Or: 6 SFM 12-20-8ID

TECHNICAL DATA

The liner drill bushings are permanently pressed into a drill jig or fixture plate to provide a precise and stable location for renewable drill bushings in addition to protecting the hole in the jig plate from wear caused by frequent drill bushing replacement.

CONCENTRICITY:
(Total indicator reading) Bushings 1/8" to 1" I.D. - Concentricity 0" to .0003" (Max). Other sizes - Concentricty 0" to .0005" (Max). On counterbored bushings above tolerances will be met at the drill exit end.

RADIUS:
All bushings feature a blended and polished radius at drill entrance unless otherwise specified.

LEAD:
All bushings feature a concentric ground lead in additionto a chamfer on exit end of bushing.

STEEL:
Our bushings are manufactured from selected steels known for their long wear and stability. Bushings are also available from other materials at extra cost (bronze, M-2, D-2, stainless steel, etc.) (see also page 2)

HARDNESS:
Rockwell C 62-64 in the hole.

APPLICATION DATA
The liner drill bushing, type L, is used with our renewable drill bushings and are permanently pressed into a drill jig or fixture plate. The liner drill bushing provides a precise and stable location for renewable drill bushings in addition to protecting the hole in the jig plate from wear caused by frequent drill bushing replacement.
The inside diameter is ground for correct slip fit with renewable drill bushings.
The liner drill bushings can be installed flush with the jig plate without counterboring the mounting hole and they can be mounted closer together than the head liner. The head liner bushings are preferable where space permits and when heavy axial loads are anticipated.

INSTALLATION DATA
(Cast iron or unhardened steel jig plates) To maintain accuracy in the production operation, extra care must be taken in mounting hole preparation for liner bushing installation. Factors to consider are diametral interference fits, alignment, chip clearance, and proximity of bushing to workpiece.
a) INTERFERENCE FITS
In any press fit installation, metal is displaced. Usually, a combination of bushing closure and jig plate distortion results; therefore the best practice is to use the minimum interference necessary to retain the bushing in the jig plate. In most installations diametral interference of 0.0005 to 0.0008 inch is adequate forinstallation of liner bushings.
b) MOUNTING HOLES
An important point to consider is the roundness of the mounting hole. Because bushings tend to assume the shape of the hole into which they are pressed it is recommended that all mounting holes be jig bored or sized with a reamer to assure roundness. An ordinary twist drill will seldom produce a hole that is accurately sized and truly round.
c) BUSHING INSTALLATION
Before installing a liner bushing always lubricate the inside diameter of the mounting hole and the outside diameter of the bushing.
Bushings installed without lubricant may pick up metal and score the mounting hole during installation. Lubricated bushings are more easily removed for replacement with less chance of damaging the jig plate. Use a hand arbor to press the liner bushing into the jig plate whenever possible. If not, use some other means such as drawing the bushing into the jig plate with two steel plates and a nut and bolt. A hammer should be used only if no other methods are possible and then never strike the bushing directly; use a block to take the hammer blows. Whichever method is used, care should be taken to maintain centerline perpendicularity, otherwise inaccuracies may result in the production operation.

NOTE:
Chip clearance: Due to the abrasive action of metal particles sufficient clearance should be provided between the drill bushing and the workpiece to allow for removal of chips. Careful consideration of this point will aid in producing accurate holes. (A rule of thumb is, the greater the clearance the greater chance of error.)

Example: The recommended chip clearance for metal producing small chips, such as cast iron, equals one-half the drill diameter. The recommended chip clearance for metals producing long chips, such as cold-rolled steel, equals one to one and one-half times the drill diameter.

Maximum accuracy: Use drill bushings of different lengths to obtain the combined advantages of adequate chip removal and precise accuracy.

Example: Use drill bushing that is short enough to provide chip clearance during the drilling operation. Next, use a drill bushing long enough to contact or closely approach the work piece for the reaming operation.