HOW TO MAKE A LAPPING FILM SUBSTRATE

NOTE: This is a rough draft and work in progress. Expect errors. Expect typos. The content of this page is the work of @rbscebu and used with permission.

One substrate piece is required. Different grades of lapping film can be easily changed on the substrate. The substrate needs to be perfectly flat, stiff, light and about 20mm to 30mm thick. There are two main popular choices for a substrate; acrylic or composite (acrylic sheet on ceramic tile and PVC foam or balsa wood).

Acrylic (most popular)

This must be a piece at least 20mm and up to about 30mm thick. No “manufacturing” is required as it can generally be purchased ready-cut to size (300mm x 73mm). Make sure that it is cast acrylic (the most common) and not extruded acrylic that tends to crack more easily. Colour of course does not matter. Acrylic can be cut with a jig-saw fitted with a suitable blade. Search the internet for the best way to do this with a jig-saw. If desired, you can “break” the bottom and side corners of the acrylic with sandpaper to make it more comfortable to hold in-hand.

Thick cast acrylic may be available at a good glazier’s or they may be able to direct you to where is can be obtained.

Composite

A composite substrate can be used if you do not have ready access to suitably thick acrylic, or if you want a lighter mass than an acrylic substrate. This substrate requires the most work to “manufacture”.

• A 295mm x 73mm x about 6mm (minimum) thick piece of cast acrylic. Make sure that it is cast acrylic (the most common) and not extruded acrylic that tends to crack more easily. Colour of course does not matter. Acrylic can be cut with a jig-saw fitted with a suitable blade. Search the internet for the best way to do this with a jig-saw.
  Cast acrylic may be available at a good glazier’s or they may be able to direct you to where is can be obtained. It should also be available on line at eBay, Amazon, AliExpress, etc..
• A piece of smooth (not embossed) piece of ceramic tile about 295mm x 73mm x about 8mm thick (preferably not with a gloss finish). If more than 73mm wide, it will need to cut down to 73mm wide. You can do this yourself if you know how and what to do. A suitable tile is readily available from most home improvement/tile stores or some hardware stores. They may even cut it to size for you.
  If your piece of tile has a gloss finish, you will need to sand the gloss surface to a reasonably matt finish so that the adhesive will bond to the surface.
• One of:
  • A piece of PVC foam 300mm x 75mm x 15mm to 20mm thick. You can build the PVC foam thickness up by gluing multiple pieces of PVC foam together. Do not use contact or other solvent based adhesive. The PVC foam can generally be purchased at better hobby stores or on line. Cut the foam with a box cutter and steel rule to the required size of 300mm x 75mm.
    OR
  • A piece of light (low mass) wood such as balsa wood 300mm x 75mm x 15mm to 20mm thick. You can build the balsa thickness up by gluing multiple pieces of balsa wood together with contact adhesive. This balsa wood can generally be purchased at better hobby stores or on line. Cut the balsa wood with a box cutter and steel rule to the required size of 300mm x 75mm.
• Glue to bond the foam/balsa wood piece to the tile piece. A structural epoxy glue (not quick-drying) should do. This will be a permanent bond that you should not need to be broken.
  
  Note: DO NOT use a solvent based glue (e.g., contact adhesive) on PVC foam as it dissolves the PVC foam.
  
• A 25mm paint brush and about 250ml of acrylic paint (your choice of colour). The paint is used to further seal the foam/balsa wood from moisture and it looks better.

To put the composite substrate together:

1. If the tile has ridges on its undersurface, you will need to grind these off so that the PVC foam/balsa wood has a reasonably smooth surface to bond to. This grinding can be done with a course (say 400 grit) whetstone.
2. Glue the piece of foam/balsa wood to the underside (non-finished side) of the piece of tile. Allow the glue to set (about 24 hours). Although not required if done properly, you can use weights to hold the bond together while the glue sets – just be careful that the foam and tile remain in alignment.
3. Once the glue is set, apply two (or preferably 3) coats of acrylic paint to the foam/balsa wood and sides of the tile in accordance with the paint manufacturer’s instructions. Try not to get any paint onto the top surface of the tile. If you get paint on the tile’s top surface, remove it with a dishwashing plastic scouring pad once the paint has dried.
4. Using contact adhesive or rubber glue, bond the 300mm (12”) x 75mm (3”) piece of cast acrylic to the top surface of the piece of tile. Allow the glue to set for about 24 hours.

A completed composite lapping film substrate being clear acrylic mounted on a piece of white tile mounted on balsa wood and painted is shown in Fig. III(A) 1.