Tip #53
Shopsmith Ovararm Pin Router
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Building Fixtures

For reasons of durability, most fixtures are made from particleboard or other similar materials that are covered with plastic laminate. These materials will withstand long periods of continuous use without wearing down and changing the profile of your pattern. This type of material is readily available from cabinet shops and hardware stores as cut-outs for sinks from countertops and is usually very inexpensive.

If laminate covered particle-board is not available in your area, it is suggested that you use hardwoods such as oak, maple or cherry. . . or a high-quality plywood without any “voids” or holes in the edge grain. Remember, the key to building a long-lasting fixture is to make it with durable materials that will withstand long periods of continuous use without wearing and altering your desired profile.

There are two basic ways to build routing system fixtures: us-ing an existing product or using a template.

Using An Existing Product-The first and easiest way to do this is to start with an existing product and use it as a template to guide your bit through the process of cutting the grooves in your fixture blank.

To begin, cut out a fixture blank that is 1" to 2" larger than the dimensions of your item. Start by drilling countersunk pilot holes for the holding screws in the existing item. Then, attach the item to be duplicated to the particleboard side of your fixture blank with screws or nails (Figure 22-35). Be sure to position the attaching screws or nails in a location where they will not be seen or be in the path of the router bit when you make your cuts.

Next, select the size straight bit you will be using to make your profile cuts (usually a 3/8" straight carbide bit) and thread the matching pin into the center hole of the pin insert in the table. Align the pin and bit perfectly by using the base of a combination square (Figure 22-36) or a guide block with a same size (3/8" in this case) through-hole (Figure 22-37).

Once the machine is aligned properly, set the depth-stop rod to make a cut about 3/8" deep in the surface of the fixture.

Turn the fixture over with the product to be duplicated on the bottom and start your router motor. Slide the fixture forward until the guide pin touches the edge of the product and lower the rotating bit into the laminate material about 1/8". Twist the quill feed handle to lock it into position.

Guide the product around its profile (against the rotation of the bit), being sure to always maintain contact with the guide pin during operations (Figure 22-38). Repeat this process two more times until you have cut your groove in the laminate surface of your fixture to a depth of about 7/16" to 1/2". Remove the existing product from the fixture. To make dupli-cates of this product, simply screw a blank workpiece to the particleboard side of the fixture, drop the groove in the laminate side of the fixture over the protruding table pin, and make your profile cuts. It's that simple! Note: By cutting another groove (shown with broken lines in Figure 22-29) in the fixture, you can also cut out a plaque-shaped picture frame, as well as a smaller plaque, all at once.

Using A Template-A template is a wood or plastic shape that is mounted to the fixture blank and used as a guide to cut the grooves in the fixture blank when making a fixture.

To make a template, first trace the desired shape onto a piece of stiff paper or cardboard to create a pattern (a pattern is the paper or cardboard “master” of your shape that is then traced or glued onto the template blank).

Then, cut out the shape of the design and trace the pattern onto a 1/2" thick piece of plywood or plastic. Once the pattern is traced onto the template blank, cut out the shape with a scroll saw, bandsaw or sabre saw. Remember that the grooves in your fixture will only be as smooth and perfect as the template you use to cut them with . . . so take extra care in cutting out and sanding the template so that it's as perfect as possible. Note: When building or working with intricate-shaped projects, it's a good idea to use the original template to trace the pattern of your project on your workpiece (or, when making your fixture, on the top side of the fixture) so you can clearly see each area as it is being cut.

Next, use screws or nails to affix the completed template to the particleboard side of a fixture blank that is slightly larger than the design. Warning: Be careful not to locate screws or nails in the path of your bit.

Insert and align the matching bit and guide pin. When cutting out designs with tight curves, you may have to use a bit and pin combination that is smaller than 3/8".

Turn your fixture over with the template on the bottom, set the depth-of-cut as described earlier and turn on the router motor.

Ease your pattern towards the pin until it makes contact, lower the rotating bit into the laminate side of the fixture and cut the grooves to a depth of about 7/16", as described previously for making a fixture from an existing product.

If your template is intricate with lots of cut-outs, you will have to move your bit from cut-out to cut-out, raising and lowering the bit for each one. Note: If a cut-out is wider than the diameter of the pin and bit you are using, you must always maintain firm pres-sure against the pin while you guide the template through the cuts. If you allow the fixture to switch from one side of the cut-out to the other during operations, your fixture groove will become wider than the bit and could cause a loss of precision and a rough cut when duplicating your workpieces.

Important Tips on Building Fixtures
Screw-on Fixtures-Caution: Be sure to countersink al/screw heads on the laminate side of your fixture soit will glide smoothly across the routing system table without marring the table surface.

Warning: Be certain all hold-down screws are located in areas that are not in the path of the router bit.

Drive-on Fixtures-Once the screws are positioned in the fixture, sharpen the points with a file to make it easier for them to grip your workpiece.

To ease insertion and removal of workpieces, drill a 1" diameter hole in the fixture bottom (away from the path of the router bit during cutting) to allow you to push the workpiece out after it is cut.

Clamp-in Fixtures-After you have cut the guiding grooves in the fixture base, attach 3/4" thick side and end rails to the base with screws and glue. Be sure the sides stick up above the base the same distance as the thickness of your project workpiece.

If your fixture has a floating bar to hold your workpiece, use T-nuts set into counterbored recesses and thumbscrews to apply adequate pressure against the floating clamp bar to hold the workpiece during operations (Figure 22-39).

An alternative to the floating bar clamping system is eccentric cams that can be rotated 1/2 turn or less to grip the workpiece tirmly (Figure 22-40).

Drop-in Fixtures-For extra holding power, you can add protruding drive-on screw points to drop-in fixtures.

To ease insertion and removal of workpieces, drill a 1" diameter hole in the fixture bottom (away from the path of the router bit during cutting) to allow you to push the workpiece out after it is cut.

All Fixtures-When making a fixture that contains small areas where all stock is to be removed (and the scrap will not be held in position by screws), remove all stock from this area on the fixture, as well. This will allow you to rout out the entire area in shallow passes and prevent the scrap from grabbing when you cut out your workpiece.

Valuable Tips for Working with Fixtures

• Wax the laminate side of fixtures frequently to help them glide smoothly over the table surface.
• Clean the sawdust and debris out of the pattern grooves of your fixture occasionally to prevent jamming and help keep the fixture operating smoothly.
• If a fixture is expected to be used in a production environment for making a large number of the same item, use your original "master" fixture to make one or two more fixtures before it has a chance to wear out and lose its accuracy.
• When cutting out workpieces with a fixture, never allow your bit to cut into the particleboard side of the fixture more than 1/32" to 1/16".
• If you occasionally need to reduce the size of a project made on a fixture by a small amount, this can be done by using a smaller guide pin and a larger bit when cutting out your workpiece. Remember to work carefully and always guide your stock against the outside edges of your fixture grooves when doing this.

• Figure 22-41. By changing to an edge cutting bit, you can use your fixture to shape the edges of a workpiece after it is cut out.

  If the edges of your project must be shaped after the profile is cut out, this can be done with the workpiece still attached to the fixture by merely switching bits (Figure 22-41). By changing to a smaller guide pin, you can alter the profile of your decorative cut...but remember to always guide your fixture against either the outside or the inside edges of the grooves during this entire operation. If you switch groove sides in mid-cut, you will change the shape of your decorative cut.
• If you will be making a large number of the same project with shaped edges, it's a good idea to make several identical fixtures so you won't have to keep changing from a straight bit (for making cut-outs) to a profiled bit (for shaping the edges).

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