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• HEAD PRESS FIT, TYPE "H" - TECHNICAL INFORMATION

TECHNICAL DATA

This drill bushing is preferable where heavy axial loads may force a headless bushing out of the jig plate.

STANDARD SIZES:
Standard sizes in a given I.D. range are sizes listed in the decimal equivalent chart either as a fraction, number or letter size. Any other decimal or millimeter size within a given range is considered special and will be priced accordingly.

TO ORDER:
Specify Type and "Reamer Bushing". Reamer bushings will be furnished with correct tolerance on all fraction, number, letter and all decimal sizes. (Priced as specials.)

COUNTERBORE:
Bushings with small holes are counterbored leaving correct drill bearing, to facilitate chip removal and lubrication.

NO COUNTERBORE:
Bushings normally counterbored may be ordered without counterbore by specifying "No Counterbore" or using abbreviation "N CB." (Priced as specials and non-returnable.)

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

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

LEAD:
All bushings feature a concentric ground lead in addition to 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 head press fit, type H, drill bushing is similar to the headless press fit except that it has a head or shoulder on the drill entry end and must be counterbored for flush mounting.
This bushing is permanently pressed into the jig plate or fixture and is generally used where replacement due to wear is not anticipated during the life of the tooling and where a single operation such as drilling only or reaming only is performed.
The head press fit bushings are preferable in any application where heavy axial loads may eventually force a headless bushing out of the jig plate.

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 press fit bushing and liner installation. Factors to consider are diametral interference fits, alignment, chip clearance, and proximity of bushing to work piece.

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 0.0003 to 0.0005 inch is adequate for installation of head press fit 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 head press fit 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 bushing or liner 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 bushing long enough to contact or closely approach the work piece for the reaming operation.

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