Design and Engineering Data for Lead Screw Linear Actuators
Screw Accuracy All of our lead screws are manufactured using a precision rolling process for screw manufacturing. Standard lead accuracy for lead screws is .0006 in./in. (mm/mm).
End Machining MicroMo can custom machine screws to your specifications or provide cut-to-length screws for your own machining.
Critical Speed This is the rotational speed at which a screw may experience vibration or other dynamic problems. To minimize critical speed problems: use a longer lead, choose a larger diameter or increase bearing mount support.
Lengths Lengths can be specified up to 12 ft. (4M) from stock, (depending on diameter and lead). Cut to length screws are offered in 6" increments (6", 12, 18,....) +1.0"/-0".
Lead Advancement per revolution. All screws are listed by lead, not pitch. Lead = Pitch x Number of Starts
Pitch Crest-to-crest distance or one divided by threads per inch. (On a multiple start thread, the pitch equals the lead divided by the number of starts.)
Traverse Speed The nut materials we use provide long wear-life over a wide variety of conditions. However, very high loads and/or speeds will accelerate nut wear. Special materials may be required for these situations. We offer the following guidelines for continuous duty linear traversing speeds for optimum life:
Lead
Traverse Speed
1/10" - ½"
4 in./sec.
1/2" - 1"
10 in./sec.
1" - 2 ½"
30 in./sec.
1 - 12mm
100mm/sec.
12 - 25mm
250mm/sec.
25 - 60mm
60mm/sec.
Maximum Load Although MicroMo Anti-Backlash Assemblies are capable of withstanding relatively high loads without catastrophic failure, these units have been designed to operate under the loading shown in the size charts.
Efficiency Efficiency is the relationship of work input to work output. It should not be confused with mechanical advantage. Listed efficiencies are theoretical values based on TFE coated screws.
Torque The required motor torque to drive a lead screw assembly is the sum of three components: the inertial torque, drag torque, and torque to move load. It must be noted that this is the torque necessary to drive the lead screw assembly alone. Additional torque associated with driving frictional bearings and motor shafts, moving components, and drag due to general assembly misalignment must also be considered.
Inertial Torque: Tj= I a Where I = screw inertia a = angular acceleration
Drag Torque MicroMo Anti-Backlash Assemblies are typically supplied with drag torque of 1 to 7 oz.-in. The magnitude of the drag torque is dependent on the standard factory settings or settings specified by the customer. Generally, the higher the preset force, the better the Anti-Backlash characteristics.
Torque-to-Move-Load
Screw Straightness Screw straightness is measured as Total Indicator Runout(TIR). The standard MicroMo straightness for lead screws is .003"/ft. MicroMo can provide tighter specifications on customer request. All screws are hand straightened before shipping.
