Why don’t pullers use acme thread screws?

[Firebrick43]

Acme

5/8 is 8 TPI

3/4 is 6 TPI

They can be finer but they won’t be acme standard threads.

Acme threads deliver lower mechanical efficiency than standard V-threads due to higher friction from their trapezoidal geometry, but they excel at handling heavy axial loads and power transmission. [1, 2, 3]

Mechanical Advantage and Efficiency

• • Standard V-threads (60-degree angle): Provide higher linear force per unit of torque and better mechanical efficiency in standard fasteners because of a steeper helix angle and tighter fit. However, they are prone to stripping under heavy dynamic loads. [1, 2]
  • Acme threads (29-degree trapezoidal angle): Feature increased friction caused by the wedging action of their sloped flank sides. This reduces their mechanical efficiency (typically around 40–50% even when lubricated) compared to ideal square or standard tightening threads

Is this an AI quote????

Did you read the links? At least link 1 and link 2 contradict the statement proceeding the links entirely. I don't do Instagram so on link 3.

Here is a direct quote from link 1...

"1. Flank Angle and Friction Dynamics​

The most visually apparent difference between ACME thread and normal thread is the flank angle—29 degrees versus 60 degrees. The steep 60-degree angle of a normal thread acts like a wedge. As you tighten a bolt, the radial force pushes outward, creating high friction. This is perfect for a fastener that you want to remain permanently fixed. However, if you try to use a 60-degree thread to continuously move a heavy load (like a machine table), the wedging action causes severe friction, rapid heat generation, and accelerated mechanical wear.

The 29-degree angle of the ACME thread drastically reduces this radial wedging force. When torque is applied to turn an ACME lead screw, the force is directed much more linearly along the axis of the screw. This fundamental difference between ACME thread and normal thread physics allows the ACME mechanism to move heavy loads with significantly less rotational effort and far less wear on the mating nut."



The video in link 2 even gives the math to calculate the thread efficient in relation to its angle. I think why AI is confused is that its comparing square threads to acme thread. In that case because of the angle acme threads are less efficient than square threads. But the same math makes 60 degree threads 50 percent less efficient than acme threads.

More proof that AI is ****.

 

[u3b3rg33k]

Acme

5/8 is 8 TPI

3/4 is 6 TPI

They can be finer but they won’t be acme standard threads.





Is this an AI quote????

Did you read the links? At least link 1 and link 2 contradict the statement proceeding the links entirely. I don't do Instagram so on link 3.

Here is a direct quote from link 1...

"1. Flank Angle and Friction Dynamics​

The most visually apparent difference between ACME thread and normal thread is the flank angle—29 degrees versus 60 degrees. The steep 60-degree angle of a normal thread acts like a wedge. As you tighten a bolt, the radial force pushes outward, creating high friction. This is perfect for a fastener that you want to remain permanently fixed. However, if you try to use a 60-degree thread to continuously move a heavy load (like a machine table), the wedging action causes severe friction, rapid heat generation, and accelerated mechanical wear.

The 29-degree angle of the ACME thread drastically reduces this radial wedging force. When torque is applied to turn an ACME lead screw, the force is directed much more linearly along the axis of the screw. This fundamental difference between ACME thread and normal thread physics allows the ACME mechanism to move heavy loads with significantly less rotational effort and far less wear on the mating nut."



The video in link 2 even gives the math to calculate the thread efficient in relation to its angle. I think why AI is confused is that its comparing square threads to acme thread. In that case because of the angle acme threads are less efficient than square threads. But the same math makes 60 degree threads 50 percent less efficient than acme threads.

More proof that AI is ****.

heh I asked AI how to keep a motor under it's rated limit, and it told me to use the drive's protection current limit feature, and to NOT use the PI logic with amperage as the input value. I asked it specifically to tell me how to use the PI logic.
lol!

 

[Steve_P]

Fair enough. With regards to the back drive - why is this not an issue for a vise?

As long as the thread is fine enough, it won't back drive. A 3/4-10 thread with moly lube won't backdrive with a bronze nut. I’ve used that combo a lot in designs with great results. A 3/4-4 will backdrive under the same conditions.

Nook has a great engineering guide that addresses all of the issues: backdriving, buckling, critical speed...... with charts and calculations to help you to select a screw for an application.

The reason there are so many coarse pitch Acme threads like 4 TPI is for high linear speed for the nut. There are limits on how fast you can spin a 6' long screw until it elasticity deforms into a wet noodle that looks like a sine wave- the critical speed.

There is a simple formula to calculate if a thread will backdrive where you put in the screw pitch, lubrication, bronze or plastic nut.... and you come up with an efficiency number. IIRC, if its below 40% it wont backdrive; above it will. Obviously if you're right around the split number you need to be careful.

I didn't see any pitches above 10 TPI when I scanned the tables, so this is most likely the geometric limit as I mentioned. You cannot reach typical UNF pitches with Acme.

 

[whateg01]

I didn't see any pitches above 10 TPI when I scanned the tables, so this is most likely the geometric limit as I mentioned. You cannot reach typical UNF pitches with Acme.

Machinery 's handbook lists 16 tpi acme

 

[L.Cheapo]

Fun Fact:

Toothpaste tubes use a buttress thread for the cap.

Why that is, I have no clue.

I never looked, but because of this post, I did today, and you are correct.

Guessing because they should, in theory, only have force in one direction?