Shortly after getting back into building R/C airplanes I joined RC Universe and I came across discussions about building using magnets instead of pins. I liked what I saw and decided to go this route myself. My primary resource for creating my magnetic setup is Airfield Models. This is a wonderful site that will suck many hours from your day.
I used Paul's plan for building all of the vertical jigs and presses. I made mine from 1/4" birch plywood I had left over from my Cozy project. I made the following sizes:
I then went to Master Magnetics, Inc. and ordered 350 of the fixture magnets and two rolls of the 1" magnetic tape.
Besides the vertical fixtures described at Airfield Models I came up with an additional device used to securely hold down various pieces of wood up to about 3/8" thick.
Here are pictures of my various magnetic tools:
After cutting all of the fixtures I added all of the magnets. Four magnets per fixture, two 1" 10-24
bolts, and two #10 nuts. Times 42 fixtures. At this stage I was just hand tightening all the nuts.
The next step shows how I really tightened them down.
The front hole in each fixture is 1/4" instead of 3/16". This allows you to ensure that the front
edge of the fixture is perfectly perpendicular to your work bench. That's the primary purpose of
these fixtures - providing a straight and vertical edge. The vertical press is secondary.
To make this work out I hand tightened all the magnets onto the fixture. The magnets could still rotate at this point. Next I put the fixture on the metal surface of my work bench. I put a piece of paper down first so the magnets wouldn't scratch the paint. Using a square I ensured the fixture was nice and straight. I then used a screw driver and wrench and tightened the bolt and nut at the 1/4" hole (closest to the straight face). I then tighented the other bolt and nut. I then double checked the fixture was perpendicular to the work bench. When removing the fixture I tilt it to the side so the magnets don't have a chance to rotate. They are pretty tight but over time they could rotate resulting in a fixture that isn't perfectly straight.
Here are all the fixtures after getting all of the magnets in place. If you look carefully you
will see that the 10 5.5" and the 4 7.5" fixtures have an extra hole drilled in them. These are
1/4" holes that will hold a 1/4" steel or aluminum rod to be used as a wing jig. The idea is to
slide the wing ribs onto the rods to ensure they are all aligned properly. Some kits and scratch
built wings are made this way.
Here are the vertical presses put in place. I made nine of the presses (was supposed to be ten but
I screwed one up). But I only had eight #2 bolts so that for now I only have 8 presses. That should
be enough. They can be moved to any of the fixtures as needed. These were all build exactly as
I just didn't go so far as adding a nice finish.
I decided to make another magnetic tool to help hold down various pieces such as spars and other
sticks and such. These adjustable hold downs will work with stock up to about 3/8" this. The idea
is that you loosen the wing nut, place the magnet next to the part to hold down, lightly press
the wood hold down against the part, and tighten the wing nut. I also plan on a couple that use
two magents with two or three wood hold downs and a longer bolt. This will allow a stronger
hold down that will straddle the part.
Doing some quick tests these hold downs work much better on warped wood than just placing a couple of magnets on either side of the piece and relying on friction to hold the part down.
Here is how I made the hold downs. The wood is a rectangle the same size as the magnet -
1" x 13/16". I then drilled a #10 hole in the middle of the wood piece so the #10 bolt would pass
through. Using the table saw I cut the slot to size to match the hole. The wood block is held in
place with a 3/4" #10 bolt, lock washer, and wing nut. I added the lock washer too make it easier
to tighten the wing nut without the bold turning. This makes is much quicker to adjust the hold
down height by not needing any tools.
The following set of pictures show some of the jigs I made to help make it easier to produce the vertical fixtures and the hold downs.
To ensure all of the vertical fixtures were identical (except for height) I made this drill
press jig to ensure all the magnet holes were in the same place. I first drilled the 3/16" hole
in all of the fixtures then the 1/4" hole.
I used one fixture as a template. I marked the exact location of the two holes. I then made this jig. It's simply a base with two stops at a 90° angle. I then put the fixture in this jig and then moved the jig into place so the drill was exactly where it needed to be. I then clamped the jig down. I could now slap in a fixture against the jig stops, drill the hole, and then repeat with the next fixture. With this jig I was able to drill all 42 fixtures with perfectly placed holes in just a few minutes.
For the second hole in each fixture I left the jig in place where it was for the first hole. The
trick was to add this additional block to the jig. It's a simple rectangle whose width matches
the distance between the centerlines of the two holes. I switch the drill bit to the second hole
size, placed this block in the jig, and then placed each fixture into the jig just as before. Just
make sure the new block added to the jig has parallel faces along the long edges.
When notching the vertical presses I used the same technique decribed at
Like the presses the hold downs were nothed in two passes. The first pass cuts one side of the
notch. I then flipped the hold down around and made the second pass. Assuming you have everything
aligned and centered properly the two edges of the notch are now perfectly cut. Now I just cut out
the remaining middle portion of the notch.
TODO - The last magnetic tool is a set of aluminum angle straight edges with magentic tape applied along one side.