Countersinking - Cessna 510 Mustang Structural Repair Manual

1. General
A. For all-around purposes, the micro-stop countersink, fitted with a removable cutter, is the most efficient countersinking tool
for use with portable equipment.
B. The shaft of the micro-stop countersinking tool rotates on a bearing inside an adjustable "locking sleeve and foot piece
assembly." The foot piece (or "stop" as it is often called), threads onto the shaft bearing, for depth adjustments.
C. Markings, indicating depth differentials in 0.001 inch (0.254 mm) increments, surround the beveled circumference of the
locking sleeve to help make depth adjustments.
D. The adjustment is made by pulling the sleeve back and turning the stop, to increase or reduce the depth of the cut. The
sleeve is then dropped back into its original position to lock.
NOTE: Make sure that the locking splines intermesh; only then is the adjustment locked.
E. The stop countersink can be adjusted or set up on the part to be countersunk, if the following precautions are taken:
(1) Be sure the adjustable foot piece is extended far enough to make sure that the cut will not be too deep.
(2) Gradually increase the depth adjustment until the depth and diameter of the hole are the same as the size of the
fastener head.
(3) If you are at all doubtful of the accuracy of the adjustment, try the countersink on a piece of scrap sheet stock before
you use it.
F. The pilot pin aligns the spinning cutter as it cuts into the material. The pilot pin should be approximately 0.002 inch (0.051
mm) less in diameter than the fastener hole. This lets the cutter spin without binding in the hole. Cutter-pilots which are
more than 0.002 inch (0.051 mm) smaller than the hole size, will allow the cutter to wobble and make a lopsided
countersink.
G. Cutters are available in a variety of cutting angles. The most frequently used cutters are 100-degree. NACA type rivet
heads of fluid tight rivets use 82-degree countersinks. The cutting angle is stamped on each cutter.
CAUTION: Make certain the cutter is tightened in the countersink shaft before you use the stop countersink.
H. When the stop countersink tool is used, it must be held as shown in Figure 1.
I. When using the stop countersink, follow these rules:
(1) Before you use, check countersink cutter for pilot size, sharpness, degrees of cutter, and true running.
(2) Back up the countersink to a safe depth of cut, then gradually increase depth to proper setting.
(3) Hold countersink at a 90-degree angle to material.
(4) Take full depth of cut each time.
(5) Apply pressure directly behind the countersink.
(6) Stop face must be highly polished to prevent marring the material.
(7) Select the size and length fastener to be installed and use it to judge depth of countersink.
(8) Do not let the stop spin on the material.
J. Countersink requirements are described in Figure 2.
Copyright © Textron Aviation Inc.
Retain printed data for historical reference only. For future maintenance, use only current data.

COUNTERSINKING

FOR TRAINING PURPOSES ONLY
ISSUE 02 , JAN 2018
Model 510 Structural Repair Manual (Rev 2)
51-40-08-0 (Original Issue)
Print Date: Wed Mar 21 05:12:02 CDT 2018
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