Chamberlain 3950, LiftMaster 3950 Addendum

DOOR COMPATIBILITY FOR MODEL 3950

IMPORTANT INSTALLATION INSTRUCTIONS

It is important to identify the door type before attempting an installation of the
Model 3950 door operator.

MOUNTING OPTIONS:

Standard wall mount using the brackets included with the operator.

1

Outside bracket mount using the optional mounting bracket Model 3950MB.

2

Inside bracket mount using the optional mounting bracket Model 3950MB.
If standard wall mount brackets are not acceptable for installation, optional

3

Model 3950MB mounting brackets may be required. To order visit
www.liftmaster.com or contact door supplier.

NOTE: The inside mounting option takes away from clear door opening.

LIVE OR DEAD SHAFT DOOR IDENTIFICATION

LIVE SHAFT DOOR - The axle rotates with the drum and door assembly when the door is opened or closed.
DEAD SHAFT DOOR - The axle is locked in place while the door opens and closes.

ADDENDUM

Rotating Axle

Live Shaft Door Dead Shaft Door

Figure 1 - Door Type Identifi cation

Fixed Axle

LIVE SHAFT REQUIREMENTS

Live Shaft doors are automated by the Model 3950 driving a chain which spans the drive sprocket and the door sprocket. The door
sprocket is attached to the door axle which spins the drums and rolls the door curtain. The assembly is held up by door brackets and the
door guides. (Figure 2)

Drum

Wall

Drum
Bracket

Door
Guide

Axle

Figure 2 - Live Shaft Components

Minimum Side Room

The minimum amount of side room depends on the mounting option for the Model 3950. For a standard wall mount or outside bracket
mount using the optional mounting bracket Model 3950MB, a minimum of 11" is required to the outside of the door opening. If inside
mounted, minimum of 3.75" clearance for “Wall” dimension is required. (Figure 3)

Wall

2.5"

11"

Wall

Figure 3 - Live Shaft Clearances

Minimum Shaft Length Past Door Bracket

A minimum of 1.5" of shaft is required (2.5" recommended) for mounting the door sprocket to the Live Door Shaft. (Figure 3)

2

DEAD SHAFT REQUIREMENTS

Dead Shaft Door Construction

Axle

Door
Bracket

Door
Guide

Drum Spring

2nd Drum

Figure 4 - Dead Shaft Door Construction

Spring Clearance

The Model 3950 requires that the internal door springs do not interfere with the 4.5" mounting pattern on the end drum (Figure 4 ).
Some door manufacturers require the door to be ordered with a modifi cation (ex. Prep for Operator), so that an extra drum
(Figure 4 – 2nd Drum) is added on the end of the door barrel to provide an unobstructed platform for door sprocket mounting.

Inspect for interference by sliding the sprocket on the door shaft to drum and aligning with the 2.25" from center, 3 equally spaced hole
pattern. Sprocket mounting holes should not be obstructed by the door spring for a minimum depth of 3". (Figure 6 – Bolt Clearance).
See Figure 8 for Mounting Template.

3

Mounting Hole
(PEM nut may be present)

2.25"

Figure 5 – Drum Holes To Inspect For Obstruction

Door Construction

The Dead Shaft Door must not have more than a 2" inset from the curtain edge to the drum. The Model 3950 comes with a selection of
spacers that can be used in conjunction to provide a maximum 3" of spacing.

4

2" Max Inset

2.5" Min.
Clearance

3" Bolt
Clearance

Figure 6 - Dead Shaft Door Offset

Drum Condition

The door drum on the side on which the Model 3950 is to be mounted must not be bent or damaged in order for installation to be
successful. If bent, the drive chain may not align to the sprocket well and could derail the chain.

Minimum Side Room

The minimum amount of side room depends on the mounting option for the Model 3950. For a standard wall mount to the outside of the
door opening, a minimum of 11" is required for the operator, however, the door brackets must also be considered if they interfere with
operator installation. Dead Shaft Door brackets should be moved away from the door assembly to provide enough room for the desired
operator mounting position.

5

OPERATOR DRIVE OPTIONS WHEN USING MODEL 3950MB MOUNTING BRACKET

The operator drive sprocket can be attached in one of three positions when inside mounted or one of two positions if outside mounted
that provide offset from the outer edge of the door guides: Refer to table below (Figure 7) for details.

Figure 7 Operator Drive Options

Outside Mount

Alignments

Inside Mount

Alignments

OUTSIDE MOUNT ALIGNMENTS

Sprocket inner position 1"

Sprocket middle position 5/8"

INSIDE MOUNT ALIGNMENTS

Sprocket inner position 1"

Sprocket middle position 1-3/8"

Sprocket outer position 1-5/8"

6

2.25"

6.5"

3.25"

1.625"

.39" holes 120° apart

6.5"

Figure 8 - Mounting Hole Template

7

01-35863B All Rights Reserved

© 2010, The Chamberlain Group, Inc.