TM 5-1940-321-13&P
(1)
Since both straight cut and bias cut patches look the same, it is a good practice to mark the
patches. This will allow identifying a bias cut patch without having to stretch it with your hands. When
cutting a circular shaped patch, there is no edge to place parallel to the edge of the material; therefore,
the circular patch may be cut from anywhere in the fabric. The circular shaped patch will stretch more in
the direction of 45 degree to the threads and less in the direction parallel to the threads; therefore, a
circular patch to be applied to an area of the craft with compound curves should be marked before it is
cut.
( 2 ) The markings can indicate the direction of stretch (bias direction) or the
direction on the threads (warp or weft direction). Figure F-4 illustrates how to
mark and lay out bias cut patches on fabric.
Figure F-4. Determining the Bias Angle and Marking Fabric before Patches are Cut.
F-3. SCUFFING FABRIC. New hypalon neoprene fabric and all previously glued fabric must be scuffed
before gluing. Scuffing removes a very small amount of coating from the fabric to expose fresh material
which allows it to properly bond with the glue. Strongan fabric and parts made of PVC such as the D-ring
pads and carrying handles are not scuffed except to remove old glue. Wooden components must be
scuffed lightly to remove the paint and expose fresh, clean wood before fabric can be glued to the wood.
Scuffing on very small areas can be accomplished manually using a pumice stone (see appendix E, list
of tools). A pumice stone is included in the repair kit provided with each F530 IAB. Power tools are
normally used for scuffing hypalon neoprene fabric at the repair facility. New hypalon neoprene fabric
stock to be used for patching is normally scuffed in large sections prior to being cut into patches.
Strongan fabric is not scuffed. Material being cut into patches. Strongan fabric is not scuffed. Material
should not be scuffed more than 48 hours before gluing since exposure to air causes the freshly scuffed
plastic to heal. A small disk sander (see appendix E, list of tools) with a 100 grit sanding disk is used to
scuff large sections of new fabric as shown in figure C-5. Weights placed on the hypalon neoprene fabric
stock will keep it flat during scuffing. When scuffing on a hard surface such as a table, a foam pad must
be used under the fabric to avoid damaging the fabric. When scuffing an area on the craft, the craft
should be inflated to only 180 mbar (2.61 PSI). Small areas are scuffed using a dremmel tool with an
aluminum oxide grinding stone (see list of tools, appendix B). The dremmel tool provides greater control
for small areas. Scuffing with a dremmel tool is shown in figure F-6. Apply the following rules when
scuffing:
F-5
