I'm sure Bruce will cover this very thoroughly. But, templates and fixtures can be attached by various methods. Double stick tape works just fine for most hobbyists, but that is slow in a production setting. Many production shops use a vacuum pump along with vacuum gasket tape. The part is simply "sucked" to the template and held very securely. Often times, handles will be mounted to give a firm grip and to keep hands well away from danger.
Roscoe basses has a number of videos posted which show some of their fixtures which use vacuum.
Yes, thank you for posting that! You saved me a whole lot of writing. That's great quick video showing a pin router in action, using a good production-level fixture. He's routing the perimeter of a body with a straight cut, in three passes of depth.
See how he works the spindle with the foot pedal, as I described a couple of posts above. Pressing the pedal pneumatically lowers the spindle to a depth set by the indexing depth stop up on the head. He routs all the way around, hits the pedal again, and the spindle raises up. Clicks the depth stop to the next position, taps the pedal, spindle goes down to the next depth. Repeat. That's the basic operating sequence of a pin router.
Notice how the fixture is big and flat and the operator is sliding it around on the table using the handles at the outer edges. It slides around easily, but you have to be careful. Making the fixture somewhat heavy with outboard handles helps him keep it under control and resist the torque of the cutting. There's some serious horsepower turning that bit. If it grabs and digs in, it's going to try to spin the fixture around. And maybe take you with it. That's where things go flying and people get hurt.
He doesn't show the details of how the fixture is made, but the top surface has routed grooves and seals in the shape of the body, along with some kind of marks or pins to align it. The red rubber hose connected to the back of the fixture goes to a vacuum pump, and he has a switch somewhere to turn it on and off. If the fixture is made well, the vacuum will hold the body blank in place very tightly. It will release and re-clamp in a couple of seconds. Vacuum hold-down systems are very popular with pin routers and CNC machines. My buddy Rob Allen, right down the hall, uses vacuum fixtures for most hold-down operations in his CNC machine.
There are many other ways to clamp down the workpiece. A classic in factories 50 years ago is to use De-Sta-Co style toggle clamps. These are made in many designs and sizes. The lever snaps it closed or opens it up in a second. They are commonly used on industrial fixtures. I have several boxes of them that I picked up at surplus stores for cheap.
You can also make your own wooden hold-down clamps with bolts and wing-nuts. And there's always screws and pins. Most of my collar-routing fixtures and templates are aligned on the workpieces with 1/8" steel dowel pins. In some places, I use flat-head machine screws going down through extra waste areas of the workpiece, threading into T-nuts in the fixture.
And, yes, you can use double-sided tape for one-off jobs. But you need to be careful. Use good tape, plenty, and widely spaced. There's a lot of torque trying to kick that workpiece around in all directions. Tape can creep out of position under side load, which can ruin your part.
That's the top side of the fixture. You need to figure out some way to clamp the blank down, solidly and repeatably.
The bottom side of the fixture, which you can't see in the video, has the pattern. It's probably 3/4" MDF, cut to the actual size and shape of the body outline. It has to be aligned accurately to the workpiece above. The pin rides around it as he slides the fixture around the table.
It looks like the fixture has a "skirt" around the outside of the pattern on the bottom. This keeps the bulk of the wood chips out from underneath, so they don't get jammed between the pin and the pattern. That would create a lump on the perimeter of the body.
Obviously, on an inverse pin router, it's all inverted. The pattern goes on top and the blank is on the bottom.
You can see that dust and wood chips are a real problem that you have to deal with in these machines. The overhead pin routers in particular, with no guards, throw a big arc of chips. When Mike would rout a couple of bodies on the big green machine, it would make a circle of wood chips on the floor about 15' diameter. You can see the mess in that video.
The Onsrud inverted pin routers are somewhat neater. They have a dust collection chute built in, and will pull most of the chips down into it.
I plan to fit the big green machine with some kind of a hood hooked up to my big dust collector. That's going to take some experimenting.
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It will manually make a copy of nearly any 3D pattern. Carved tops (inside and out), body contours, necks... you name it. It is basically a manually operated X/Y table with gravity fed Z (vertical) cutterhead. A cheap alternative to a fully a automated CNC although... they are becoming pretty affordable these days!
