Lead screws

Roton's 59284 steel screw and 90222 bronze nut use 0.1 in/rev lead. An assumed 100 rpm gives 10 in/min nominal feed. For 100 lbf axial load, the catalog torque ratio 0.051 in-lbf/lbf gives 5.1 in-lbf. Using its separately rounded 31% efficiency gives about 5.13 in-lbf. Check starting and acceleration torque, supports, wear, lubrication and thermal duty separately. Table 4, 1/2–10 row.

Sliding motion conversion

Relative screw–nut rotation produces axial motion. A sliding lead screw carries thrust through its threads, while a ball screw uses rolling contact. Friction, heat, wear and backdriving depend on the design. Haydon Kerk Pittman, Lead Screws 101, p. 1, Roton, Efficiency and Backdriving.

The nut mount and screw end supports transmit thrust to the structure. Use separate guidance for side loads and overturning moments. Align the screw with the guide to limit binding and wear. Haydon Kerk Pittman, pp. 2–3, Roton, End Fixity.

Pitch, lead, starts and thread form

Pitch is the axial spacing between adjacent threads. Lead is the axial advance in one relative revolution. Starts are the independent helices on the shaft. Their geometric relationship is:

lead = pitch × number of starts
nominal travel = lead × relative revolutions

Pitch and lead coincide for a single-start screw. A hypothetical 2 mm-pitch, four-start screw has an 8 mm/rev lead. A designation containing a diameter and a number of turns does not by itself resolve this distinction: Nook explicitly uses effective turns per inch in its Acme designations, whereas the Roton family used below separately identifies threads per inch, starts and lead. Nook, Acme Screw Thread Form Terms; Roton, 1/2–10 right-hand Acme family.

Square, Acme and metric trapezoidal threads are related power-screw forms, with different flank geometry and conventions. Nook describes conventional general-purpose and centralizing Acme forms as having a nominal thread depth of half the pitch and a 29° included angle; trapezoidal forms have a 30° included angle. Its description also explicitly notes that some Nook sizes have a 40° angle. Stub Acme is shallower than half the pitch. Centralizing forms reduce major-diameter clearance, but the reduced clearance does not make the nut suitable for operating side loads. These manufacturer descriptions do not establish interchangeability among forms, brands or tolerance classes. Nook, Thread Types.

Friction, efficiency and holding behavior

A screw thread acts like a ramp wrapped around a cylinder. Increasing lead angle generally trades mechanical advantage for greater advance per turn. Whether an axial load can turn the screw backward depends on lead angle, thread geometry and friction. Nut material and screw coating can change friction and efficiency even when diameter and lead remain the same. Forward-drive efficiency and backdrive efficiency describe different directions of power transmission; a forward-efficiency value alone is not a holding test. Haydon Kerk Pittman, pp. 1–2; Roton, Efficiency and Backdriving.

Roton describes its Acme series as single-start, with lead angles of 5° or less, and says they resist backdriving under most conditions. That qualification matters: a low-lead sliding screw is not a universal brake or a demonstrated means of safe load holding. Haydon Kerk Pittman calls for manufacturer consultation where non-backdriving behavior is required; its high-lead worked example needs a brake to keep a vertical load from descending when motor power is removed. Roton, Self-Locking Lead Screws; Haydon Kerk Pittman, pp. 2, 4.

For a first-order steady-load calculation, the whitepaper gives:

T = F × lead / (2π × η)
n = v / lead

T = drive torque
F = axial thrust
η = forward-drive efficiency as a fraction
n = relative rotational speed
v = axial speed

Force and lead must use compatible torque units: lbf and inches produce in-lbf; newtons and metres produce N·m. The time basis must also agree in the speed equation: inches per minute divided by inches per revolution gives revolutions per minute. These relationships do not establish breakaway torque, acceleration torque, separate bearing or seal losses, motor margins or acceptable thermal duty. Haydon Kerk Pittman, p. 2, Equations 1–2.

A bounded Roton screw-and-nut example

Roton lists the 59284 steel Acme screw and 90222 bronze threaded-mount nut in its 1/2–10 right-hand family; each product also appears among the other's related products. This supports the named pairing within that supplier family. It does not establish compatibility with another nominally similar screw or nut. Roton 59284; Roton 90222.

Roton specifies a plain oil-dip finish for its Acme screws and recommends that bronze Acme nuts be well lubricated with good-quality extreme-pressure grease compatible with the operating environment. The cited exact-part information does not establish a lubricant product, interval, temperature range, maximum rpm, continuous-duty allowance or lead-accuracy tolerance for this pair. Roton relates operating wear to load, speed, lubrication, contamination and heat, and recommends application testing. The catalog load ratings therefore do not by themselves establish complete-axis capacity or service life. Roton, General Information; Wear Life of Power Screws.

Derived arithmetic, not measured performance

Using the nominal 0.1 in/rev lead, 10 relative revolutions correspond to 1 in of nominal travel. An assumed 100 rpm corresponds to 10 in/min. For an illustrative 100 lbf axial force, the tabulated torque ratio gives:

100 lbf × 0.051 in-lbf/lbf = 5.1 in-lbf

Using the separately tabulated 31% efficiency in the simplified torque equation gives about 5.13 in-lbf; the two rounded catalog quantities need not reconstruct one another exactly. These calculations are neither measurements nor approval of the assumed force, speed, duty cycle or motor. Converting the nominal lead to 2.54 mm/rev changes the units, not the thread form or its accuracy. The source values are Roton's family specification and Table 4; the torque relationship is from Haydon Kerk Pittman, p. 2.

Backlash, accuracy and wear

Nominal lead describes theoretical travel. Lead accuracy concerns the difference between theoretical and actual travel; it is not the same property as commanded motion increments or reversal lost motion. Roton uses increasing screw/nut backlash as an indicator of wear and describes progressive thinning of nut threads. The named pair's nominal lead does not establish initial backlash, positional accuracy or a replacement threshold. Nook, Lead Accuracy; Roton, Wear Life of Power Screws; Monitoring Wear.

Sliding contact also produces heat. High load, speed or duty can damage lubricant and material; acceptable wear depends on the complete application. Roton discusses life evaluation through backlash, drive torque and nut temperature under controlled load and speed. A polymer nut introduces its own pressure–velocity and thermal limits: Haydon Kerk Pittman shows how thrust, speed and local pressure affect such a nut, including the adverse effect of moment loading. Those polymer limits do not transfer to the bronze 90222 nut. Roton, Wear Life and Monitoring Wear; Haydon Kerk Pittman, pp. 2–4.

Buckling, end supports and critical speed

A slender screw loaded in compression can buckle before reaching its static load limit. Unsupported length, minor diameter and end restraint therefore matter alongside nut ratings. End supports also determine resistance to rotational vibration: Roton distinguishes free, supported and fixed ends, with different abilities to resist axial, radial and moment loads. A nut rating does not resolve the capacity of an end-machined shaft, bearing, housing or mounting structure. Roton, Column Loading and End Fixity.

Critical speed is a separate limit from compression buckling or sliding-contact heating. Haydon Kerk Pittman's simplified calculation assumes a screw material with elastic modulus 28 Mpsi, such as 303 stainless steel, with root diameter and support span in inches:

critical speed (rpm) = MF × 4.7 × 10^6 × RD / L²

RD = screw root diameter, in
L  = distance between supports, in
MF = mounting factor in the whitepaper

Its mounting factors are 0.36 for rigid/free, 1 for simple/simple, 1.47 for rigid/simple and 2.23 for rigid/rigid. The whitepaper says rotational speed is typically limited to 75% of its calculated critical speed to account for minor misalignment and manufacturing tolerances. These coefficients and the margin belong to that model and its conditions. Haydon Kerk Pittman, p. 2, Table 1 and Equation 3.

In that manufacturer's own example, a 0.169 in root diameter, 16 in simple/simple span and the stated material assumption give approximately 3,103 rpm critical speed and 2,327 rpm after its 75% margin. That example concerns a 303 stainless/acetal screw system, not the Roton steel/bronze pair. Roton's separate critical-speed calculator uses its own coefficient and support factors; mixing coefficients or treating either result as a universal speed rating would remove essential assumptions. No numerical buckling load or allowable speed is established here for 59284/90222. Haydon Kerk Pittman, p. 4; Roton, Critical Speed.

Evidence scope

The manufacturer descriptions support the mechanisms, conditional calculations and named product values above. They do not establish a universal fit, lubrication schedule, self-locking guarantee, torque, life or positional accuracy. Application behavior also depends on the load spectrum and orientation, guide alignment, end-support arrangement, span, duty, environment and holding requirements.

The four-page Lead Screws 101 whitepaper prints document code MCM2018_023A_102018 on page 4. Its PDF creation/modification metadata date of October 1, 2018 is separate from that printed code and does not establish another edition. Roton and Nook technical pages are undated web references accessed October 31, 2026. Thread-form coverage is limited to manufacturer descriptions; full ASME, ISO and DIN standards were not accessed. The cited values are supplier statements and derived arithmetic, not measurements of a delivered machine.