Hardware

I pc. PVC pipe. 2" dia. (nominal) x 1 ft"

1 brass barbed hose connector, male

2 threaded inserts, V*m-20

2 plastic knobs with '/T-20 x 1" studs;

4DK-46 from Reid Tool Supply Co. (800-253-0421)

2 compression springs. Va~ I.D. x Vr," long

3 flathead wood screws. #6x1"

2 steel rods, same dia. as router's edge-guide rods X approx. 4"

'Phenolic and polycarbonate are recommended. Acrylic is acceptable.

Vacuum tape

Vz" steel rod

Plastic knob with stud

Compression spring Adjustment bar

Pivot plate

Barbed hose connector

PVC pipe

Pivot base nolic, though a base made from dear polycarbonate or acrylic might be easier to position. Cut the pivot base to the dimensions specified by the Cutting List. You want to be able to use the corners of the base to align it on a pivot point marked (with crosshairs) on a workpiece. Thus, you must be certain that the base is square, but also that the center of the square is marked. (If you are using polycarbonate or acrylic. leave the protective masking paper on it and make all the layout marks on it. Apply a strip of masking tape to the phenolic, and make the mark on it.) Carefully drill a '.»-inch-diameter hole through the plate at that point.

3. Rout the circular groove for the pivot collar.

Use the Trammel Baseplate on page 39 on a plunge router for this operation. Use a bit that matches the wall thickness of the PVC pipe as closely as possible. I used a /6-inch bit. Set up the trammel baseplate by cutting test rings in scrap material, then fitting the PVC pipe into them. When you've achieved a good fit. n>ul the groove in the pivot base, using the hole drilled in the center as your pivot. Make the groove-only !* inch deep, just enough to catch the pipe and serve as a reservoir for the special glue that will bond the pipe to the plate.

4. Drill and thread the vacuum port. Make the VACUUM TRAMMEL PLAN VIEWS

TOP VIEW -

port by redrilling the center hole (the one you just used as a pivot). Determine the size of hole needed for the vacuum connector you will use (I used a brass barbed hose connector with a '/4-inch-18 NPT male thread on it).and drill out the hole to that size. Then tap the hole for the connector. Note that National Pipe Thread (NPT) is significantly different from the National Coarse threads on fasteners, so use the correct tap. See the section "Cutting 'ITireads" in the appendix.

5. Glue the post to the pivot base. I experimented with several glues before settling on Devcon's Plastic Welder which I bought at the local harcware store. Mix the glue's two constituents and spread it in the circular groove in the pivot base. Set the collar into place. Use a small-diameter dowel to build up a fillet of glte around the inside and outside of the collar, to reinforce the joint.

Set the assembly aside while the glue cures. No clamping is nccessary.

6. Cut the pivot plate. This is the plate that fits over the pivot post, tying the router to the pivot. It, too, is plastic in my prototype, though you could make it of plvwtxxl.

7. Shape the pivot plate. Lay out the shape of the

SIDE VIEW

Vacuum

Reid #DK-46 plastic knob

Compression spring Adjustment bar—s

Pivot collar f (PVC pipe)

Trammel rod

Transition plate

Pivot base

Pivot plate

PIVOT BASE PLAN

BOTTOM VIEW

Vacuum tape plate as shown in the drawing Pii>ot Plate Plan. The break in the ring allows you to fit the trammel on the pivot base after it's been vacuum-set on the workpiece. The slot is wide enough for the vacuum hose to pass through.

On black phenolic, you aren't going to be able to see any layout lines. So apply strips of masking tape to the plastic before doing the layout work. An alternative is to apply a sheet of paper to the plastic with artist's spray adhesive.

Drill a 1 »-inch-diameter hole at the pivot point indicated in the Bottom View of the Pivot Plate Plan drawing.

lav out the arc and the tangents that extend from the arc to the corners of the adjustment bar. Cut the tangents; the band saw is ideal for this, though other tools with do the job.

Next use carpet tape to bond the plate to a backup scrap that's big enough to be clamped or dogged to the workbench. (This may seem an ironic approach, since we're talking about a vacuum-clamped jig. Rut the truth is. vacuum clamping doesn't work in every situation, and this is one in which it won't work.)

Using the trammel baseplate, rout the arc. Later, after you've separated the plate from the scrap, you can file or sand the edge to fair and smooth the transition from arc to

PIVOT BASE PLAN

W phenolic

Glue the collar to the base using a special two-part glue called Devcon's Plastic Welder. Pushing a plunger on the package dispenses equal amounts of the two constituents, which must be mixed. Spread the thoroughly mixed glue on the bottom edge of the collar and in the groove in the base. Then press the two parts together.

PIVOT PLATE PLAN

TOP VIEW

END VIEW

Plastic knob with VC-20 X I" steel stud

PIVOT PLATE PLAN

TOP VIEW

SECTION VIEW

Plastic knob with VC-20 X I" steel stud

Compression spring, r---

END VIEW

Threaded insert. m VC-20 ** P,lot hole

Trammel rod f -r I Phenolic pivot plate

BOTTOM VIEW

BOTTOM VIEW

tangent, and to buff up the appearance of the plate's edges For now, leave the plate stuck to the scrap.

8. Rout the pivot hole. Use the plunge router fitted with the trammel baseplate for this operation. As you did when routing the groove in the pivot base, make test cuts in scrap to adjust the router and trammel. You want a fairly tight fit of the post in the hole. A bit of resistance as the plate turns on the post isn't a problem, but slop is. If the q) plate can rattle a bit on the post, you will not get satisfac-torv cuts using the trammel. So make sure the trammel adjustment is just right before making the cut in the plate.

After routing the hole, separate the plate from the ¡3 backup scrap. Cut the hose-clearance slot on the band saw or with a saber saw. File the comers of this slot to soften them, and smooth the transitions from arcs to straights Clean the edges of the plate using fine sandpaper or a scraper.

0j u

«m 9- Make the adjustment bar. Cut the hardwood ^ to size. I used cherry, but many other hardwoods will do just fine.

Lay out and drill the holes for the trammel rods, as well as for the locking knobs. Opting for sturdincss, I used Vz-inch rods. I bored %»-inch-diamctcr holes for them in the adjustment bar. To lock the pivot plate in position on the rods. I used small plastic knobs with '/i-inch-diamctcr, 1-inch-long studs turned into threaded inserts.

Drill the pilot holes, using the drill size specified for the inserts you use. Drive the inserts.

10. Mount the bar on the pivot plate. Clamp the pans together. Lay out, drill, and countersink pilots for the mounting screws. Drive the screws.

11. Make the rods. The trammel assembly has two sets of rods. One is set is the pair of trammel rods that extend from the transition plate to the pivot plate. I used Vz-inch steel rods for this purpose: you can certainly substitute smaller-diameter rods. The Hardware List specifics 36-inch-long rods. You can make them longer or shorter, as you

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Wood Working for Amateur Craftsman

Wood Working for Amateur Craftsman

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