No manual interruption is required at any stage, which makes the back spot facing tool most ideal for machines with auto-cycle like VMC:

 How it works?

1. Rotate Anti-clockwise and wind folds in.

2. While rotating in anti-clockwise direction lower the ABSF tool into the bore.

3. Give some clearance from the bore’s lower face and rotate in clockwise direction for wing to fold out.

4. Rotating in clockwise direction begin the cutting feed.

5. Lower the tool, rotate in anti clockwise direction for the wing to fold in and retract out of the bore.

 Features:

• Can also be used on conventional radial drills, milling & boring machines

• Available for holes from Ø 7 mm onwards.

• Back spot facing tools From Ø 7 mm to Ø 12 mm, offered with solid HSS wing

• Back spot facing tools from Ø 12 mm onwards, offered with inserted carbide

• e7 tolerance on the guiding shank for a good guide as well as entry & rotational clearance

• Coolant through offered optionally

• Co-axially jig-bored pivot holes & blue-matched wing seating transferring the cutting load to the shank, thereby preventing damage to the wing.

• Case hardened shank & hardened wing & other parts for wear-resistance & longer life

Generally, the ratio of maximum back spot facing dia with respect to the corresponding pilot dia is 2:1. Since a back spot facing tool is normally custom-built, there is no general thumb rule for the back spot facing dia with respect to the corresponding pilot dia. The holding shank can be cylindrical (suitable for side lock holders), Morse taper, ISO, BT, and Metric, depending upon the machine spindle taper. The rear counter boring tool is meant for producing one specific back spot facing dia through one specified bore. Therefore, these back spot facing tools are ideal for a large batch production or mass production.

The below given graph shows for a particular sized hole, upto which size of back spot face can be done. It also shows which kind of wing and inserts will be used. Click on the image to view a larger picture

OPERATION

Make the axis of guiding pilot shank of the automatic rear counter boring tool true to the axis of the pilot hole. Use cotter / drive-key for preventing the tool from falling down while cutting. The back spot facing tool enters the pre-drilled pilot bore in an anti-clock wise rotation of the spindle. The wing is so designed that even if it is open, it folds into the pocket on touching the job in anti-clockwise rotation. After the wing come clear of the pilot bore in anti-clock wise rotation, reverse the spindle rotation to clockwise; due to centrifugal force, the wing automatically opens up; with feed it cuts. After the spot facing is over, take the back spot facing tool little away from the job; then reverse the spindle rotation to anti-clockwise and pull the automatic back spot facing tool out of the bore. The wing automatically folds into the pocket on coming in contact with the job in anti-clockwise rotation.

CUTTING PARAMETERS
SPOT FACE DIA (in mm)	SPINDLE SPEED (RPM)	SPOT FACE DIA  (in mm)	SPINDLE SPEED (RPM)	SPOT FACE DIA (in mm)	SPINDLE SPEED (RPM)
9 to 11 *	575	18to 21*	285	36 to 45	320
12 to14*	450	22 to 25	550	46 to 55	260
15 to17*	360	26 to 35	450	56 to 65	215

Tools for this range of back spot facing are generally with HSS wings and feed rates of 0.05 & 0.03 mm per rev. in CI & MS are generally recommended. For the rest, 0.2 and 0.15 mm per rev in CI & MS, respectively are recommended, since Carbide inserts are generally used in this range. Cutting parameters depend on machine condition, clamping rigidity, hardness of job etc. For intermittent cutting, spindle speeds may almost be doubled, while feed rates are to be reduced by 30%. These are indicative parameters. Actual parameters are to be established only by trial and error.

EXAMPLE PROGRAM

Program Lines	Description
G54 G17 G90	G17=X-Y plane, G90=Absolute dimension, G54 = Work Offset)   Please note you can change G54 to G55/G56/G57 etc. as per your machine.
T1D1	Tool Call. This can be any other tool call. Program as per your machine.
G0Z100	Rapid movement to 100 mm above the job height.
G0X0Y0	Rapid movement to centre of the hole.
G0Z20	Rapid movement to 20 mm above the job height.
M4S500	Spindle Rotation at 800 RPM in counter-clockwise direction. To enter the bore.
G0Z5	Rapid movement to 5 mm above the job height.
G1Z-85F250	Feed at 250 mm/min till Z depth of -85 mm. The cutting edge is 40 mm above tool zero. The length of the hole is 35 mm. Total travel is 40+35 mm + 10 mm safety = 85 mm.
M08	Coolant on.
M03S360	Spindle Rotation at 360 RPM in clockwise direction for cutting.
G4F2	G4F2 = Dwell of 2 seconds.
G1Z-76 F100	Feed approach to 1 mm below cutting at 100 mm/min
G1Z-65 F20	Cutting feed at 20 mm/min for spot facing of 10 mm depth.
G1Z-85 F250	Retracting back to Z-85 in feed of 250 mm/min
M04S800	Spindle Rotation at 800 RPM in counter-clockwise direction. To enter the bore. To exit the bore.
G4F2	G4F2 = Dwell of 2 seconds.
M09	Coolant Off
G1Z5F250	Retracting out of the bore to Z5 in feed of 250 mm/min
G0Z100	Retract in rapid to Z100.
M30	Cycle Stop.

Note: This program is as per Siemens Sinumerik CNC Standards, some G codes and M codes may vary for CNC of other makes. Please use this only as a reference to make CNC programs for your machines. The parameters like feeds and speeds need to be manipulated as per your  requirement.

ASSEMBLY

Press the pivot pin in the bore, provided on the tool shank. Position the wing in the pocket through the pivot pin. Screw on the pivot screw through the tapped hole till its point enters the cone, provided in the bottom of the wing. Tighten the pivot screw till the clearance between the pivot pin and pivot screw is just sufficient for the wing to freely swing in and swing out of the pocket, at the same time avoiding any axial and radial play. Lock this position by tightening the lock screw through the aluminum binder. It is advisable to release the pivot screw by about 30% before locking, so as to nullify the possible thermal expansion during cutting. Do not over tighten the insert clamping screw. Solid HSS wings are with integral pivot pin. Regrind the blunt cutting edges of HSS wings.

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