previous rfq page next index page home page 5 ball and acme screw drive mechanisms this section will introduce most of the more common types of drive mechanisms found in linear motion machinery ideally a drive system should not support any loads with all the loads being handled by a bearing system topics discussed will include but not be limited to the mechanism of actuation efficiency accuracy load transfer speed pitch life cycle application and maintenance each type of drive system will be accompanied by a diagram and useful equations when applicable some of the terms used with screws the most common drive component are as follows lead pitch of threads of starts outer diameter root diameter stub critical shaft speed advance of the nut along the length of the screw per revolution distance between corresponding points on adjacent thread forms pitch lead of starts number of teeth found along a unit length of the screw 1 pitch number of helical grooves cut into the length o
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previous rfq page next index page home page technical information ball screws are very similar to lead screws with the exception of a ball bearing train riding between the screw ball nut balls and nut in a recirculating raceway this raceway is generally ball screw lubricated which allows for predictable service life due to the increased number of mating and moving parts matching tolerances becomes more critical the screw threads have rounded shapes to conform to the shape of the balls the function terminology and formulas are the same as found with lead screws however the performance ball return of ball screws is far superior the rolling action of the balls ve rsustheslidingactionofthe ac menut ball screw system provides significant advantages advantages of ball screw drives are increased efficiency typically up to 90 ญ 95 which allows required motor torque to be lower predictable service life low wear rate and maintenance costs disadvantages include limited material choice higher ini
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previous rfq page next index page home page total force 100 lbs lead 0.20 inches efficiency 0.9 ball screw 100 lbs ื 0.20 inches t ญญญญญญญญญญญญญญญญญญญ 3.54 lb-inches 2 0.9 total force 25 lbs lead 0.10 inches efficiency 49 25 lbs ื 0.10 inches t ญญญญญญญญญญญญญญญญญญญ 0.81 lb-inches 2 49 3 3 the torque required should be well below the torque rating of the motor chosen a modest factor of safety should be added to the torque required so that unexpected dynamic loads are safely handled by the driving system selecting and sizing screw drive systems when choosing a particular screw for a given application there are several factors to be considered required rpm critical speed and maximum compressive strength are the most important design features that determine screw design parameters and can be calculated according to the following equations since thread style design is irrelevant in these calculations the same equations and charts can be used for both lead screws and ball screws be
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previous rfq page next index page home page technical information travel rate vs length for standard acme screws travel rate in inches per minute 100000 80000 60000 40000 30000 20000 travel rate in inches min 1 information technical critical speed 10000 8000 6000 4000 3000 2000 purpose this graph was designed to simplify the selection of the proper lead screw so as to avoid lengths and speeds which will result in vibration of the assembly critical speed the factors which can be controlled after a particular maximum length is determined are method of bearing support and choice of lead screw diameter 1000 800 600 400 300 200 25161 37161 37101 37122 100 80 60 40 30 20 31084 37084 43082 50101 62101 75101 31032 37081 62102 75061 10 one end fixed other end free both ends supported one end fixed other end supported both ends fixed ref a ref b ref c ref d 6 12 18 24 30 36 42 inches use of the graph 1 choose preferred bearing support means based on design considerations 2 on the proper bearin
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previous rfq page next index page home page compression load vs length for standard ball screws acme screws column loads 40000 30000 20000 compression load in lbs 10000 8000 6000 4000 3000 2000 purpose this graph was designed to simplify the selection of the proper lead screw so as to avoid buckling when subjected to the axial loading by means of the nut the factors which can be controlled after a particular maximum length is determined are method of bearing support and choice of lead screw diameter 75101 75061 62081 43082 37161 37081 25161 31082 10 15 37101 81084 20 37121 31122 25 30 inches 37122 37084 75081 62101 62102 50101 1000 800 600 400 300 200 43084 ref one end fixed a other end free both ends supported ref b 100 5 10 20 30 40 50 60 inches one end fixed ref c other end supported ref d 14 28 42 57 71 85 inches both ends fixed 20 40 60 80 100 120 inches use of the graph 1 choose preferred bearing support means based on design considerations 2 on the proper bearing support horizo
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previous rfq page next index page home page technical information 1 information technical critical speed load load and speed limits on 16 mm ball screws critical speed speed rpm bearing support types ff ญ fixed fixed length mm critical load fo ญ fixed open fs ญ fixed simple load kg ss ญ simple simple length mm 24 www.techno-isel.com
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previous rfq page next index page home page critical speed load load and speed limits on 25 mm ball screws critical speed speed rpm bearing support types ff ญ fixed fixed length mm critical load fo ญ fixed open fs ญ fixed simple load kg ss ญ simple simple length mm techquestions@techno-isel.com 25 technical 1 information technical information
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previous rfq page next index page home page technical information ball acme screw assembly life expectancy 16 mm life expectancy pitch 2.5 4 5 5 10 10 20 20 ca l ญญญญ fm 3 life rev s life rev s 1 information technical 26 specifications axial load n screw dynamic ca static dia 16 3500 5500 16 2600 4200 6 4600 7200 25 5100 12600 16 4200 6500 25 5100 12600 16 1900 2500 25 3570 8800 x 106 l life expectancy expressed in number of revolutions ca dynamic load rating n [for acme nuts see design load column on catalog pages axial load n fm average axial load n 25 mm life expectancy example for 10 mm pitch screw 16 mm dia ca 4200 n carrying an average axial load fm 200 n 45 lbs the expected life is l 4200 ญญญญ 200 3 x 106 9.261 x 109 revolutions at an average of 1000 rpm this will result in 9.261 x 109 revolutions 1 hour ญญญญญญญญญญญญญญญญญญ x ญญญญญญญญญญ 154 000 hours 60 minutes 1000 rpm of expected operational life note that the nature of the motion jerky smooth etc will affect the
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previous rfq page next index page home page lead screw formulas and sample calculations linear speed ipm steps second 1 linear speed ญญญญญญญญญญญญญญญญ x 60 x ญญญ steps revolution p where p lead screw pitch in threads per inch axial force lb 2 force ญญญญ xtxpx eff 16 where t torque oz ท in p lead screw pitch in threads per inch eff efficiency expressed as a decimal 90 0.90 ท note ball screws are generally 85 to 95 efficient acme lead screw efficiency is generally 35 to 45 but can be as high as 85 a calculating the torque required to accelerate a mass moving horizontally and driven by a ball bearing lead screw and nut the total torque the motor must provide includes the torque required to a b c d accelerate the weight accelerate the lead screw accelerate the motor rotor overcome the frictional force w motor to calculate the rotational equivalent of weight w 1 1 2 ieq w x ญญญญ x ญญญ 2 p 2 where w weight lb p pitch threads per inch ieq equivalent polar inertia lb ท in2 ท to
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previous rfq page next index page home page technical information 1 1 i eq w x ญญญ x .025 1000 x ญญญ x .025 1.0 lb ท in2 p2 25 1 information technical 28 ท i screw d 4 x length x .028 5.06 x 48 x .028 6.8 lb ท in 2 i rotor 2.5 lb ท in2 ท i total 10.3 lbทin ท ท ญญญญญญญญญญญญญญญญญญญญญญญญญญญญญญญญญญญญญญญญญญ 2 velocity is 0.15 feet per second which is equal to 1800 steps per second motor steps in 1.8ฐ increments torque to accelerate system x 1.8 1 1800 3.1416 x 1.8 1 t 2 x io x ญญญ x ญญญญญญญญ x ญญญ 2 x 10.3 x ญญญญญ x ญญญญญญญญญญญญ x ญญญ 484 oz in t 180 24 0.1 180 24 ท torque to overcome friction f .393 xtxpx eff 6 ญญญญ f 16 t ญญญญญญญญญญญญญ ญญญญญญญญญญญญญ 0.22 oz in .393 x p x eff .393 x 5 x 0.90 ท where f frictional force lb t torque ozทin p lead screw pitch threads per inch total torque required 0.22 oz in 484.00 oz in 484.22 oz in after determining the required motor size it is recommended to add a 20 factor of safety so that unexpected dynamic loads are easily handle
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previous rfq page next index page home page and most of the available voltage motor manufacturers usually offer alternative windings and care should be taken to select the most appropriate example leadscrew length 80 in leadscrew diameter 1.5 in leadscrew pitch 2.54 in table weight 1000 lb linear table speed required 472 inches/min acceleration time 120 ms d4 l inertia of leadscrew j ญญญญญญ 11.25 lb in2 36 ท w inertia of table j ญญญญญญ 3.88 lb in2 40 p 2 ท linear table driven by dc motor total inertia 15.13 lb in ท 2 maximum speed 472 min 1200 rpm equivalent to 4000 full steps/sec acceleration torque j t ญญญญญญ 660 oz in 4.65 n m 764 t ท ท this takes no account of motor inertia so a suitable motor will be capable of producing around 1000 oz in torque again as with stepper selection it is recommended to add a 20 factor of safety so that unexpected dynamic loads are easily handled by the motor ท techquestions@techno-isel.com 29 technical 1 information technical information
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previous rfq page next index page home page ball acme screw application worksheet name phone 1 information technical 30 company name fax address 1 address 2 city state zip brief description of application e-mail max load max speed max accel please use this area for any notes or diagrams travel complete cycle time orientation accuracy needed anti-backlash nut required yes no integral flange nut required yes no finished end required yes no supply drawing note finished ends for oem quantities only i.e 25 or higher end bearings required yes no base mount or flange mount of end bearings www.techno-isel.com
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