METAL BODY REPAIR - OD1653 - LESSON l/TASK 1
2 Garnet, a semiprecious jewel, is the most important of the
natural minerals.
3 Emery and flint break down easily and are better suited for
household use than for industry.
4 For dry sanding, high quality hide glues are used for anchoring
abrasive grains to the disk backing. For wet sanding, resins are used as
the bonding agent.
(b) Coated abrasives fall into two additional classifications, based on
how widely the minerals are spaced. If the minerals are close together, it
is referred to as close coat. If the minerals are widely spaced, it is
referred to as an open coat.
(c) Close coat abrasives are applied in such quantity as to completely
cover the backing.
(d) Open coat abrasives are applied so as to cover from 50 to 75 percent
of the backing.
(e) The open coating provides increased pliability and good cutting
speed under light pressures. Open coated abrasives are used where the
surface being ground is of such nature that closely spaced abrasive minerals
would rapidly fill up, such as sanding paint or wood. Following is a
suggested use of three of the most common disks.
1 The No. 24 disk is coated with a coarse open coat abrasive. It
must be used with reasonable caution to prevent making deep scratches in the
surface. This disk is most generally used in rough sanding surfaces that
have been painted. Sand until a small volume of sparks is noticed coming
from beneath the disk; when these appear, stop sanding.
2 Close coat No. 36 disk is used for several purposes in the body
shop. It is most generally used for removing welds and in place of the body
file in revealing high and low spots in the bumping operations.
3 Close coat No. 50 disk has only one function: performing
finishing operations on metal surfaces such as steel and soldered panels.
This disk will remove scratches left by No. 24 and No. 36 sanding disks.
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