Introduction: PCB Assembly Fixture
Do you build a lot of printed circuit boards, and wish you had one of those neat board holder-fixture things, but can’t imagine spending $100 - $400 when they seem so simple? That’s us, exactly. So we invented this nifty thing, a PCB fixture you can make yourself. You will need access to some basic (or advanced) sheet metal tools and machines, and about $30 of materials; or you can get a kit from Zeppelin Design Labs.
The fixture consists of a Frame and its Stand. The Frame (02) consists of four Perimeter Rails, two Middle Rails (one equipped with Clamps), and an Upper Rail equipped with Clamps. The rails, in turn, are made of a Top layer and a Bottom layer of steel sheet metal laminated to a stack of aluminum Filler pieces. The Stand (03) consists of a Front, Rear and Base. The kit includes all of the sheet metal parts cut and bent, plus all the hardware (03a). You just stick the parts together with carpet tape, drill some holes, and assemble with a screw driver. Follow these instructions whether you are assembling the kit, or building from scratch.
What You Will Need:
- For the Frame, a piece of 24 gauge sheet metal at least 13” x 19”. For the Stand, another piece about 13” x 26”.
- For the Filler material, we used about 200 square inches of 040 aluminum (.040” thick), double-stacked to make spacers 0.080” thick. We started with a piece about 13” x 15”. You can use any dense, rigid material that you can cut, and that is THICKER than a PC board, which is usually 0.60 – 0.65” (1/16” = 0.625”). Do NOT use cardboard! It is too squashy and will peel apart. 040 aluminum is common and easy to find, and you can cut it yourself with a good shear and some practice. You could also use three layers of 24 gauge sheet metal (steel). This would require a piece about 13” x 22”.
- A roll of carpet tape.
- Some electrical tape or duct tape.
- Hardware (04):
- 4 pcs Machine Screw #10x1/2” Pan Head
- 4 pcs Machine Screw #10x3/8” Pan Head
- 8 pcs #10 Split Ring Lock Washer
- 8 pcs #10 hex nut
- 8 pcs #4 hex nut
- 8 pcs Machine Screw Pan Head
- 4 little rubber feet that are at least 5/16” thick (optional)
- Straight-cutting shear (snip), or foot shear, or power shear
- Cheek bender, or hand brake, or power autobrake
- Drill press
- Screw driver
- Utility knife
Step 1: Cut Out the Parts
Cut the sheet metal and filler pieces according to the Cut List Table. Use a big, straight-cutting snip, or much better, a “guillotine” shear. We used a fancy power shear (05-07).
Step 2: Bend the Clamps, Rail Tops, and Stand Base
Identify the Perimeter Rail Tops (4 pcs), the Upper Rail Top (1 pc), the Clamps (8 pcs) and the big Stand Base. Use a cheek bender or brake to make a bend 90˚ x 0.30” (5/16”, 8 mm) along one long edge of the Rail components, and along both long edges of the Clamps and the Base (08-10). If your material has a “good” side and a “bad” side, then bend the Rails with the good side on the outside of the L; bend the Clamps with the good side inside the U; and bend the Base with the good side outside the U (11-12).
Step 3: Double Up the Filler Pieces
Some sheet metal products are shipped with a clear plastic film on one or both sides to protect the finish. Remove any film from all the filler parts now (13). Apply a piece of carpet tape to cover one side of one Filler piece (14). You don’t want any tape or adhesive leaking out from between layers of filler, so don’t let the tape overhang both sides. Neatly trim the tape with the utility knife (15). Remove the backing and carefully mate to a matching Filler piece. Stand the two parts on edge on your table top to keep the long edges perfectly flush. Carefully align the ends (16-17). Squeeze the Filler Sandwich as tight as you can, being careful not to bend it (18). Repeat for all 7 pairs of Filler pieces.
Step 4: Mark the Perimeter Rails
Sort out the four Perimeter Rail Filler Sandwiches and one of the four Perimeter Rail Tops (with a bend along one edge.) You need to scratch a mark across one end of each of these Filler Sandwiches, using the Top Rail as a straight edge. Hold the Perimeter Rail Top flat and tight across the end of a Perimeter Rail Filler Sandwich. This is how these two parts will fit together later. Scratch or draw a mark across one end of the Filler (19). Repeat for one end of all four of these Fillers.
Step 5: Stick Bottoms to the Perimeter Rails
Stick a piece of carpet tape to a Perimeter Rail Filler Sandwich, starting at the mark you made and completely covering the surface (20). Carefully trim the tape and peel off the backing. Carefully line up a Perimeter Rail Bottom with the mark, using the table top to keep the long edges neatly flush (21). Squeeze the Perimeter Rail Bottom tight onto the Filler Sandwich. Repeat for all four Perimeter Rails (22-23).
Step 6: Stick Tops to the Perimeter Rails
Apply carpet tape to the other side of the Perimeter Rail Sandwich just as you did in Step 5. Before peeling off the backing, dry fit the Perimeter Rail Top to the Filler Sandwich as shown (24-25). Study the picture carefully. One edge of the Rail gets the bend, the other edge gets a little slot. I accidentally make these backwards about half the time, resulting in no slot for holding the circuit board. Practice lining everything up. It is very important to hold the parts perpendicular to the table top so as to create a uniform slot along the length of the rail. When ready, peel off the tape backing(26) and stick the Perimeter Rail Top to the Filler Sandwich (27-29). Repeat for all four Perimeter Rails.
Step 7: Stick the Bottom to the Upper Rail Filler
Apply carpet tape to one side of the Upper Rail Filler Sandwich, holding it back at least 0.08” (2 mm) from both ends (30). Trim, remove the backing, and very carefully stick the corresponding Upper Rail Bottom piece to it. Use the table top to keep one edge lined up, and use your fingers and eyes to accurately center the Upper Rail Bottom end-to-end along the Filler (31).
Step 8: Stick the Top to the Upper Rail
Apply tape to the other side of the Upper Rail just like in Step 7. Remember to keep the tape from overhanging the side of the Rail where you are forming the little slot that will hold the circuit boards; let the tape overhang the other side. Trim the tape and dry fit the Upper Rail Top as shown for practice (31a). Double check that you are about to create a slot along one edge of the rail, opposite the bend, as described in Step 6 (31b). Now remove the backing and carefully stick the Upper Rail Top to the Filler Sandwich.
Step 9: Stick the Tops to the Middle Rails
The Middle Rails only have Tops, because the two sides are identical. Apply tape to one side of the Middle Rail Filler Sandwich just as you did in Step 7. Dry fit the parts to center a Top both end-to-end and side-to-side upon the Filler Sandwich (32-33). This is the trickiest step in the project, because you have to center the Middle Rail Top in all directions along the Filler without the assistance of the table top. You might find it easier to place the Middle Rail Top onto the Filler, or vice versa. When confident, remove the backing and carefully stick the parts together (34-37).
Applying the other Middle Rail Top is easier, because now you can stand the Middle Rail up on edge on the table top (38-39). If you completely botch this step, it is possible to pass a utility knife blade between the parts to separate them, and you can try again.
You are done with the carpet tape!
Step 10: Form the Stand Front and Rear
If you have access to advanced sheet metal bending skills and tools, then you might try your hand at forming these parts yourself (39a). Download the provided drawing, which includes dimensions and bending sequence. Alternatively, these parts are provided fully-formed in the kit (39b); or you can skip trying to bend these, and make the parts instead out of scraps of wood, trimmed on a table saw.
Step 11: Mark the Parts for Drilling
Download the provided template, print it full size, and cut out the pieces (40). Stick the templates to the corresponding parts, and use a nail or punch to mark the various hole locations (41-42). Note only one Middle Rail gets marked. You can allow yourself a tolerance of about ±1/16” (1 mm).
Note that to mark the Stand Base, you can use the template to mark two diagonally opposite corners; then flip the template over face-down and mark the other two corners (43-44).
Step 12: Drill #4 Holes
Use a 1/8” drill bit in a press to carefully drill the #4 holes:
- One at one end of each Perimeter Rail(45)
- One near each of the four corners of the Stand Base(46)
- One near each end of the Stand Front and Stand Rear. Fit the formed Front and Rear to the Base; mark and drill the holes. (47-49)
Step 13: Label the Perimeter Rails
Dry fit the four Perimeter Rails together to form the square Frame. Label the corresponding ends with washable marker (50).
Step 14: Drill #10 Holes
Use a 3/16” bit to drill the #10 holes where indicated:
- Assemble the Frame, one corner at a time. Hold the parts tight and square, and drill straight through all the layers (51-53).
- Drill a hole through both ends of one Middle Rail(54)
- Drill a hole through all 8 Clamps (55).
- Now place a Clamp at either end of the Upper Rail as shown and mark the Rail (56-58). Label the Clamps and the Upper Rail so you can fit them together again later. Drill these last two holes through the Upper Rail (59).
Check the exit-side of your holes for burrs. Use a deburring tool, or a larger drill bit, to remove them.
Step 15: Apply the Clamp Pads
Place two squares of vinyl electrical tape, or one piece of thick duct tape, on the bottom of each Clamp, opposite the hole (60-61.) These will give the Clamps the grip they need to hold fast.
Step 16: Install the Clamps
Gather together the Upper Rail, the Middle Rail with holes, the eight Clamps, and the hardware shown (62). If your material has plastic film on it, remove it as you go along. Use the #10x1/2” screws to assemble the Clamps to the Rails. It goes like this: Screw, washer, clamp (63), rail (64), clamp, washer (65), nut (66). Do not tighten at this time; leave the clamps loose and free to swing.
Step 17: Put It All Together
- Peel back the protective film from the ends of the Perimeter Rails, but don’t lose track of the joint labeling! At one end of each Perimeter Rail, fit a #4 screw through the Top plate and fasten with a nut. (This keeps the layers from peeling apart.) Tighten the nuts (67).
- Assemble the frame with #10x3/8” screws and nuts at each corner, keeping all the joints tight and the whole frame square (68-71). Again, run the screws in through the Top plate. Tighten the nuts. Remove the last of the film.
- If you are building from the kit, poke the remaining four #4 screws through the provided rubber feet (72). (If you are working from scratch, with your own supplies, you probably obtained peel-and-stick feet, so skip this step.) Assemble the Stand with screws and nuts as shown (72a-72c). Don’t over-tighten the screws or they are likely to pop right through the rubber feet. If that happens, just stick the foot to the base with carpet tape.
- Drop the frame onto the Stand (73). We reckon the frame is right-side-up when the bent edges are pointing down. If the fit is tight or loose, you can bend the Stand Front and Rear a little.
- Place the Middle Rail without clamps diagonally into the frame (74). Carefully engage the exposed tips of the Middle Rail into the slots in the Perimeter Rails (75). Swing the Middle Rail into place. It will be tight, and then it will snap into place (76). Slide it down to the bottom of the frame. It will start out sticky, but will loosen up with use. If you left a lot of tape residue sticking out from between layers of metal, this may be unacceptably sticky. You’ll have to scrape some of the glue out of the rail slots with a scrap of sheet metal or something. If the rail is still too tight, shorten it by sanding down the ends a hair.
- Add the Middle Rail with Clamps. Swing the top clamps out of the way; fit the ends into the slots as before (77); snap into place (78); and swing the clamps over the Perimeter Rails (79).
- Repeat with the Upper Rail (80-81). This rail has a slot on only one side. Be sure to install it so the slot is pointed down toward the other rails.
That’s it! Your fixture is done!
Step 18: Using Your Fantabulous PCB Assembly Fixture
By fitting two of the rails with Clamps, your Fixture has tremendous flexibility. We will explain how we use it at Zeppelin Design Labs; you will use it as you see fit.
Work the three rails to the top of the frame.
Slip a circuit board into the bottom right corner of the fixture, engaging two slots. Repeat in the opposite corner.
Slide the Middle Rail down to engage the top edges of the boards (82).
Repeat with a second row of boards and the next Middle Rail. Tighten the clamps on the rail to keep it from sliding up, which would allow all your boards to drop out (83-84).
Fit a third row of boards if desired, and clamp them into place with the Upper Rail (85-86).
That’s it! This arrangement should be steady and stable. Try flipping the whole frame over to access the other side of the boards.
You can fit boards of various sizes into one setup, as long as each row contains boards of all one size. You can use the two rails with clamps to hold one large board in the center of the frame. Don’t try to pack more boards into the frame than you can reasonably handle. The more small boards you try to install, the more likely they will fall out, which will frustrate you and waste your time.
Some of the edges may be sharp. Be careful how you handle the Fixture. If the exposed edges of the rails bother you, you could wrap a strip of electrical tape over them.
Don’t force a sticky rail! It will eventually slip and cut or pinch your finger! Work the rail gently at one end and then the other.
You may need to clean the slots from time to time. Scrape them out with a scrap of sheet metal. We do not recommend you use any solvent or oil, because you do not want to soften the tape that holds the fixture together.
If the rails remain too sticky in the frame even after careful cleaning, you can shorten the rails a hair by rubbing the ends with medium grit sandpaper. You can also try lubricating the slots with dry silicone lubricant spray. Do not use graphite dry-lube, since this stuff conducts electricity, and it’s the last thing you want contaminating your circuit boards!!
If a rail ever delaminates, either add a nut and bolt at its midpoint, or remove its screws, slice it apart with a utility knife, and replace the carpet tape.