Airfield Models - How To

Make Fixtures for a Magnetic Building Board System

May 05, 2015



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Airfield Models (http://www.airfieldmodels.com/)Make Upright Fixtures for a Magnet Building System

The fixtures I use with my magnetic building board are very easy to make.  A drill press and table saw greatly simplify parts fabrication, but a hand held drill, coping saw and hobby knife can accomplish the same thing.

Please do not let the lack of power tools prevent you from making fixtures similar to these.  Once you start building with them, you will love them.

 
 
Make cardstock patterns to draw the blanks. Determine the sizes you want to make and cut cardstock patterns.  If you have power tools, then you should probably make several of each size while you have your tools set up.

I have found the most useful size to be 5-1/2" so I made about a dozen of them.  I already have plenty of the sizes listed above, so for this tutorial I am making 7-1/2" tall fixtures.

Note that all measurements are from the top or bottom and the front face.  What this means is that no matter how many different size fixtures you make, the tools will have the same settings.  This will make more sense as we move along.

A set of fixture blanks. I use my scroll saw to cut the fixture blanks.  Before moving to the next step, be sure the front face is sanded flat and that the bottom edge is square to the face.
Set up your drill press to drill the magnet mounting holes. If you have a drill press, then by all means use it.  Before I had this nice micro-adjustment table, I used to make a 90 corner by gluing a couple of scraps of wood to the table with CA.

When finished, I slip a single edge razor blade under the scrap to remove it.  Waxing the table helps it pop off easily.

Drill the holes in all the fixtures. Slide the fixture into place and drill the magnet mounting holes.
Make one hole slightly larger to make it easier to square the fixtures. Drill one hole 1/4" and the other 3/16".  It does not matter which hole is larger.  The oversize hole allows the fixture to be squared to the building board.
Make the cut-outs for the vertical presses. If you do not anticipate needing vertical presses then you can skip straight to sanding the fixtures for the finish.  However, it is easiest to do the work now, so I suggest you go ahead with it.

Set the blade on your table saw to the depth shown on the drawing.  Set the fence so the cut is proper distance from the top of the fixture.

Make this first cut on all the fixtures before moving the fence to make the second cut.  I recommend that you make the cut-out undersize at first and then make fine adjustments to the fence to zero it in.

Move the work slowly through the saw to reduce tear-out on the back side.

It is helpful if you've already made the vertical press attachments so you can check the fit.

Mark the location of the vertical press mounting bolt. After you've made the vertical presses, slide one on the fixture and mark the hole location.

If you set up power tools as I have done, then all the holes and cut-outs in the fixtures should be accurate enough that you only need to mark one fixture.  But it is not a bad idea to check them all just in case.

Drill the holes for the vertical press mounting bolts. Set up your drill press again using the pencil mark.  Drill the holes to mount the vertical presses in all of the fixtures.

I use 2-56 bolts to mount the vertical press so these holes are drilled 3/32".

Sand the fixture and give it you choice of finish.  Clear lacquer is a good choice. All that is left to do with the fixture is prepare it for finish.  Sand it smooth and knock the edges off all the corners.  Pay special attention to the front face so that there is nothing sharp or jagged that can damage your model.

I brush on 2-3 coats of flat lacquer and rub out the final coat with fine steel wool (#0000).

If you are messy with glue, then you may want to use furniture wax on the front edge of the fixture to prevent gluing it to your plane unless you need speed brakes anyway.

All the parts and hardware for a complete fixture assembly with a vertical press. All the parts for one complete fixture assembly.  Four magnets are held in place with two #10 x 1" bolts and secured with hex nuts.  Packages of 100 nuts and bolts can be purchased at places such as Home Depot.

One 2-56 x 1" socket head bolt with two #2 washers and a #2 lock nut are used to secure the vertical press to the fixture.  Hardware is available from Micro-Fasteners.

The thumbscrews were the most expensive piece of hardware at approximately $0.70 for a pair of them.  You only need a handful of them though.

Assemble the fixture so it is square to the board. The oversize hole allows the fixture to be squared to board easily.  Lightly snug the hardware initially and use a good square to align the fixture.  When you are satisfied, tighten it down.

Do not over-tighten the bolts.  The magnets are brittle and will break.

The fixture should be slighly raised from the board to allow adjustment. Note that the fixture is raised above the board.

Hardware used for fixtures

You can get all the hardware you need (except #2) from a local hardware store.  Pick up #2 hardware used to attach the vertical presses from your local hobby shop or Micro Fasteners.

You'll need (2 ea) 10-24 x 1" bolts and nuts to attach magnets to the fixtures.  Washers aren't needed  10-32 bolts are larger in diameter and do not fit through the holes in the magnets.

The vertical presses are held in place with a 2-56 bolt, washer and lock nut.  In most cases the press doesn't need to be bolted to the press.  Just slide it on and use it.

The press part of the vertical press is a 10-24 x 2" thumbscrew (or whatever bolt head shape you feel most comfortable turning by hand).

 
 

What size fixtures to make

The more sizes you make the more flexible your system will be.

You can make the fixtures as tall as you want.  Low fixtures are nice for clamping straightedges and blocking small components in place.

Ideally you want a fixture that is just slightly taller than whatever is being jigged at any give fixture station.  There is no one size fits all.

For example, the fixtures you see against the fuselage in the photo below are the right size for what they are holding.  Imagine using the fixtures that are against the wing in place of the ones against the fuselage.  I would always be bumping into them and they'd be a lot in the way.

Tall fixtures hold a wing in alignment.

Tall fixtures make it much easier to achieve accurate wing alignment:

  1. Draw a fuselage centerline on your board.

  2. Draw a wing line perpendicular to the fuselage center line at the approximate location of the wing leading edge.

  3. Mark a point on the wing line exactly the same distance from the fuselage centerline (halfway or more to each wing tip).

  4. Lock the fuselage to the board on the fuselage centerline using magnetic fixtures.

  5. Roughly center and align the wing using a tape measure.

  6. Place tall fixtures at the leading edge of the wing where you marked.

  7. Adjust the leading edge fixtures so that they are an equal distance from the wing line you drew.  Both fixtures should contact the wing leading edge.  If the wing is flexible ensure the jigs just touch the wing but don't flex it.

  8. Center the wing such that the wing tips are an equal distance from the fuselage centerline.

  9. Make sure each wing tip is an equal distance above the board and the wing incidence is correct.  The wing saddle may need to be adjusted by sanding or trimming.

  10. Check all your measurements.  Make adjustments as necessary.

  11. Lock the wing by adding a pair of fixtures at the trailing edge and one at each tip.  Use vertical presses mounted to magnetic fixtures to hold the wing tightly to the saddle if necessary.  Again, use as many fixtures as necessary to make sure the wing can't move.

  12. Drill and tap for the wing bolts.

 
 

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