When shims are required to be angled, wedge shaped, or anything other than flat squares and rectangles, specific steps have to be taken to offset the difficulty these angles create.
The first decision in manufacturing a made to order shim is material. Steel or Plastic Shims, and all the sub-materials that could be involved? Typically, our made to order plastic shims are HDPE, High Density Polyethylene or HIPS, High Impact Polystyrene. Steel shims and steel wedges are usually Grade 50 carbon steel or 303/304 stainless. When deciding on material of course the function and demands of the application are the dominant criteria, but if possible take into consideration plastic costs less and is much easier to machine than steel, hence will significantly lower cost and shorten delivery time of the finished product.
The Slotted Wedge Shim shown in Fig. 1 illustrates the steps required to manufacture this item. Unless a wedge is poured, using an injection mold or sand cast mold, it will be machined from flat stock. The shim in Fig. 1 is 4-1/2" x 4-1/2" x 9/16" thick. The flat stock starts out as sheets 48" x 96" x 5/8" thick. It is first cut into squares, 4-1/2" x 4-1/2". The next step, the angle, is the most difficult and critical. It can be saw cut or milled. The difficulty lies in securing the part.
If saw cut, the stock is cut standing upright with the saw blade cutting an angle from one corner diagonally across to the other. The result is two angled pieces. Allowing for a 1/16" wide cut the remaining wedges are 9/16" at the thick end. Sounds simple but the vice, tool and clamps that hold a piece like this in place confront a dimension not present if the wedge is being made of steel. Even with a compression strength of between 7,000 psi and 12,000 psi the plastic is considerably softer than steel and subject to movement and flexibility. As the blade passes through the work-piece is vibrating and can move off line or break loose from its fixture.
If the piece is being milled it will lay flat and either a vertical or horizontal mill will remove the unwanted material. In this case only one wedge shim will be produced. The remainder of the material will be milled away. The same problem exists as with saw cutting. It is difficult to secure the piece well enough to hold it in the correct position for the full milling process. While more difficult to mill, steel shims can be fixed in place using magnetic vises. Plastic must be held exclusively by clamps.
Once the wedge angle is fabricated the slot is relatively easy. At 13/16" wide it is the most common shot width so The Steel Supply Company own stamping punches that enable the slot to be formed in one down-stroke. These are the same punches used to make our slotted steel shims.