Table of Contents

Rack and Pinion
A rack and pinion is a type of linear actuator that consists of a circular gear (Pinion) engaging a linear gear (Rack), which operate to translate rotational motion into linear motion.

Driving the rack linearly will cause the pinion to be driven into a rotation. Driving the pinion into rotation causes the rack to be driven linearly. A rack and pinion drive can use both straight and helical gears.

STRAIGHT GEAR / SPUR GEAR HELICAL GEAR

Helical Gears are preferred due to their quieter operation and higher load bearing capacity. The maximum force that can be transmitted in a rack and pinion mechanism is determined by the tooth pitch and the size of the pinion.
EXAMPLES
RACK AND PINION RAILWAY
In a Rack railway, the rotation of a pinion mounted on a locomotive or a railroad car engages a rack placed between the rails and helps to move the train up a steep gradient.

RACK AND PINION STEERING
A rack-and-pinion gearset is enclosed in a metal tube, with each end of the rack protruding from the tube. A rod, called a tie rod, connects to each end of the rack. The pinion gear is attached to the steering shaft. When you turn the steering wheel, the gear spins, moving the rack. The tie rod at each end of the rack connects to the steering arm on the spindle.

Power Rack-and-pinion
When the rack-and-pinion is in a power-steering system, the rack has a slightly different design.
Part of the rack contains a cylinder with a piston in the middle. The piston is connected to the rack. There are two fluid ports, one on either side of the piston. Supplying higher-pressure fluid to one side of the piston forces the piston to move, which in turn moves the rack, providing the power assist.

Rack-and-pinion Actuators
Actuators use rack and pinion with two racks and one pinion.
Lead Screws
Lead screws act as a linkage to covert rotational motion into linear motion. Although used in a wide variety of applications, they are not efficient enough due to the large frictional energy losses.
Advantages: They have large load carrying capacity and mechanical advantage, low cost, simple to design and manufacture, and self locking capabilities.
Factors to consider while selecting lead screws: load capacity, pressure-velocity factor, efficiency, speed, duty cycle ,backlash ,life and lubrication.

Figure 1. Thread Forms/Standards for Linear Power Transmission Tools
Thread Form Image [6] Description Usage Standard
Trapezoidal
Trapezoidal outlines
High strength and ease of manufacturing
30° flank angle
Used for leadscrews (power screws)
Used where large loads are required (vice, lathe)

British and American Standard General Purpose ACME
Thread height is half the pitch length and flattened
29° flank angle
Used for leadscrews (power screws)
Used where large loads are required (vice, lathe)
ASME B1.5-1997 (R2014)
American Standard STUB ACME
Same as ACME except different height [1]
Used for leadscrews (power screws)
Used where large loads are required (vice, lathe)
ASME B1.5-1997 (R2014)
BUTTRESS (Continental)
Asymmetric thread form
Allows for low friction, withstands greater loads in one direction, but higher friction and inferior load bearing in the opposite
One side at a slant typically less than 7°, while the other is at an angle typically at 45°
Continental BUTTRESS thread form has 45°/5°
Used in the construction of artillery
Used in jacks, lifts, hydraulic sealing
Applications in automotive to water and sewer
ANSI/ASME B1.9-1973 (R2017)
British Standard BUTTRESS
45°/7°
Used in the construction of artillery
Used in jacks, lifts, hydraulic sealing
Applications in automotive to water and sewer

American National BUTTRESS
45°/7°, but internal threads are flat [2]
Used in the construction of artillery
Used in jacks, lifts, hydraulic sealing
Applications in automotive to water and sewer

Ball Screws
With a little friction, the ball screws convert linear motion into rotational motion. However due to its lower friction, ball screws tend to back drive under higher load and are expensive.
Advantages: More efficient, runs at cool temperatures.
Preload is the tension created in a fastener when it is tightened. Connections using preloaded bolts are designed to transfer load without any slip.

Standard Lead Precision Ball Screw Standard Lead Rolled Ball Screw
Standard Type equipped with Shaft Standard Nut Type Standard Nut Type Rolled Shaft and Nut
Standard off-the-shelf Type
Shaft end unfinished type
Models MDK, MBF, BNF, BIF and BNFN Shaft end finished type
Model BNK Preload type
Models SBN, DIK, DKN, BIF and BNFN Non-preload type
Models HBN, DK, BNF and BNT Preload type
Model JPF Non-preload type
Models MTF, BTK and BNT
BIF

SBN

BTK
MDK & MBF
BIF

MTF
BNF elm

DIK elm

BNT
DKN elm

BNFN

Large-Lead Precision Ball Screw Large-Lead Rolled
Ball Screw

Standard Nut Type Rolled Shaft and Nut
Standard off-the-shelf Type
Preload type
Models SBK and BLW
Non-preload type
Models BLK and WGF
Non-preload type
Models BLK, WTF and CNF
BLW
BLK & WGF
BLK/WTF
SBK
CNF
Rotary Nut
Series

Rotary Nut Precision
Ball Screw Rotary Nut Rolled Ball
Screw Ball Screws/Splines
Standard-lead, preload type
Model DIR Large-lead, non-preload type
Model BLR Large-lead, non-preload type
Model BLR Stroke, rotation type
Models BNS and BNS-A Stroke type
Models NS and NS-A

BNS
NS
BNS-A
NSA

References
[1] “Trapezoidal thread form,” Wikipedia, 10-Feb-2021. [Online]. Available: https://en.wikipedia.org/wiki/Trapezoidal_thread_form. [Accessed: 04-Mar-2021].
[2] “Buttress thread,” Wikipedia, 11-Feb-2021. [Online]. Available: https://en.wikipedia.org/wiki/Buttress_thread. [Accessed: 04-Mar-2021].
[3] “Types of Ball Screws,” THK, 11-Feb-2021. [Online]. Available: https://pdf4pro.com/cdn/types-of-ball-screws-cbm-ind-43a263.pdf [Accessed: 10-Jun-2021].
[4] “Ball Screws,” THK, 11-Feb-2021. [Online]. Available: https://tech.thk.com/en/products/pdf_download.php?file=511E_15_BallScrew.pdf [Accessed: 10-Jun-2021].
[5] “Rack and pinion,” Wikipedia, 19-May-2021. [Online]. Available: https://en.wikipedia.org/wiki/Rack_and_pinion [Accessed: 10-Jul-2021].
[6] “Rack and pinion steering: Everything you need to know", "Hearst Autos Research", https://www.caranddriver.com/research/a31267607/rack-and-pinion-steering/ [Accessed: 10-Jul-2021].

Contributors:
User Last Update
Lesley Lang 1284 days ago

Figure 1. Thread Forms/Standards for Linear Power Transmission Tools
Thread Form	Image [6]	Description	Usage	Standard
Trapezoidal		Trapezoidal outlines High strength and ease of manufacturing 30° flank angle	Used for leadscrews (power screws) Used where large loads are required (vice, lathe)
British and American Standard General Purpose ACME		Thread height is half the pitch length and flattened 29° flank angle	Used for leadscrews (power screws) Used where large loads are required (vice, lathe)	ASME B1.5-1997 (R2014)
American Standard STUB ACME		Same as ACME except different height [1]	Used for leadscrews (power screws) Used where large loads are required (vice, lathe)	ASME B1.5-1997 (R2014)
BUTTRESS (Continental)		Asymmetric thread form Allows for low friction, withstands greater loads in one direction, but higher friction and inferior load bearing in the opposite One side at a slant typically less than 7°, while the other is at an angle typically at 45° Continental BUTTRESS thread form has 45°/5°	Used in the construction of artillery Used in jacks, lifts, hydraulic sealing Applications in automotive to water and sewer	ANSI/ASME B1.9-1973 (R2017)
British Standard BUTTRESS		45°/7°	Used in the construction of artillery Used in jacks, lifts, hydraulic sealing Applications in automotive to water and sewer
American National BUTTRESS		45°/7°, but internal threads are flat [2]	Used in the construction of artillery Used in jacks, lifts, hydraulic sealing Applications in automotive to water and sewer

Standard Lead Precision Ball Screw				Standard Lead Rolled Ball Screw
Standard Type equipped with Shaft		Standard Nut Type		Standard Nut Type	Rolled Shaft and Nut Standard off-the-shelf Type
Shaft end unfinished type Models MDK, MBF, BNF, BIF and BNFN	Shaft end finished type Model BNK	Preload type Models SBN, DIK, DKN, BIF and BNFN	Non-preload type Models HBN, DK, BNF and BNT	Preload type Model JPF	Non-preload type Models MTF, BTK and BNT
BIF		SBN			BTK
MDK & MBF		BIF			MTF
BNF elm		DIK elm			BNT
		DKN elm
		BNFN

Large-Lead Precision Ball Screw		Large-Lead Rolled Ball Screw
Standard Nut Type		Rolled Shaft and Nut Standard off-the-shelf Type
Preload type Models SBK and BLW	Non-preload type Models BLK and WGF	Non-preload type Models BLK, WTF and CNF
BLW	BLK & WGF	BLK/WTF
SBK	BLK & WGF	CNF

Rotary Nut Series
Rotary Nut Precision Ball Screw		Rotary Nut Rolled Ball Screw	Ball Screws/Splines
Standard-lead, preload type Model DIR	Large-lead, non-preload type Model BLR	Large-lead, non-preload type Model BLR	Stroke, rotation type Models BNS and BNS-A	Stroke type Models NS and NS-A
			BNS	NS
			BNS-A	NSA

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