi would produce about 80lbs force, (not power, hp=torquexspeed or work=forcexdistance for example). At say 1000rpm the stepper would give 100ipm.

The same stepper on 20tpi would produce about 160lbs force and 50ipm at 1000rpm. The acceleration is entirely a function of mass and inertia or weight of gantry and friction loads.

Some software controls acceleration too, below the mechanical max to avoid lost steps amongst other stuff.

For what its worth I'm using PacSci 116oz steppers on Acme1/2 10 and it works well with a 40lb gantry/router on linear bearings. Still learning but I'm happy at 60ipm rapid.

[fyffe555]

Ger21,

I've replaced 3/8 16 allthread with 1/2 10 Acme on the same machine. I appear to get both more speed and power from the 1/2 10, can set up to take deeper cuts faster. Theres a noticable difference. I'm using the same pacsci 116oz which I think you gave me some help on a while ago(?) and turbocnc.

So - I think on my machine at least, at the ipm speed range I'm running at the 1/2 10 is better because the 'gearing' is better suited to the torque. The nut has a little less drag on 1/2 10 but its hard to tell. Obviously changed the turbo cnc setup to match. Tried running my drivers in 1/4step and its much quieter and smoother. Just need to build a bigger stronger stiffer machine now....