TIPS AND TECHNIQUES:

Installing End Caps on Big-Hole Beads

by Larry Barefield

 

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End Caps: Tools, materials, and procedure (for 3/8 holes

Photos Below

TOOLS

• Assorted hammers

o Try different ones to see which you like best (I prefer one with a bit

more heft.).

o Rawhide or wood will not mar the metal; makes buffing easier.

• A circle cutter www.contenti.com  Item #190-009)

• A scribe

• A center finder (woodworking store or, possibly, Home Depot, Hardware

store )

• A center punch (Home Depot, Hardware store)

• A dapping set [punches and block www.contenti.com  Item # 190-225);

you’ll use the 3/4 and 7/8 punches and corresponding dapping block holes.]

• Files ( a flat fine cut and a 1/4 round chainsaw)

• Some kind of center hole generating method

o A Step drill (hardware store, Home Depot),

o A small set of dividers, and

o One 1/2 flare x 1/2 m.i.p. union and a short flare nut [ to hold end the end cap while drilling the hole [hardware store, Home Depot, or MSC [www1.mscdirect.com) part # 36984383 and 36984169) or

o A Lever punch (MSC part # 09271057 and 09272428)

• A vice

• A small metal plate (with a hole made with the drill bit listed below)

• One 13/64 drill bit (hardware store, Home Depot)

• A tubing cutter (hardware store, Home Depot)

• A Dremel tool, buffs, and buffing compound

• A torch of some type

• Water for quenching the copper tubing when annealing it

• Safety equipment (safety glasses and gloves)

• An ample supply of cuss words

 

MATERIALS

 

• Sheet goods:

o ~.025 thickness copper or aluminum [purchase from hardware store, hobby shop, or MSC (part #s 09426057 and 32008948).

• Tubing

o 3/8 copper may be obtained at a hardware store or Home Depot.

o 3/8 aluminum may be obtained from MSC, part # 32000812

 

PROCEDURE

• Anneal the metal materials

o Anneal the copper tubing by heating it to a dull red and plunging it into water

o Anneal the aluminum tubing by it heating to ~775 degrees F in your annealing oven and allowing it to cool to room temperature slowly

o Do not anneal the sheet material because annealing will make it too soft and the domes/caps will flatten out during the riveting process

• Cut the circles

 

• Mark the center of the circle using the scribe and the center finder, and prick the center with the punch

 

• Dome the circle with the dapping punch and block (if you use a step drill,place the punch mark down; if you are using a lever punch, place markup)

 

• Make a hole (Set the dividers to ~3/16 and scribe a circle around thepunch mark. Using the nut, lock the dome on the flare fitting. Use a stepdrill to make a hole about 5/16 dia. and check for concentricity; if ok, drill

out to 3/8. If not, use some of those cuss words and the chainsaw file to enlarge the hole in the correct direction; using the scribed circle as a guide. The lever punch is self explanatory)

 

• Scrub the faces of the end caps on the file to remove burrs, etc.

 

• Select a well annealed bead with no projections, bumps, etc. on the ends where the caps will fit.

 

• Hold an end cap on each end of the bead and push the tubing through the assembly until it projects a little less than 1/2 the diameter of the bead hole (about 5/32) past the end cap.

 

• Scribe a mark next to the end cap and measure the distance to the end of the tubing.

 

• Scribe a mark next to the other end cap, measure out the amount of projection and make a mark on the tubing at that point. You have now established the overall length of the tube/rivet (we’ll start calling it a rivet now) and you have located the position of the bead/end cap assembly on the rivet

 

• Secure your 13/64 drill bit upside down in the vice and put the plate on it. Place the bead/end cap/rivet assembly over the drill bit and slightly loosen the vice and slide the drill bit up or down until the end is just below the

upper end of the bead.

 

• Select a dapping punch that that is slightly larger than the inside diameter of the rivet, place it on the rivet and tap it to slightly spread the end.

 

• Flip the assembly over and do the same to the other end (you may wish to use a thin rubber band to hold the end caps and bead in the center of the rivet while you are doing this).

 

• Select a larger punch and repeat the previous two steps.

 

• Continue flipping the bead and using larger punches until you notice that the blows to the punch are causing the rivet flanges to flatten out where they contact the metal plate. Then, flip the rivet on the drill bit and using light blows with the hammer tap until the flanges of the rivet are horizontal (at 90 degrees to the axis of the rivet).

 

• When the flanges are flat, use light hammer blows to turn the flange down so that it evenly contacts the end cap all the way around.

 

• Take the drill bit out of the vice and use it as a mandrel to hold the bead for polishing. Using a gloved hand, hold the bead on the drill bit with your thumb (to keep it from spinning) and polish it with a liberally rouged felt buff in the Dremel. You can use the flare fitting referenced above, a small pilot drill (~1/16), and a step drill to make holes without a punch. This method has an advantage: you can correct an off center hole by stopping short of full hole diameter and correcting with a Dremel and a grinding burr.

 

Here’s how it works:

Place the domed end cap on the flare portion of the fitting and screw on the cap.

End cap is ready for pilot hole. Note the short piece of pipe and glove to protect the hand.

Drilling the pilot hole.

The pilot hole complete.

Beginning the hole with the step drill.

Stopping short of the mark (desired Dia. Full Dia. If already centered one step smaller if the hole needs to be corrected.)

If the hole is off center, mark the thicker side to be ground.

 Carefully remove material and finish with the step drill.

 

And that’s all there is to it.

Happy end capping,

Larry Barefield

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